Science.gov

Sample records for airy-heiskanen isostatic model

  1. A deterministic approach toward isostatic gravity residuals: A case study from South America

    SciTech Connect

    Chapin, D.A.

    1994-12-31

    Isostatic gravity residuals are based upon geologic models, therefore they provide a reasonable basis of comparison over large areas for reconnaissance studies. To help define the best isostatic model for South America, a new deterministic methodology overcomes the deficiencies of other empirically-based methods. The basis for the model was the Airy-Heiskanen (1958) isostatic model, which assumes that surface topography is supported by crustal thickening. The three key parameters -- (a) the crustal thickness at sea-level, (b) the surface reduction density, and (c) the density contrast between the crust and the mantle -- were determined directly from the elevation, free-air gravity, and Bouguer gravity datasets. The results of this work were not only an isostatic residual map, but methodology which cross-checks the data for quality control purposes. The final isostatic residual map can be used in confidence for basin evaluation throughout the continent of South America.

  2. A new approach to assess isostatic compensation of topography in continental domain from GOCE gravity gradients

    NASA Astrophysics Data System (ADS)

    Cadio, Cécilia; Saraswati, Anita; Cattin, Rodolphe; Mazzotti, Stéphane

    2016-11-01

    Estimating how topography is maintained provides insights into the different factors responsible for surface deformations and their relative roles. Here, we develop a new and simple approach to assess the degree of isostatic compensation of continental topography at regional scale from GOCE gravity gradients. We calculate the ratio between the radial gradient observed by GOCE and that calculated from topography only. From analytical and statistical formulations, simple relationships between this ratio and the degree of compensation are obtained under the Airy-Heiskanen isostasy hypothesis. Then, a value of degree of compensation at each point of study area can be easily deduced. We apply our method to the Alaska-Canada Cordillera and validate our results by comparison with a standard isostatic gravity anomaly model and additional geophysical information for this area. Both our GOCE-based results and the isostatic anomaly show that Airy-Heiskanen isostasy prevails for the Yukon Plateau whereas additional mechanisms are required to support topography below the Northwest Territories Craton and the Yakutat collision zone.

  3. Bouguer gravity anomaly and isostatic residual gravity maps of the Tonopah 1 degree by 2 degrees Quadrangle, central Nevada

    USGS Publications Warehouse

    Plouff, Donald

    1992-01-01

    A residual isostatic gravity map (sheet 2) was prepared so that the regional effect of isostatic compensation present on the Bouguer gravity anomaly map (sheet 1) would be minimized. Isostatic corrections based on the Airy-Heiskanen system (Heiskanen and Vening Meinesz, 1958, p. 135-137) were estimated by using 3-minute topographic digitization and applying the method of Jachens and Roberts (1981). Parameters selected for the isostatic model were 25 km for the normal crustal thickness at sea level, 2.67 g/cm3 for the density of the crust, and 0.4 g/cm3 for the contrast in density between the crust and the upper mantle. These parameters were selected so that the isostatic residual gravity map would be consistent with isostatic residual gravity maps of the adjacent Walker Lake quadrangle (Plouff, 1987) and the state of Nevada (Saltus, 1988c).

  4. Comparisons of global topographic/isostatic models to the Earth's observed gravity field

    NASA Technical Reports Server (NTRS)

    Rummel, Reiner; Rapp, Richard H.; Suenkel, Hans; Tscherning, C. Christian

    1988-01-01

    The Earth's gravitational potential, as described by a spherical harmonic expansion to degree 180, was compared to the potential implied by the topography and its isostatic compensation using five different hypothesis. Initially, series expressions for the Airy/Heiskanen topographic isostatic model were developed to the third order in terms of (h/R), where h is equivalent rock topography and R is a mean Earth radius. Using actual topographic developments for the Earth, it was found that the second and third terms of the expansion contributed 30 and 3 percents, of the first of the expansion. With these new equations it is possible to compute depths (D) of compensation, by degree, using 3 different criteria. The results show that the average depth implied by criterion I is 60 km while it is about 33 km for criteria 2 and 3 with smaller compensation depths at the higher degrees. Another model examined was related to the Vening-Meinesz regional hypothesis implemented in the spectral domain. Finally, oceanic and continental response functions were derived for the global data sets and comparisons made to locally determined values.

  5. Topographic/isostatic evaluation of new-generation GOCE gravity field models

    NASA Astrophysics Data System (ADS)

    Hirt, C.; Kuhn, M.; Featherstone, W. E.; GöTtl, F.

    2012-05-01

    We use gravity implied by the Earth's rock-equivalent topography (RET) and modeled isostatic compensation masses to evaluate the new global gravity field models (GGMs) from European Space Agency (ESA)'s Gravity Field and Steady-State Ocean Circulation Explorer (GOCE) satellite gravimetry mission. The topography is now reasonably well-known over most of the Earth's landmasses, and also where conventional GGM evaluation is prohibitive due to the lack (or unavailability) of ground-truth gravity data. We construct a spherical harmonic representation of Earth's RET to derive band-limited topography-implied gravity, and test the somewhat simplistic Airy/Heiskanen and Pratt/Hayford hypotheses of isostatic compensation, but which did not improve the agreement between gravity from the uncompensated RET and GOCE. The third-generation GOCE GGMs (based on 12 months of space gravimetry) resolve the Earth's gravity field effectively up to spherical harmonic degree ˜200-220 (˜90-100 km resolution). Such scales could not be resolved from satellites before GOCE. From the three different GOCE processing philosophies currently in use by ESA, the time-wise and direct approaches exhibit the highest sensitivity to short-scale gravity recovery, being better than the space-wise approach. Our topography-implied gravity comparisons bring evidence of improvements from GOCE to gravity field knowledge over the Himalayas, Africa, the Andes, Papua New Guinea and Antarctic regions. In attenuated form, GOCE captures topography-implied gravity signals up to degree ˜250 (˜80 km resolution), suggesting that other signals (originating, e.g., from the crust-mantle boundary and buried loads) are captured as well, which might now improve our knowledge on the Earth's lithosphere structure at previously unresolved spatial scales.

  6. Constrained optimisation of the parameters for a simple isostatic Moho model

    NASA Astrophysics Data System (ADS)

    Lane, R. J.

    2010-12-01

    In a regional-scale integrated 3D crustal mapping project for the offshore Capel-Faust region, approximately 800 km east of the Australian east coast, gravity data were being used by the Geoscience Australia Remote Eastern Frontiers team to evaluate the viability of an interpretation of the upper crustal sequence that had been derived from a network of 2D seismic lines. A preliminary gravity forward modelling calculation for this sequence using mass density values derived from limited well log and seismic velocity information indicated a long wavelength misfit between this response and the observed data. Rather than draw upon a mathematical function to account for this component of the model response (e.g., low order polynomial), a solution that would lack geological significance, I chose to first investigate whether the gravity response stemming from the density contrast across the crust-mantle boundary (i.e., the Moho) could account for this misfit. The available direct observations to build the Moho surface in the 3D geological map were extremely sparse, however. The 2D seismic data failed to provide any information on the Moho. The only constraints on the depth to this interface within the project area were from 2 seismic refraction soundings. These soundings were in the middle of a set of 11 soundings forming a profile across the Lord Howe Rise. The use of relatively high resolution bathymetry data coupled with an Airy-Heiskanen isostatic model assumption was investigated as a means of defining the form of the Moho surface. The suitability of this isostatic assumption and associated simple model were investigated through optimisation of the model parameters. The Moho depths interpreted from the seismic refraction profile were used as the observations in this exercise. The output parameters were the average depth to the Moho (Tavg), upper crust density (RHOzero), and density contrast across the lower crust and upper mantle (RHOone). The model inputs were a grid

  7. Three-dimensional gravity modeling of the geologic structure of Long Valley caldera

    SciTech Connect

    Carle, S.F.

    1988-11-10

    A 48-mGal gravity low coincides with Long Valley caldera and is mainly attributed to low-density caldera fill. Gravity measurements by Unocal Geothermal have been integrated with U.S. Geological Survey data, vastly improving gravity station coverage throughout the caldera. A strong regional gravity trend is mainly attributed to isostasy. A ''best fitting'' (based on regional control of basement densities) Airy-Heiskanen isostatic model was used for the regional correction. A three-dimensional, multiple-unit gravity modeling program with iterative capabilities was developed to model the residual gravity. The density structure of Long Valley caldera and vicinity was modeled with 22 discrete density units, most of which were based on geologic units. Information from drill hole lithologies, surface geology, and structural geology interpretations constrain the model. Some important points revealed by the three-dimensional gravity modeling are that (1) the volume of ejected magma associated with the Bishop Tuff eruption is greater than previously thought, (2) the caldera structure is strongly influenced by precaldera topography and the extensions of major, active faults, (3) the main west ring fracture is coincident with the Inyo Domes--Mono Craters fracture system, (4) a relatively low-density region probably underlies the caldera, and (5) a silicic magma chamber may underlie Devils Postpile. copyright American Geophysical Union 1988

  8. Isostatic Model and Isostatic Gravity Anomalies of the Arabian Plate and Surroundings

    NASA Astrophysics Data System (ADS)

    Kaban, Mikhail K.; El Khrepy, Sami; Al-Arifi, Nassir

    2016-04-01

    The isostatic modeling represents one of the most useful "geological" reduction methods of the gravity field. With the isostatic correction, it is possible to remove a significant part of the effect of deep density heterogeneity, which dominates in the Bouguer gravity anomalies. Although there exist several isostatic compensation schemes, it is usually supposed that a choice of the model is not an important factor to first order, since the total weight of compensating masses remains the same. We compare two alternative models for the Arabian plate and surrounding area. The Airy model gives very significant regional isostatic anomalies, which cannot be explained by the upper crust structure or disturbances of the isostatic equilibrium. Also, the predicted "isostatic" Moho is very different from existing seismic observations. The second isostatic model includes the Moho, which is based on seismic determinations. Additional compensation is provided by density variations within the lithosphere (chiefly in the upper mantle). According to this model, the upper mantle under the Arabian Shield is less dense than under the Platform. In the Arabian platform, the maximum density coincides with the Rub' al Khali, one of the richest oil basin in the world. This finding agrees with previous studies, showing that such basins are often underlain by dense mantle, possibly related to an eclogite layer that has caused their subsidence. The mantle density variations might be also a result of variations of the lithosphere thickness. With the combined isostatic model, it is possible to minimize regional anomalies over the Arabian plate. The residual local anomalies correspond well to tectonic structure of the plate. Still very significant anomalies, showing isostatic disturbances of the lithosphere, are associated with the Zagros fold belt, the collision zone of the Arabian and Eurasian plates.

  9. Worldwide complete spherical Bouguer and isostatic anomaly maps

    NASA Astrophysics Data System (ADS)

    Bonvalot, S.; Balmino, G.; Briais, A.; Peyrefitte, A.; Vales, N.; Biancale, R.; Gabalda, G.; Reinquin, F.

    2011-12-01

    We present here a set of digital maps of the Earth's gravity anomalies (surface "free air", Bouguer and isostatic), computed at Bureau Gravimetric International (BGI) as a contribution to the Global Geodetic Observing Systems (GGOS) and to the global geophysical maps published by the Commission for the Geological Map of the World (CGMW). The free air and Bouguer anomaly concept is extensively used in geophysical interpretation to investigate the density distributions in the Earth's interior. Complete Bouguer anomalies (including terrain effects) are usually computed at regional scales by integrating the gravity attraction of topography elements over and beyond a given area (under planar or spherical approximations). Here, we developed and applied a worldwide spherical approach aimed to provide a set of homogeneous and high resolution gravity anomaly maps and grids computed at the Earth's surface, taking into account a realistic Earth model and reconciling geophysical and geodetic definitions of gravity anomalies. This first version (1.0) has been computed by spherical harmonics analysis / synthesis of the Earth's topography-bathymetry up to degree 10800. The detailed theory of the spherical harmonics approach is given in Balmino et al., (Journal of Geodesy, submitted). The Bouguer and terrain corrections have thus been computed in spherical geometry at 1'x1' resolution using the ETOPO1 topography/bathymetry, ice surface and bedrock models from the NOAA (National Oceanic and Atmospheric Administration) and taking into account precise characteristics (boundaries and densities) of major lakes, inner seas, polar caps and of land areas below sea level. Isostatic corrections have been computed according to the Airy Heiskanen model in spherical geometry for a constant depth of compensation of 30km. The gravity information given here is provided by the Earth Geopotential Model (EGM2008), developed at degree 2160 by the National Geospatial Intelligence Agency (NGA) (Pavlis

  10. World Gravity Map: a set of global complete spherical Bouguer and isostatic anomaly maps and grids

    NASA Astrophysics Data System (ADS)

    Bonvalot, S.; Balmino, G.; Briais, A.; Kuhn, M.; Peyrefitte, A.; Vales, N.; Biancale, R.; Gabalda, G.; Reinquin, F.

    2012-04-01

    We present here a set of digital maps of the Earth's gravity anomalies (surface free air, Bouguer and isostatic), computed at Bureau Gravimetric International (BGI) as a contribution to the Global Geodetic Observing Systems (GGOS) and to the global geophysical maps published by the Commission for the Geological Map of the World (CGMW) with support of UNESCO and other institutions. The Bouguer anomaly concept is extensively used in geophysical interpretation to investigate the density distributions in the Earth's interior. Complete Bouguer anomalies (including terrain effects) are usually computed at regional scales by integrating the gravity attraction of topography elements over and beyond a given area (under planar or spherical approximations). Here, we developed and applied a worldwide spherical approach aimed to provide a set of homogeneous and high resolution gravity anomaly maps and grids computed at the Earth's surface, taking into account a realistic Earth model and reconciling geophysical and geodetic definitions of gravity anomalies. This first version (1.0) has been computed by spherical harmonics analysis / synthesis of the Earth's topography-bathymetry up to degree 10800. The detailed theory of the spherical harmonics approach is given in Balmino et al., (Journal of Geodesy, 2011). The Bouguer and terrain corrections have thus been computed in spherical geometry at 1'x1' resolution using the ETOPO1 topography/bathymetry, ice surface and bedrock models from the NOAA (National Oceanic and Atmospheric Administration) and taking into account precise characteristics (boundaries and densities) of major lakes, inner seas, polar caps and of land areas below sea level. Isostatic corrections have been computed according to the Airy-Heiskanen model in spherical geometry for a constant depth of compensation of 30km. The gravity information given here is provided by the Earth Geopotential Model (EGM2008), developed at degree 2160 by the National Geospatial

  11. Adapting isostatic microbial growth parameters into non-isostatic models for use in dynamic ecosystems

    NASA Astrophysics Data System (ADS)

    Spangler, J.; Schulz, C. J.; Childers, G. W.

    2009-12-01

    Modeling microbial respiration and growth is an important tool for understanding many geochemical systems. The estimation of growth parameters relies on fitting experimental data to a selected model, such as the Monod equation or some variation, most often under batch or continuous culture conditions. While continuous culture conditions can be analogous to some natural environments, it often isn’t the case. More often, microorganisms are subject to fluctuating temperature, substrate concentrations, pH, water activity, and inhibitory compounds, to name a few. Microbial growth estimation under non-isothermal conditions has been possible through use of numerical solutions and has seen use in the field of food microbiology. In this study, numerical solutions were used to extend growth models under more non-isostatic conditions using momentary growth rate estimates. Using a model organism common in wastewater (Paracoccus denitrificans), growth and respiration rate parameters were estimated under varying static conditions (temperature, pH, electron donor/acceptor concentrations) and used to construct a non-isostatic growth model. After construction of the model, additional experiments were conducted to validate the model. These non-isostatic models hold the potential for allowing the prediction of cell biomass and respiration rates under a diverse array of conditions. By not restricting models to constant environmental conditions, the general applicability of the model can be greatly improved.

  12. Segmentation of the Andean margin by isostatic models and gradients

    NASA Astrophysics Data System (ADS)

    Schaller, T.; Andersen, J.; Götze, H.-J.; Koproch, N.; Schmidt, S.; Sobiesiak, M.; Splettstößer, S.

    2015-04-01

    The gravity gradients of the South American continental margin are the highest on Earth. These gradients are proxies for the strong horizontal stresses due to the convergent movement of the Nazca plate and the overriding South American plate. The frequently occurring large earthquakes in this zone suggest a correlation of gravity anomalies and seismogenic structures which is the major target of our research. Numerical analyses of the Central Andean gravity field were conducted using different techniques such as isostatic calculations, inversion and edge detection while varying the key parameters of the respective methods. Also, a constrained 3D density model was built through forward modelling of the terrestrial Bouguer anomaly. The results point out that a Vening-Meinesz model with a rigidity of 1023 Nm fits optimally the isostatic behaviour of the Central Andes. For numerical inversion the following parameters provided best results: density contrasts between 430-500 kg/m3, compensation depths of 30-40 km and a 400/300-km-wavelength filter. Moho depths obtained from the different methods agree reasonably well in the continental and oceanic area but defer the most in the transition zone between the two. In this coastal area, north-south segmentation of the residual fields is evident. The respective gravity defined segments correspond well with the extent of large earthquake rupture planes in the southern part of the investigation area. We propose that this segmentation is reflected by changing thicknesses of high density crustal bodies modelled in the 3D density model. These old batholiths fit extremely well to high-velocity domains from seismic tomography. Further seismic asperity structures also display a good correlation with different features of the residual fields.

  13. Towards accurate observation and modelling of Antarctic glacial isostatic adjustment

    NASA Astrophysics Data System (ADS)

    King, M.

    2012-04-01

    The response of the solid Earth to glacial mass changes, known as glacial isostatic adjustment (GIA), has received renewed attention in the recent decade thanks to the Gravity Recovery and Climate Experiment (GRACE) satellite mission. GRACE measures Earth's gravity field every 30 days, but cannot partition surface mass changes, such as present-day cryospheric or hydrological change, from changes within the solid Earth, notably due to GIA. If GIA cannot be accurately modelled in a particular region the accuracy of GRACE estimates of ice mass balance for that region is compromised. This lecture will focus on Antarctica, where models of GIA are hugely uncertain due to weak constraints on ice loading history and Earth structure. Over the last years, however, there has been a step-change in our ability to measure GIA uplift with the Global Positioning System (GPS), including widespread deployments of permanent GPS receivers as part of the International Polar Year (IPY) POLENET project. I will particularly focus on the Antarctic GPS velocity field and the confounding effect of elastic rebound due to present-day ice mass changes, and then describe the construction and calibration of a new Antarctic GIA model for application to GRACE data, as well as highlighting areas where further critical developments are required.

  14. Importance of far-field Topographic and Isostatic corrections for regional density modeling

    NASA Astrophysics Data System (ADS)

    Szwillus, Ebbing, Holzrichter

    2016-07-01

    The long-wavelength gravity field contains information about processes in the sub-lithospheric mantle. As satellite-derived gravity models now provide the long to medium-wavelength gravity field at unprecedented accuracy, techniques used to process gravity data need to be updated. We show that when determining these long-wavelengths, the treatment of topographic and isostatic effects is a likely source of error. We constructed a global isostatic model and calculated global topographic and isostatic effect. These calculations were done for ground stations as well as stations at satellite height. We considered both gravity and gravity gradients. Using these results, we determined how much of the gravity signal comes from distant sources. We find that a significant long-wavelength bias is introduced if far-field effects on the topographic effect are neglected. However, due to isostatic compensation far-field effects of the topographic effect are to a large degree compensated by the far-field isostatic effect. This means that far-field effects can be reduced effectively by always considering topographic masses together with their compensating isostatic masses. We show that to correctly represent the ultra-long wavelengths, a global background model should be used. This is demonstrated both globally and for a continental-scale case area in North America. In the case of regional modeling, where the ultra-long wavelengths are not of prime importance, gravity gradients can be used to help minimize correction errors caused by far-field effects.

  15. Importance of far-field topographic and isostatic corrections for regional density modelling

    NASA Astrophysics Data System (ADS)

    Szwillus, Wolfgang; Ebbing, Jörg; Holzrichter, Nils

    2016-10-01

    The long-wavelength gravity field contains information about processes in the sublithospheric mantle. As satellite-derived gravity models now provide the long to medium-wavelength gravity field at unprecedented accuracy, techniques used to process gravity data need to be updated. We show that when determining these long-wavelengths, the treatment of topographic-isostatic effect (TIE) and isostatic effects (IE) is a likely source of error. We constructed a global isostatic model and calculated global TIE and IE. These calculations were done for ground stations as well as stations at satellite height. We considered both gravity and gravity gradients. Using these results, we determined how much of the gravity signal comes from distant sources. We find that a significant long-wavelength bias is introduced if far-field effects on the topographic effect are neglected. However, due to isostatic compensation far-field effects of the topographic effect are to a large degree compensated by the far-field IE. This means that far-field effects can be reduced effectively by always considering topographic masses together with their compensating isostatic masses. We show that to correctly represent the ultra-long wavelengths, a global background model should be used. This is demonstrated both globally and for a continental-scale case area in North America. In the case of regional modelling, where the ultra-long wavelengths are not of prime importance, gravity gradients can be used to help minimize correction errors caused by far-field effects.

  16. Isostatic gravity map of the Death Valley ground-water model area, Nevada and California

    USGS Publications Warehouse

    Ponce, D.A.; Blakely, R.J.; Morin, R.L.; Mankinen, E.A.

    2001-01-01

    An isostatic gravity map of the Death Valley groundwater model area was prepared from over 40,0000 gravity stations as part of an interagency effort by the U.S. Geological Survey and the U.S. Department of Energy to help characterize the geology and hydrology of southwest Nevada and parts of California.

  17. Global isostatic geoid anomalies for plate and boundary layer models of the lithosphere

    NASA Technical Reports Server (NTRS)

    Hager, B. H.

    1981-01-01

    Commonly used one dimensional geoid models predict that the isostatic geoid anomaly over old ocean basins for the boundary layer thermal model of the lithosphere is a factor of two greater than that for the plate model. Calculations presented, using the spherical analogues of the plate and boundary layer thermal models, show that for the actual global distribution of plate ages, one dimensional models are not accurate and a spherical, fully three dimensional treatment is necessary. The maximum difference in geoid heights predicted for the two models is only about two meters. The thermal structure of old lithosphere is unlikely to be resolvable using global geoid anomalies. Stripping the effects of plate aging and a hypothetical uniform, 35 km, isostatically-compensated continental crust from the observed geoid emphasizes that the largest-amplitude geoid anomaly is the geoid low of almost 120 m over West Antarctica, a factor of two greater than the low of 60 m over Ceylon.

  18. Isostaticity and Controlled Force Transmission in the Cytoskeleton: A Model Awaiting Experimental Evidence

    PubMed Central

    Blumenfeld, Raphael

    2006-01-01

    A new model is proposed for force transmission through the cytoskeleton (CSK). A general discussion is first presented on the physical principles that underlie the modeling of this phenomenon. Some fundamental problems of conventional models—continuous and discrete—are examined. It is argued that mediation of focused forces is essential for good control over intracellular mechanical signals. The difficulties of conventional continuous models in describing such mediation are traced to a fundamental assumption rather than to their being continuous. Relevant advantages and disadvantages of continuous and discrete modeling are discussed. It is concluded that favoring discrete models is based on two misconceptions, which are clarified. The model proposed here is based on the idea that focused propagation of mechanical stimuli in frameworks over large distances (compared to the mesh size) can only occur when considerable regions of the CSK are isostatic. The concept of isostaticity is explained and a recently developed continuous isostaticity theory is briefly reviewed. The model enjoys several advantages: it leads to good control over force mediation; it explains nonuniform stresses and action at a distance; it is continuous, making it possible to model force propagation over long distances; and it enables prediction of individual force paths. To be isostatic, or nearly so, CSK networks must possess specific structural characteristics, and these are quantified. Finally, several experimental observations are interpreted using the new model and implications are discussed. It is also suggested that this approach may give insight into the dynamics of reorganization of the CSK. Many of the results are amenable to experimental measurements, providing a testing ground for the proposed picture, and generic experiments are suggested. PMID:16912215

  19. Density Structure, Isostatic Balance and Tectonic Models of the Central Tien Shan

    NASA Astrophysics Data System (ADS)

    Kaban, Mikhail K.; Yuanda, T. Reiza

    2014-11-01

    A new combined satellite-terrestrial model of the gravity field is used together with seismic data for construction of a density model of the lithosphere of the Central Tien Shan and for estimation of its isostatic balance. The Tien Shan is one of the most active intraplate orogens in the world, located about 1,500 km north of the convergence between Indian and Eurasian plate, and surrounded by stable Kazakh platform to the north and the Tarim block to the south. Although this area was extensively studied during recent decades, several principal problems, related to its structure and tectonics, remain unsolved up to now: (1) various geodynamic scenarios have been discussed so far to explain tectonic evolution, such as direct "crustal shortening," intracontinental subduction and some others, but no definite evidence for any of them has been found. (2) Still, it is not clear why Tien Shan grows so far from the plate boundary at the Himalayan collision zone. Gravity modeling can provide valuable constraints to resolve these questions. The results of this study show that: (1) there exists a very strong deflection of the Tien Shan lithosphere from isostatic equilibrium. At the same time, the patterns of the isostatic anomalies are very different in the Western and Central Tien Shan. The latter one is characterized by much stronger variations. The best fit of the modeling results is found for the model according to which the Tarim plate partially underthrusts the Central Tien Shan; (2) negative density anomalies in the upper mantle under the central block possibly relate to magmatic underplating during the initial stage of the tectonic evolution. Therefore, the weak lithosphere could be the factor that initiates mountain building far away from the collision zone. Alternatively, this might be a gap after detachment of the eclogised lower crust and lithospheric lid, which is filled with the hot asthenospheric material.

  20. MohoIso: A MATLAB program to determine crustal thickness by an isostatic and a global gravitational model

    NASA Astrophysics Data System (ADS)

    Bagherbandi, Mohammad

    2012-07-01

    This paper focuses on the modeling of the boundary between Earth's crust and upper mantle using a gravimetric-isostatic model. Here a MATLAB code is presented based on the gravimetric-isostatic model i.e. the Vening Meinesz-Moritz model. Inverse problems in isostasy consist in making the isostatic anomalies to be zero under a certain isostatic hypothesis. The Vening Meinesz-Moritz problem is to determine the Moho depth such that the compensating attraction totally compensates the Bouguer gravity anomaly on the Earth's surface, implying that the isostatic anomaly vanishes on the Earth's surface. The main idea is easy but the theoretical analysis is somewhat difficult. Here a practical method to recover the Moho depth from the gravity data is used in the MATLAB code (MohoIso.m) based on the Vening Meinesz-Moritz method. The code has been designed based on different sub-codes. The body of the main code works according to the vectorization technique, because this technique causes that the speed of code increases. One of the important possible limitations for the code is over-flow and under-flow for higher degrees in the fully normalized associated Legendre function. This problem occurs in the subroutine applied in this study, it limits the numerical study up to degrees 1800-2000.

  1. An Empirical Model of Glacial-Isostatic Crustal Movements and Shore-Level Displacement in Scandinavia

    NASA Astrophysics Data System (ADS)

    Passe, T.; Moren, L.

    2002-05-01

    Crustal movements and shore-level displacement will affect subsurface conditions of importance for the performance and safety of deep geological repositories for spent nuclear fuel. To support performance and safety analysis an empirical model of the glacio-isostatic movements and shore-level displacement for the area covered by the Scandinavian ice sheet during the Weichselian glaciation has been developed. The purpose of the work was to compile data from different sites in Scandinavia to a generally applicable description of the evolution since the last deglaciation. The model is strictly empirical. The intention is not to explain the complex glacio-isostatic processes but merely to provide a tool for interpretations and evaluations of both geological observations and results from geophysical modelling. The model was initially based on detailed lake-tilting investigations. These made it possible to express the course of glacio-isostatic uplift in mathematical terms without using rheological assumptions. In addition to the lake-tilting information the model is based on 72 shore-level curves from all over Scandinavia and information concerning present relative uplift recorded by precision levelling and tide gauge data. The main uplift, still in progress, is mainly calculated from two factors designated the down load factor and the inertia factor. The down load factor represent the subsidence/uplift at the time for the maximal subsidence/uplift rate, and the inertia factor describes the evolution of the subsidence/uplift with time. There is a strong linear correlation between the inertia factor and lithosphere thickness. The model has been incorporated into a GIS (Geographic Information System) application, and can be illustrated together with other GIS data. The purpose of the modelling was to illustrate the course of events since the last deglaciation and the model is based on Late Weichselian and Holocen information. However, scenarios of past and future shore

  2. Glacial isostatic adjustment using GNSS permanent stations and GIA modelling tools

    NASA Astrophysics Data System (ADS)

    Kollo, Karin; Spada, Giorgio; Vermeer, Martin

    2013-04-01

    Glacial Isostatic Adjustment (GIA) affects the Earth's mantle in areas which were once ice covered and the process is still ongoing. In this contribution we focus on GIA processes in Fennoscandian and North American uplift regions. In this contribution we use horizontal and vertical uplift rates from Global Navigation Satellite System (GNSS) permanent stations. For Fennoscandia the BIFROST dataset (Lidberg, 2010) and North America the dataset from Sella, 2007 were used respectively. We perform GIA modelling with the SELEN program (Spada and Stocchi, 2007) and we vary ice model parameters in space in order to find ice model which suits best with uplift values obtained from GNSS time series analysis. In the GIA modelling, the ice models ICE-5G (Peltier, 2004) and the ice model denoted as ANU05 ((Fleming and Lambeck, 2004) and references therein) were used. As reference, the velocity field from GNSS permanent station time series was used for both target areas. Firstly the sensitivity to the harmonic degree was tested in order to reduce the computation time. In the test, nominal viscosity values and pre-defined lithosphere thicknesses models were used, varying maximum harmonic degree values. Main criteria for choosing the suitable harmonic degree was chi-square fit - if the error measure does not differ more than 10%, then one might use as well lower harmonic degree value. From this test, maximum harmonic degree of 72 was chosen to perform calculations, as the larger value did not significantly modify the results obtained, as well the computational time for observations was kept reasonable. Secondly the GIA computations were performed to find the model, which could fit with highest probability to the GNSS-based velocity field in the target areas. In order to find best fitting Earth viscosity parameters, different viscosity profiles for the Earth models were tested and their impact on horizontal and vertical velocity rates from GIA modelling was studied. For every

  3. Modelling the Laurentide Ice Sheet using improved ice margin chronologies and glacio-isostatic observations

    NASA Astrophysics Data System (ADS)

    Gowan, Evan; Tregoning, Paul; Purcell, Anthony; Lambeck, Kurt

    2013-04-01

    Creating models of the Laurentide ice sheet is challenging, due to the deficiency of chronological constraints and the uneven spatial resolution of data to determine the evolution of the glacio-isostatic response after deglaciation. Previous models relied on uncalibrated radiocarbon constrained margins that proved to have deficiencies in recent studies. Additionally, many recent Laurentide ice sheet models have been developed by incorporating climatic parameters that are poorly resolved for the late glacial period. We present a new ice sheet model by an iterative process of changing basal shear stress values and ice sheet margin location. A particular focus of this study is to determine the thickness and extent of the western Laurentide ice sheet, where there were few well dated observations of glacio-isostatic motion until recently. The volume of an ice sheet during long periods depends mostly on basal shear stress and margin position, which are the main parameters that we vary to fit our model to glacio-isostatic observations. We build our ice model using the assumption of perfectly plastic, steady-state conditions, with variable basal shear stress. Basal shear stress values depend on the surficial geology underlying the ice, and are at a minimum in offshore regions that have soft, deformable sediments, and at a maximum in areas with exposed crystalline bedrock. This approach may not capture dynamic and short lived features of the ice sheet, such as ice streams and stagnant ice, but gives an approximation of average conditions to produce ice volumes that fit geophysical observations. We adjust the margin location when the shear stress conditions alone cannot account for the observed glacio-isostatic response. The constraints on the response include relative sea level benchmarks, sea level highstand positions and proglacial lakes. We repeat the analysis using different rheological profiles to determine the dependence the Earth model has on the estimation of ice

  4. Spherical harmonic modelling to ultra-high degree of Bouguer and isostatic anomalies

    NASA Astrophysics Data System (ADS)

    Balmino, G.; Vales, N.; Bonvalot, S.; Briais, A.

    2012-07-01

    The availability of high-resolution global digital elevation data sets has raised a growing interest in the feasibility of obtaining their spherical harmonic representation at matching resolution, and from there in the modelling of induced gravity perturbations. We have therefore estimated spherical Bouguer and Airy isostatic anomalies whose spherical harmonic models are derived from the Earth's topography harmonic expansion. These spherical anomalies differ from the classical planar ones and may be used in the context of new applications. We succeeded in meeting a number of challenges to build spherical harmonic models with no theoretical limitation on the resolution. A specific algorithm was developed to enable the computation of associated Legendre functions to any degree and order. It was successfully tested up to degree 32,400. All analyses and syntheses were performed, in 64 bits arithmetic and with semi-empirical control of the significant terms to prevent from calculus underflows and overflows, according to IEEE limitations, also in preserving the speed of a specific regular grid processing scheme. Finally, the continuation from the reference ellipsoid's surface to the Earth's surface was performed by high-order Taylor expansion with all grids of required partial derivatives being computed in parallel. The main application was the production of a 1' × 1' equiangular global Bouguer anomaly grid which was computed by spherical harmonic analysis of the Earth's topography-bathymetry ETOPO1 data set up to degree and order 10,800, taking into account the precise boundaries and densities of major lakes and inner seas, with their own altitude, polar caps with bedrock information, and land areas below sea level. The harmonic coefficients for each entity were derived by analyzing the corresponding ETOPO1 part, and free surface data when required, at one arc minute resolution. The following approximations were made: the land, ocean and ice cap gravity spherical

  5. A model of the western Laurentide Ice Sheet, using observations of glacial isostatic adjustment

    NASA Astrophysics Data System (ADS)

    Gowan, Evan J.; Tregoning, Paul; Purcell, Anthony; Montillet, Jean-Philippe; McClusky, Simon

    2016-05-01

    We present the results of a new numerical model of the late glacial western Laurentide Ice Sheet, constrained by observations of glacial isostatic adjustment (GIA), including relative sea level indicators, uplift rates from permanent GPS stations, contemporary differential lake level change, and postglacial tilt of glacial lake level indicators. The later two datasets have been underutilized in previous GIA based ice sheet reconstructions. The ice sheet model, called NAICE, is constructed using simple ice physics on the basis of changing margin location and basal shear stress conditions in order to produce ice volumes required to match GIA. The model matches the majority of the observations, while maintaining a relatively realistic ice sheet geometry. Our model has a peak volume at 18,000 yr BP, with a dome located just east of Great Slave Lake with peak thickness of 4000 m, and surface elevation of 3500 m. The modelled ice volume loss between 16,000 and 14,000 yr BP amounts to about 7.5 m of sea level equivalent, which is consistent with the hypothesis that a large portion of Meltwater Pulse 1A was sourced from this part of the ice sheet. The southern part of the ice sheet was thin and had a low elevation profile. This model provides an accurate representation of ice thickness and paleo-topography, and can be used to assess present day uplift and infer past climate.

  6. Glacial isostatic adjustment associated with the Barents Sea ice sheet: A modelling inter-comparison

    NASA Astrophysics Data System (ADS)

    Auriac, A.; Whitehouse, P. L.; Bentley, M. J.; Patton, H.; Lloyd, J. M.; Hubbard, A.

    2016-09-01

    The 3D geometrical evolution of the Barents Sea Ice Sheet (BSIS), particularly during its late-glacial retreat phase, remains largely ambiguous due to the paucity of direct marine- and terrestrial-based evidence constraining its horizontal and vertical extent and chronology. One way of validating the numerous BSIS reconstructions previously proposed is to collate and apply them under a wide range of Earth models and to compare prognostic (isostatic) output through time with known relative sea-level (RSL) data. Here we compare six contrasting BSIS load scenarios via a spherical Earth system model and derive a best-fit, χ2 parameter using RSL data from the four main terrestrial regions within the domain: Svalbard, Franz Josef Land, Novaya Zemlya and northern Norway. Poor χ2 values allow two load scenarios to be dismissed, leaving four that agree well with RSL observations. The remaining four scenarios optimally fit the RSL data when combined with Earth models that have an upper mantle viscosity of 0.2-2 × 1021 Pa s, while there is less sensitivity to the lithosphere thickness (ranging from 71 to 120 km) and lower mantle viscosity (spanning 1-50 × 1021 Pa s). GPS observations are also compared with predictions of present-day uplift across the Barents Sea. Key locations where relative sea-level and GPS data would prove critical in constraining future ice-sheet modelling efforts are also identified.

  7. Hot Isostatic Pressing (HIP) Model Developments for P/M Alloy 690N{sub 2}

    SciTech Connect

    J.W. Sears; J. Xu

    2001-08-30

    Powder Metallurgy (P/M) Alloy 690N{sub 2}, the P/M derivative of Inconel 690 (IN 690), has been shown to have a higher elevated temperature yield strength and superior stress corrosion cracking (SCC) resistance than IN 690. The property improvements seen in P/M Alloy 690N{sub 2} are due to interstitial nitrogen strengthening and precipitation hardening resulting from the formation of fine titanium/chromium--carbo-nitrides. The application of P/M Alloy 690N{sub 2} has had limited use, because of the high costs involved in producing wrought products from powder. Hot Isostatic Pressing (HIP) modeling to produce near net shapes should provide a more economical route for exploiting the benefits of Alloy 690N{sub 2}. The efforts involved in developing and verifying the P/M Alloy 690N{sub 2} HIP model are disclosed. Key to the deployment of HIP modeling is the development of the method to fabricate HIP powder containers via laser powder deposition.

  8. A new glacial isostatic adjustment model of the Innuitian Ice Sheet, Arctic Canada

    NASA Astrophysics Data System (ADS)

    Simon, K. M.; James, T. S.; Dyke, A. S.

    2015-07-01

    A reconstruction of the Innuitian Ice Sheet (IIS) is developed that incorporates first-order constraints on its spatial extent and history as suggested by regional glacial geology studies. Glacial isostatic adjustment modelling of this ice sheet provides relative sea-level predictions that are in good agreement with measurements of post-glacial sea-level change at 18 locations. The results indicate peak thicknesses of the Innuitian Ice Sheet of approximately 1600 m, up to 400 m thicker than the minimum peak thicknesses estimated from glacial geology studies, but between approximately 1000 to 1500 m thinner than the peak thicknesses present in previous GIA models. The thickness history of the best-fit Innuitian Ice Sheet model developed here, termed SJD15, differs from the ICE-5G reconstruction and provides an improved fit to sea-level measurements from the lowland sector of the ice sheet. Both models provide a similar fit to relative sea-level measurements from the alpine sector. The vertical crustal motion predictions of the best-fit IIS model are in general agreement with limited GPS observations, after correction for a significant elastic crustal response to present-day ice mass change. The new model provides approximately 2.7 m equivalent contribution to global sea-level rise, an increase of +0.6 m compared to the Innuitian portion of ICE-5G. SJD15 is qualitatively more similar to the recent ICE-6G ice sheet reconstruction, which appears to also include more spatially extensive ice cover in the Innuitian region than ICE-5G.

  9. A data-driven model of present-day glacial isostatic adjustment in North America

    NASA Astrophysics Data System (ADS)

    Simon, Karen; Riva, Riccardo

    2016-04-01

    Geodetic measurements of gravity change and vertical land motion are incorporated into an a priori model of present-day glacial isostatic adjustment (GIA) via least-squares inversion. The result is an updated model of present-day GIA wherein the final predicted signal is informed by both observational data with realistic errors, and prior knowledge of GIA inferred from forward models. This method and other similar techniques have been implemented within a limited but growing number of GIA studies (e.g., Hill et al. 2010). The combination method allows calculation of the uncertainties of predicted GIA fields, and thus offers a significant advantage over predictions from purely forward GIA models. Here, we show the results of using the combination approach to predict present-day rates of GIA in North America through the incorporation of both GPS-measured vertical land motion rates and GRACE-measured gravity observations into the prior model. In order to assess the influence of each dataset on the final GIA prediction, the vertical motion and gravimetry datasets are incorporated into the model first independently (i.e., one dataset only), then simultaneously. Because the a priori GIA model and its associated covariance are developed by averaging predictions from a suite of forward models that varies aspects of the Earth rheology and ice sheet history, the final GIA model is not independent of forward model predictions. However, we determine the sensitivity of the final model result to the prior GIA model information by using different representations of the input model covariance. We show that when both datasets are incorporated into the inversion, the final model adequately predicts available observational constraints, minimizes the uncertainty associated with the forward modelled GIA inputs, and includes a realistic estimation of the formal error associated with the GIA process. Along parts of the North American coastline, improved predictions of the long-term (kyr

  10. Isostatic gravity map of the Death Valley ground-water model area, Nevada and California

    SciTech Connect

    Ponce, D.A.; Blakely, R.J.; Morin, R.L.; Mankinen, E.A.

    2002-03-12

    Gravity investigations of the Death Valley ground-water model area are part of an interagency effort by the U.S. Geological Survey (USGS) and the U.S. Department of Energy (Interagency agreement DE-AI08-96NV11967) to help characterize the geology and hydrology of southwestern Nevada and parts of California. The Death Valley ground-water model is located between lat 35 degrees 00' and 38 degrees 15' N., and long 115 degrees and 118 degrees W. An isostatic gravity map of the Death Valley ground-water model was prepared from over 40,000 gravity stations, most of which are publicly available on a CD-ROM of gravity data of Nevada (Ponce, 1997). The map also includes gravity data recently collected by the U.S. Geological Survey (Mankinen and others, 1998; Morin and Blakely, 1999). A subset of these gravity data in the Nevada Test Site and vicinity were described in detail by Harris and others (1989) who included information on gravity meters used, dates of collection, sources, descriptions of base stations, plots of data, and digital and paper lists of principal facts. For display purposes only, gravity data within Yucca Flat were thinned by a factor of 10. The digital gravity data set was gridded at an interval of 400 m using a computer program (Webring, 1981) based on a minimum curvature algorithm by Briggs (1974). The resulting grid was then interpolated to a 200-m grid to minimize pixel size, and then it was color contoured.

  11. An assessment of the ICE6G_C(VM5a) glacial isostatic adjustment model

    NASA Astrophysics Data System (ADS)

    Purcell, A.; Tregoning, P.; Dehecq, A.

    2016-05-01

    The recent release of the next-generation global ice history model, ICE6G_C(VM5a), is likely to be of interest to a wide range of disciplines including oceanography (sea level studies), space gravity (mass balance studies), glaciology, and, of course, geodynamics (Earth rheology studies). In this paper we make an assessment of some aspects of the ICE6G_C(VM5a) model and show that the published present-day radial uplift rates are too high along the eastern side of the Antarctic Peninsula (by ˜8.6 mm/yr) and beneath the Ross Ice Shelf (by ˜5 mm/yr). Furthermore, the published spherical harmonic coefficients—which are meant to represent the dimensionless present-day changes due to glacial isostatic adjustment (GIA)—contain excessive power for degree ≥90, do not agree with physical expectations and do not represent accurately the ICE6G_C(VM5a) model. We show that the excessive power in the high-degree terms produces erroneous uplift rates when the empirical relationship of Purcell et al. (2011) is applied, but when correct Stokes coefficients are used, the empirical relationship produces excellent agreement with the fully rigorous computation of the radial velocity field, subject to the caveats first noted by Purcell et al. (2011). Using the Australian National University (ANU) groups CALSEA software package, we recompute the present-day GIA signal for the ice thickness history and Earth rheology used by Peltier et al. (2015) and provide dimensionless Stokes coefficients that can be used to correct satellite altimetry observations for GIA over oceans and by the space gravity community to separate GIA and present-day mass balance change signals. We denote the new data sets as ICE6G_ANU.

  12. Sediment basin modeling through GOCE gradients controlled by thermo-isostatic constraints

    NASA Astrophysics Data System (ADS)

    Pivetta, Tommaso; Braitenberg, Carla

    2015-04-01

    Exploration of geodynamic and tectonic structures through gravity methods has experienced an increased interest in the recent years thank's to the possibilities offered by satellite gravimetry (e.g. GOCE). The main problem with potential field methods is the non-uniqueness of the underground density distributions that satisfy the observed gravity field. In terrestrial areas with scarce geological and geophysical information, valid constraints to the density model could be obtained from the application of geodynamic models. In this contribution we present the study of the gravity signals associated to the thermo-isostatic McKenzie-model (McKenzie, 1978) that predicts the development of sedimentary basins from the stretching of lithosphere. This model seems to be particularly intriguing for gravity studies as we could obtain estimates of densities and thicknesses of crust and mantle before and after a rifting event and gain important information about the time evolution of the sedimentary basin. The McKenzie-model distinguishes the rifting process into two distinct phases: a syn-rift phase that occurs instantly and is responsible of the basin formation, the thinning of lithosphere and the upwelling of hot asthenosphere. Then a second phase (post-rift), that is time dependent, and predicts further subsidence caused by the cooling of mantle and asthenosphere and subsequently increase in rock density. From the application of the McKenzie-model we have derived density underground distributions for two scenarios: the first scenario involves the lithosphere density distribution immediately after the stretching event; the second refers to the density model when thermal equilibrium between stretched and unstretched lithospheres is achieved. Calculations of gravity anomalies and gravity gradient anomalies are performed at 5km height and at the GOCE mean orbit quota (250km). We have found different gravity signals for syn-rift (gravimetric maximum) and post-rift (gravimetric

  13. An assessment of the ICE6G_C (VM5A) glacial isostatic adjustment model

    NASA Astrophysics Data System (ADS)

    Purcell, Anthony; Tregoning, Paul; Dehecq, Amaury

    2016-04-01

    The recent release of the next-generation global ice history model, ICE6G_C(VM5a) [Peltier et al., 2015, Argus et al. 2014] is likely to be of interest to a wide range of disciplines including oceanography (sea level studies), space gravity (mass balance studies), glaciology and, of course, geodynamics (Earth rheology studies). In this presentation I will assess some aspects of the ICE6G_C(VM5a) model and the accompanying published data sets. I will demonstrate that the published present-day radial uplift rates are too high along the eastern side of the Antarctic Peninsula (by ˜8.6 mm/yr) and beneath the Ross Ice Shelf (by ˜5 mm/yr). Further, the published spherical harmonic coefficients - which are meant to represent the dimensionless present-day changes due to glacial isostatic adjustment (GIA) - will be shown to contain excessive power for degree ≥ 90, to be physically implausible and to not represent accurately the ICE6G_C(VM5a) model. The excessive power in the high degree terms produces erroneous uplift rates when the empirical relationship of Purcell et al. [2011] is applied but, when correct Stokes' coefficients are used, the empirical relationship will be shown to produce excellent agreement with the fully rigorous computation of the radial velocity field, subject to the caveats first noted by Purcell et al. [2011]. Finally, a global radial velocity field for the present-day GIA signal, and corresponding Stoke's coefficients will be presented for the ICE6GC ice model history using the VM5a rheology model. These results have been obtained using the ANU group's CALSEA software package and can be used to correct satellite altimetry observations for GIA over oceans and by the space gravity community to separate GIA and present-day mass balance change signals without any of the shortcomings of the previously published data-sets. We denote the new data sets ICE6G_ANU.

  14. Formation of hyperextended rifted margins: Insights from flexural isostatic forward tectonic stratigraphic modeling and observations from fossil analogues

    NASA Astrophysics Data System (ADS)

    Mohn, G.; Kusznir, N. J.; Manatschal, G.

    2013-12-01

    The understanding of how continental lithosphere thins and ruptures leading to the formation of a new plate boundary represent a fundamental question in Earth Sciences. In particular the mechanisms controlling the extreme thinning of the continental crust, documented at many present-day rifted margins, are still poorly known. Many questions remain of the fundamental processes controlling the extensional deformation of the continental crust and lithosphere, including fault geometries and their evolution in space and time, the occurrence of decoupling horizons within the continental crust and the importance of depth dependent thinning processes. In this contribution, we aim to investigate the control of these key factors on continental crust and lithosphere thinning processes by coupling field observations from fossil analogues of rifted margins with flexural isostatic forward tectonic and stratigraphic modeling. Remnants of the Alpine Tethys rifted margins preserved in the Alpine orogeny in Western Europe represent an ideal natural laboratory providing direct access to rifted continental margin structures. This natural laboratory provides insights on fault geometry and kinematics, subsidence history and as well the nature of the basement rocks involved in rifting processes. These observations represent the input parameters to constrain the flexural isostatic forward modeling. Through this modeling, we produce isostatically balanced sections reproducing the geometries observed in the fossil analogues. Our results suggest that crust and lithosphere hyperextension results from the combination of both pure and simple shear deformation. The model predicts the critical role of intra-crustal decoupling horizons confirming the importance of depth-dependent thinning through polyphased rifting events. This ongoing work includes the analysis and modeling of present-day rifted margin examples such as the Iberia-Newfoundland rifted margins. These modeling results give critical

  15. Glacial isostatic adjustment model with composite 3-D Earth rheology for Fennoscandia

    NASA Astrophysics Data System (ADS)

    van der Wal, Wouter; Barnhoorn, Auke; Stocchi, Paolo; Gradmann, Sofie; Wu, Patrick; Drury, Martyn; Vermeersen, Bert

    2013-07-01

    Models for glacial isostatic adjustment (GIA) can provide constraints on rheology of the mantle if past ice thickness variations are assumed to be known. The Pleistocene ice loading histories that are used to obtain such constraints are based on an a priori 1-D mantle viscosity profile that assumes a single deformation mechanism for mantle rocks. Such a simplified viscosity profile makes it hard to compare the inferred mantle rheology to inferences from seismology and laboratory experiments. It is unknown what constraints GIA observations can provide on more realistic mantle rheology with an ice history that is not based on an a priori mantle viscosity profile. This paper investigates a model for GIA with a new ice history for Fennoscandia that is constrained by palaeoclimate proxies and glacial sediments. Diffusion and dislocation creep flow law data are taken from a compilation of laboratory measurements on olivine. Upper-mantle temperature data sets down to 400 km depth are derived from surface heatflow measurements, a petrochemical model for Fennoscandia and seismic velocity anomalies. Creep parameters below 400 km are taken from an earlier study and are only varying with depth. The olivine grain size and water content (a wet state, or a dry state) are used as free parameters. The solid Earth response is computed with a global spherical 3-D finite-element model for an incompressible, self-gravitating Earth. We compare predictions to sea level data and GPS uplift rates in Fennoscandia. The objective is to see if the mantle rheology and the ice model is consistent with GIA observations. We also test if the inclusion of dislocation creep gives any improvements over predictions with diffusion creep only, and whether the laterally varying temperatures result in an improved fit compared to a widely used 1-D viscosity profile (VM2). We find that sea level data can be explained with our ice model and with information on mantle rheology from laboratory experiments

  16. Modelling the density contrast and depth of the Moho discontinuity by seismic and gravimetric-isostatic methods with an application to Africa

    NASA Astrophysics Data System (ADS)

    Bagherbandi, Mohammad; Sjöberg, Lars E.

    2012-06-01

    The crustal thickness (Moho depth) is of interest in several geosciences applications, such as geography, geophysics and geodesy. Usually the crustal depth and density variations are estimated by seismic survey data. As such data collection is very time-consuming and expensive an attractive option could be to use a gravimetric/isostatic model. In this case, realistic estimates for the crustal density and Moho density contrast (MDC) are important. In this study, we first use the seismic crustal thickness of CRUST2.0 model as a known parameter in combination with gravimetric data in estimating the crust-mantle density contrast by the isostatic model of Vening Meinesz-Moritz. We present different models to estimate the MDC and its impact on the modelling of the gravimetric-isostatic Moho depth. The theory is applied to estimate the Moho depth of the African continental crust by using different models for the MDC: (a) constant value (0.6 g/cm3), (b) Pratt-Hayford's model, (c) CRUST2.0 as input to three gravimetric/isostatic models based on Vening Meinesz-Moritz theory. The isostatic models agree by 5.8-7.1 km in the rms with the regional seismic model at a resolution of 2° × 2°, and the smallest rms difference at a resolution of 1° × 1° is of 7.2 km. For comparison, the rms differences of CRUST2.0 and the regional seismic model are 8.8 and 9.1 km at the resolutions of 2° (interpolated) and 1°, respectively. The result suggests that the gravimetric/isostatic Moho model can be used in densification of the CRUST2.0 Moho geometry, and to improve it in areas with poor data.

  17. NKG201xGIA - first results for a new model of glacial isostatic adjustment in Fennoscandia

    NASA Astrophysics Data System (ADS)

    Steffen, Holger; Barletta, Valentina; Kollo, Karin; Milne, Glenn A.; Nordman, Maaria; Olsson, Per-Anders; Simpson, Matthew J. R.; Tarasov, Lev; Ågren, Jonas

    2016-04-01

    Glacial isostatic adjustment (GIA) is a dominant process in northern Europe, which is observed with several geodetic and geophysical methods. The observed land uplift due to this process amounts to about 1 cm/year in the northern Gulf of Bothnia. GIA affects the establishment and maintenance of reliable geodetic and gravimetric reference networks in the Nordic countries. To support a high level of accuracy in the determination of position, adequate corrections have to be applied with dedicated models. Currently, there are efforts within a Nordic Geodetic Commission (NKG) activity towards a model of glacial isostatic adjustment for Fennoscandia. The new model, NKG201xGIA, to be developed in the near future will complement the forthcoming empirical NKG land uplift model, which will substitute the currently used empirical land uplift model NKG2005LU (Ågren & Svensson, 2007). Together, the models will be a reference for vertical and horizontal motion, gravity and geoid change and more. NKG201xGIA will also provide uncertainty estimates for each field. Following former investigations, the GIA model is based on a combination of an ice and an earth model. The selected reference ice model, GLAC, for Fennoscandia, the Barents/Kara seas and the British Isles is provided by Lev Tarasov and co-workers. Tests of different ice and earth models will be performed based on the expertise of each involved modeler. This includes studies on high resolution ice sheets, different rheologies, lateral variations in lithosphere and mantle viscosity and more. This will also be done in co-operation with scientists outside NKG who help in the development and testing of the model. References Ågren, J., Svensson, R. (2007): Postglacial Land Uplift Model and System Definition for the New Swedish Height System RH 2000. Reports in Geodesy and Geographical Information Systems Rapportserie, LMV-Rapport 4, Lantmäteriet, Gävle.

  18. Lithospheric thickness jumps at the S-Atlantic continental margins from satellite gravity data and modelled isostatic anomalies

    NASA Astrophysics Data System (ADS)

    Shahraki, Meysam; Schmeling, Harro; Haas, Peter

    2016-04-01

    Isostatic equilibrium is a good approximation for passive continental margins. In these regions, geoid anomalies are proportional to the local dipole moment of density-depth distributions, which can be used to constrain the thickness of lithospheric jumps and corresponding tectonic stress. We analysed satellite derived geoid data and, after filtering, extracted typical averaged profiles across the Western and Eastern passive margins of the South Atlantic. They show geoid jumps of 8.1 m and 7.0 m for the Argentinian and African sides, respectively. Together with topography data and reasonable assumptions about densities these jumps are interpreted as isostatic geoid anomalies and yield best-fitting crustal and lithospheric thicknesses. They reveal a small asymmetry between the African and S-American crusts and lithospheres by a few kilometers. On both sides, the continental lithosphere is about 15 - 30km thicker than the oceanic lithosphere. To keep such geoid jumps stable over O(100Ma) fully dynamic models show that lithospheric viscosities must be of the order of 1e23 Pa s.

  19. Sensitivity of palaeotidal models of the northwest European shelf seas to glacial isostatic adjustment since the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Ward, Sophie L.; Neill, Simon P.; Scourse, James D.; Bradley, Sarah L.; Uehara, Katsuto

    2016-11-01

    The spatial and temporal distribution of relative sea-level change over the northwest European shelf seas has varied considerably since the Last Glacial Maximum, due to eustatic sea-level rise and a complex isostatic response to deglaciation of both near- and far-field ice sheets. Because of the complex pattern of relative sea level changes, the region is an ideal focus for modelling the impact of significant sea-level change on shelf sea tidal dynamics. Changes in tidal dynamics influence tidal range, the location of tidal mixing fronts, dissipation of tidal energy, shelf sea biogeochemistry and sediment transport pathways. Significant advancements in glacial isostatic adjustment (GIA) modelling of the region have been made in recent years, and earlier palaeotidal models of the northwest European shelf seas were developed using output from less well-constrained GIA models as input to generate palaeobathymetric grids. We use the most up-to-date and well-constrained GIA model for the region as palaeotopographic input for a new high resolution, three-dimensional tidal model (ROMS) of the northwest European shelf seas. With focus on model output for 1 ka time slices from the Last Glacial Maximum (taken as being 21 ka BP) to present day, we demonstrate that spatial and temporal changes in simulated tidal dynamics are very sensitive to relative sea-level distribution. The new high resolution palaeotidal model is considered a significant improvement on previous depth-averaged palaeotidal models, in particular where the outputs are to be used in sediment transport studies, where consideration of the near-bed stress is critical, and for constraining sea level index points.

  20. Hot isostatic pressing: Conference proceedings

    SciTech Connect

    Froes, F.H.; Hebeisen, J.; Widmer, R.

    1996-12-31

    The International Conference on Hot Isostatic Pressing was held on May 20-22, 1996, in Andover, Massachusetts. This conference discussed the state-of-the-art of hot isostatic pressing (HIP) and competing compaction techniques. HIP allows complex cost-effective near net shapes to be produced from powder products, densification of castings thereby enhancing performance, retention of metastable structures such as nano-sized grains, and even creative food processing. Sections in the conference covered such items as fundamentals, mathematical modeling, equipment and instrumentation, advanced materials and processes, composite materials, casting densification, surface treatments, HIP bonding, and competing technologies. Forty five papers were processed separately for inclusion on the data base.

  1. The timing of the Black Sea flood event: Insights from modeling of glacial isostatic adjustment

    NASA Astrophysics Data System (ADS)

    Goldberg, Samuel L.; Lau, Harriet C. P.; Mitrovica, Jerry X.; Latychev, Konstantin

    2016-10-01

    We present a suite of gravitationally self-consistent predictions of sea-level change since Last Glacial Maximum (LGM) in the vicinity of the Bosphorus and Dardanelles straits that combine signals associated with glacial isostatic adjustment (GIA) and the flooding of the Black Sea. Our predictions are tuned to fit a relative sea level (RSL) record at the island of Samothrace in the north Aegean Sea and they include realistic 3-D variations in viscoelastic structure, including lateral variations in mantle viscosity and the elastic thickness of the lithosphere, as well as weak plate boundary zones. We demonstrate that 3-D Earth structure and the magnitude of the flood event (which depends on the pre-flood level of the lake) both have significant impact on the predicted RSL change at the location of the Bosphorus sill, and therefore on the inferred timing of the marine incursion. We summarize our results in a plot showing the predicted RSL change at the Bosphorus sill as a function of the timing of the flood event for different flood magnitudes up to 100 m. These results suggest, for example, that a flood event at 9 ka implies that the elevation of the sill was lowered through erosion by ∼14-21 m during, and after, the flood. In contrast, a flood event at 7 ka suggests erosion of ∼24-31 m at the sill since the flood. More generally, our results will be useful for future research aimed at constraining the details of this controversial, and widely debated geological event.

  2. Vertical motions in Northern Victoria Land inferred from GPS: A comparison with a glacial isostatic adjustment model

    USGS Publications Warehouse

    Mancini, F.; Negusini, M.; Zanutta, A.; Capra, A.

    2007-01-01

    Following the densification of GPS permanent and episodic trackers in Antarctica, geodetic observations are playing an increasing role in geodynamics research and the study of the glacial isostatic adjustment (GIA). The improvement in geodetic measurements accuracy suggests their use in constraining GIA models. It is essential to have a deeper knowledge on the sensitivity of GPS data to motionsrelated to long-term ice mass changes and the present-day mass imbalance of the ice sheets. In order to investigate the geodynamic phenomena in Northern Victoria Land (NVL), GPS geodetic observations were made during the last decade within the VLNDEF (Victoria Land Network for Deformation control) project. The processed data provided a picture of the motions occurring in NVL with a high level of accuracy and depicts, for the whole period, a well defined pattern of vertical motion. The comparison between GPS-derived vertical displacementsand GIA is addressed, showing a good degree of agreement and highlighting the future use of geodetic GPS measurements as constraints in GIA models. In spite of this agreement, the sensitivity of GPS vertical rates to non-GIA vertical motions has to be carefully evaluated.

  3. Model of the western Laurentide Ice Sheet from glacio-isostatic adjustment analysis and revised margin locations

    NASA Astrophysics Data System (ADS)

    Gowan, E. J.; Tregoning, P.; Purcell, A.

    2013-12-01

    Uncertainties in ice sheet extent and thickness during the retreat of the western Laurentide Ice Sheet from the last glacial maximum affect estimates of its contribution to global climate and sea level change during the late Pleistocene and early Holocene. These difficulties arise due to a lack of chronological constraints on the timing of margin retreat in many areas and a lack of observations of the glacio-isostatic deformation due the ice sheet. We present a model of the western Laurentide ice sheet in North America based on new ice margin reconstructions and well dated glacial lake strandlines. The model of the Laurentide ice sheet is constructed based on the assumption of perfectly plastic, steady state conditions with temporally variable basal shear stress and margin location. Initial models of basal shear stress were based on modern surficial geology and geography, and adjusted in an iterative process to reflect the volume of ice needed to fit observations of earth deformation caused by the ice sheet. The ice margins were developed by determining the minimum timing of retreat and using that as a constraint on the absolute maximum possible ice margin location. By using the ice margin as the starting point of modelling, assumptions on the location of ice domes and saddles were avoided. Initial results of the modelling indicate that ice thickness remained below 1500 m throughout the Western Canadian Sedimentary Basin region at the last glacial maximum as a result of low basal shear stress. Modelled flow direction matches geomorphic ice flow indicators lending confidence to the glaciological model. Ice sheet margin retreat was limited until after 15,000 cal yr BP. The most significant ice volume losses happened after retreat from southern Alberta and after retreat began on the Canadian Shield.

  4. Formation of hyperextended rifted margins: Insights from flexural isostatic structural-stratigraphic modeling and observations from present-day rifted margins

    NASA Astrophysics Data System (ADS)

    Mohn, Geoffroy; Kusznir, Nick; Manatschal, Gianreto

    2014-05-01

    The understanding of how continental lithosphere extends, thins and ruptures leading to the formation of a new divergent plate boundary represent a fundamental question in Earth Sciences. In particular the mechanisms controlling the extreme pre-breakup stretching and thinning of the continental crust and lithosphere, documented at many present-day rifted margins, are still poorly known. Many questions remain of the fundamental processes controlling the extensional deformation of the continental crust and lithosphere, including fault geometries and their evolution in space and time, the occurrence of decoupling horizons within the continental crust and the importance of depth-dependent lithosphere thinning processes. We investigate the control of these key factors on continental crust and lithosphere thinning processes by combining seismic reflection and drill-hole observations from present-day Iberia-Newfoundland rifted margins with flexural isostatic forward tectonic and stratigraphic modeling. These observations made at present-day rifted margins constrain the input parameters used in the flexural isostatic forward modeling. At the same time, the forward tectonic and stratigraphic modeling provides validation of the interpretation of the seismic reflection data. Through this modeling, we produce isostatically and thermally balanced sections reproducing the geometries observed along the Iberia-Newfoundland rifted margins. Our results suggest that crustal and lithospheric thinning results from the combination of both pure- and simple-shear deformation. The model predicts the critical role of intra-crustal decoupling horizons confirming the importance of depth-dependent thinning through polyphased rifting events.

  5. Comparative analysis of Vening-Meinesz Moritz isostatic models using the constant and variable crust-mantle density contrast - a case study of Zealandia

    NASA Astrophysics Data System (ADS)

    Bagherbandi, Mohammad; Tenzer, Robert

    2013-04-01

    We compare three different numerical schemes of treating the Moho density contrast in gravimetric inverse problems for finding the Moho depths. The results are validated using the global crustal model CRUST2.0, which is determined based purely on seismic data. Firstly, the gravimetric recovery of the Moho depths is realized by solving Moritz's generalization of the Vening-Meinesz inverse problem of isostasy while the constant Moho density contrast is adopted. The Pratt-Hayford isostatic model is then facilitated to estimate the variable Moho density contrast. This variable Moho density contrast is subsequently used to determine the Moho depths. Finally, the combined least-squares approach is applied to estimate jointly the Moho depths and density contract based on a priori error model. The EGM2008 global gravity model and the DTM2006.0 global topographic/bathymetric model are used to generate the isostatic gravity anomalies. The comparison of numerical results reveals that the optimal isostatic inverse scheme should take into consideration both the variable depth and density of compensation. This is achieved by applying the combined least-squares approach for a simultaneous estimation of both Moho parameters. We demonstrate that the result obtained using this method has the best agreement with the CRUST2.0 Moho depths. The numerical experiments are conducted at the regional study area of New Zealand's continental shelf.

  6. Modelling Late Cenozoic isostatic elevation changes in the Barents Sea and their implications for oceanic and climatic regimes: preliminary results

    NASA Astrophysics Data System (ADS)

    Butt, Faisal A.; Drange, Helge; Elverhøi, Anders; Otterå, Odd Helge; Solheim, Anders

    2002-08-01

    Late Cenozoic isostatic changes in the elevation of the Barents Sea are simulated using a numerical model. Isopach maps of the deposits off present-day Bear Island and Storfjorden troughs made earlier are used to calculate the thickness of sediment cover removed from the respective drainages basins at various time intervals during the last 2.3 Ma. Results indicate that Barents Sea was subaerially exposed at 2.3 Ma and major parts of it became submarine after 1 Ma. Barents Sea today receives around 40% of the warm and saline North Atlantic waters flowing into the Scotland-Greenland Ridge and about half of the Atlantic water entering the Arctic Ocean. It thus has an important role to play in the present-day ocean circulation pattern in the Polar North Atlantic region and water-mass transformations that take place in the Greenland-Iceland-Norwegian Sea and the Arctic Ocean. The effects of an uplifted Barents Sea on the oceanic regime and the Arctic sea-ice cover under the present-day forcings fields are studied using the Miami Isopycnic Coordinate Ocean Model. Preliminary results indicate that a subaerial Barents Sea causes an increased input of warm Atlantic waters into the Arctic Ocean through the Fram Strait which results in warming of the Atlantic water masses in the Arctic Ocean, followed by a reduction in the sea-ice cover. The obtained findings can be used to explain the apparent discrepancy in the late Cenozoic record of the sub-Arctic and Arctic regions whereby Fennoscandia, Iceland and Greenland are envisaged to have been covered by major ice sheets during late Pliocene whereas high Arctic areas such as Svalbard and NE Greenland were apparently free of any major ice.

  7. Holocene sea-level changes along the North Carolina Coastline and their implications for glacial isostatic adjustment models

    USGS Publications Warehouse

    Horton, B.P.; Peltier, W.R.; Culver, S.J.; Drummond, R.; Engelhart, S.E.; Kemp, A.C.; Mallinson, D.; Thieler, E.R.; Riggs, S.R.; Ames, D.V.; Thomson, K.H.

    2009-01-01

    We have synthesized new and existing relative sea-level (RSL) data to produce a quality-controlled, spatially comprehensive database from the North Carolina coastline. The RSL database consists of 54 sea-level index points that are quantitatively related to an appropriate tide level and assigned an error estimate, and a further 33 limiting dates that confine the maximum and minimum elevations of RSL. The temporal distribution of the index points is very uneven with only five index points older than 4000 cal a BP, but the form of the Holocene sea-level trend is constrained by both terrestrial and marine limiting dates. The data illustrate RSL rapidly rising during the early and mid Holocene from an observed elevation of -35.7 ?? 1.1 m MSL at 11062-10576 cal a BP to -4.2 m ?? 0.4 m MSL at 4240-3592 cal a BP. We restricted comparisons between observations and predictions from the ICE-5G(VM2) with rotational feedback Glacial Isostatic Adjustment (GIA) model to the Late Holocene RSL (last 4000 cal a BP) because of the wealth of sea-level data during this time interval. The ICE-5G(VM2) model predicts significant spatial variations in RSL across North Carolina, thus we subdivided the observations into two regions. The model forecasts an increase in the rate of sea-level rise in Region 1 (Albemarle, Currituck, Roanoke, Croatan, and northern Pamlico sounds) compared to Region 2 (southern Pamlico, Core and Bogue sounds, and farther south to Wilmington). The observations show Late Holocene sea-level rising at 1.14 ?? 0.03 mm year-1 and 0.82 ?? 0.02 mm year-1 in Regions 1 and 2, respectively. The ICE-5G(VM2) predictions capture the general temporal trend of the observations, although there is an apparent misfit for index points older than 2000 cal a BP. It is presently unknown whether these misfits are caused by possible tectonic uplift associated with the mid-Carolina Platform High or a flaw in the GIA model. A comparison of local tide gauge data with the Late Holocene RSL

  8. Constraints of GRACE on the Ice Model and Mantle Rheology in Glacial Isostatic Adjustment Modeling in North-America

    NASA Astrophysics Data System (ADS)

    van der Wal, W.; Wu, P.; Sideris, M.; Wang, H.

    2009-05-01

    GRACE satellite data offer homogeneous coverage of the area covered by the former Laurentide ice sheet. The secular gravity rate estimated from the GRACE data can therefore be used to constrain the ice loading history in Laurentide and, to a lesser extent, the mantle rheology in a GIA model. The objective of this presentation is to find a best fitting global ice model and use it to study how the ice model can be modified to fit a composite rheology, in which creep rates from a linear and non-linear rheology are added. This is useful because all the ice models constructed from GIA assume that mantle rheology is linear, but creep experiments on rocks show that nonlinear rheology may be the dominant mechanism in some parts of the mantle. We use CSR release 4 solutions from August 2002 to October 2008 with continental water storage effects removed by the GLDAS model and filtering with a destriping and Gaussian filter. The GIA model is a radially symmetric incompressible Maxwell Earth, with varying upper and lower mantle viscosity. Gravity rate misfit values are computed for with a range of viscosity values with the ICE-3G, ICE-4G and ICE-5G models. The best fit is shown for models with ICE-3G and ICE-4G, and the ICE-4G model is selected for computations with a so-called composite rheology. For the composite rheology, the Coupled Laplace Finite-Element Method is used to compute the GIA response of a spherical self-gravitating incompressible Maxwell Earth. The pre-stress exponent (A) derived from a uni- axial stress experiment is varied between 3.3 x 10-34/10-35/10-36 Pa-3s-1, the Newtonian viscosity η is varied between 1 and 3 x 1021 Pa-s, and the stress exponent is taken to be 3. Composite rheology in general results in geoid rates that are too small compared to GRACE observations. Therefore, simple modifications of the ICE-4G history are investigated by scaling ice heights or delaying glaciation. It is found that a delay in glaciation is a better way to adjust ice

  9. A Least Squares Collocation Approach with GOCE gravity gradients for regional Moho-estimation

    NASA Astrophysics Data System (ADS)

    Rieser, Daniel; Mayer-Guerr, Torsten

    2014-05-01

    The depth of the Moho discontinuity is commonly derived by either seismic observations, gravity measurements or combinations of both. In this study, we aim to use the gravity gradient measurements of the GOCE satellite mission in a Least Squares Collocation (LSC) approach for the estimation of the Moho depth on regional scale. Due to its mission configuration and measurement setup, GOCE is able to contribute valuable information in particular in the medium wavelengths of the gravity field spectrum, which is also of special interest for the crust-mantle boundary. In contrast to other studies we use the full information of the gradient tensor in all three dimensions. The problem outline is formulated as isostatically compensated topography according to the Airy-Heiskanen model. By using a topography model in spherical harmonics representation the topographic influences can be reduced from the gradient observations. Under the assumption of constant mantle and crustal densities, surface densities are directly derived by LSC on regional scale, which in turn are converted in Moho depths. First investigations proofed the ability of this method to resolve the gravity inversion problem already with a small amount of GOCE data and comparisons with other seismic and gravitmetric Moho models for the European region show promising results. With the recently reprocessed GOCE gradients, an improved data set shall be used for the derivation of the Moho depth. In this contribution the processing strategy will be introduced and the most recent developments and results using the currently available GOCE data shall be presented.

  10. Holocene relative sea-level change, isostatic subsidence and the radial viscosity structure of the mantle of northwest Europe and the southern North Sea: Observational and model results

    NASA Astrophysics Data System (ADS)

    Vink, A.; Steffen, H.; Reinhardt, L.; Frechen, M.; Kaufmann, G.

    2009-04-01

    A thorough understanding of the causes and effects of differential relative sea-level (RSL) rise in the southern North Sea region since the end of the Last Glacial Maximum is important to help predict future morphological development along the intensively utilised northwest European coastal zone. In this study, a comprehensive observational database of Holocene RSL index points from northwest Europe (Belgium, the Netherlands, northwest Germany, southern North Sea) has been compiled in order to compare and reassess the data collected from the different countries/regions and by different workers on a common time-depth scale. RSL-rise varies in magnitude and form between these regions, revealing a complex pattern of differential crustal movement which cannot be solely attributed to tectonic activity. It clearly contains a non-linear, glacio- and/or hydro-isostatic subsidence component, which is only small on the Belgian coastal plain but increases significantly to a value of ca. 7.5 m relative to Belgium since 8 cal. kyr BP along the northwest German coast. The subsidence is at least in part related to the post-glacial collapse of the so-called peripheral forebulge which developed around the Fennoscandian centre of ice loading during the Last Glacial Maximum. The RSL data have been compared to geodynamic Earth models in order to infer the radial viscosity structure of the Earths mantle underneath NW Europe (lithosphere thickness, upper and lower mantle viscosity), and conversely to predict RSL and reconstruct palaeoshorelines in regions where we have only few observational data (e.g. in the German Bight). A very broad range of Earth parameters fit the Belgian RSL data, suggesting that glacial isostatic adjustment (GIA) only had a minor effect on Belgian crustal dynamics during and after the last ice age. In contrast, a narrow range of Earth parameters define the southern North Sea region, reflecting the greater influence of GIA on these deeper/older samples. Modelled

  11. Gravity field and isostatic state of Ethiopia and adjacent areas

    NASA Astrophysics Data System (ADS)

    Woldetinsae, G.; Götze, H.-J.

    2005-01-01

    Over 35,000 onshore and offshore gravity stations have been compiled in order to test isostatic models against geologic structures over a part of the Afro-Arabian shield. The area of Ethiopia covers an important part of this system because it contains the major section of the ≈5000 km Afro-Arabian rift and includes the transition between the Arabo-Nubian-Shield (ANS) and the Mozambique Belt (MB). Isostatic residual anomalies have been calculated using both Airy and Vening-Meinesz (flexural rigidity D = 10 22 Nm) models. The isostatic residual anomalies outline the major Precambrian belts, the Cenozoic rifts and associated major structures. Positive residual anomalies associated with the main Ethiopian Rift (MER) and Kenyan rift systems could be the expressions of an axial intrusive body and swarms of local faults and fractures. The residual anomalies indicate relative stability in the MER and increased tectonic activity in the areas of the Red Sea, Gulf of Aden and Afar. Near-zero isostatic residuals flank the MER and Kenya rifts and are found within the Danakil Alps and some plateau regions. The small mean isostatic residual anomaly (about 8 mGal) and the isostatic analysis show a slight positive bias indicating under compensation. The undercompensation may imply that there are upper crustal features that are not compensated regionally (probably supported by the rigidity of the lithosphere) and isostatic disequilibrium in the region. Therefore, the high topography of Ethiopia and East African plateau is partly compensated by thicker crust (broad negative isostatic regional anomaly) and partly by dynamic forces. The results of the qualitative interpretation form the basis of continuing three-dimensional gravity modelling and quantitative analysis that also integrates data from eastern Sudan.

  12. Sensitivity of glacial isostatic adjustment models with shallow low-viscosity earth layers to the ice-load history in relation to the performance of GOCE and GRACE

    NASA Astrophysics Data System (ADS)

    Schotman, H. H. A.; Vermeersen, L. L. A.

    2005-08-01

    The GOCE satellite mission, which is planned by ESA for launch in August 2006, is designed to map the static global gravity field with centimeter accuracy in geoid height at 100 km or better resolution. Such a global high resolution gravity field might be able to constrain properties of shallow low-viscosity zones (LVZs) using glacial isostatic adjustment (GIA) models. In (L.L.A. Vermeersen, The potential of GOCE in constaining the structure of the crust and lithosphere from post-gracial rebound, Space Sci. Rev. 108 (2003) 105-113.) and (W. van der Wal, H.H.A. Schotman, L.L.A. Vermeersen, Geoid heights due to a crustal low viscosity zone in glacial isostatic adjustment modeling; a sensitivity analysis for GOCE, Geophys. Res. Lett. 31 (2004) 10.1029/2003GL019139.) it is shown that a crustal low-viscosity zone (CLVZ) introduces variations in geoid height up to several decimeters with spatial scales down to hundred kilometers underneath and just outside formerly glaciated areas. In (W. van der Wal, H.H.A. Schotman, L.L.A. Vermeersen, Geoid heights due to a crustal low viscosity zone in glacial isostatic adjustment modeling; a sensitivity analysis for GOCE, Geophys. Res. Lett. 31 (2004) 10.1029/2003GL019139.) it is shown that the response is sensitive to both changes in the properties of the CLVZ and the Late Pleistocene ice-load history. In this study we quantify the sensitivity to ice-load history, and investigate the effect of an asthenospheric low-viscosity zone (ALVZ) just below the lithosphere. We show, using spherical harmonic degree amplitudes, that GOCE is predicted to be sensitive to differences in the load history up to degree 130 for a CLVZ and degree 70 for an ALVZ. The sensitivity of GRACE, using the realized performance over a 111-day period (GGM01S, (B.D. Tapley, S. Bettadpur, M. Watkins, C. Reigber, The gravity recovery and climate experiment: Mission overview and early results, Geophys. Res Lett. 31 (2004) 10.1029/2004GL019920.)) is limited to lower

  13. The thickness history of the northern sector of the Laurentide Ice Sheet: an assessment of glacial isostatic adjustment models, sea-level measurements, and vertical land motion rates

    NASA Astrophysics Data System (ADS)

    Simon, K. M.; James, T. S.; Henton, J. A.; Dyke, A.

    2014-12-01

    The fit of glacial isostatic adjustment (GIA) model predictions to 24 relative sea-level histories and an additional 18 present-day GPS-measured vertical land motion rates constrains the thickness and volume history of the central and northern Laurentide Ice Sheet. The predictions of the best-fit GIA model indicate respective peak ice thicknesses west and east of Hudson Bay of 3.4-3.6 km and approximately 4 km. These values represent, respectively, a large decrease, and a moderate increase, to the load thickness compared to ICE-5G. This result is generally consistent with other GIA studies focussing on space-geodetic constraints. The large reduction to the ice load west of Hudson Bay also reduces the vertical mantle response along the margins of the load centre, which improves the fit to relative sea-level data from the southern Canadian Arctic Archipelago. The fit of GIA model predictions to relative sea-level data from the Baffin Sector of the Laurentide Ice Sheet indicate peak ice thicknesses there of 1.2-1.3 km, a modest reduction compared to ICE-5G. On Baffin Island, the modelled elastic crustal response of the Earth to present-day ice mass changes is large. Accounting for this effect improves the agreement between GPS measurements of vertical crustal motion and the GIA model predictions. However, work is needed to incorporate more detailed observations and modelling of present-day changes to glaciers and ice caps. Overall, the fit to the data is most strongly improved in the region west of Hudson Bay (the χ2 RSL misfit is reduced by a factor of ~4) although the entire revised reconstruction for the central and northern Laurentide Ice Sheet provides an improved fit to both the regional RSL data (the cumulative χ2 misfit is reduced by a factor of >2) and the GPS data (the RMS misfit is reduced by a factor of 9).

  14. Glacio-isostatic Adjustment Modeling of new Relative Sea-level Observations From the Northern Cascadia Subduction Zone, British Columbia, Canada

    NASA Astrophysics Data System (ADS)

    James, T. S.; Gowan, E. J.; Wada, I.

    2008-12-01

    Late-glacial sea-level curves located above the Cascadia Subduction Zone (CSZ) in southwestern British Columbia show that glacio-isostatic adjustment (GIA) was rapid when the Cordilleran ice sheet collapsed in the late Pleistocene. GIA models developed to explain the sea-level observations employ an ice sheet model modified from previous studies. The Earth models vary radially and feature an elastic lithosphere and a linear Maxwell viscoelastic mantle with the VM2 viscosity structure in the deeper parts of the mantle. The thickness and viscosity of a laterally homogeneous asthenosphere are systematically varied to find the combinations that best explain the sea-level observations. The observations can be equally well fit across a wide range of asthenospheric thicknesses, provided that the asthenospheric viscosity is varied from 3 x 1018 Pa s for a thin (140 km) asthenosphere to 1019 Pa s at 220 km thickness to 4 x 1019 Pa s for a thick (380 km) asthenosphere. The sea-level observations are located in the CSZ forearc above the stagnant mantle wedge. Thus, the model viscosity values probably pertain largely to the viscosity of the oceanic mantle beneath the subducting Juan de Fuca plate, although a contribution from the hot, low- viscosity arc and backarc continental mantle is also likely. Effective viscosities for the upper mantle due to tectonics (subduction) were computed using the strain-rates and temperatures of a geodynamic model of the CSZ and a wet-olivine power-law rheology. The effective viscosities agree well with GIA model viscosities of 1019 Pa s or less, corresponding to an asthenosphere of one or two hundred kilometers thickness. Models of the megathrust earthquake cycle at young subduction zones that feature oceanic mantle asthenosphere viscosities larger than about 1019 Pa s need to be modified to incorporate the new constraints provided by the GIA modeling. An implication for megathrust earthquake models of a reduction in oceanic asthenospheric

  15. Lithosphere and upper-mantle structure of the southern Baltic Sea estimated from modelling relative sea-level data with glacial isostatic adjustment

    NASA Astrophysics Data System (ADS)

    Steffen, H.; Kaufmann, G.; Lampe, R.

    2014-06-01

    thickness as determined with ICE-5G does not agree with the lithosphere models. Hence, more investigations have to be undertaken to sufficiently determine structures such as the Ringkøbing-Fyn High as seen with seismics with the help of glacial isostatic adjustment modelling.

  16. Modelling the influence of Lake Agassiz on Glacial Isostatic Adjustment and deglaciation of the Laurentide ice sheet

    NASA Astrophysics Data System (ADS)

    Berends, Tijn; van de Wal, Roderik; de Boer, Bas; Bradley, Sarah

    2016-04-01

    ANICE is a 3-D ice-sheet-shelf model, which simulates ice dynamics on the continental scale. It uses a combination of the SIA and SSA approximations and here it is forced with benthic δ18O records using an inverse routine. It is coupled to SELEN, a model, which solves the gravitationally self-consistent sea-level equation and the solid earth deformation of a spherically symmetrical rotating Maxwell visco-elastic earth, accounting for all major GIA effects. The coupled ANICE-SELEN model thus captures ice-sea-level feedbacks and can be used to accurately simulate variations in local relative sea-level over geological time scales. In this study it is used to investigate the mass loss of the Laurentide ice-sheet during the last deglaciation, accounting in particular for the presence of the proglacial Lake Agassiz by way of its GIA effects and its effect on the ice sheet itself. We show that the mass of the water can have a significant effect on local relative sea-level through the same mechanisms as the ice-sheet - by perturbing the geoid and by deforming the solid earth. In addition we show that calving of the ice-shelf onto the lake could have had a strong influence on the behaviour of the deglaciation. In particular, when allowing lake calving, the ice-sheet retreats rapidly over the deepening bed of Hudson Bay during the deglaciation, resulting in a narrow ice dam over Hudson Strait. This dam collapses around 8.2 Kyr causing a global sea level rise of approximately 1 meter - an observation that agrees well with field data (for example, LaJeunesse and St. Onge, 2008). Without lake calving the model predicts a drainage towards the Arctic ocean in the North.

  17. Glacial isostatic uplift of the European Alps

    NASA Astrophysics Data System (ADS)

    Mey, Juergen; Scherler, Dirk; Wickert, Andrew D.; Egholm, David L.; Tesauro, Magdala; Schildgen, Taylor F.; Strecker, Manfred R.

    2016-04-01

    Present-day vertical movements of the Earth's surface are mostly due to tectonic deformation, volcanic processes, and crustal loading/unloading. In tectonically stable regions of North America and Scandinavia, vertical movements are almost entirely attributable to glacial isostatic rebound after the melting of the Laurentide and Fennoscandian ice sheets. In contrast, the Pleistocene Alpine icecap grew on a younger mountain belt that formed by collision of the European and African plates, still subject to shortening. Therefore, measured uplift is potentially a composite signal of tectonic shortening and unloading after deglaciation and concomitant erosion. Deciphering the contributions of tectonics and crustal unloading to present-day uplift rates in formerly-glaciated mountain belts is a prerequisite to using uplift data to estimate the viscosity structure of the Earth's mantle, a key variable in geodynamics. We evaluate the post-LGM glacial-isostatic rebound of the Alps following a 4-tiered procedure. First, we estimated the thickness distribution of sedimentary valley fills to create a bedrock map of the entire mountain belt. Second, this map was used as topographic basis for the reconstruction of the Alpine icecap using a numerical ice-flow model. Third, we estimated the equilibrium deflection of the Alpine lithosphere, using the combined loads of ice and sediments with a variable effective elastic thickness. Finally, we used an exponential decay function to infer the residual deflection and the present-day uplift rate for a range of upper mantle viscosities. Our analysis shows that virtually all of the geodetically measured surface uplift in the Swiss and the Austrian Alps can be attributed to glacial unloading and redistribution of sediments, assuming an upper-mantle viscosity lower than that inferred for an old craton (e.g., Fennoscandia), but higher than that for a region with recent crustal thinning (e.g., Basin and Range province).

  18. Supersymmetry protected topological phases of isostatic lattices and kagome antiferromagnets

    NASA Astrophysics Data System (ADS)

    Lawler, Michael J.

    2016-10-01

    I generalize the theory of phonon topological band structures of isostatic lattices to frustrated antiferromagnets. I achieve this with a discovery of a many-body supersymmetry (SUSY) in the phonon problem of balls and springs and its connection to local constraints satisfied by ground states. The Witten index of the SUSY model demands the Maxwell-Calladine index of mechanical structures. "Spontaneous supersymmetry breaking" is identified as the need to gap all modes in the bulk to create the topological isostatic lattice state. Since ground states of magnetic systems also satisfy local constraint conditions (such as the vanishing of the total spin on a triangle), I identify a similar SUSY structure for many common models of antiferromagnets including the square, triangluar, kagome, pyrochlore nearest-neighbor antiferromagnets, and the J2=J1/2 square-lattice antiferromagnet. Remarkably, the kagome family of antiferromagnets is the analog of topological isostatic lattices among this collection of models. Thus, a solid-state realization of the theory of phonon topological band structure may be found in frustrated magnetic materials.

  19. The Isostatic State of Ethiopia and Adjacent Areas

    NASA Astrophysics Data System (ADS)

    Woldetinsae, G.; Götze, H.-J.

    2003-04-01

    Over 35000 onshore and offshore gravity stations have been compiled in order to test isostatic models and perform geologic correlations over a large section of the Afro-Arabian shield. Ethiopia is an important part of this system because it contains the major section of the ca. 5000km Afro-Arabian rift and it includes the transition between the Arabo-Nubian-Shield (ANS) and Mozambique Belt (MB). Isostatic residual anomalies have been calculated using both Airy and Vening-Meinsez models. These anomalies outline the major Precambrian belts, the Cenozoic rifts and associated major structures. Positive residual anomalies associated with the Main Ethiopian Rift (MER) and Kenyan rift systems could be the expression of an axial intrusive body and swarms of local faults and fractures. The residual anomalies indicate relative stability in the MER and increased tectonic activity over the areas of the Red Sea, Gulf of Aden and Afar. Near-zero isostatic residuals flank the MER and Kenya rifts and are found within the Danakil Alps and some plateau regions. A series of NW-SE and E-W trending features are evident in the different isostatic residual maps. These parallel features include, from north to south, the Najid fault system, Red Sea axial zone, Melka Werer cross structure, the Anza rift and the Aswa shear zone. Additional NW-SE structures are apparent in the southern rift system, although these features are somewhat diffuse. Curvature enhanced maps are also useful for mapping fracture zones, major gravity lineaments and, in some cases, orientation of faults. Important areas from a metallogenesis point of view have been identified for further examination. The results of the qualitative interpretation form the basis of continuing three-dimensional gravity modelling and qualitative analysis that also integrates data from eastern Sudan.

  20. The complex isostatic equilibration of Australia's deep crust.

    NASA Astrophysics Data System (ADS)

    Aitken, Alan; Gross, Lutz; Altinay, Cihan

    2016-04-01

    A recent study, using a new finite-element based gravity inversion method has modelled in high-resolution the density and pressure fields for the Australian continent. Here we analyse the pressure results to consider how Australia's lower-crust and Moho contribute to the isostatic equilibration of topography and crustal masses. We find that the situation is more complex than the commonly applied model of isostatic compensation through crustal thickness variations. Key differences include low pressure-variability at ca. 30-35 km, suggesting that the thickness of the felsic-intermediate crust equilibrates most of the upper-crustal loads; increasing pressure-variability between 30-50 km, suggesting that positively buoyant deep-crustal roots generate disequilibrium. These large roots have previously been inferred to represent mafic underplates. Pressure-variability in the uppermost lithospheric mantle reduces to a minimum at ~125 km depth, suggesting that these loads are compensated by dense mantle at ~100 km depth, rather than by crustal loads or topography. This raises the notion that Australia's lithosphere is isostatically compensated at two levels: Crustal compensation involving topography and the felsic to intermediate crust; and deep-lithosphere compensation involving the mafic lower crust and lithospheric mantle. Rather than its traditional role of compensating for crustal masses, the Moho in this case appears to be a source of isostatic disequilibrium, acting in a separate cell with lithospheric mantle density sources. These results imply that, for cratonised continents like Australia, the notion of crustal isostasy is a poor descriptor of the system.

  1. Separation of dynamic and isostatic components of the Venusian gravity and topography and determination of the crustal thickness of Venus

    NASA Astrophysics Data System (ADS)

    Yang, An; Huang, Jinshui; Wei, Daiyun

    2016-09-01

    Assuming that the long-wavelength geoid and topography of Venus are supported by both mantle convection and Airy isostasy, we propose a method to separate the dynamic and isostatic components of the Venusian gravity and topography with the aid of the dynamic admittance from numerical models of mantle convection and the isostatic admittance from an Airy isostatic model. The global crustal thickness is then calculated based on the isostatic component of the gravity and topography. The results show that some highland plateaus such as Ishtar Terra and Ovda Regio have thick crust, which are largely supported by isostatic compensation. Other highland plateaus such as Thetis and Phoebe Regiones appear to have superimposed contributions from crustal thickening and dynamic support. Volcanic rises such as Atla and Beta Regiones have thin crust, which is consistent with the postulation that these volcanic rises are mainly the products of dynamic uplift caused by mantle plumes.

  2. Numerical simulation of Glacial Isostatic Adjustment

    NASA Astrophysics Data System (ADS)

    Miglio, E.

    2015-12-01

    In the Earth's crust, stress can be subdivided into tectonic background stress, overburden pressure, and pore-fluid pressure. The superposition of the first two and the variation of the third part are key factors in controlling movement along faults. Furthermore, stresses due to sedimentation and erosion contribute to the total stress field. In deglaciated regions, an additional stress must be considered: the rebound stress, which is related to rebounding of the crust and mantle after deglaciation. During the growth of a continental ice sheet, the lithosphere under the iceload is deformed and the removal of the ice load during deglaciation initiates a rebound process. The uplift is well known in formerly glaciated areas, e.g.North America and Scandinavia, and in currently deglaciating areas, e.g.Alaska, Antarctica, and Greenland. The whole process of subsiding and uplifting during the growth and melting of an iceload and all related phenomena is known as glacial isostatic adjustment. During the process of glaciation, the surface of the lithosphere is depressed underneath the ice load and compressional flexural stresses are induced in the upper lithosphere, whereas the bottom of the lithosphere experiences extensional flexural stresses; an additional vertical stress due to the ice load is present and it decreases to zero during deglaciation. During rebound, flexural stresses relax slowly. These stresses are able to change the original stress directions and regime.In this work we aim to study the effect of the GIA process in the context of petroleum engineering. The main aspect we will focus on is the mathematical and numerical modeling of the GIA including thermal effects. We plan also to include a preliminary study of the effect of the glacial erosion. All these phenomena are of paramount importance in petroleum engineering: for example some reservoir have been depleted due to tilting caused by both GIA, erosion and thermal effects.

  3. A glacial isostatic adjustment model for the central and northern Laurentide Ice Sheet based on relative sea level and GPS measurements

    NASA Astrophysics Data System (ADS)

    Simon, K. M.; James, T. S.; Henton, J. A.; Dyke, A. S.

    2016-06-01

    The thickness and equivalent global sea level contribution of an improved model of the central and northern Laurentide Ice Sheet is constrained by 24 relative sea level histories and 18 present-day GPS-measured vertical land motion rates. The final model, termed Laur16, is derived from the ICE-5G model by holding the timing history constant and iteratively adjusting the thickness history, in four regions of northern Canada. In the final model, the last glacial maximum (LGM) thickness of the Laurentide Ice Sheet west of Hudson Bay was ˜3.4-3.6 km. Conversely, east of Hudson Bay, peak ice thicknesses reached ˜4 km. The ice model thicknesses inferred for these two regions represent, respectively, a ˜30 per cent decrease and an average ˜20-25 per cent increase to the load thickness relative to the ICE-5G reconstruction, which is generally consistent with other recent studies that have focussed on Laurentide Ice Sheet history. The final model also features peak ice thicknesses of 1.2-1.3 km in the Baffin Island region, a modest reduction relative to ICE-5G and unchanged thicknesses for a region in the central Canadian Arctic Archipelago west of Baffin Island. Vertical land motion predictions of the final model fit observed crustal uplift rates well, after an adjustment is made for the elastic crustal response to present-day ice mass changes of regional ice cover. The new Laur16 model provides more than a factor of two improvement of the fit to the RSL data (χ2 measure of misfit) and a factor of nine improvement to the fit of the GPS data (mean squared error measure of fit), compared to the ICE-5G starting model. Laur16 also fits the regional RSL data better by a factor of two and gives a slightly better fit to GPS uplift rates than the recent ICE-6G model. The volume history of the Laur16 reconstruction corresponds to an up to 8 m reduction in global sea level equivalent compared to ICE-5G at LGM.

  4. Variations in Crustal Structure, Lithospheric Flexural Strength, and Isostatic Compensation Mechanisms of Mars

    NASA Astrophysics Data System (ADS)

    Ding, M.; Lin, J.; Zuber, M. T.

    2014-12-01

    We analyze gravity and topography of Mars to investigate the spatial variations in crustal thickness, lithospheric strength, and mechanisms of support of prominent topographic features on Mars. The latest gravity model JGMRO110c (released in 2012) from the Mars Reconnaissance Orbiter mission has a spatial block size resolution of ~97 km (corresponding to degree-110), enabling us to resolve crustal structures at higher spatial resolution than those determined from previous degree-80 and 85 gravity models [Zuber et al., 2000; McGovern et al., 2002, 2004; Neumann et al., 2004; Belleguic et al., 2005]. Using the latest gravity data, we first inverted for a new version of crustal thickness model of Mars assuming homogeneous crust and mantle densities of 2.9 and 3.5 g/cm3. We calculated "isostatic" topography for the Airy local isostatic compensation mechanism, and "non-isostatic" topography after removing the isostatic part. We find that about 92% of the Martian surface is in relatively isostatic state, indicating either relatively small lithospheric strength and/or small vertical loading. Relatively isostatic regions include the hemispheric dichotomy, Hellas and Argyre Planitia, Noachis and Arabia Terra, and Terra Cimmeria. In contrast, regions with significant amount of non-isostatic topography include the Olympus, Ascraeus, Arsia, Pavonis, Alba, and Elysium Mons, Isidis Planitia and Valles Marineris. Their relatively large "non-isostatc topography" implies relatively strong lithospheric strength and large vertical loading. Spectral analysis of the admittance and correlation relationship between gravity and topography were conducted for the non-isostatic regions using the localized spectra method [Wieczorek and Simons, 2005, 2007] and thin-shell lithospheric flexural approximation [Forsyth, 1985; McGovern et al., 2002, 2004]. The best-fitting models reveal significant variations in the effective lithospheric thickness with the greatest values for the Olympus Mon

  5. Modelling of glacial isostatic adjustment in the Barents Sea region: Earth rheology inferred from various ice load scenarios for the last glacial cycle

    NASA Astrophysics Data System (ADS)

    Auriac, Amandine; Whitehouse, Pippa L.; Bentley, Michael J.; Patton, Henry; Hubbard, Alun; Lloyd, Jerry M.

    2015-04-01

    The Barents Sea, bordered by Norway to the south, Svalbard to the north and Novaya Zemlya to the east, was covered by ice during the last glacial cycle. The extent and thickness of the marine-based ice sheet as well as timing of glaciation / deglaciation are, however, difficult to constrain, partly due to the few terrestrial areas available. There are various models for the ice load history in this region, but large discrepancies remain between them depending on the dataset used as constraint (e.g. sea-level data, temperature record or geomorphology data). Our aim here is to compare and find the best ice load scenario for this region over the last glacial cycle and solve for the Earth structure in the area. To achieve this, we model the present-day crustal deformation and sea-level variations during the last deglaciation by solving the sea-level equation. We use a wide range of Earth models, where we vary the lithosphere thickness and the upper and lower mantle viscosities, as well as four ice load scenarios. The first three ice load scenarios come from published studies, and include the ICE-5G model as well as models from M. Siegert and J.-O. Näslund, while the last one is currently being developed at the University of Tromsø, Norway. We compare the modelled sea-level predictions to relative sea-level curves at key locations around the Barents Sea using chi square, which enables us to infer the best Earth structure and ice history. We also compare the predicted surface deformation from our best model with GPS observations from stations located around the Barents Sea. The GPS provides a constraint on the present-day evolution of deformation in the area and is complementary to the relative sea-level data, which constrain the long-term deformation. First results show that the published ice load scenarios are not accurate enough to reproduce the sea level curves around the Barents Sea, regardless of the Earth model tried. However, the last model, currently being

  6. Glacial Isostatic Adjustment and Contemporary Sea Level Rise: An Overview

    NASA Astrophysics Data System (ADS)

    Spada, Giorgio

    2016-08-01

    Glacial isostatic adjustment (GIA) encompasses a suite of geophysical phenomena accompanying the waxing and waning of continental-scale ice sheets. These involve the solid Earth, the oceans and the cryosphere both on short (decade to century) and on long (millennia) timescales. In the framework of contemporary sea-level change, the role of GIA is particular. In fact, among the processes significantly contributing to contemporary sea-level change, GIA is the only one for which deformational, gravitational and rotational effects are simultaneously operating, and for which the rheology of the solid Earth is essential. Here, I review the basic elements of the GIA theory, emphasizing the connections with current sea-level changes observed by tide gauges and altimetry. This purpose is met discussing the nature of the "sea-level equation" (SLE), which represents the basis for modeling the sea-level variations of glacial isostatic origin, also giving access to a full set of geodetic variations associated with GIA. Here, the SLE is employed to characterize the remarkable geographical variability of the GIA-induced sea-level variations, which are often expressed in terms of "fingerprints". Using harmonic analysis, the spatial variability of the GIA fingerprints is compared to that of other components of contemporary sea-level change. In closing, some attention is devoted to the importance of the "GIA corrections" in the context of modern sea-level observations, based on tide gauges or satellite altimeters.

  7. Mid-pacific mountains revisited

    NASA Astrophysics Data System (ADS)

    Kroenke, Loren W.; Kellogg, James N.; Nemoto, Kenji

    1985-06-01

    The Mid-Pacific Mountains are guyots whose volcanic pedestals have been constructed on a broad basement plateau, the flanks of which are downfaulted. Edifice construction may have been controlled by an orthogonal system of intersecting faults trending roughly ENE and NNW. Low amplitude gravity anomalies observed over the Mid-Pacific Mountains indicate complete Airy-Heiskanen isostatic compensation, crustal thickening, and eruption on thin elastic lithosphere. Tholeiites of the Mid-Pacific Mountains resemble lavas of Iceland and the Galapagos Islands. The orthogonal fault system, low gravity anomalies, and lava chemistry of the Mid-Pacific Mountains can be explained by eruption on or near a great ENE-trending rift system.

  8. Space-geodetic constraints on glacial isostatic adjustment in Fennoscandia.

    PubMed

    Milne, G A; Davis, J L; Mitrovica, J X; Scherneck, H G; Johansson, J M; Vermeer, M; Koivula, H

    2001-03-23

    Analysis of Global Positioning System (GPS) data demonstrates that ongoing three-dimensional crustal deformation in Fennoscandia is dominated by glacial isostatic adjustment. Our comparison of these GPS observations with numerical predictions yields an Earth model that satisfies independent geologic constraints and bounds both the average viscosity in the upper mantle (5 x 10(20) to 1 x 10(21) pascal seconds) and the elastic thickness of the lithosphere (90 to 170 kilometers). We combined GPS-derived radial motions with Fennoscandian tide gauge records to estimate a regional sea surface rise of 2.1 +/- 0.3 mm/year. Furthermore, ongoing horizontal tectonic motions greater than approximately 1 mm/year are ruled out on the basis of the GPS-derived three-dimensional crustal velocity field. PMID:11264528

  9. Space-Geodetic Constraints on Glacial Isostatic Adjustment in Fennoscandia

    NASA Astrophysics Data System (ADS)

    Milne, G. A.; Davis, J. L.; Mitrovica, Jerry X.; Scherneck, H.-G.; Johansson, J. M.; Vermeer, M.; Koivula, H.

    2001-03-01

    Analysis of Global Positioning System (GPS) data demonstrates that ongoing three-dimensional crustal deformation in Fennoscandia is dominated by glacial isostatic adjustment. Our comparison of these GPS observations with numerical predictions yields an Earth model that satisfies independent geologic constraints and bounds both the average viscosity in the upper mantle (5 × 1020 to 1 × 1021 pascal seconds) and the elastic thickness of the lithosphere (90 to 170 kilometers). We combined GPS-derived radial motions with Fennoscandian tide gauge records to estimate a regional sea surface rise of 2.1 +/- 0.3 mm/year. Furthermore, ongoing horizontal tectonic motions greater than ~1 mm/year are ruled out on the basis of the GPS-derived three-dimensional crustal velocity field.

  10. The kinetics of dolomite reaction rim growth under isostatic and non-isostatic pressure conditions

    NASA Astrophysics Data System (ADS)

    Helpa, V.; Rybacki, E.; Morales, L. G.; Abart, R.; Dresen, G. H.

    2013-12-01

    During burial and exhumation, rocks are simultaneously exposed to metamorphic reactions and tectonic stresses. Therefore, the reaction rate of newly formed minerals may depend on chemical and mechanical driving forces. Here, we investigate the reaction kinetics of dolomite (CaMg[CO3]2) rim growth by solid-state reactions experiments on oriented calcite (CaCO3) and magnesite (MgCO3) single crystals under isostatic and non-isostatic pressure conditions. Cylindrical samples of 3-5 mm length and 7 mm diameter were drilled and polished perpendicular to the rhombohedral cleavage planes of natural clear crystals. The tests were performed using a Paterson-type deformation apparatus at P = 400 MPa confining pressure, temperatures, T, between 750 and 850°C, and reaction durations, t, of 2 - 146 h to calculate the kinetic parameters of dolomite rim growth under isostatic stress conditions. For non-isostatic reaction experiments we applied in addition differential stresses, σ, up to 40 MPa perpendicular to the contact interface at T = 750°C for 4 - 171 h duration, initiating minor inelastic deformation of calcite. The thickness of the resulting dolomite reaction rims increases linearly with the square root of time, indicating a diffusion-controlled reaction. The rims consist of two different textural domains. Granular dolomite grains (≈ 2 -5 μm grain size) form next to calcite and elongated palisade-shaped grains (1-6 μm diameter) grow perpendicular to the magnesite interface. Texture measurements with the electron backscatter diffraction technique indicate that the orientations of dolomite grains are mainly influenced by the orientation of the calcite educt crystal, in particular in the granular rim. To some extent, the texture of dolomite palisades is also influenced by the orientation of magnesite. The thickness of the two individual layers increases with temperature. At 400 MPa isostatic pressure, T = 750°C and t = 29 hours, a 5 μm thick granular dolomite layer

  11. Hot isostatic pressing of titanium based materials

    SciTech Connect

    Froes, F.H.; Widmer, R.; Hebeisen, J.

    1996-12-31

    The importance of titanium in demanding aerospace and terrestrial applications is presented, and the necessity to reduce cost to increase use is discussed. Hot isostatic pressing (HIP`ing) can be utilized with titanium based materials to obtain cost reduction and to enhance performance. The science/technology of various facets of the titanium scenario where HIP`ing can be used to advantage is presented, including powder metallurgy, castings, metal matrix composites and use of thermochemical processing. The major application of HIP`ing for titanium based materials is in castings; followed by blended elemental concepts. Much work has been conducted on continuous fiber reinforced materials, with the first use in actual commercial components likely to occur in engine components. Discontinuously reinforced products are already in use in aerospace and terrestrial applications. For the future, developing processing such as mechanical alloying, nanostructured materials and rapidly solidified product could benefit from compaction by HIP`ing. 55 refs., 30 figs.

  12. Glass Coats For Hot Isostatic Pressing

    NASA Technical Reports Server (NTRS)

    Ecer, Gunes M.

    1989-01-01

    Surface voids sealed from pressurizing gas. Coating technique enables healing of surface defects by hot isostatic pressing (HIP). Internal pores readily closed by HIP, but surface voids like cracks and pores in contact with pressurizing gas not healed. Applied to casting or weldment as thick slurry of two glass powders: one melts at temperature slightly lower than used for HIP, and another melts at higher temperature. For example, powder is glass of 75 percent SiO2 and 25 percent Na2O, while other powder SiO2. Liquid component of slurry fugitive organic binder; for example, mixture of cellulose acetate and acetone. Easy to apply, separates voids from surrounding gas, would not react with metal part under treatment, and easy to remove after pressing.

  13. Hot Isostatic Pressing of 60-Nitinol

    NASA Technical Reports Server (NTRS)

    Stanford, Malcolm K.

    2015-01-01

    The effects of varying the time, temperature and pressure during consolidation of 60-Nitinol (Nickel Titanium alloy) by hot isostatic pressing (HIP) were examined. Six HIP cycles with a cycle time of either 2 or 20 hours, temperature of 900 or 1000 degrees Centigrade, and a chamber pressure of either 100 or 200 millipascals were used. The cycle representing the shortest cycle time at the highest temperature and pressure (2 hours/1000 degrees Centigrade/200 millipascals) produced material with the highest hardness (720 Vickers Pyramid Number (HV)). A modest increase in average grain size and significant porosity reduction were observed in material subjected to the longest cycle time at the highest temperature, regardless of the pressure applied. The intent of this study is to facilitate the technology transfer involved in the processing of this material.

  14. Erosion, isostatic response, and the missing peneplains

    NASA Astrophysics Data System (ADS)

    Phillips, Jonathan D.

    2002-06-01

    The peneplain—a low-relief erosional plain worn to near base level—is a venerable concept in geomorphology, geology, and geography. Yet despite more than a century of effort, no convincing example of a contemporary peneplain has been identified, and the identification of relict peneplains is uncertain and controversial. As a peneplain is a logical outcome during a period of long tectonic stability, the paucity or absence of peneplains is problematic. Most explanations are based on the notion that the periods of tectonic stability required for peneplain formation are too long to allow the features to fully develop, or that Neogene tectonics has precluded recent peneplanation. This paper proposes an alternative explanation, generally consistent with those given above, which can also explain the absence of peneplains in regions experiencing long tectonic stability. If erosion or deposition rates are related to elevation and if isostatic response (uplift or subsidence) is related to erosional unloading or depositional loading, the relationship between these components is dynamically unstable. This is demonstrated mathematically. This instability implies that no particular state or mode of topographic evolution, including peneplanation, is likely to persist in the face of variations or perturbations that influence any system component. Thus, formation of a peneplain would require tectonic stability and also relative constancy in sea level (or rates and direction of sea level change), climate, biotic influences on erosion or deposition, and any other factors that modify erosion, deposition, elevation fields, or isostatic responses. This would explain an absence of geologically contemporary peneplains and a rarity of well-developed peneplains in the geologic record.

  15. Isostatic gravity map of the Point Sur 30 x 60 quadrangle and adjacent areas, California

    USGS Publications Warehouse

    Watt, J.T.; Morin, R.L.; Langenheim, V.E.

    2011-01-01

    This isostatic residual gravity map is part of a regional effort to investigate the tectonics and water resources of the central Coast Range. This map serves as a basis for modeling the shape of basins and for determining the location and geometry of faults in the area. Local spatial variations in the Earth's gravity field (after removing variations caused by instrument drift, earth-tides, latitude, elevation, terrain, and deep crustal structure), as expressed by the isostatic anomaly, reflect the distribution of densities in the mid- to upper crust, which in turn can be related to rock type. Steep gradients in the isostatic gravity field often indicate lithologic or structural boundaries. Gravity highs reflect the Mesozoic granitic and Franciscan Complex basement rocks that comprise both the northwest-trending Santa Lucia and Gabilan Ranges, whereas gravity lows in Salinas Valley and the offshore basins reflect the thick accumulations of low-density alluvial and marine sediment. Gravity lows also occur where there are thick deposits of low-density Monterey Formation in the hills southeast of Arroyo Seco (>2 km, Marion, 1986). Within the map area, isostatic residual gravity values range from approximately -60 mGal offshore in the northern part of the Sur basin to approximately 22 mGal in the Santa Lucia Range.

  16. A new method of computation of the isostatic anomaly and its application to the Rhine graben

    NASA Astrophysics Data System (ADS)

    Bernabe, Y.

    1981-11-01

    Using a preexisting mathematical model, a mathematical assumption of linearity is used to compute isostatic anomalies directly from geodetic and gravimetric data. When applied to the Rhine graben, the method yields satisfactory results which justify it a posteriori. The compensation depth is thought to be greater than 120 km. It is noted that the computation of a model of the distribution of compensation masses inside the earth necessitates further mathematical assumptions which make the results physically questionable.

  17. Hot isostatic pressing of ceramic waste from spent nuclear fuel.

    SciTech Connect

    Bateman, K.J.; Rigg, R.H.; Wiest, J.D.

    2002-03-08

    Argonne National Laboratory has developed a process to immobilize waste salt containing fission products, uranium, and transuranic elements as chlorides in a glass-bonded ceramic waste form. This salt was generated in the electrorefining operation used in electrometallurgical treatment of spent Experimental Breeder Reactor-II fuel. The ceramic waste process culminated with a hot isostatic pressing operation. This paper reviews the installation and operation of a hot isostatic press in a radioactive environment. Processing conditions for the hot isostatic press are presented for non-irradiated material and irradiated material. Sufficient testing was performed to demonstrate that a hot isostatic press could be used as the final step of the processing of ceramic waste for the electrometallurgical spent fuel treatment process.

  18. Hot isostatic press waste option study report

    SciTech Connect

    Russell, N.E.; Taylor, D.D.

    1998-02-01

    A Settlement Agreement between the Department of Energy and the State of Idaho mandates that all high-level radioactive waste now stored at the Idaho Chemical Processing Plant be treated so that it is ready to move out of Idaho for disposal by the target date of 2035. This study investigates the immobilization of all Idaho Chemical Processing Plant calcine, including calcined sodium bearing waste, via the process known as hot isostatic press, which produces compact solid waste forms by means of high temperature and pressure (1,050 C and 20,000 psi), as the treatment method for complying with the settlement agreement. The final waste product would be contained in stainless-steel canisters, the same type used at the Savannah River Site for vitrified waste, and stored at the Idaho National Engineering and Environmental Laboratory until a national geological repository becomes available for its disposal. The waste processing period is from 2013 through 2032, and disposal at the High Level Waste repository will probably begin sometime after 2065.

  19. Assessment of Glacial Isostatic Adjustment in Greenland using GPS

    NASA Astrophysics Data System (ADS)

    Khan, S. A.; Bevis, M. G.; Sasgen, I.; van Dam, T. M.; Wahr, J. M.; Wouters, B.; Bamber, J. L.; Willis, M. J.; Knudsen, P.; Helm, V.; Kuipers Munneke, P.; Muresan, I. S.

    2015-12-01

    The Greenland GPS network (GNET) was constructed to provide a new means to assess viscoelastic and elastic adjustments driven by past and present-day changes in ice mass. Here we assess existing glacial isostatic adjustments (GIA) predictions by analysing 1995-2015 data from 61 continuous GPS receivers located along the margin of the Greenland ice sheet. Since GPS receivers measure both the GIA and elastic signals, we isolate GIA, by removing the elastic adjustments of the lithosphere due to present-day mass changes using high-resolution fields of ice surface elevation change derived from satellite and airborne altimetry measurements (ERS1/2, ICESat, ATM, ENVISAT, and CryoSat-2). For most GPS stations, our observed GIA rates contradict GIA predictions; particularly, we find huge uplift rates in southeast Greenland of up to 14 mm/yr while models predict rates of 0-2 mm/yr. Our results suggest possible improvements of GIA predictions, and hence of the poorly constrained ice load history and Earth structure models for Greenland.

  20. Glacial Isostatic Adjustment - a hot topic in cold regions

    NASA Astrophysics Data System (ADS)

    Whitehouse, Pippa

    2016-04-01

    Glacial Isostatic Adjustment (GIA) modelling tackles the classic geodynamical problem of determining the solid Earth response to surface load changes by ice and ocean water whilst at the same time solving for the gravitationally-consistent redistribution of ice sheet meltwater across the global ocean. Understanding this process is important for quantifying both present-day ice mass balance and the response of ice sheets to past and future climatic change. The two fundamental unknowns in this problem are (i) the rheology of the solid Earth, and (ii) the history of global ice sheet change. In this talk I will discuss the myriad of approaches that are used to constrain these two components. In particular, I will focus on Antarctica, where the presence of a continuously-evolving ice sheet, situated on top of one of the most rheologically-diverse regions of the planet, provides us with a challenge that can only be resolved by drawing on knowledge from across the fields of geodynamics, glaciology, geology, geodesy and seismology.

  1. Processing zirconia by sintering/hot isostatic pressing

    SciTech Connect

    Druschitz, A.P. )

    1988-05-01

    Sintering followed by hot isostatic pressing is a potential method for improving the mechanical properties of ceramic materials. Encouraging data have been presented and published but these data do not clearly show the origin of the benefits. Here, the effects of green density, time, temperature, and pressure on sintered density, grain size, and pore size of slip-cast ZrO{sub 2}-3 mol% Y{sub 2}O{sub 3} are described. The data demonstrate that, when compared to pressureless sintering, the sintering/hot isostatic pressing process produces an equivalent maximum density at reduced temperature and significant reductions in pore size, but no reduction in minimum grain size. The maximum density obtainable by the sinter/hot isostatic pressing process was limited by both open porosity and large pores; the processing conditions required to produce the maximum process advantage are described.

  2. Joining of ceramics of different biofunction by hot isostatic pressing

    SciTech Connect

    Li, Jianguo . Center for Dental Technology and Biomaterials); Harmansson, L. ); Soeremark, R. . Dept. of Prosthodontics)

    1993-10-01

    Monolithic zirconia (Z) and zirconia-hydroxyapatite (Z/HA) composites were joined by cold isostatic pressing (CIP at 300 MPa) and subsequently by glass-encapsulated hot isostatic pressing (HIP at 1225 C, 1 h and 200 MPa). The physical and mechanical properties of the materials were measured. The fracture surface was studied using a light microscope. The results indicate a strength level of the joint similar to that of the corresponding composite material (Z/HA), 845 and 860 MPa, respectively. Similar experiments with monolithic alumina (A) and alumina-hydroxyapatite (A/HA) were carried out without success. Cracking occurred in the joint area during the cold isostatic pressing process. It seems that ceramics with high green strength and similar green density are essential when joining ceramics by combined CIP and HIP processes.

  3. Hot Isostatic Pressing (HIP): Techniques, applications and economical use

    NASA Astrophysics Data System (ADS)

    Bousack, H.

    1985-01-01

    Hot isostatic pressing (HIP) is used to regenerate defect components exposed to dynamic and permanent static loads causing pore formation. It consists in compacting and bonding of powders and solids by encapsulation. The HIP-equipment consists of a high pressure vessel, an oven and a rare gas system for production of isostatic pressure. The compacting procedure using diffusion and deformation processes depends on the pressing temperature. It is used in the production of hard metals, superalloys, fiber composites and ceramic components. It saves energy material and costs.

  4. A benchmark study for glacial isostatic adjustment codes

    NASA Astrophysics Data System (ADS)

    Spada, G.; Barletta, V. R.; Klemann, V.; Riva, R. E. M.; Martinec, Z.; Gasperini, P.; Lund, B.; Wolf, D.; Vermeersen, L. L. A.; King, M. A.

    2011-04-01

    The study of glacial isostatic adjustment (GIA) is gaining an increasingly important role within the geophysical community. Understanding the response of the Earth to loading is crucial in various contexts, ranging from the interpretation of modern satellite geodetic measurements (e.g. GRACE and GOCE) to the projections of future sea level trends in response to climate change. Modern modelling approaches to GIA are based on various techniques that range from purely analytical formulations to fully numerical methods. Despite various teams independently investigating GIA, we do not have a suitably large set of agreed numerical results through which the methods may be validated; a community benchmark data set would clearly be valuable. Following the example of the mantle convection community, here we present, for the first time, the results of a benchmark study of codes designed to model GIA. This has taken place within a collaboration facilitated through European Cooperation in Science and Technology (COST) Action ES0701. The approaches benchmarked are based on significantly different codes and different techniques. The test computations are based on models with spherical symmetry and Maxwell rheology and include inputs from different methods and solution techniques: viscoelastic normal modes, spectral-finite elements and finite elements. The tests involve the loading and tidal Love numbers and their relaxation spectra, the deformation and gravity variations driven by surface loads characterized by simple geometry and time history and the rotational fluctuations in response to glacial unloading. In spite of the significant differences in the numerical methods employed, the test computations show a satisfactory agreement between the results provided by the participants.

  5. Hot Isostatic Press Manufacturing Process Development for Fabrication of RERTR Monolithic Fuel Plates

    SciTech Connect

    Crapps, Justin M.; Clarke, Kester D.; Katz, Joel D.; Alexander, David J.; Aikin, Beverly; Vargas, Victor D.; Montalvo, Joel D.; Dombrowski, David E.; Mihaila, Bogdan

    2012-06-06

    We use experimentation and finite element modeling to study a Hot Isostatic Press (HIP) manufacturing process for U-10Mo Monolithic Fuel Plates. Finite element simulations are used to identify the material properties affecting the process and improve the process geometry. Accounting for the high temperature material properties and plasticity is important to obtain qualitative agreement between model and experimental results. The model allows us to improve the process geometry and provide guidance on selection of material and finish conditions for the process strongbacks. We conclude that the HIP can must be fully filled to provide uniform normal stress across the bonding interface.

  6. The spherical terrain correction and its effect on the gravimetric-isostatic Moho determination

    NASA Astrophysics Data System (ADS)

    Abrehdary, M.; Sjöberg, L. E.; Bagherbandi, M.

    2016-01-01

    In this study, the Moho depth is estimated based on the refined spherical Bouguer gravity disturbance and DTM2006 topographic data using the Vening Meinesz-Moritz gravimetric-isostatic hypothesis. In this context, we compute the refined spherical Bouguer gravity disturbances in a set of 1° × 1° blocks. The spherical terrain correction, a residual correction to each Bouguer shell, is computed using rock heights and ice sheet thicknesses from the DTM2006 and Earth2014 models. The study illustrates that the defined simple Bouguer gravity disturbance corrected for the density variations of the oceans, ice sheets and sediment basins and also the non-isostatic effects needs a significant terrain correction to become the refined Bouguer gravity disturbance, and that the isostatic gravity disturbance is significantly better defined by the latter disturbance plus a compensation attraction. Our study shows that despite the fact that the lateral variation of the crustal depth is rather smooth, the terrain affects the result most significantly in many areas. The global numerical results show that the estimated Moho depths by the simple and refined spherical Bouguer gravity disturbances and the seismic CRUST1.0 model agree to 5.6 and 2.7 km in RMS, respectively. Also, the mean value differences are 1.7 and 0.2 km, respectively. Two regional numerical studies show that the RMS differences between the Moho depths estimated based on the simple and refined spherical Bouguer gravity disturbance and that using CRUST1.0 model yield fits of 4.9 and 3.2 km in South America and yield 3.2 and 3.4 km in Fennoscandia, respectively.

  7. Plumes in the mantle. [free air and isostatic gravity anomalies for geophysical interpretation

    NASA Technical Reports Server (NTRS)

    Khan, M. A.

    1973-01-01

    Free air and isostatic gravity anomalies for the purposes of geophysical interpretation are presented. Evidence for the existance of hotspots in the mantle is reviewed. The prosposed locations of these hotspots are not always associated with positive gravity anomalies. Theoretical analysis based on simplified flow models for the plumes indicates that unless the frictional viscosities are several orders of magnitude smaller than the present estimates of mantle viscosity or alternately, the vertical flows are reduced by about two orders of magnitude, the plume flow will generate implausibly high temperatures.

  8. Hot Isostatic Press (HIP) vitrification of radwaste concretes

    SciTech Connect

    Siemer, D.D.; Scheetz, B.; Gougar, M.L.D.

    1995-12-01

    Properly formulated and properly ``canned`` radwaste concretes can be readily hot-isostatically-pressed (HIPed) into materials that exhibit performance equivalent to typical radwaste-type glasses. The HIPing conditions (temperature/pressure) required to turn a concrete waste form into a ``vitrified`` waste form are quite mild and therefore consistent with both safety and high productivity. This paper describes the process and its products with reference to its potential application to Idaho Chemical Processing Plant (ICPP) reprocessing wastes.

  9. Glacial Isostatic Adjustment Observed with VLBI and SLR

    NASA Technical Reports Server (NTRS)

    Argus, D.; Peltier, W.; Watkins, M.

    1999-01-01

    In global geodetic solutions vertical rates of site motion are usually estimated relative to the geocenter (center of figure) of the solid earth. The velocity of the geocenter is estimated assuming that the plates are rigid, that the velocities of the plates equal those in NUVEL-1A (DeMets et al. 1990, 1994) and that the uplift, subsidence, and intraplate deformation due to glacial isostatic adjustment is negligible.

  10. Fabrication of Monolithic RERTR Fuels by Hot Isostatic Pressing

    SciTech Connect

    Jan-Fong Jue; Blair H. Park; Curtis R. Clark; Glenn A. Moore; Dennis D. Keiser, Jr.

    2010-11-01

    The RERTR (Reduced Enrichment for Research and Test Reactors) Program is developing advanced nuclear fuels for high-power test reactors. Monolithic fuel design provides higher uranium loading than that of the traditional dispersion fuel design. Hot isostatic pressing is a promising process for low-cost batch fabrication of monolithic RERTR fuel plates for these high-power reactors. Bonding U Mo fuel foil and 6061 Al cladding by hot isostatic press bonding was successfully developed at Idaho National Laboratory. Due to the relatively high processing temperature, the interaction between fuel meat and aluminum cladding is a concern. Two different methods were employed to mitigate this effect: (1) a diffusion barrier and (2) a doping addition to the interface. Both types of fuel plates have been fabricated by hot isostatic press bonding. Preliminary results show that the direct fuel/cladding interaction during the bonding process was eliminated by introducing a thin zirconium diffusion barrier layer between the fuel and the cladding. Fuel plates were also produced and characterized with a silicon-rich interlayer between fuel and cladding. This paper reports the recent progress of this developmental effort and identifies the areas that need further attention.

  11. Criticality and isostaticity in fiber networks

    NASA Astrophysics Data System (ADS)

    Mao, Xiaoming; Stenull, Olaf; Lubensky, Tom C.; Broedersz, Chase P.; Mackintosh, Fred C.

    2011-03-01

    We investigated the elastic response of model semiflexible networks based on diluted periodic lattices, using a new effective medium theory and numerical simulations. In this model, central forces link nearest neighbor sites and bending forces link second neighbor sites along fibers. We found that by turning on fiber bending rigidity, the central force rigidity critical point became unstable, and the lattices lose rigidity at a lower threshold that is independent of fiber bending rigidity. We calculated scaling relations and exponents at both critical points. In addition to the bending and stretching dominated regimes, we identified a novel bend-stretch coupled regime in the vicinity of the central force critical point, in which the shear modulus exhibits a fractional power-law dependence on both the fiber bending and stretching rigidities. This work has been supported in part by NSF-DMR-0804900 and FOM/NWO.

  12. Criticality and isostaticity in fibre networks

    NASA Astrophysics Data System (ADS)

    Broedersz, Chase P.; Mao, Xiaoming; Lubensky, Tom C.; Mackintosh, Frederick C.

    2011-12-01

    Disordered fibre networks are the basis of many man-made and natural materials, including structural components of living cells and tissue. The mechanical stability of such networks relies on the bending resistance of the fibres, in contrast to rubbers, which are governed by entropic stretching of polymer segments. Although it is known that fibre networks exhibit collective bending deformations, a fundamental understanding of such deformations and their effects on network mechanics has remained elusive. Here we introduce a lattice-based model of fibrous networks with variable connectivity to elucidate the roles of single-fibre elasticity and network structure. These networks exhibit both a low-connectivity rigidity threshold governed by fibre-bending elasticity and a high-connectivity threshold governed by fibre-stretching elasticity. Whereas the former determines the true onset of network rigidity, we show that the latter exhibits rich zero-temperature critical behaviour, including a crossover between various mechanical regimes along with diverging strain fluctuations and a concomitant diverging correlation length.

  13. Effect of hot isostatic pressing on RBa sub 2 Cu sub 3 O sub 7 superconductors

    SciTech Connect

    Sadananda, K.; Singh, A.K.; Iman, M.A.; Osofsky, M.; Le Tourneau, V.; Richards, L.E. )

    1988-09-01

    In an effort to make dense, consolidated superconductors, the hot isostatic pressing process was applied to the RBa{sub 2}Cu{sub 3}O{sub 7} system, where R is a rare-earth element. The authors have demonstrated the applicability of the hot isostatic pressing process to produce a fine-grained consolidated solid which can be cut into any desired form. The grain refinement that occurred during hot isostatic pressing was related to the fracture of coarse-grained particles during pressurization. Hot isostatic pressing combined with post-annealing increased the superconducting onset temperature to >95 K. Because of the grain refinement and the higher {Tc} achieved, the superconductor material processed by hot isostatic pressing is also expected to have higher current density, J{sub c}, than its sintered counterpart. The hot isostatic pressing process was also used successfully for the system Bi-Sr-Ca-Cu-O to make dense, bulk superconducting material.

  14. Theory of supersymmetry ``protected'' topological phases of isostatic lattices and highly frustrated magnets

    NASA Astrophysics Data System (ADS)

    Lawler, Michael

    I generalize the theory of phonon topological band structures of isostatic lattices to highly frustrated antiferromagnets. I achieve this with a discovery of a many-body supersymmetry (SUSY) in the phonon problem of balls and springs which also applies to geometrically frustrated magnets. The Witten index of the SUSY model, when restricted to the single body problem (meaningful for linearized phonons), is then shown to be the Calladine-Kane-Lubensky index of mechanical structures that forms the cornerstone of the phonon topological band structure theory. ``Spontaneous supersymmetry breaking'' is then identified as the need to gap all modes in the bulk to create the topological state. The many-body SUSY formulation shows that the topology is not restricted to a band structure problem but extends to systems of coupled bosons and fermions that are in principle also realizable in solid state systems. The analogus supersymmetry of the magnon problem turns out to be particularly useful for highly frustrated magnets with the kagome family of antiferromagnets an analog of topological isostatic lattices. Thus, a solid state realization of the theory of phonon topological band structure may be found in highly frustrated magnets. However, our results show that this topology is protected not

  15. Canning Of Powdered Metal For Hot Isostatic Pressing

    NASA Technical Reports Server (NTRS)

    Juhas, John J.

    1989-01-01

    Quality of specimen enhanced by improved canning process. Method developed for canning specimens for hot isostatic pressing. Specimen placed inside refractory-metal ring, then sandwiched between two refractory-metal face sheets. Assembly placed inside die, then positioned in vacuum hot press. Heated to set temperature at prescribed vacuum to burn off all of binder in specimen. Advantages: powder-metallurgy composite totally purged of binder sealed in can in single operation, maintains size, shape, and uniformity of specimen. Weld region does not recrystallize, and little possibility of cracking.

  16. Manufacture of die casting dies by hot isostatic pressing. CRADA final report

    SciTech Connect

    Viswanathan, S.; Ren, W.; Luk, K.; Brucher, H.G.

    1998-09-01

    The reason for this Cooperative Research and Development Agreement (CRADA) between the Oak Ridge National Laboratory (ORNL) and Doehler-Jarvis was to investigate the manufacture die-casting dies with internal water-cooling lines by hot-isostatic pressing (HIPing) of H13 tool steel powder. The use of HIPing will allow the near-net-shape manufacture of dies and the strategic placement of water-cooling lines during manufacture. The production of near-net-shape dies by HIPing involves the generation of HIPing diagrams, the design of the can that can be used for HIPing a die with complex details, strategic placement of water-cooling lines in the die, computer modeling to predict movement of the water lines during HIPing, and the development of strategies for placing water lines in the appropriate locations. The results presented include a literature review, particle analysis and characterization of H13 tool steel powder, and modeling of the HIPing process.

  17. An isostatic study of the Karoo basin and underlying lithosphere in 3-D

    NASA Astrophysics Data System (ADS)

    Scheiber-Enslin, Stephanie E.; Ebbing, Jörg; Webb, Susan J.

    2016-08-01

    A 3-D density model of the crust and upper mantle beneath the Karoo basin is presented here. The model is constrained using potential field, borehole and seismic data. Uplift of the basin by the end of the Cretaceous has resulted in an unusually high plateau (>1000 m) covering a large portion of South Africa. Isostatic studies show the topography is largely compensated by changes in Moho depths (˜35 km on-craton and >45 km off-craton) and changes in lithospheric mantle densities between the Kaapvaal Craton and surrounding regions (˜50 kg m-3 increase from on- to off-craton). This density contrast is determined by inverted satellite gravity and gravity gradient data. The highest topography along the edge of the plateau (>1200 m) and a strong Bouguer gravity low over Lesotho, however, can only be explained by a buoyant asthenosphere with a density decrease of around 40 kg m-3.

  18. High-pressure combinatorial process integrating hot isostatic pressing.

    PubMed

    Fujimoto, Kenjiro; Morita, Hiroki; Goshima, Yuji; Ito, Shigeru

    2013-12-01

    A high-pressure combinatorial process integrating hot isostatic pressing (HIP) was developed by providing a reaction vessel with a high-pressure tightness based on a commercial flange. The reaction vessel can be used up to 200 MPa and 500 °C under HIP processing condition. Preparation of spinel-type MgAl2O4 from Mg(OH)2, Al(OH)3 and AlOOH was performed using the reaction vessel under 200 MPa and 500 °C as demonstration. The entire powder library was characterized using powder X-ray diffraction patterns, and the single phase of spinel-type MgAl2O4 was obtained from Mg(OH)2+Al(OH)3. These assessments corresponded with previously published data. PMID:24168067

  19. Hot isostatic pressing of glass-zeolite composites

    SciTech Connect

    Hash, M.C.; Pereira, C.; Lewis, M.A.

    1996-05-01

    Glass-zeolite waste forms are being developed for immobilizing the chloride waste salt generated from the electrometallurgical treatment of spent fuel. Glass-zeolite composites with high densities were made using hot isostatic pressing (HIP) techniques. Processing parameters were investigated to yield desirable structural ceramic properties such as mechanical, chemical, and thermal stability. Limits for these parameters were determined by differential thermal and thermogravimetric analysis. The resulting ceramic properties such as bulk density, open or apparent porosity, and leach resistance were determined. In addition, phase equilibria and particle-size distribution were observed by optical light and electron microscopy. Pre-HIP processing techniques were also studied to ensure intimate mixing of the glass and zeolite powders. Particle size distributions resulting from dry blending procedure are appropriate for needed flow and packing characteristics.

  20. Hot-isostatic-press joining of cemented carbides

    SciTech Connect

    Miodownik, M.; Derby, B.

    1999-12-01

    Hot isostatic pressing (HIPing) is investigated as a technique for joining the cermet AC-15% Co to itself. Encapsulation of the specimens prior to HIPing was carried out using steel encapsulation, glass encapsulation, and self-encapsulation. The bonds were evaluated using a four-point-bend method. It is shown that the glass and steel encapsulation methods have a number of inherent problems which make them inappropriate for near net shape processing. In contrast the novel self-encapsulation method, described for the first time in this communication, is both simple and effective, producing joined material with bulk strength. The concept of self-encapsulation is potentially widely applicable for joining composite materials.

  1. An apparatus for studying scintillator properties at high isostatic pressures

    SciTech Connect

    Gaume, R. M.; Lam, S.; Gascon, M.; Feigelson, R. S.; Setyawan, W.; Curtarolo, S.

    2013-01-15

    We describe the design and operation of a unique hydraulic press for the study of scintillator materials under isostatic pressure. This press, capable of developing a pressure of a gigapascal, consists of a large sample chamber pressurized by a two-stage hydraulic amplifier. The optical detection of the scintillation light emitted by the sample is performed, through a large aperture optical port, by a photodetector located outside the pressure vessel. In addition to providing essential pressure-dependent studies on the emission characteristics of radioluminescent materials, this apparatus is being developed to elucidate the mechanisms behind the recently observed dependency of light-yield nonproportionality on electronic band structure. The variation of the light output of a Tl:CsI crystal under 511-keV gamma excitation and hydrostatic pressure is given as an example.

  2. Heinrich events driven by feedback between ocean forcing and glacial isostatic adjustment

    NASA Astrophysics Data System (ADS)

    Bassis, J. N.; Petersen, S. V.; Cathles, L. M. M., IV

    2015-12-01

    One of the most puzzling glaciological features of the past ice age is the episodic discharge of large volumes of icebergs from the Laurentide Ice Sheet, known as Heinrich events. It has been suggested that Heinrich events are caused by internal instabilities in the ice sheet (e.g. the binge-purge oscillation). A purely ice dynamic cycle, however, is at odds with the fact that every Heinrich event occurs during the cold phase of a DO cycle, implying some regional climate connection. Recent work has pointed to subsurface water warming as a trigger for Heinrich events through increased basal melting of an ice shelf extending across the Hudson Strait and connecting with the Greenland Ice Sheet. Such a large ice shelf, spanning the deepest part of the Labrador Sea, has no modern analog and limited proxy evidence. Here we use a width averaged "flowline" model of the Hudson Strait ice stream to show that Heinrich events can be triggered by ocean forcing of a grounded terminus without the need for an ice shelf. At maximum ice extent, bed topography is depressed and the terminus is more sensitive to a subsurface thermal forcing. Once triggered, the retreat is rapid, and continues until isostatic rebound of the bed causes local sea level to drop sufficiently to arrest retreat. Topography slowly rebounds, decreasing the sensitivity to ocean forcing and the ice stream re-advances at a rate that is an order of magnitude slower than collapse. This simple feedback cycle between a short-lived ocean trigger and slower isostatic adjustment can reproduce the periodicity and timing of observed Heinrich events under a range of glaciological and solid earth parameters. Our results suggest that not only does the solid Earth play an important role in regulating ice sheet stability, but that grounded marine terminating portions of ice sheets may be more sensitive to ocean forcing than previously thought.

  3. Preliminary isostatic gravity map of the Sonoma volcanic field and vicinity, Sonoma and Napa Counties, California

    USGS Publications Warehouse

    Langenheim, V.E.; Roberts, C.W.; McCabe, C.A.; McPhee, D.K.; Tilden, J.E.; Jachens, R.C.

    2006-01-01

    This isostatic residual gravity map is part of a three-dimensional mapping effort focused on the subsurface distribution of rocks of the Sonoma volcanic field in Napa and Sonoma counties, northern California. This map will serve as a basis for modeling the shapes of basins beneath the Santa Rosa Plain and Napa and Sonoma Valleys, and for determining the location and geometry of faults within the area. Local spatial variations in the Earth's gravity field (after accounting for variations caused by elevation, terrain, and deep crustal structure explained below) reflect the distribution of densities in the mid to upper crust. Densities often can be related to rock type, and abrupt spatial changes in density commonly mark lithologic boundaries. High-density basement rocks exposed within the northern San Francisco Bay area include those of the Mesozoic Franciscan Complex and Great Valley Sequence present in the mountainous areas of the quadrangle. Alluvial sediment and Tertiary sedimentary rocks are characterized by low densities. However, with increasing depth of burial and age, the densities of these rocks may become indistinguishable from those of basement rocks. Tertiary volcanic rocks are characterized by a wide range in densities, but, on average, are less dense than the Mesozoic basement rocks. Isostatic residual gravity values within the map area range from about -41 mGal over San Pablo Bay to about 11 mGal near Greeg Mountain 10 km east of St. Helena. Steep linear gravity gradients are coincident with the traces of several Quaternary strike-slip faults, most notably along the West Napa fault bounding the west side of Napa Valley, the projection of the Hayward fault in San Pablo Bay, the Maacama Fault, and the Rodgers Creek fault in the vicinity of Santa Rosa. These gradients result from juxtaposing dense basement rocks against thick Tertiary volcanic and sedimentary rocks.

  4. Interaction between climate, volcanism, and isostatic rebound in Southeast Alaska during the last deglaciation

    NASA Astrophysics Data System (ADS)

    Praetorius, Summer; Mix, Alan; Jensen, Britta; Froese, Duane; Milne, Glenn; Wolhowe, Matthew; Addison, Jason; Prahl, Fredrick

    2016-10-01

    Observations of enhanced volcanic frequency during the last deglaciation have led to the hypothesis that ice unloading in glaciated volcanic terrains can promote volcanism through decompression melting in the shallow mantle or a reduction in crustal magma storage time. However, a direct link between regional climate change, isostatic adjustment, and the initiation of volcanism remains to be demonstrated due to the difficulty of obtaining high-resolution well-dated records that capture short-term climate and volcanic variability traced to a particular source region. Here we present an exceptionally resolved record of 19 tephra layers paired with foraminiferal oxygen isotopes and alkenone paleotemperatures from marine sediment cores along the Southeast Alaska margin spanning the last deglacial transition. Major element compositions of the tephras indicate a predominant source from the nearby Mt. Edgecumbe Volcanic Field (MEVF). We constrain the timing of this regional eruptive sequence to 14.6-13.1 ka. The sudden increase in volcanic activity from the MEVF coincides with the onset of Bølling-Allerød interstadial warmth, the disappearance of ice-rafted detritus, and rapid vertical land motion associated with modeled regional isostatic rebound in response to glacier retreat. These data support the hypothesis that regional deglaciation can rapidly trigger volcanic activity. Rapid sea surface temperature fluctuations and an increase in local salinity (i.e., δ18Osw) variability are associated with the interval of intense volcanic activity, consistent with a two-way interaction between climate and volcanism in which rapid volcanic response to ice unloading may in turn enhance short-term melting of the glaciers, plausibly via albedo effects on glacier ablation zones.

  5. Glacial isostatic adjustment of the British Isles: new constraints from GPS measurements of crustal motion

    NASA Astrophysics Data System (ADS)

    Bradley, S. L.; Milne, G. A.; Teferle, F. N.; Bingley, R. M.; Orliac, E. J.

    2009-07-01

    We compared estimates of crustal velocities within Great Britain based on continuous global positioning system (CGPS) measurements to predictions from a model of glacial isostatic adjustment (GIA). The observed and predicted values for vertical motion are highly correlated indicating that GIA is the dominant geodynamic process contributing to this field. In contrast, motion of the Eurasian plate dominates the horizontal motion component. A model of plate motion was adopted to remove this signal in order to estimate intraplate horizontal motion associated with GIA. However, a coherent pattern of horizontal motion was not evident in the resulting velocity field. We adopted a recently published model of the British-Irish ice sheet to predict vertical crustal motion for a large number of spherically symmetric Earth viscosity models. Our results show that the adopted ice model is capable of producing a high-quality fit to the observations. The CGPS-derived estimates of vertical motion provide a useful constraint on the average value of viscosity within the upper mantle. Values of model lithospheric thickness and lower mantle viscosity are less well resolved, however. A suite of predictions based on an alternative ice model indicates that the vertical motion data are relatively insensitive to uncertainties in the ice loading history and so the constraints on upper mantle viscosity are robust.

  6. A new Approach to Combine GRACE and ICESat Observations to Estimate Glacial Isostatic Adjustment in East Antarctic

    NASA Astrophysics Data System (ADS)

    Kallenberg, B.; Tregoning, P.; Purcell, A. P.

    2014-12-01

    Monitoring and understanding ongoing changes in Antarctic mass balance is of great interest, as the melting of the ice sheet would significantly contribute to global sea level changes. While scientists agree that the West Antarctic ice sheet is losing mass, opinions about the East Antarctic ice sheet are more widespread, with some areas showing an increase in mass. In recent years satellite missions have significantly contributed to the understanding of ongoing changes within the polar ice sheets, and became an important tool in detecting variations in ice height, ice mass and bedrock isostasy. The Gravity Recovery And Climate Experiment (GRACE) mission detects mass loss in regions where the ice sheet has its bed well below sea level and where warmer ocean water penetrates beneath the ice sheet, melting it from the base. Meanwhile an increase in mass has been observed in regions along the East Antarctic coastline, raising the question whether GRACE detects glacial isostatic adjustment due to ice mass loss or an actual increase in snowfall, contributing positively to surface mass balance. To improve our understanding on the contribution of glacial isostatic adjustment and surface mass balance to mass variations, we developed a new approach on how to subtract elevation changes observed by satellite altimetry from observed mass changes as detected by GRACE. We have established our own firn compaction model that we apply to the altimetry data to subtract changes due to the densification of snow, before using the ICESat observations. We will present results of the firn compaction model and our approach on combining GRACE and ICESat observations to separate the contribution of glacial isostatic adjustment from ongoing surface mass changes in East Antarctica.

  7. High-strength silicon carbides by hot isostatic pressing

    NASA Technical Reports Server (NTRS)

    Dutta, Sunil

    1989-01-01

    Silicon carbide has strong potential for heat engine hardware and other high-temperature applications because of its low density, good strength, high oxidation resistance, and good high-temperature creep resistance. Hot isostatic pressing (HIP) was used for producing alpha and beta silicon carbide (SiC) bodies with near-theoretical density, ultrafine grain size, and high strength at processing temperatures of 1900 to 2000 C. The HIPed materials exhibited ultrafine grain size. Furthermore, no phase transformation from beta to alpha was observed in HIPed beta-SiC. Both materials exhibited very high average flexural strength. It was also shown that alpha-SiC bodies without any sintering aids, when HIPed to high final density, can exhibit very high strength. Fracture toughness K (sub C) values were determined to be 3.6 to 4.0 MPa m (sup 1/2) for HIPed alpha-SiC and 3.7 to 4.1 MPa m (sup 1/2) for HIPed beta-SiC. In the HIPed specimens strength-controlling flaws were typically surface related. In spite of improvements in material properties such as strength and fracture toughness by elimination of the larger strength-limiting flaws and by grain size refinement, HIPing has no effect on the Weibull modulus.

  8. Summary of Calcine Disposal Development Using Hot Isostatic Pressing

    SciTech Connect

    Bateman, Ken; Wahlquist, Dennis; Hart, Edward; McCartin, William

    2015-03-01

    Battelle Energy Alliance, LLC, has demonstrated the effectiveness of the hot isostatic press (HIP) process for treatment of hazardous high-level waste known as calcine that is stored at the Idaho Nuclear Technology and Engineering Center (INTEC) at Idaho National Laboratory. HIP trials performed with simulated calcines at Idaho National Laboratory’s Materials and Fuels Complex and an Australian Nuclear Science and Technology Organization facility from 2007 to 2010 produced a dense, monolithic waste form with increased chemical durability and effective (storage) volume reductions of ~10 to ~70% compared to granular calcine forms. In December 2009, the U.S. Department of Energy signed an amended Record of Decision selecting HIP technology as the treatment method for the 4,400 m3 of granular zirconia and alumina calcine stored at INTEC. Testing showed that HIP treatment reduces the risks associated with radioactive and hazardous constituent release, post-production handling, and long-term (repository) storage of calcines and would result in estimated storage cost savings in the billions of dollars. Battelle Energy Alliance has the ability to complete pilot-scale HIP processing of INTEC calcine, which is the next necessary step in implementing HIP processing as a calcine treatment method.

  9. Process and equipment development for hot isostatic pressing treatability study

    SciTech Connect

    Bateman, Ken; Wahlquist, Dennis; Malewitz, Tim

    2015-03-01

    Battelle Energy Alliance (BEA), LLC, has developed processes and equipment for a pilot-scale hot isostatic pressing (HIP) treatability study to stabilize and volume reduce radioactive calcine stored at Idaho National Laboratory (INL). In 2009, the U. S. Department of Energy signed a Record of Decision with the state of Idaho selecting HIP technology as the method to treat 5,800 yd^3 (4,400 m^3) of granular zirconia and alumina calcine produced between 1953 and 1992 as a waste byproduct of spent nuclear fuel reprocessing. Since the 1990s, a variety of radioactive and hazardous waste forms have been remotely treated using HIP within INL hot cells. To execute the remote process at INL, waste is loaded into a stainless-steel or aluminum can, which is evacuated, sealed, and placed into a HIP furnace. The HIP simultaneously heats and pressurizes the waste, reducing its volume and increasing its durability. Two 1 gal cans of calcine waste currently stored in a shielded cask were identified as candidate materials for a treatability study involving the HIP process. Equipment and materials for cask-handling and calcine transfer into INL hot cells, as well as remotely operated equipment for waste can opening, particle sizing, material blending, and HIP can loading have been designed and successfully tested. These results demonstrate BEA’s readiness for treatment of INL calcine.

  10. High-strength silicon carbides by hot isostatic pressing

    NASA Technical Reports Server (NTRS)

    Dutta, Sunil

    1988-01-01

    Silicon carbide has strong potential for heat engine hardware and other high-temperature applications because of its low density, good strength, high oxidation resistance, and good high-temperature creep resistance. Hot isostatic pressing (HIP) was used for producing alpha and beta silicon carbide (SiC) bodies with near-theoretical density, ultrafine grain size, and high strength at processing temperatures of 1900 to 2000 C. The HIPed materials exhibited ultrafine grain size. Furthermore, no phase transformation from beta to alpha was observed in HIPed beta-SiC. Both materials exhibited very high average flexural strength. It was also shown that alpha-SiC bodies without any sintering aids, when HIPed to high final density, can exhibit very high strength. Fracture toughness K (sub C) values were determined to be 3.6 to 4.0 MPa m (sup 1/2) for HIPed alpha-SiC and 3.7 to 4.1 MPa m (sup 1/2) for HIPed beta-SiC. In the HIPed specimens strength-controlling flaws were typically surface related. In spite of improvements in material properties such as strength and fracture toughness by elimination of the larger strength-limiting flaws and by grain size refinement, HIPing has no effect on the Weibull modulus.

  11. Coherent potential approximation of random nearly isostatic kagome lattice.

    PubMed

    Mao, Xiaoming; Lubensky, T C

    2011-01-01

    The kagome lattice has coordination number 4, and it is mechanically isostatic when nearest-neighbor sites are connected by central-force springs. A lattice of N sites has O(√N) zero-frequency floppy modes that convert to finite-frequency anomalous modes when next-nearest-neighbor (NNN) springs are added. We use the coherent potential approximation to study the mode structure and mechanical properties of the kagome lattice in which NNN springs with spring constant κ are added with probability P=Δz/4, where Δz=z-4 and z is the average coordination number. The effective medium static NNN spring constant κ(m) scales as P(2) for P≪κ and as P for P≫κ, yielding a frequency scale ω*~Δz and a length scale l*~(Δz)(-1). To a very good approximation at small nonzero frequency, κ(m)(P,ω)/κ(m)(P,0) is a scaling function of ω/ω*. The Ioffe-Regel limit beyond which plane-wave states become ill-defined is reached at a frequency of order ω*.

  12. Anomalous secular sea-level acceleration in the Baltic Sea caused by glacial isostatic adjustment

    NASA Astrophysics Data System (ADS)

    Spada, Giorgio; Galassi, Gaia; Olivieri, Marco

    2014-05-01

    Observations from the global array of tide gauges show that global sea-level has been rising at an average rate of 1.5-2 mm/yr during the last ˜ 150 years (Spada & Galassi, 2012). Although a global sea-level acceleration was initially ruled out, subsequent studies have coherently proposed values of ˜1 mm/year/century (Olivieri & Spada, 2012). More complex non-linear trends and abrupt sea-level variations have now also been recognized. Globally, they could manifest a regime shift between the late Holocene and the current rhythms of sea-level rise, while locally they result from ocean circulation anomalies, steric effects and wind stress (Bromirski et al. 2011). Although isostatic readjustment affects the local rates of secular sea-level change, a possible impact on regional acceleration have been so far discounted (Woodworth et al., 2009) since the process evolves on a millennium scale. Here we report a previously unnoticed anomaly in the long-term sea-level acceleration of the Baltic Sea tide gauge records, and we explain it by the classical post-glacial rebound theory and numerical modeling of glacial isostasy. Contrary to previous assumptions, our findings demonstrate that isostatic compensation plays a role in the regional secular sea-level acceleration. In response to glacial isostatic adjustment (GIA), tide gauge records located along the coasts of the Baltic Sea exhibit a small - but significant - long-term sea-level acceleration in excess to those in the far field of previously glaciated regions. The sign and the amplitude of the anomaly is consistent with the post-glacial rebound theory and with realistic numerical predictions of GIA models routinely employed to decontaminate the tide gauges observations from the GIA effects (Peltier, 2004). Model computations predict the existence of anomalies of similar amplitude in other regions of the globe where GIA is still particularly vigorous at present, but no long-term instrumental observations are available to

  13. Optimal locations of sea-level indicators in glacial isostatic adjustment investigations

    NASA Astrophysics Data System (ADS)

    Steffen, H.; Wu, P. P. C.; Wang, H.

    2015-12-01

    Knowledge of the Glacial Isostatic Adjustment (GIA) process allows us to understand mantle rheology and dynamics, ice sheet thickness history and climate change. In order to further constrain GIA models and improve our current knowledge of GIA, more observations (e.g. relative sea-levels (RSL), GPS, gravity measurements, tide-gauges) are desirable to resolve the following parameters of GIA: 1.Ice thickness, 2.Lithospheric thickness, 3.Radial viscosity profile (background viscosity profile for modeling), 4.Lateral viscosity changes in view of thermal versus chemical origin of the 3D structures in the mantle.We discuss global sensitivities of RSL data of the last 18,000 years. This also includes indicative RSL-like data (e.g., lake levels) on the continents far off the coasts. We present detailed sensitivity maps for the four parameters above for up to nine dedicated times. Assuming an observational accuracy of 2 m of RSL data of all ages (based on analysis of currently available data), we highlight areas (or optimal locations) around the world where, if the environmental conditions allowed its deposition and survival until today, RSL data of at least this accuracy may help to quantify the GIA modeling parameters above.

  14. Thermomechanical behavior of an austenitic stainless steel powder during hot isostatic pressing

    SciTech Connect

    Bouaziz, O.; Baccino, R.; Dellis, C.; Moret, F.

    1996-12-31

    Near-net-shape Hot Isostatic Pressing of powder can be an alternative technique to manufacture complex stainless steel parts for nuclear industry that are produced today by casting. Such a development requires the use of a numerical modelling code in order to predict the exact shape of the densified part. CEA/CEREM has developed a FEM code including Abouaf`s model to simulate the powder thermomechanical behavior. An extensive experimental program has been defined to determine Abouaf`s model parameters for a gas atomized austenitic stainless steel powder (AISI 316LN). In contrast to previous experimental works that were essentially focused on densification at stabilized forming temperature (1,125 C in the authors` case), this study was also concerned by the temperature and pressure raising stage in which the major deformations occur. This paper presents, in a first part, the HIP and uniaxial compression tests results in a very large temperature range from 800 to 1,125 C. The second part is devoted to the microstructural evolution of the material with temperature, pressure and density.

  15. Using isostatic scenarios to assess coherence between continuous and instantaneous sea level indicators through the last interglacial

    NASA Astrophysics Data System (ADS)

    Williams, Felicity; Tamisiea, Mark E.; Rohling, Eelco J.; Hibbert, Fiona; Zhao, Cheng

    2014-05-01

    As a given volume of ice melt will not have a uniform impact on sea level, glacial isostatic adjustment is an essential tool for reconciling sea level indicators taken from multiple locations across the globe. We generate four ice loading histories based on the continuous ice volume record of de Boer, the δ18O stack of Lisiecki and Raymo, the composite relative sea level record of Waelbroeck, and our Red Sea relative sea level curve. Using these ice histories we model relative sea level curves for locations where fossil coral sea level indicators have been published and compiled into a standardised database. Although we apply screening criteria to the coral datapoints, preferentially focusing on those samples that are less likely to have undergone diagenic alteration, the fit between the sea level curves and the coral indicators is unsatisfactory. The relative sea level curves do not replicate the duration and amplitude of maximum sea level that is found in the coral record during MIS5e. We therefore explore three isostatic scenarios, whereby ice volume is reduced over the interglacial, the duration of the interglacial is extended, and the duration of the preceding glacial is extended in order to constrain possible explanations for the variations between the different records. We find that the continuous records require either a longer interglacial period or a combination of longer interglacial duration and less interglacial ice volume in order to more closely replicate the coral record.

  16. Preliminary Isostatic Gravity Map of Joshua Tree National Park and Vicinity, Southern California

    USGS Publications Warehouse

    Langenheim, V.E.; Biehler, Shawn; McPhee, D.K.; McCabe, C.A.; Watt, J.T.; Anderson, M.L.; Chuchel, B.A.; Stoffer, P.

    2007-01-01

    This isostatic residual gravity map is part of an effort to map the three-dimensional distribution of rocks in Joshua Tree National Park, southern California. This map will serve as a basis for modeling the shape of basins beneath the Park and in adjacent valleys and also for determining the location and geometry of faults within the area. Local spatial variations in the Earth's gravity field, after accounting for variations caused by elevation, terrain, and deep crustal structure, reflect the distribution of densities in the mid- to upper crust. Densities often can be related to rock type, and abrupt spatial changes in density commonly mark lithologic or structural boundaries. High-density basement rocks exposed within the Eastern Transverse Ranges include crystalline rocks that range in age from Proterozoic to Mesozoic and these rocks are generally present in the mountainous areas of the quadrangle. Alluvial sediments, usually located in the valleys, and Tertiary sedimentary rocks are characterized by low densities. However, with increasing depth of burial and age, the densities of these rocks may become indistinguishable from those of basement rocks. Tertiary volcanic rocks are characterized by a wide range of densities, but, on average, are less dense than the pre-Cenozoic basement rocks. Basalt within the Park is as dense as crystalline basement, but is generally thin (less than 100 m thick; e.g., Powell, 2003). Isostatic residual gravity values within the map area range from about 44 mGal over Coachella Valley to about 8 mGal between the Mecca Hills and the Orocopia Mountains. Steep linear gravity gradients are coincident with the traces of several Quaternary strike-slip faults, most notably along the San Andreas Fault bounding the east side of Coachella Valley and east-west-striking, left-lateral faults, such as the Pinto Mountain, Blue Cut, and Chiriaco Faults (Fig. 1). Gravity gradients also define concealed basin-bounding faults, such as those beneath the

  17. Synthesis and densification of Ni{sub 3}(Si, Ti) intermetallics by hot isostatic pressing

    SciTech Connect

    Van Dyck, S.; Delaey, L.; Froyen, L.; Buekenhout, L.

    1996-12-31

    The production of complex parts from Ni{sub 3}(Si, Ti) intermetallic materials by reactive powder metallurgy offers significant advantages over more conventional processing techniques. The main problem associated with reactive powder metallurgy is controlling the exothermic reaction accompanying the synthesis of the intermetallic compound. The uncontrolled release of heat during the conversion of the reactants into nickel silicide leads to unacceptable deformation and melting of the part. The thermal evolution of a part during reactive synthesis of the intermetallic phase is described based on kinetic and heat transfer equations, giving the temperature and phase change as a function of the applied temperature cycle and the mass and size of the part under consideration. From this model, methods for controlling the exothermic reaction during synthesis are derived. When preparing nickel silicides by reactive powder metallurgy, the application of external pressure is required to eliminate porosity and to obtain good mechanical properties. The properties of materials produced by hot isostatic pressing, with different methods of reaction control, are compared to materials prepared from prealloyed powders. It is shown that by reactive HIP, materials can be obtained with a fracture strength exceeding 2,000 MPa.

  18. Mechanics of hot isostatic pressing of a densified unidirectional SiC/Ti composite

    SciTech Connect

    Bahei-El-Din, Y.A.; Dvorak, G.J.

    1995-07-01

    The effect of standard and modified hot isostatic pressing programs on local residual stresses is investigated with an axisymmetric micromechanical model of a unidirectional SCS6/Ti-15-3 composite, made of an elastic fiber and a thermo-viscoplastic matrix. The processing parameters studied include the cooling rate under sustained pressure, the magnitude of the hydrostatic stress, and the ratios of the axial transverse components. Local stresses in the fiber and in the matrix at their interface are evaluated after cooling from 980 C to room temperature, and during reheating to 500 and 980 C. As in the previous studies, the results indicate that inelastic deformation of the matrix along the cooling path, promoted here by slow cooling rates at sustained pressure, is responsible for reduction of the residual stresses in the fibrous composite. The magnitudes of the local residual stresses at room temperature are nearly linear functions of the logarithm of the cooling rate. Higher processing pressures also contribute to residual stress reduction, and especially so when the transverse pressure component is much higher than the axial.

  19. Isostatic and dynamic support of high topography on a North Atlantic passive margin

    NASA Astrophysics Data System (ADS)

    Kathrine Pedersen, Vivi; Huismans, Ritske S.; Moucha, Robert

    2016-04-01

    Substantial controversy surrounds the origin and recent evolution of high topography along passive continental margins in the North Atlantic, with suggested age of formation ranging from early Paleozoic Caledonian orogenesis to Neogene uplift of a Mesozoic peneplain. Here we focus on the well-documented high passive margin in southwestern Scandinavia, and quantify the relative contributions of crustal isostasy and dynamic topography in controlling the present topography. We find that most topography is compensated by the crustal structure, suggesting a topographic age related to ~400 Myr old Caledonian orogenesis. In addition, we infer that dynamic uplift (~300 m) has rejuvenated existing topography locally in the coastal region within the last ~10 Myr due to mantle convection. Such uplift has, in combination with a general eustatic sea-level fall and concurrent erosion-driven isostatic rock-column uplift, the potential to increase erosion of coastal-near regions and explain observations that have traditionally been interpreted in favor of the peneplain uplift model. We conclude that high topography along the Scandinavian margin cannot represent remnants of a peneplain uplifted within the last ~20 Myr. Topography must have been high since the Caledonian orogeny.

  20. Preliminary isostatic residual gravity anomaly map of Paso Robles 30 x 60 minute quadrangle, California

    USGS Publications Warehouse

    McPhee, D.K.; Langenheim, V.E.; Watt, J.T.

    2011-01-01

    This isostatic residual gravity map is part of an effort to map the three-dimensional distribution of rocks in the central California Coast Ranges and will serve as a basis for modeling the shape of basins and for determining the location and geometry of faults within the Paso Robles quadrangle. Local spatial variations in the Earth\\'s gravity field, after accounting for variations caused by elevation, terrain, and deep crustal structure reflect the distribution of densities in the mid- to upper crust. Densities often can be related to rock type, and abrupt spatial changes in density commonly mark lithological or structural boundaries. High-density rocks exposed within the central Coast Ranges include Mesozoic granitic rocks (exposed northwest of Paso Robles), Jurassic to Cretaceous marine strata of the Great Valley Sequence (exposed primarily northeast of the San Andreas fault), and Mesozoic sedimentary and volcanic rocks of the Franciscan Complex [exposed in the Santa Lucia Range and northeast of the San Andreas fault (SAF) near Parkfield, California]. Alluvial sediments and Tertiary sedimentary rocks are characterized by low densities; however, with increasing depth of burial and age, the densities of these rocks may become indistinguishable from those of older basement rocks.

  1. Volcanism, isostatic residual gravity, and regional tectonic setting of the Cascade volcanic province

    SciTech Connect

    Blakely, R.J.; Jachens, R.C. )

    1990-11-10

    A technique to locate automatically boundaries between crustal blocks of disparate densities was applied to upward continued isostatic residual gravity data. The boundary analysis delineates a narrow gravitational trough that extends the length of the Pliocene and Quaternary volcanic arc from Mount Baker in northern Washington to Lassen Peak in California. Gravitational highs interrupt the trough at two localities: A northwest trending high in southern Washington and a northeast trending high between Mount Shasta and Lassen Peak. The latter anomaly is one of a set of northeast trending anomalies that, within the Quaternary arc, appear related to volcanic segmentation proposed previously on the basis of spatial compositional distributions of volcanoes. These northeast trending anomalies extend hundreds of kilometers northeast of the arc, are caused by sources in the upper crust, and in some cases are related to exposed pre-Tertiary rocks. Segmentation models invoke geometric characteristics of the subducting plate as the primary factor controlling location and chemistry of volcanism, and these northeast trending gravity sources also may be a product of disturbance of the upper crust by the subduction process. More likely, the gravity sources may reflect upper crustal structures older than the High Cascades, possibly relicts from earlier accretionary events or more recent crustal deformation, that have actively influenced the spatial location of more recent volcanism. Much of the Pliocene and Quaternary volcanism of the Cascade arc has concentrated on or near contacts between crustal blocks of disparate density. These contacts may promote the ascension of magma to the Earth's surface.

  2. Volcanism, isostatic residual gravity, and regional tectonic setting of the Cascade Volcanic Province

    NASA Astrophysics Data System (ADS)

    Blakely, Richard J.; Jachens, Robert C.

    1990-11-01

    A technique to locate automatically boundaries between crustal blocks of disparate densities was applied to upward continued isostatic residual gravity data. The boundary analysis delineates a narrow gravitational trough that extends the length of the Pliocene and Quaternary volcanic arc from Mount Baker in northern Washington to Lassen Peak in California. Gravitational highs interrupt the trough at two localities: a northwest trending high in southern Washington and a northeast trending high between Mount Shasta and Lassen Peak. The latter anomaly is one of a set of northeast trending anomalies that, within the Quaternary arc, appear related to volcanic segmentation proposed previously on the basis of spatial and compositional distributions of volcanoes. These northeast trending anomalies extend hundreds of kilometers northeast of the arc, are caused by sources in the upper crust, and in some cases are related to exposed pre-Tertiary rocks. Segmentation models invoke geometric characteristics of the subducting plate as the primary factor controlling location and chemistry of volcanism, and these northeast trending gravity sources also may be a product of disturbance of the upper crust by the subduction process. More likely, the gravity sources may reflect upper crustal structures older than the High Cascades, possibly relicts from earlier accretionary events or more recent crustal deformation, that have actively influenced the spatial location of more recent volcanism. Much of the Pliocene and Quaternary volcanism of the Cascade arc has concentrated on or near contacts between crustal blocks of disparate density. These contacts may promote the ascension of magma to the Earth's surface.

  3. Low-angle normal faulting and isostatic response in the Gulf of Suez: Evidence from seismic interpretation and geometric reconstruction

    NASA Technical Reports Server (NTRS)

    Perry, S. K.; Schamel, S.

    1985-01-01

    Tectonic extension within continental crust creates a variety of major features best classed as extensional orogens. These features have come under increasing attention in recent years, with the welding of field observation and theoretical concepts. Most recent advances have come from the Basin and Range Province of the southwestern United States and from the North Sea. Application of these geometric and isostatic concepts, in combination with seismic interpretation, to the southern Gulf of Suez, an active extensional orogen, allows generation of detailed structural maps and geometrically balanced sections which suggest a regional structural model. Geometric models which should prove to be a valuable adjunct to numerical and thermal models for the rifting process are discussed.

  4. Dry Bag Isostatic Pressing for Improved Green Strength of Nuclear Fuel Pellets

    SciTech Connect

    G. W. Egeland; L. D. Zuck; W. R. Cannon; P. A. Lessing; P. G. Medvedev

    2010-11-01

    Dry bag isostatic pressing is proposed for mass production of nuclear fuel pellets. Dry bag isostatically pressed rods of a fuel surrogate (95% CeO2-5% HfO2) 200 mm long by 8 mm diameter were cut into pellets using a wire saw. Four different binder and two different CeO2 powder sources were investigated. The strength of the isostatically pressed pellets for all binder systems measured by diametral compression was about 50% higher than pellets produced by uniaxial dry pressing at the same pressure. It was proposed that the less uniform density of uniaxially pressed pellets accounted for the lower strength. The strength of pellets containing CeO2 powder with significantly higher moisture content was five times higher than pellets containing CeO2 powder with a low moisture content. Capillary pressure of the moisture was thought to supply the added binding strength.

  5. High density crystalline boron prepared by hot isostatic pressing in refractory metal containers

    DOEpatents

    Hoenig, Clarence L.

    1993-01-01

    Boron powder is hot isostatically pressed in a refractory metal container to produce a solid boron monolith with a bulk density at least 2.22 g/cc and up to or greater than 2.34 g/cc. The refractory metal container is formed of tantalum, niobium, tungsten, molybdenum or alloys thereof in the form of a canister or alternatively plasma sprayed or chemical vapor deposited onto a powder compact. Hot isostatic pressing at 1800.degree. C. and 30 KSI (206.8 MPa) argon pressure for four hours produces a bulk density of 2.34 g/cc. Complex shapes can be made.

  6. High density-high purity graphite prepared by hot isostatic pressing in refractory metal containers

    DOEpatents

    Hoenig, Clarence L.

    1994-01-01

    Porous graphite in solid form is hot isostatically pressed in a refractory metal container to produce a solid graphite monolith with a bulk density greater than or equal to 2.10 g/cc. The refractory metal container is formed of tantalum, niobium, tungsten, molybdenum or alloys thereof in the form of a canister or alternatively plasma sprayed, chemically vapor deposited, or coated by some other suitable means onto graphite. Hot isostatic pressing at 2200.degree. C. and 30 KSI (206.8 MPa) argon pressure for two hours produces a bulk density of 2.10 g/cc. Complex shapes can be made.

  7. High density crystalline boron prepared by hot isostatic pressing in refractory metal containers

    DOEpatents

    Hoenig, C.L.

    1993-08-31

    Boron powder is hot isostatically pressed in a refractory metal container to produce a solid boron monolith with a bulk density at least 2.22 g/cc and up to or greater than 2.34 g/cc. The refractory metal container is formed of tantalum, niobium, tungsten, molybdenum or alloys thereof in the form of a canister or alternatively plasma sprayed or chemical vapor deposited onto a powder compact. Hot isostatic pressing at 1,800 C and 30 PSI (206.8 MPa) argon pressure for four hours produces a bulk density of 2.34 g/cc. Complex shapes can be made.

  8. High density-high purity graphite prepared by hot isostatic pressing in refractory metal containers

    DOEpatents

    Hoenig, C.L.

    1994-08-09

    Porous graphite in solid form is hot isostatically pressed in a refractory metal container to produce a solid graphite monolith with a bulk density greater than or equal to 2.10 g/cc. The refractory metal container is formed of tantalum, niobium, tungsten, molybdenum or alloys thereof in the form of a canister or alternatively plasma sprayed, chemically vapor deposited, or coated by some other suitable means onto graphite. Hot isostatic pressing at 2,200 C and 30 KSI (206.8 MPa) argon pressure for two hours produces a bulk density of 2.10 g/cc. Complex shapes can be made. 1 fig.

  9. Removal of glass adhered to sintered ceramics in hot isostatic pressing

    NASA Technical Reports Server (NTRS)

    1985-01-01

    In the hot isostatic pressing of ceramic materials in molten glass using an inert gas as a pressing medium, glass adhered to the sintered ceramics is heated to convert it to a porous glass and removed. Thus, Si3N4 powder was compacted at 5000 kg/sq cm, coated with a 0.5 mm thick BN, embedded in Pyrex glass in a graphite crucible, put inside a hot isostatic press containing Argon, hot pressed at 1750 C and 100 kg/sq cm; cooled, taken out from the crucible, heated at 1100 C for 30 minutes, cooled, and then glass adhered to the sintered body was removed.

  10. Geologic and isostatic map of the Nenana Basin area, central Alaska

    USGS Publications Warehouse

    Frost, G.M.; Barnes, D.F.; Stanley, R.G.

    2002-01-01

    datum, digital terrain corrections, and conversion to isostatic gravity so that geologic structures on the margin of the Alaska Range are more clearly portrayed (Simpson and others, 1986). Computation procedures are described in part by Barnes (1972, 1984), Jachens and Roberts (1981), and Barnes and others (1994). The calculations used a crustal density of 2.67 g/cm 3 , a density contrast at the base of the isostatic root of 0.4 g/cm 3 , and a root thickness at sea level of 25 km. The distribution of data within the map area is uneven and locally controls the shape of the computer-generated contours. Altimetry was used for most of the elevation control and its inconsistency is responsible for many of the small contour irregularities. Ninety percent of the measurements are estimated to have an accuracy of about 1.5 mgal or about a quarter of the 5 mgal contour interval. Data collection and analysis were assisted by R.V. Allen, R.C. Jachens, M.A. Fisher, T.R. Bruns, J.G. Blank, J.W. Bader, Z.C. Valin, J.W. Cady, R.L. Morin, and P.V. Woodward. The most promising area for petroleum exploration is a prominent 25 mgal isostatic gravity low north of Nenana (T. 2 S., R. 8 W.). This gravity low probably corresponds to the deepest part of a sedimentary basin filled by Cenozoic strata that includes nonmarine fluvial and lacustrine deposits of the Eocene to Miocene Usibelli Group. Smaller gravity lows are associated with outcrops of these sedimentary rocks north of Suntrana (T. 12 S., R. 6-9 W.) and Sable Pass (T. 16 S., R. 11 W.). A broad low on the north flank of the Alaska Range east of the Wood River (T. 10 S., R. 1 E.) indicates another basin under the Tanana lowland that extends eastward off the map area towards Delta Junction, where its presence was confirmed by both gravity and seismic data (Barnes and others, 1991). Gravity modelling suggests that the base of the Usibelli Group in the area north of Nenana (T. 2 S., R. 8 W.) is about 3,000 to 3,350 m beneath t

  11. Geodetic Observations of Glacial Isostatic Adjustment in Southeast Alaska and its Implication of Earth Rheology

    NASA Astrophysics Data System (ADS)

    Hu, Y.; Freymueller, J. T.

    2012-12-01

    Benefiting from a denser network and more Global Positioning System (GPS) data, we derived velocities of the GPS stations in southeast Alaska with higher time resolution and accuracy than previously published data. GPS stations have recorded rapid uplift rates of up to 34 mm/yr over the last two decades, although uplift rates have varied with time over that period. We have refined previous geodynamic models of glacial isostatic adjustment in southeast Alaska and hope to improve our understanding of Earth rheology, using recently published digital elevation model analyses of recent glacier thickness changes. Thickness changes of Alaska, Yukon and British Columbia glaciers are based on Berthier et al. (2010). We ironed out the blank areas of their published data and constructed a 10-km gridded mass change model. Displacements were calculated by approximating the spatial load changes using 10-km diameter discs. Load model histories follow the Little Ice Age (LIA) load history compiled by Larsen et al. (2005). In our Earth model, the variable parameters include lithospheric elastic thickness, 30 - 120 km, and asthenosphere viscosity 10^18 - 2.5 x 10^19 Pa s. The same fixed parameters as in previous models include the asthenosphere thickness of 110 km and upper mantle viscosity 4 x 10^20 Pa s. In our best-fit model, the lithospheric elastic thickness is estimated to be 50 km, ~20% smaller than previous models. The asthenosphere viscosity is determined to be ~1.5 x 10^19 Pa s, ~3 times larger than previous estimates. Berthier, E., E. Schiefer, G. K. C. Clarke, B. Menounos, and F. Rémy (2010), Contribution of Alaskan glaciers to sea-level rise derived from satellite imagery, Nat. Geosci., 3, 92-95, doi:10.1038/ngeo737. Larsen, C. F., R. J. Motyka, J. T. Freymueller, K. A. Echelmeyer, and E. R. Ivins (2005), Rapid viscoelastic uplift in southeast Alaska caused by post-Little Ice Age glacial retreat, Earth Planet. Sci. Lett., 237, 548-560, doi:10.1016/j.epsl.2005.06.032.

  12. GPS Measurement of Tectonic Deformation and Isostatic Rebound in Marie Byrd Land, Antarctica

    NASA Astrophysics Data System (ADS)

    Donnellan, A.; Luyendyk, B. P.

    2001-12-01

    The Ross embayment and western Marie Byrd Land are part of the West Antarctic rift system. The region is undergoing active deformation, but the rates and causes of deformation are essentially unknown. In December 1998 we installed three continuous and autonomous global positioning system (GPS) stations on outcrops in western Marie Byrd Land, with baselines between stations of about 100 kilometers. We recovered data for the sites in Marie Byrd Land during the 1998--1999 season and additional data in November 1999, November 2000, and January 2001. Results from three years of data collection indicate essentially no extension between McMurdo station (MBL4) and the network. The results show an overall length rate of -0.7+/- 3.5~mm/yr between MCM4 and the wMBL network. With additional years of measurements we should be able to discriminate whether this rate is near zero or not to about 1~mm/yr. We also expect to detect strain gradients within wMBL. The network also suggests a dome of uplift centered near the Rockefeller Mountains, with the maximum rate being in the Rockefeller Mountains of 12+/- 8~mm/yr. This is consistent with proposed post-glacial rebound for the region. The strain data from wMBL and the Transantarctic Mountains will enable us to construct models for tectonic extension and glacial rebound in the West Antarctic rift. The results will help determine whether active tectonic deformation is occurring in the Ross embayment. Crustal uplift could be occurring in western Marie Byrd Land due to isostatic rebound following the last glacial age. Tectonic extension, occurring in the embayment, could greatly influence global plate circuit calculations and constrain our understanding of the history of extension in the embayment and the consequent uplift history of the Transantarctic Mountains.

  13. Use of GRACE determined secular gravity rates for glacial isostatic adjustment studies in North-America

    NASA Astrophysics Data System (ADS)

    van der Wal, Wouter; Wu, Patrick; Sideris, Michael G.; Shum, C. K.

    2008-10-01

    Monthly geopotential spherical harmonic coefficients from the GRACE satellite mission are used to determine their usefulness and limitations for studying glacial isostatic adjustment (GIA) in North-America. Secular gravity rates are estimated by unweighted least-squares estimation using release 4 coefficients from August 2002 to August 2007 provided by the Center for Space Research (CSR), University of Texas. Smoothing is required to suppress short wavelength noise, in addition to filtering to diminish geographically correlated errors, as shown in previous studies. Optimal cut-off degrees and orders are determined for the destriping filter to maximize the signal to noise ratio. The halfwidth of the Gaussian filter is shown to significantly affect the sensitivity of the GRACE data (with respect to upper mantle viscosity and ice loading history). Therefore, the halfwidth should be selected based on the desired sensitivity. It is shown that increase in water storage in an area south west of Hudson Bay, from the summer of 2003 to the summer of 2006, contributes up to half of the maximum estimated gravity rate. Hydrology models differ in the predictions of the secular change in water storage, therefore even 4-year trend estimates are influenced by the uncertainty in water storage changes. Land ice melting in Greenland and Alaska has a non-negligible contribution, up to one-fourth of the maximum gravity rate. The estimated secular gravity rate shows two distinct peaks that can possibly be due to two domes in the former Pleistocene ice cover: west and south east of Hudson Bay. With a limited number of models, a better fit is obtained with models that use the ICE-3G model compared to the ICE-5G model. However, the uncertainty in interannual variations in hydrology models is too large to constrain the ice loading history with the current data span. For future work in which GRACE will be used to constrain ice loading history and the Earth's radial viscosity profile, it is

  14. Expanded Analysis of Hot Isostatic Pressed Iodine-Loaded Silver-Exchanged Mordenite

    SciTech Connect

    Jubin, R. T.; Bruffey, S. H.; Patton, K. K.

    2014-09-30

    variations, and an expanded temperature range. Each sample was analyzed with the approach used in Phase I. In all cases, there is nothing in the SEM or XRD analyses that indicates creation of any AgI-containing silicon phase, with the samples being found to be largely amorphous. Phase III of this study has been initiated and is the final phase of scoping tests. It will expand upon the test matrix completed in Phase II and will examine the durability of the pressed pellets through product consistency testing (PCT) studies. Transformation of the component material into a well-characterized iodine-containing mineral phase would be desirable. This would limit the additional experimental testing and modeling required to determine the long-term stability of the pressed pellet, as much of that information has already been learned for several common iodine-containing minerals. However, this is not an absolute requirement, especially if pellets produced by hot isostatic pressing can be demonstrated through initial PCT studies to retain iodine well despite their amorphous composition.

  15. Inverting Glacial Isostatic Adjustment with Paleo Sea Level Records using Bayesian Framework and Burgers Rheology

    NASA Astrophysics Data System (ADS)

    Caron, L.; Metivier, L.; Greff-Lefftz, M.; Fleitout, L.; Rouby, H.

    2015-12-01

    Glacial Isostatic Adjustment models most often assume a mantle with a viscoelastic Maxwell rheology and a given ice history model. Here we use a Bayesian Monte Carlo with Markov Chains formalism to invert the global GIA signal simultaneously for the mechanical properties of the mantle and for the volume of the various ice-sheets using as starting ice models two distinct previously published ice histories. Burgers as well as Maxwell rheologies are considered.The fitted data consist of 5720 paleo sea level records from the last 35kyrs, with a world-wide distribution. Our ambition is to present not only the best fitting model, but also the range of possible solutions (within the explored space of parameters) with their respective probability of explaining the data, and thus reveal the trade-off effects and range of uncertainty affecting the parameters. Our a posteriori probality maps exhibit in all cases two distinct peaks: both are characterized by an upper mantle viscosity around 5.1020Pa.s but one of the peaks features a lower mantle viscosity around 3.1021Pa.s while the other indicates lower mantle viscosity of more than 1.1022Pa.s. The global maximum depends upon the starting ice history and the chosen rheology: the first peak (P1) has the highest probability only in the case with a Maxwell rheology and ice history based on ICE-5G, while the second peak (P2) is favored when using ANU-based ice history or Burgers rheology, and is our preferred solution as it is also consistent with long-term geodynamics and gravity gradients anomalies over Laurentide. P2 is associated with larger volumes for the Laurentian and Fennoscandian ice-sheets and as a consequence of total ice volume balance, smaller volumes for the Antactic ice-sheet. This last point interfers with the estimate of present-day ice-melting in Antarctica from GRACE data. Finally, we find that P2 with Burgers rheology favors the existence of a tectosphere, i.e. a viscous sublithospheric layer.

  16. Progress on Antarctic Glacial Isostatic Adjustment and GRACE constraints on ice loss (Invited)

    NASA Astrophysics Data System (ADS)

    Ivins, E. R.; James, T. S.; Wahr, J. M.; Schrama, E. J.; Simon, K. M.; Landerer, F. W.; Watkins, M. M.; Wiese, D. N.

    2013-12-01

    Preparations for the Intergovermental Panel on Climate Change: Assessment Report 5 (IPCC AR5) has placed pressure on various research groups to accelerate the pace of their work in order to meet the Report deadlines. While this stimulates both positive and negative bi-products, it helped to focus attention to irreconcilable mass balance determinations for the Antarctic Ice Sheet (AIS) using space and airborne data. A glaring ';sore-thumb' for determining AIS trends from Gravity Recovery and Climate Experiment (GRACE) satellite data is the large signal of glacial isostatic adjustment (GIA) that is poorly constrained and possibly of the same magnitude as the present-day mass change. The report published in Science (vol. 338, pp. 1183-89) by S13 [Shepherd et al. 2013] met this challenge head-on by investing heavily in improving the GIA models with new GPS data, and new chronological constraints on ice sheet evolution across the Antarctic continent. This new data has emerged only within the last five years, and it came at a fortuitous time for advancing the IPCC AR5 goals. In this presentation we speak to the improvements developed in a recent JGR Solid Earth publication (14 June 2013). We extend the analysis using all of the official 05 releases of the analysis centers, including the JPL-mascon fields. The total error budgets of GIA correction are poorly determined, in spite of the great model improvements witnessed in the past 5 years. S12 reported the uncertainty for space-based sea level sourcing during 1992-2011 to Antarctica at roughly 0.23 mm/yr. Although GRACE 2002-2013 estimates vary, the uncertainly is about half this value. Here we examine how much of that uncertainty is still caused by GIA models and discuss how new classes of GIA models, and the collection of yet new GPS and ice constraint data for Antarctica, will enhance the value of a GRACE Follow-On mission. However, there will be a limit to constraining GIA, and a limit, therefore, to GIA error due to

  17. The rotational feedback on linear-momentum balance in glacial isostatic adjustment

    NASA Astrophysics Data System (ADS)

    Martinec, Zdenek; Hagedoorn, Jan

    2015-04-01

    The influence of changes in surface ice-mass redistribution and associated viscoelastic response of the Earth, known as glacial-isostatic adjustment (GIA), on the Earth's rotational dynamics has long been known. Equally important is the effect of the changes in the rotational dynamics on the viscoelastic deformation of the Earth. This signal, known as the rotational feedback, or more precisely, the rotational feedback on the sea-level equation, has been mathematically described by the sea-level equation extended for the term that is proportional to perturbation in the centrifugal potential and the second-degree tidal Love number. The perturbation in the centrifugal force due to changes in the Earth's rotational dynamics enters not only into the sea-level equation, but also into the conservation law of linear momentum such that the internal viscoelastic force, the perturbation in the gravitational force and the perturbation in the centrifugal force are in balance. Adding the centrifugal-force perturbation to the linear-momentum balance creates an additional rotational feedback on the viscoelastic deformations of the Earth. We term this feedback mechanism as the rotational feedback on the linear-momentum balance. We extend both the time-domain method for modelling the GIA response of laterally heterogeneous earth models and the traditional Laplace-domain method for modelling the GIA-induced rotational response to surface loading by considering the rotational feedback on linear-momentum balance. The correctness of the mathematical extensions of the methods is validated numerically by comparing the polar motion response to the GIA process and the rotationally-induced degree 2 and order 1 spherical harmonic component of the surface vertical displacement and gravity field. We present the difference between the case where the rotational feedback on linear-momentum balance is considered against that where it is not. Numerical simulations show that the resulting difference

  18. The rotational feedback on linear-momentum balance in glacial isostatic adjustment

    NASA Astrophysics Data System (ADS)

    Martinec, Zdeněk; Hagedoorn, Jan

    2014-12-01

    The influence of changes in surface ice-mass redistribution and associated viscoelastic response of the Earth, known as glacial isostatic adjustment (GIA), on the Earth's rotational dynamics has long been known. Equally important is the effect of the changes in the rotational dynamics on the viscoelastic deformation of the Earth. This signal, known as the rotational feedback, or more precisely, the rotational feedback on the sea level equation, has been mathematically described by the sea level equation extended for the term that is proportional to perturbation in the centrifugal potential and the second-degree tidal Love number. The perturbation in the centrifugal force due to changes in the Earth's rotational dynamics enters not only into the sea level equation, but also into the conservation law of linear momentum such that the internal viscoelastic force, the perturbation in the gravitational force and the perturbation in the centrifugal force are in balance. Adding the centrifugal-force perturbation to the linear-momentum balance creates an additional rotational feedback on the viscoelastic deformations of the Earth. We term this feedback mechanism, which is studied in this paper, as the rotational feedback on the linear-momentum balance. We extend both the time-domain method for modelling the GIA response of laterally heterogeneous earth models developed by Martinec and the traditional Laplace-domain method for modelling the GIA-induced rotational response to surface loading by considering the rotational feedback on linear-momentum balance. The correctness of the mathematical extensions of the methods is validated numerically by comparing the polar-motion response to the GIA process and the rotationally induced degree 2 and order 1 spherical harmonic component of the surface vertical displacement and gravity field. We present the difference between the case where the rotational feedback on linear-momentum balance is considered against that where it is not

  19. Consolidation of Si3N4 without additives (by hot isostatic pressing)

    NASA Technical Reports Server (NTRS)

    Yeh, H. C.

    1983-01-01

    The potential of using hot isostatic pressing (HIP'ing) technique to produce dense silicon nitride materials without or with a reduced amount of additives (much less than 5 w/o) was investigated. Hot isostatic pressing technique can provide higher pressure and temperature than hot pressing can, thus has the potential of requiring less densification aids to consolidate Si3N4 materials. It was anticipated that if such dense materials could be fabricated, the high temperature strength of the material should be improved significantly. Observations on the phase transformation, densification behavior, and microstructures of the samples are also documented. Density, microhardness, four point bend strength (room temperature and 1370 C) were measured on selected densified materials.

  20. High density hexagonal boron nitride prepared by hot isostatic pressing in refractory metal containers

    DOEpatents

    Hoenig, Clarence L.

    1992-01-01

    Boron nitride powder with less than or equal to the oxygen content of starting powder (down to 0.5% or less) is hot isostatically pressed in a refractory metal container to produce hexagonal boron nitride with a bulk density greater than 2.0 g/cc. The refractory metal container is formed of tantalum, niobium, tungsten, molybdenum or alloys thereof in the form of a canister or alternatively plasma sprayed or chemical vapor deposited onto a powder compact. Hot isostatic pressing at 1800.degree. C. and 30 KSI (206.8 MPa) argon pressure for four hours produces a bulk density of 2.21 g/cc. Complex shapes can be made.

  1. Strength of hot isostatically pressed and sintered reaction bonded silicon nitrides containing Y2O3

    NASA Technical Reports Server (NTRS)

    Sanders, William A.; Mieskowski, Diane M.

    1989-01-01

    The hot isostatic pressing of reaction bonded Si3N4 containing Y2O3 produced specimens with greater room temperature strengths than those by high pressure nitrogen sintering of the same material. Average room temperature bend strengths for hot isostatically pressed reaction bonded silicon nitride and high pressure nitrogen sintered reaction bonded silicon nitride were 767 and 670 MPa, respectively. Values of 472 and 495 MPa were observed at 1370 C. For specimens of similar but lower Y2O3 content produced from Si3N4 powder using the same high pressure nitrogen sintering conditions, the room temperature strength was 664 MPa and the 1370 C strength was 402 MPa. The greater strengths of the reaction bonded silicon nitride materials in comparison to the sintered silicon nitride powder material are attributed to the combined effect of processing method and higher Y2O3 content.

  2. Effect of Surface Preparation on CLAM/CLAM Hot Isostatic Pressing diffusion bonding joints

    NASA Astrophysics Data System (ADS)

    Li, C.; Huang, Q.; Zhang, P.

    2009-04-01

    Surface preparation is essential for the Hot Isostatic Pressing (HIP) diffusion bonding of RAFM steels. Hot Isostatic Pressing (HIP) diffusion bonding experiments on China Low Activation Martensitic (CLAM) steel was performed to study the effect of surface preparation. A few approaches such as hand lapping, dry-milling and grinding etc., were used to prepare the faying surfaces of the HIP joints. Different sealing techniques were used as well. The HIP parameters were 150 MPa/3 h/1150 °C. After post HIP heat treatment (PHHT), the tensile and Charpy impact tests were carried out. The results showed that hand lapping was not suitable to prepare the faying surfaces of HIP diffusion bonding specimens although the surface roughness by hand lapping was very low.

  3. Development of monolithic nuclear fuels for RERTR by hot isostatic pressing

    SciTech Connect

    Jue, J.-F.; Park, Blair; Chapple, Michael; Moore, Glenn; Keiser, Dennis

    2008-07-15

    The RERTR Program (Reduced Enrichment for Research and Test Reactors) is developing advanced nuclear fuels for high power test reactors. Monolithic fuel design provides a higher uranium loading than that of the traditional dispersion fuel design. In order to bond monolithic fuel meat to aluminum cladding, several bonding methods such as roll bonding, friction stir bonding and hot isostatic pressing, have been explored. Hot isostatic pressing is a promising process for low cost, batch fabrication of monolithic RERTR fuel plates. The progress on the development of this process at the Idaho National Laboratory will be presented. Due to the relatively high processing temperature used, the reaction between fuel meat and aluminum cladding to form brittle intermetallic phases may be a concern. The effect of processing temperature and time on the fuel/cladding reaction will be addressed. The influence of chemical composition on the reaction will also be discussed. (author)

  4. Powder processing of nitrides (excluding hot isostatic processing). (Latest citations from Engineered Materials abstracts). Published Search

    SciTech Connect

    1996-02-01

    The bibliography contains citations concerning the properties and processing of metal nitride ceramics and refractories. Citations consider compacting and sintering processes. Phase transformations, crystallization, and devitrification processes are considered. Aluminum nitride, boron nitride, silicon nitride, silicon oxynitride, and titanium nitride are among materials discussed. The use of hot isostatic pressing is considered in a separate bibliography. (Contains 50-250 citations and includes a subject term index and title list.) (Copyright NERAC, Inc. 1995)

  5. Existence of isostatic, maximally random jammed monodisperse hard-disk packings.

    PubMed

    Atkinson, Steven; Stillinger, Frank H; Torquato, Salvatore

    2014-12-30

    We generate jammed packings of monodisperse circular hard-disks in two dimensions using the Torquato-Jiao sequential linear programming algorithm. The packings display a wide diversity of packing fractions, average coordination numbers, and order as measured by standard scalar order metrics. This geometric-structure approach enables us to show the existence of relatively large maximally random jammed (MRJ) packings with exactly isostatic jammed backbones and a packing fraction (including rattlers) of [Formula: see text]. By contrast, the concept of random close packing (RCP) that identifies the most probable packings as the most disordered misleadingly identifies highly ordered disk packings as RCP in 2D. Fundamental structural descriptors such as the pair correlation function, structure factor, and Voronoi statistics show a strong contrast between the MRJ state and the typical hyperstatic, polycrystalline packings with [Formula: see text] that are more commonly obtained using standard packing protocols. Establishing that the MRJ state for monodisperse hard disks is isostatic and qualitatively distinct from commonly observed polycrystalline packings contradicts conventional wisdom that such a disordered, isostatic packing does not exist due to a lack of geometrical frustration and sheds light on the nature of disorder. This prompts the question of whether an algorithm may be designed that is strongly biased toward generating the monodisperse disk MRJ state. PMID:25512529

  6. Multiproxy assessment of Holocene relative sea-level changes in the western Mediterranean: sea-level variability and improvements in the definition of the isostatic signal

    NASA Astrophysics Data System (ADS)

    Vacchi, Matteo; Rovere, Alessio; Marriner, Nick; Morhange, Christophe; Spada, Giorgio; Fontana, Alessandro

    2016-04-01

    After the review of 918 radiocarbon dated Relative Sea-Level (RSL) data-points we present here the first quality-controlled database constraining the Holocene sea-level histories of the western Mediterranean Sea (Spain, France, Italy, Slovenia, Croatia, Malta and Tunisia). We reviewed and standardized the geological RSL data-points using a new multi-proxy methodology based on: (1) modern taxa assemblages in Mediterranean lagoons and marshes; (2) beachrock characteristics (cement fabric and chemistry, sedimentary structures); and (3) the modern distribution of Mediterranean fixed biological indicators. These RSL data-points were coupled with the large number of archaeological RSL indicators available for the western Mediterranean. We assessed the spatial variability of RSL histories for 22 regions and compared these with the ICE-5G VM2 GIA model. In the western Mediterranean, RSL rose continuously for the whole Holocene with a sudden slowdown at ~7.5 ka BP and a further deceleration during the last ~4.0 ka BP, after which time observed RSL changes are mainly related to variability in isostatic adjustment. The sole exception is southern Tunisia, where data show evidence of a mid-Holocene high-stand compatible with the isostatic impacts of the melting history of the remote Antarctic ice sheet. Our results indicate that late-Holocene sea-level rise was significantly slower than the current one. First estimates of GIA contribution indicate that, at least in the northwestern sector, it accounts at least for the 25-30% of the ongoing sea-level rise recorded by Mediterranean tidal gauges. Such contribution is less constrained at lower latitudes due to the lower quality of the late Holocene index points. Future applications of spatio-temporal statistical techniques are required to better quantify the gradient of the isostatic contribution and to provide improved context for the assessment of 20th century acceleration of Mediterranean sea-level rise.

  7. GPS observations of glacial isostatic adjustment into the Antarctic Interior

    NASA Astrophysics Data System (ADS)

    Konfal, S. A.; Wilson, T. J.; Bevis, M. G.; Kendrick, E. C.; Dalziel, I. W.; Smalley, R.; Willis, M. J.; Heeszel, D.; Wiens, D. A.

    2013-12-01

    Continuous GPS measurements of crustal motions made on bedrock along the Transantarctic Mountains (TAM) into the interior of Antarctica have been acquired by the Antarctic Network (ANET) component of the Polar Earth Observing Network (POLENET). Vertical motions increase into the interior, in broad agreement with current models of GIA, but the magnitudes of observed motions are substantially lower than predicted. Slower rates of uplift due to GIA can be attributed to several factors, including errors in ice history, a superposed solid earth response to modern ice mass change, and/or the influence of laterally varying earth properties on the GIA response. Observed horizontal motions in the same region are toward, rather than away from, the site of major ice mass loss in the Ross Embayment adjacent to the TAM. When compared to earth structure mapped by seismology, the horizontal crustal motions are consistently near-perpendicular to the very strong gradient in crust and mantle properties, with motion toward the weaker, West Antarctic side from the stronger, East Antarctic side. 3D representation of crustal displacements highlights the correlation between observed motions and the earth properties gradient in the region. These new results are perhaps the first confirmation of predictions from modeling studies that horizontal motions can be deflected or even reversed in response to lateral variations in earth properties. Laterally-varying earth models, incorporating the new GPS and seismology constraints, are required for more accurate estimates of GIA in Antarctica.

  8. Receiver function analysis of the crust and upper mantle in Fennoscandia - isostatic implications

    NASA Astrophysics Data System (ADS)

    Frassetto, Andrew; Thybo, Hans

    2013-11-01

    -like model for isostatic compensation. Because the Scandes mountains occupy the location of the ancient Caledonian orogeny, which created presumably much thicker crust and lithosphere by ca. 400 Ma, much of the dense lower crust or mantle lithosphere that is expected to form beneath large mountain belts must have been removed sometime afterwards to instill the current lithospheric architecture that underlies the region.

  9. An improved and extended GPS-derived 3D velocity field of the glacial isostatic adjustment (GIA) in Fennoscandia

    NASA Astrophysics Data System (ADS)

    Lidberg, Martin; Johansson, Jan M.; Scherneck, Hans-Georg; Davis, James L.

    2007-03-01

    We present a new GPS-derived 3D velocity field for the Fennoscandia glacial isostatic adjustment (GIA) area. This new solution is based upon ˜3,000 days of continuous GPS observations obtained from the permanent networks in Fennoscandia. The period encompasses a prolongated phase of stable observation conditions after the northern autumn of 1996. Several significant improvements have led to smaller uncertainties and lower systematic errors in the new solutions compared to our previous results. The GPS satellite elevation cut-off angle was lowered to 10°, we fixed ambiguities to integers where possible, and only a few hardware changes occurred over the entire network. The GAMIT/GLOBK software package was used for the GPS analysis and reference frame realization. Our new results confirmed earlier findings of maximum discrepancies between GIA models and observations in northern Finland. The reason may be related to overestimated ice-sheet thickness and glaciation period in the north. In general, the new solutions are more coherent in the velocity field, as some of the perturbations are now avoided. We compared GPS-derived GIA rates with sea-level rates from tide-gauge observations, repeated precise leveling, and with GIA model computations, which showed consistency.

  10. Scheme of 3 interfaces with local isostatic compensation on the Argentine continental margin

    NASA Astrophysics Data System (ADS)

    Pedraza De Marchi, A. C.; Ghidella, M. E.; Tocho, C.

    2013-05-01

    The segment of Argentine continental margin located between 39°S and the Malvinas platform (~49°S) is of passive type and volcanic characteristics revealed by seaward-dipping seismic reflectors sequences (SDRs). The free air gravity edge-effect associated with passive continental margins is one of the most distinctive characteristics of gravity in marine regions. This effect is in large part due to the transition between continental and oceanic crusts, because of their different thicknesses. In this presentation we investigate the Airy type isostatic compensation scheme by using three interfaces in a forward calculation with different approximations of Parker's expression to obtain the isostatic anomaly. After that we perform the inversion of the anomaly thus obtained in order to find the Moho's deflection necessary to compensate it (or minimize it) by using the same scheme of interfaces and the iterative Parker-Oldenburg method (Oldenburg, D., 1974) with more terms in the inversion. The crust-mantle interface (Moho) thus calculated represents a more realistic surface than the one calculated using one term in the inversion and the surface estimated with topographic data and sediment thickness. Even considering that the experiment constitutes a schematic assumption just to test the numerical methods involved, we find that in the comparison with the only available digitized refraction profile, the inverted Moho interface reproduces fairly well the Moho that the seismic profile yields, for the case of the iterative method. This suggests that the inverse calculation with the iterative method is sensible to the presence of the SDRS, at least for this sole profile. Keywords: isostatic anomaly, Moho, passive continental margins Oldenburg, D., 1974. The inversion and interpretation of gravity anomalíes, Geophysics, vol. 39, no. 4, p. 526-536.

  11. Isostaticity of constraints in amorphous jammed systems of soft frictionless Platonic solids.

    PubMed

    Smith, Kyle C; Fisher, Timothy S; Alam, Meheboob

    2011-09-01

    The average number of constraints per particle in mechanically stable amorphous systems of Platonic solids approaches the isostatic limit at the jamming point (→12), though average number of contacts are hypostatic. By introducing angular alignment metrics to classify the degree of constraint imposed by each contact, constraints are shown to arise as a direct result of local orientational order reflected in edge-face and face-face alignment angle distributions. With approximately one face-face contact per particle at jamming, chainlike face-face clusters form with finite extent--a signature of amorphous jammed systems.

  12. The Features of Carbon Nanotubes Grown in High Isostatic Pressure Apparatus from the Nanodiamond Powder

    NASA Astrophysics Data System (ADS)

    Buranova, Yu. S.; Kulnitskiy, B. A.; Perezhogin, I. A.; Bagramov, R. H.; Dubitsky, G. A.; Blank, V. D.

    2013-05-01

    Multiwalled carbon nanotubes were synthesized in high isostatic pressure (HIP) apparatus in nitrogen at 1650 °C and 2 MPa. The synthesis was performed with nanodiamonds as a precursor of carbon and with ferrocene as a catalyst. Transmission electron microscopy studies demonstrate that the product of the synthesis contains carbon nanotubes filled with iron-based nanoparticles. It was established that in the most of the cases these nanoparticles represent themselves iron carbide Fe3C (cementite). Several times we observed pure iron (γ- and ɛ-Fe) inside the nanotubes. The orientation of the iron and iron carbide particles with respect to the nanotubes axes was investigated.

  13. The increase in use of isostatic processing for aluminum alloy castings

    SciTech Connect

    Geaman, V.

    1996-12-31

    The castings industry originally perceived isostatic processing as a means of reducing scrap rates. Prior to the development of HIP`ing no other non-destructive technique was available which let to improved economics. However in recent years the emphasis has changed towards the exploitation of improved properties as design engineers realize that cast parts which have been HIP`d can develop capabilities similar to those of forged components. This paper presents experimental data regarding compaction during HIP and CIP processes, applied to various aluminum castings alloys which are used extensively in the Romanian automotive industry.

  14. Large scale densification of a nuclear waste ceramic by hot isostatic pressing

    SciTech Connect

    Hoenig, C.L.; Larker, H.T.

    1983-12-01

    Experimental results show that loaded bellows steel canisters, evacuated and sealed, can be cold-isostatically pressed before HIP from an initial density of 26 to 46% theoretical. Calcined powders are hygroscopic and may require degassing at 600 degrees C under vaccum, and residual gas, unless removed, is an impediment to HIP densification. Results also show that degassed synroc D powder in 50 kg quantities can be HIP densified to greater than 97% theoretical density at 1100 degrees C, 150 MPa, for 5h in a bellows canister without radial buckling. The authors believe that on the basis of this preliminary study, full-scale nuclear waste monoliths can be produced by HIP.

  15. Rift flank uplift and isostatic response to glacial erosion: Creation of a high-elevation continental margin.

    NASA Astrophysics Data System (ADS)

    McGregor, E. D.; Nielsen, S. B.; Stephenson, R. A.; Clausen, O. R.; Petersen, K. D.; Macdonald, D. I. M.

    2012-04-01

    Southern Baffin Island lies to the west of Davis Strait, which is part of a sedimentary basin system, linking Labrador Sea and Baffin Bay. It developed during Cretaceous and Palaeocene rifting that culminated in a brief period of sea-floor spreading in the late Palaeocene and Eocene. To date the cause of the high elevation southeastern margin of Baffin Island has not been a focus of much research, whereas the origin and age of elevated topography on its conjugate west Greenland margin is a matter of lively debate. For west Greenland it has been argued by some authors, from interpretations of on- and offshore data (fission track, seismic and well), that onshore topography was created by tectonically-driven uplift in the Neogene. However, we have previously demonstrated that offshore seismic and well data along the Greenland margin of Davis Strait are consistent with a model of rifting followed by thermal subsidence and fjord excavation by glaciers, where Neogene tectonic uplift is not required. For southeastern Baffin Island, we have analysed offshore seismic reflection profiles, exploration well and gravity data along the western margin of Davis Strait and conclude that rift flank uplift of older remnant topography and subsequent isostatic response to glacial erosion have produced the present-day high elevation onshore. This interpretation of the offshore evolution conforms with an onshore evolution for which elevated topography is related to erosion of pre-existing topography.

  16. Asperity generating upper crustal sources revealed by b value and isostatic residual anomaly grids in the area of Antofagasta, Chile

    NASA Astrophysics Data System (ADS)

    Sobiesiak, M.; Meyer, U.; Schmidt, S.; GöTze, H.-J.; Krawczyk, C. M.

    2007-12-01

    In our study we show that the locations of largest coseismic slip (asperities) on the fault plane of the Mw = 8.0 1995 Antofagasta earthquake in Northern Chile can be mapped by the spatial distribution of the seismic b value obtained from the aftershock sequence of the megathrust earthquake. These areas of high seismic moment release and concurrent high-b values are congruent with anomalies of the gravity isostatic residual (IR) field in the Antofagasta region. They are superimposed on the seismogenic part of the north Chilean subduction zone where the strongest coupling of the upper and lower plate is expected. The IR anomalies are interpreted to be caused by large Jurassic-Early Cretaceous batholiths which intruded into the upper crust. The observed positive correlations between high seismic b values, IR anomalies, and geologic structures enable us to propose a mechanical model for the generation of the asperities in the Antofagasta region. We suggest that the batholiths in conjunction with buoyant forces acting on the subducted slab of the Nazca plate are responsible for locking the interface where the asperities are located. This implies long-term conditions for the existence of the asperity generating tectonic situation. Concequently, the asperities around Antofagasta could be stationary features, at least for several seismic cycles. Hence we propose that the IR anomalies along the north Chilean convergent margin can be used as an indicator for high moment release and slip in future large earthquakes.

  17. Isostatic gravity map of the Monterey 30 x 60 minute quadrangle and adjacent areas, California

    USGS Publications Warehouse

    Langenheim, V.E.; Stiles, S.R.; Jachens, R.C.

    2002-01-01

    The digital dataset consists of one file (monterey_100k.iso) containing 2,385 gravity stations. The file, monterey_100k.iso, contains the principal facts of the gravity stations, with one point coded per line. The format of the data is described below. Each gravity station has a station name, location (latitude and longitude, NAD27 projection), elevation, and an observed gravity reading. The data are on the IGSN71 datum and the reference ellipsoid is the Geodetic Reference System 1967 (GRS67). The free-air gravity anomalies were calculated using standard formulas (Telford and others, 1976). The Bouguer, curvature, and terrain corrections were applied to the free-air anomaly at each station to determine the complete Bouguer gravity anomalies at a reduction density of 2.67 g/cc. An isostatic correction was then applied to remove the long-wavelength effect of deep crustal and/or upper mantle masses that isostatically support regional topography.

  18. Influence of hot isostatic pressing on ZrO2-CaO dental ceramics properties.

    PubMed

    Gionea, Alin; Andronescu, Ecaterina; Voicu, Georgeta; Bleotu, Coralia; Surdu, Vasile-Adrian

    2016-08-30

    Different hot isostatic pressing conditions were used to obtain zirconia ceramics, in order to assess the influence of HIP on phase transformation, compressive strength, Young's modulus and density. First, CaO stabilized zirconia powder was synthesized through sol-gel method, using zirconium propoxide, calcium isopropoxide and 2-metoxiethanol as precursors, then HIP treatment was applied to obtain final dense ceramics. Ceramics were morphologically and structurally characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Density measurements, compressive strength and Young's modulus tests were also performed in order to evaluate the effect of HIP treatment. The zirconia powders heat treated at 500°C for 2h showed a pure cubic phase with average particle dimension about 70nm. The samples that were hot isostatic pressed presented a mixture of monoclinic-tetragonal or monoclinic-cubic phases, while for pre-sintered samples, cubic zirconia was the single crystalline form. Final dense ceramics were obtained after HIP treatment, with relative density values higher than 94%. ZrO2-CaO ceramics presented high compressive strength, with values in the range of 500-708.9MPa and elastic behavior with Young's modulus between 1739MPa and 4372MPa. Finally zirconia ceramics were tested for biocompatibility allowing the normal development of MG63 cells in vitro.

  19. Influence of hot isostatic pressing on ZrO2-CaO dental ceramics properties.

    PubMed

    Gionea, Alin; Andronescu, Ecaterina; Voicu, Georgeta; Bleotu, Coralia; Surdu, Vasile-Adrian

    2016-08-30

    Different hot isostatic pressing conditions were used to obtain zirconia ceramics, in order to assess the influence of HIP on phase transformation, compressive strength, Young's modulus and density. First, CaO stabilized zirconia powder was synthesized through sol-gel method, using zirconium propoxide, calcium isopropoxide and 2-metoxiethanol as precursors, then HIP treatment was applied to obtain final dense ceramics. Ceramics were morphologically and structurally characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Density measurements, compressive strength and Young's modulus tests were also performed in order to evaluate the effect of HIP treatment. The zirconia powders heat treated at 500°C for 2h showed a pure cubic phase with average particle dimension about 70nm. The samples that were hot isostatic pressed presented a mixture of monoclinic-tetragonal or monoclinic-cubic phases, while for pre-sintered samples, cubic zirconia was the single crystalline form. Final dense ceramics were obtained after HIP treatment, with relative density values higher than 94%. ZrO2-CaO ceramics presented high compressive strength, with values in the range of 500-708.9MPa and elastic behavior with Young's modulus between 1739MPa and 4372MPa. Finally zirconia ceramics were tested for biocompatibility allowing the normal development of MG63 cells in vitro. PMID:26481467

  20. Hot isostatically pressed manufacture of high strength MERL 76 disk and seal shapes

    NASA Technical Reports Server (NTRS)

    Eng, R. D.; Evans, D. J.

    1982-01-01

    The feasibility of using MERL 76, an advanced high strength direct hot isostatic pressed powder metallurgy superalloy, as a full scale component in a high technology, long life, commercial turbine engine were demonstrated. The component was a JT9D first stage turbine disk. The JT9D disk rim temperature capability was increased by at least 22 C and the weight of JT9D high pressure turbine rotating components was reduced by at least 35 pounds by replacement of forged Superwaspaloy components with hot isostatic pressed (HIP) MERL 76 components. The process control plan and acceptance criteria for manufacture of MERL 76 HIP consolidated components were generated. Disk components were manufactured for spin/burst rig test, experimental engine tests, and design data generation, which established lower design properties including tensile, stress-rupture, 0.2% creep and notched (Kt = 2.5) low cycle fatigue properties, Sonntag, fatigue crack propagation, and low cycle fatigue crack threshold data. Direct HIP MERL 76, when compared to conventionally forged Superwaspaloy, is demonstrated to be superior in mechanical properties, increased rim temperature capability, reduced component weight, and reduced material cost by at least 30% based on 1980 costs.

  1. Viscosity of the asthenosphere from glacial isostatic adjustment and subduction dynamics at the northern Cascadia subduction zone, British Columbia, Canada

    NASA Astrophysics Data System (ADS)

    James, Thomas S.; Gowan, Evan J.; Wada, Ikuko; Wang, Kelin

    2009-04-01

    Late glacial sea level curves located in the Cascadia subduction zone (CSZ) fore arc in southwestern British Columbia show that glacial isostatic adjustment (GIA) was rapid when the Cordilleran Ice Sheet collapsed in the late Pleistocene. GIA modeling with a linear Maxwell rheology indicates that the observations can be equally well fit across a wide range of asthenospheric thicknesses, provided that the asthenospheric viscosity is varied from 3 × 1018 Pa s for a thin (140 km) asthenosphere to 4 × 1019 Pa s for a thick (380 km) asthenosphere. Present-day vertical crustal motion predicted by the GIA models shows rates of a few tenths of a millimeter per year, consistent with previous analyses. The model viscosities largely pertain to the viscosity of the oceanic mantle beneath the subducting Juan de Fuca slab but include a contribution from the mantle wedge above the slab. For comparison, effective viscosities for the upper mantle due to the tectonic regime (subduction) were computed using the strain rates and temperatures of an independent geodynamic model of the CSZ with a wet olivine power law rheology. The effective viscosities agree well with GIA model viscosities of 1019 Pa s or less, corresponding to an asthenosphere of 100 or 200 km thickness. The agreement suggests a significant role for power law flow in the GIA response. Regardless of the microphysical mechanisms responsible for the GIA response, the viscosity values inferred from GIA can be applied to studies of the megathrust earthquake cycle because both processes take place on comparable time scales.

  2. Optimal locations for absolute gravity measurements and sensitivity of GRACE observations for constraining glacial isostatic adjustment on the northern hemisphere

    NASA Astrophysics Data System (ADS)

    Steffen, Holger; Wu, Patrick; Wang, Hansheng

    2012-09-01

    Gravity rate of change is an important quantity in the investigation of glacial isostatic adjustment (GIA). However, measurements with absolute and relative gravimeters are laborious and time-consuming, especially in the vast GIA-affected regions of high latitudes with insufficient infrastructure. Results of the Gravity Recovery And Climate Experiment (GRACE) satellite mission have thus provided tremendous new insight as they fully cover those areas. To better constrain the GIA model (i.e. improve the glaciation history and Earth parameters) with new gravity data, we analyse the currently determined errors in gravity rate of change from absolute gravity (AG) and GRACE measurements in North America and Fennoscandia to test their sensitivity for different ice models, lithospheric thickness, background viscosity and lateral mantle viscosity variations. We provide detailed sensitivity maps for these four parameters and highlight areas that need more AG measurements to further improve our understanding of GIA. The best detectable parameter with both methods in both regions is the sensitivity to ice model changes, which covers large areas in the sensitivity maps. Also, most of these areas are isolated from sensitive areas of the other three parameters. The latter mainly overlap with ice model sensitivity and each other. Regarding existing AG stations, more stations are strongly needed in northwestern and Arctic Canada. In contrast, a quite dense network of stations already exists in Fennoscandia. With an extension to a few sites in northwestern Russia, a complete station network is provided to study the GIA parameters. The data of dense networks would yield a comprehensive picture of gravity change, which can be further used for studies of the Earth's interior and geodynamic processes.

  3. Powder processing of nitrides by hot isostatic pressing. (Latest citations from Engineered Materials abstracts). NewSearch

    SciTech Connect

    Not Available

    1994-10-01

    The bibliography contains citations concerning the use of hot isostatic pressing to process metal nitrides. Citations discuss the fabrication of components for internal combustion, advanced heat, and gas turbine engines. Ceramic matrix composites are considered. (Contains a minimum of 77 citations and includes a subject term index and title list.)

  4. Soft modes and elasticity of nearly isostatic lattices: randomness and dissipation.

    PubMed

    Mao, Xiaoming; Xu, Ning; Lubensky, T C

    2010-02-26

    The square lattice with nearest neighbor central-force springs is isostatic and does not support shear. Using the coherent potential approximation (CPA), we study how the random addition, with probability P=(z-4)/4 (z=average number of contacts), of next-nearest-neighbor (NNN) springs restores rigidity and affects phonon structure. The CPA effective NNN spring constant kappa{m}(omega), equivalent to the complex shear modulus G(omega), obeys the scaling relation, kappa{m}(omega)=kappa{m}h(omega/omega{*}), at small P, where kappa{m}=kappa{m}{'}(0) approximately P{2} and omega{*} approximately P, implying nonaffine elastic response at small P and the breakdown of plane-wave states beyond the Ioffe-Regel limit at omega approximately omega{*}. We identify a divergent length l{*} approximately P{-1}, and we relate these results to jamming.

  5. Isostatic uplift, crustal attenuation, and the evolution of an extensional detachment system in southwestern Nevada

    SciTech Connect

    Scott, R.B.

    1987-12-31

    Geological and geophysical evidence supports the existence of extensional detachments, between the Sheep Range and Death Valley. It is proposed that geographically separated pieces of detachments between Death Valley and the Sheep Range are parts of a regional detachment system that has evolved since the Miocene, and that the system consists of lenses of strata separated by an anastomosing network of low- and high-angle normal faults. This manuscript emphasizes the probability that isostatic uplift within the region of greatest crustal attenuation in this system, the Bullfrog Hills core complex, controlled the evolution of the detachment system between the breakaway zone a the Sheep Range and the core complex. Features in this system are described from east to west, which is the apparent direction of tectonic transport.

  6. Experimenting with hot isostatically pressed (HIP) nano grained bismuth-telluride-based alloys

    NASA Astrophysics Data System (ADS)

    Virta, Jouko; Tervo, Jyrki

    2012-06-01

    Hot Isostatic Pressing (HIP) is was used for compaction of nano grained bismuth-telluride samples and results were compared to Spark Plasma Sintered (SPS) samples of the same materials. The powders were essentially the same as presented by Vasilevskiy1 et al, 2010. The (BixSb1-x)2(TeySe1-y)3 thermoelectric alloys studied in this article were produced by mechanical alloying under an inert atmosphere. The p-type alloy composition corresponds to x = 0.2, y = 1 and for the n-type material x = 0.95, y = 0.95. For HIP treatment the n-and p-type powders were encapsulated in copper cylinders under protective argon atmosphere. The HIP temperature was kept low to avoid excess grain growth of the materials. The electrical conductivity, carrier mobility, carrier concentration and Seebeck coefficient of HIP and SPS compacted materials were measured and compared.

  7. Microstructure and Phase Composition of Cold Isostatically Pressed and Pressureless Sintered Silicon Nitride.

    PubMed

    Lukianova, O A; Krasilnikov, V V; Parkhomenko, A A; Sirota, V V

    2016-12-01

    The microstructure and physical properties of new Y2O3 and Al2O3 oxide-doped silicon nitride ceramics fabricated by cold isostatic pressing and free sintering were investigated. The phase composition of produced material was also studied by X-ray diffraction at room and elevated temperature. The fabricated ceramics featured a microstructure of Si5AlON7 grains with a fine-grained α-Si3N4 with a small amount of Y2SiAlON5. Described ceramics is attractive for many high-temperature structural applications due to beneficial combination of fine-grained structure with improved mechanical properties and small weight loss.

  8. Preparation of dense bulk high T/sub c/ superconducting materials using hot isostatic pressing

    SciTech Connect

    Imam, M.A.; Sadananda, K.; Osofsky, M.

    1989-03-01

    It is important to improve the intergrain contact by eliminating internal porosity in sintered products. This is accomplished for Ba-Cu-O with Er or Nd, Bi-Sr-Ca-Cu-O and Tl-Ba-Ca-Cu-O systems using hot isostatic pressing (HIP). Sintered superconducting materials were encapsulated in an evacuated stainless steel or pyrex glass containers and processed in a HIP unit a high temperatures and pressures. Optimum HIP conditions to obtain bulk samples of nearly theoretical density were determined. Results indicate that in addition to density, HIP also improved T/sub c/. Furthermore, for the 1-2-3 system, the grain size is significantly reduced during HIP and is attributed to fracturing of course particles in the sintered compact due to high strain rates experienced during the pressurization. HIP materials can be machined to any shape and size and is being used for making specimens for J/sub c/ measurements and superconducting devices.

  9. Microstructure and Phase Composition of Cold Isostatically Pressed and Pressureless Sintered Silicon Nitride.

    PubMed

    Lukianova, O A; Krasilnikov, V V; Parkhomenko, A A; Sirota, V V

    2016-12-01

    The microstructure and physical properties of new Y2O3 and Al2O3 oxide-doped silicon nitride ceramics fabricated by cold isostatic pressing and free sintering were investigated. The phase composition of produced material was also studied by X-ray diffraction at room and elevated temperature. The fabricated ceramics featured a microstructure of Si5AlON7 grains with a fine-grained α-Si3N4 with a small amount of Y2SiAlON5. Described ceramics is attractive for many high-temperature structural applications due to beneficial combination of fine-grained structure with improved mechanical properties and small weight loss. PMID:26979726

  10. Friction welding method of hot isostatic press can closure for the ICPP calcine immobilization program

    SciTech Connect

    Berry, S.M.; Reed, T.R.; Swainston, R.C

    1993-09-01

    An investigation of various closure techniques was performed in an effort to meet requirements for closure of evacuated waste cans to be used at Westinghouse Idaho Nuclear Company`s Idaho Chemical Processing Plant. Although other sealing techniques are available, welding was considered to be the best for sealing the cans. For various reasons. techniques other than welding are not suitable for cans that are subject to the Hot Isostatic Press (HIP) process. For example. elastomeric seals. solders. and brazing would,not withstand the temperature associated (approximately 1000 degrees centigrade) with the HIP process. Mechanical joining techniques such as threading, crimping, and swaging could result in the joint opening as the can wall is deformed during HIP process. Unlike the above joint methods, welding results in physical joining of the lid or plug to the can itself, thus the wall would have to be ruptured before leakage would occur. This document investigates welding techniques for application to the can closure.

  11. Manufacture of astroloy turbine disk shapes by hot isostatic pressing, volume 1

    NASA Technical Reports Server (NTRS)

    Eng, R. D.; Evans, D. J.

    1978-01-01

    The Materials in Advanced Turbine Engines project was conducted to demonstrate container technology and establish manufacturing procedures for fabricating direct Hot Isostatic Pressing (HIP) of low carbon Astroloy to ultrasonic disk shapes. The HIP processing procedures including powder manufacture and handling, container design and fabrication, and HIP consolidation techniques were established by manufacturing five HIP disks. Based upon dimensional analysis of the first three disks, container technology was refined by modifying container tooling which resulted in closer conformity of the HIP surfaces to the sonic shape. The microstructure, chemistry and mechanical properties of two HIP low carbon Astroloy disks were characterized. One disk was subjected to a ground base experimental engine test, and the results of HIP low carbon Astroloy were analyzed and compared to conventionally forged Waspaloy. The mechanical properties of direct HIP low carbon Astroloy exceeded all property goals and the objectives of reduction in material input weight and reduction in cost were achieved.

  12. Microbial diversity across a Canadian sub-Arctic, isostatically rebounding, soil transect

    NASA Astrophysics Data System (ADS)

    Trevors, J. T.; Kevan, P. G.; Tam, L.

    2010-05-01

    Seacoast to inland soil transects of 1 and 2 km were researched over 2 years to understand the microbial diversity in a post ice age, isostatically, rebounding, soil environment. Community level substrate utilization analysis and 16S rDNA eubacterial diversity were employed. The community level substrate analysis demonstrated that regardless of the location along the transect from seacoast to forest, sandy or peat soil, the microbial diversity (Shannon diversity index about 3) was virtually the same. Shannon diversity indexes based on PCR-DGGE analysis yielded values between about 0.6 and about 2 depending on the sand or peat soil type and the year the samples were collected and analyzed (2002 and 2003). Regardless of the genetic diversity, the soils exhibited similar metabolic capabilities. This is a good example of redundant, functional, physiology regardless of the species present at each location along the transects.

  13. Superior austempered ductile iron (ADI) properties achieved by prior hot isostatic pressing (HIP)

    SciTech Connect

    LaGoy, J.L.; Widmer, R.; Zick, D.H.

    1996-12-31

    Ductile iron obtained from different foundries and cast by dissimilar methods has been successfully hot isostatically pressed (HIPed) before austempering to achieve substantially higher ductilities, without significant detriment to other properties, than those reached by austempering along. HIP was attempted to solve different mechanical deficiencies in austempered ductile iron (ADI) such as the lack of ductility in higher strength grades, inconsistent mechanical properties, and service life limitations. A variety of HIP temperatures were analyzed from near the austenitizing region up to within 56 C (100 F) of the melting point of ductile iron. Microporosity was eliminated by HIP at all temperatures, and subsequent austempering revealed a uniform ADI microstructure. HIP proved successful with both unencapsulated castings and those enclosed within steel canisters. Additional benefits caused by HIP processing of ductile iron castings without the austempering treatment include a significant decrease in mechanical property data scatter, high hardness at reasonable ductility levels, and a substantially reduced scrap rate.

  14. Volcanism, isostatic residual gravity and regional tectonic setting of the Cascade volcanic province

    USGS Publications Warehouse

    Blakely, R.J.; Jachens, R.C.

    1990-01-01

    A technique to locate automatically boundaries between crustal blocks of disparate densities was applied to upward continued isostatic residual gravity data. The boundary analysis delineates a narrow gravitational trough that extends the length of the Pliocene and Quaternary volcanic arc from Mount Baker in northern Washington to Lassen Peak in California. Gravitational highs interrupt the trough at two localities: a northwest trending high in southern Washington and a northeast trending high between Mount Shasta and Lassen Peak. The gravity sources may reflect upper crustal structures older than the High Cascades, possibly relicts from earlier accretionary events or more recent crustal deformation, that have actively influenced the spatial location of more recent volcanism. Much of the Pliocene and Quaternary volcanism of the Cascade arc has concentrated on or near contacts between crustal blocks of disparate density. These contacts may promote the ascension of magma to the Earth's surface. -from Authors

  15. Insights into the Crustal Structure and Geodynamic Evolution of the Southern Granulite Terrain, India, from Isostatic Considerations

    NASA Astrophysics Data System (ADS)

    Kumar, Niraj; Singh, A. P.; Singh, B.

    2011-10-01

    The Southern Granulite Terrain of India, formed through an ancient continental collision and uplift of the earth's surface, was accompanied by thickening of the crust. Once the active tectonism ceased, the buoyancy of these deep crustal roots must have supported the Nilgiri and Palani-Cardamom hills. Here, the gravity field has been utilized to provide new constraints on how the force of buoyancy maintains the state of isostasy in the Southern Granulite Terrain. Isostatic calculations show that the seismically derived crustal thickness of 43-44 km in the Southern Granulite Terrain is on average 7-8 km more than that required to isostatically balance the present-day topography. This difference cannot be solely explained applying a constant shift in the mean sea level crustal thickness of 32 km. The isostatic analysis thus indicates that the current topography of the Southern Granulite Terrain is overcompensated, and about 1.0 km of the topographic load must have been eroded from this region without any isostatic readjustment. The observed gravity anomaly, an order of magnitude lower than that expected (-125 mGal), however, shows that there is no such overcompensation. Thermal perturbations up to Pan-African, present-day high mantle heat flow and low Te together negate the possible resistance of the lithosphere to rebound in response to erosional unloading. To isostatically compensate the crustal root, compatible to seismic Moho, a band of high density (2,930 kg m-3) in the lower crust and low density (3,210 kg m-3) in the lithospheric mantle below the Southern Granulite Terrain is needed. A relatively denser crust due to two distinct episodes of metamorphic phase transitions at 2.5 Ga and 550 Ma and highly mobilized upper mantle during Pan-African thermal perturbation reduced significantly the root buoyancy that kept the crust pulled downward in response to the eroded topography.

  16. Glacial isostatic adjustment and Holocene to contemporary source-to-sink fluxes in valley-fjord systems in western Norway

    NASA Astrophysics Data System (ADS)

    Beylich, Achim A.; Laute, Katja; Liermann, Susan

    2013-04-01

    architecture of major storage elements (talus cones, valley infills, deltas at the outlets of both drainage basins) using different geophysical methods like georadar and seismic refraction surveys are carried out to improve the quantitative knowledge on Holocene process rates and sedimentary budgets. Detailed geomorphological mapping is conducted and interpreted in combination with digital elevation models and data. The U-shaped valley morphometry is the main control of Holocene denudational surface processes in both Erdalen and Bødalen. Stepped longitudinal valley profiles within the drainage basin systems have caused that glacial isostatic adjustment has not had significant effects on surface denudational processes in the middle and upper parts of both Erdalen and Bødalen. In Erdalen the more clearly defined stepped longitudinal valley profile has resulted in larger storage (especially in larger volumes of Holocene valley infill and talus cones) and in a lower level of slope-channel coupling as compared to Bødalen. As a result, the glacial inheritance of topography is the most important factor controlling valley development since the LGM and sediment storage capacity is primarily conditioned by valley morphometry. Different periods within the Holocene with varying intensity of denudational surface processes can be identified and the glacially sculpted topography has not yet adapted to denudational surface processes acting under Holocene environmental conditions. Under the present-day environmental conditions mechanical denudation dominates over chemical denudation. Surface process rates are moderate to low, and the valley systems are altogether supply-limited. The process and denudation rates from the Erdalen and Bødalen drainage basins are compared with rates from other SedyMONT test sites (transport-limited drainage basin systems located in the Alps), and with denudational process rates in other cold environment drainage basin systems worldwide through the SEDIBUD

  17. Powder processing of nitrides (excluding hot isostatic processing). (Latest citations from Engineered Materials abstracts). NewSearch

    SciTech Connect

    Not Available

    1994-10-01

    The bibliography contains citations concerning the properties and processing of metal nitride ceramics and refractories. Citations consider compacting and sintering processes. Phase transformations, crystallization, and devitrification processes are considered. Aluminum nitride, boron nitride, silicon nitride, silicon oxynitride, and titanium nitride are among materials discussed. The use of hot isostatic pressing is considered in a separate bibliography. (Contains 250 citations and includes a subject term index and title list.)

  18. Microstructure and mechanical properties of hip-consolidated Rene 95 powders. [hot-isostatic pressed nickel-based powder metal

    NASA Technical Reports Server (NTRS)

    Shimanuki, Y.; Nishino, Y.; Masui, M.; Doi, H.

    1980-01-01

    The effects of heat-treatments on the microstructure of P/M Rene 95 (a nickel-based powder metal), consolidated by the hot-isostatic pressing (HIP), were examined. The microstructure of as-HIP'd specimen was characterized by highly serrated grain boundaries. Mechanical tests and microstructural observations reveal that the serrated grain boundaries improved ductility at both room and elevated temperatures by retarding crack propagation along grain boundaries.

  19. The Effectiveness of Hot Isostatic Pressing for Closing Porosity in Titanium Parts Manufactured by Selective Electron Beam Melting

    NASA Astrophysics Data System (ADS)

    Tammas-Williams, Samuel; Withers, Philip J.; Todd, Iain; Prangnell, Philip B.

    2016-05-01

    Ti-6Al-4V parts, produced by selective electron beam melting additive manufacturing, have been studied by X-ray computed tomography (XCT) to track pore closure during a standard hot isostatic pressing (HIPing) cycle. Comparison of repeated XCT scans before and after HIPing, on worst-case samples with different geometries, confirmed that all internal porosity was shrunk to below the resolution limit of the equipment used (~5 µm) following the HIPing cycle, apart from defects with surface connected ligaments.

  20. Cyclic fatigue resistance of yttria-stabilized tetragonal zirconia polycrystals with hot isostatic press processing.

    PubMed

    Koyama, Taku; Sato, Toru; Yoshinari, Masao

    2012-01-01

    This study investigated the influence of surface roughness and cyclic loading on fatigue resistance in Y-TZP subjected to hot isostatic pressing (HIP). Fifty Y-TZP cylinders 3.0 mm in diameter were divided into Group A (polished by centerless method; TZP-CP) or Group B (blasted and acid-etched: TZP-SB150E). Twenty five cp-titanium cylinders (Ti-SB150E) were used as a control. Static and cyclic tests were carried out according to ISO 14801. The cyclic fatigue test was performed in distilled water at 37°C. Surface morphology and roughness as well as crystal phase on the surfaces were also evaluated. Fracture force under the static test was 1,765N (TZP-CP), 1,220N (TZP-SB150E), and 850 N (yield force, Ti-SB150E). Fracture values under the cyclic test decreased to approximately 70% of those under the static tests. These results indicate that HIPed Y-TZP with a 3.0-mm diameter has sufficient durability for application to dental implants. PMID:23207222

  1. Nd:YAG transparent ceramics fabricated by direct cold isostatic pressing and vacuum sintering

    NASA Astrophysics Data System (ADS)

    Ge, Lin; Li, Jiang; Zhou, Zhiwei; Liu, Binglong; Xie, Tengfei; Liu, Jing; Kou, Huamin; Shi, Yun; Pan, Yubai; Guo, Jingkun

    2015-12-01

    The sintering behavior of neodymium doped yttrium aluminum garnet (Nd:YAG) ceramics was investigated on the basis of densification trajectory, microstructure evolution and transmittance. Nd:YAG ceramics with in-line transmittance of 83.9% at 1064 nm and 82.5% at 400 nm were obtained by direct cold isostatic pressing (CIP) at 250 MPa and solid-state reactive sintering at 1790 °C for 30 h under vacuum. Compared with the porosity and the average pore diameter of the sample from uniaxial dry-pressing followed by CIP, those from direct CIP are much smaller. The samples pressed at 250 MPa were sintered from 1500 °C to 1750 °C for 0.5-20 h to study their sintering behavior. At the temperature higher than 1500 °C, pure YAG phase is formed, followed by the densification and grain growth process. The relative density and the grain size increase with the increase of sintering time and temperature, and the sintering behavior is more sensitive to temperature than holding time. The mechanism controlling densification and grain growth at sintering temperature of 1550 °C is grain boundary diffusion.

  2. On the gravity and geoid effects of glacial isostatic adjustment in Fennoscandia - a short note

    NASA Astrophysics Data System (ADS)

    Sjöberg, L. E.

    2016-02-01

    Many geoscientists argue that there is a gravity low of 10-30 mGal in Fennoscandia as a remaining fingerprint of the last ice age and load, both vanished about 10 kyr ago. However, the extraction of the gravity signal related with Glacial Isostatic Adjustment (GIA) is complicated by the fact that the total gravity field is caused by many significant density distributions in the Earth. Here we recall a methodology originating with A. Bjerhammar 35 years ago, that emphasizes that the present land uplift phenomenon mainly occurs in the region thatwas covered by the ice cap, and it is highly correlated with the spectral window of degrees 10-22 of the global gravity field, whose lower limit fairly well corresponds to the wavelength that agrees with the size of the region. This implies that, although in principle the GIA is a global phenomenon, the geoid and gravity lows as well as the land upheaval in Fennoscandia are typically regional phenomena that cannot be seen in a global correlation study as it is blurred by many irrelevant gravity signals. It is suggested that a regional multi-regression analysis with a band-limited spectral gravity signal as the observable, a method tested already 2 decades ago, can absorb possible significant disturbing signals, e.g. from topographic and crustal depth variations, and thereby recover the GIA signal.

  3. On the gravity and geoid effects of glacial isostatic adjustment in Fennoscandia - a short note

    NASA Astrophysics Data System (ADS)

    Sjöberg, L. E.

    2015-12-01

    Many geoscientists argue that there is a gravity low of 10-30 mGal in Fennoscandia as a remaining fingerprint of the last ice age and load, both vanished about 10 kyr ago. However, the extraction of the gravity signal related with Glacial Isostatic Adjustment (GIA) is complicated by the fact that the total gravity field is caused by many significant density distributions in the Earth. Here we recall a methodology originating with A. Bjerhammar 35 years ago, that emphasizes that the present land uplift phenomenon mainly occurs in the region thatwas covered by the ice cap, and it is highly correlated with the spectral window of degrees 10-22 of the global gravity field, whose lower limit fairly well corresponds to the wavelength that agrees with the size of the region. This implies that, although in principle the GIA is a global phenomenon, the geoid and gravity lows as well as the land upheaval in Fennoscandia are typically regional phenomena that cannot be seen in a global correlation study as it is blurred by many irrelevant gravity signals. It is suggested that a regional multi-regression analysis with a band-limited spectral gravity signal as the observable, a method tested already 2 decades ago, can absorb possible significant disturbing signals, e.g. from topographic and crustal depth variations, and thereby recover the GIA signal.

  4. Age hardening in rapidly solidified and hot isostatically pressed beryllium-aluminum-silver alloys

    SciTech Connect

    Carter, D.H.; McGeorge, A.C.; Jacobson, L.A.; Stanek, P.W.

    1995-07-01

    Three different alloys of beryllium, aluminum and silver were processed to powder by centrifugal atomization in a helium atmosphere. Alloy compositions were, by weight, 50% Be, 47.5% Al, 2.5% Ag, 50% Be, 47% Al, 3% Ag, and 50% Be, 46% Al, 4% Ag. Due to the low solubility of both aluminum and silver in beryllium, the silver was concentrated in the aluminum phase, which appeared to separate from the beryllium in the liquid phase. A fine, continuous composite beryllium-aluminum microstructure was formed, which did not significantly change after hot isostatically pressing at 550 C for one hour at 30,000 psi argon pressure. Samples of HIP material were solution treated at 550 C for one hour, followed by a water quench. Aging temperatures were 150, 175, 200 and 225 C for times ranging from one half hour to 65 hours. Hardness measurements were made using a diamond pyramid indenter with a load of 1 kg. Results indicate that peak hardness was reached in 36--40 hours at 175 C and 12--16 hours at 200 C aging temperature, relatively independent of alloy composition.

  5. High temperature mechanical performance of a hot isostatically pressed silicon nitride

    SciTech Connect

    Wereszczak, A.A.; Ferber, M.K.; Jenkins, M.G.; Lin, C.K.J.

    1996-01-01

    Silicon nitride ceramics are an attractive material of choice for designers and manufacturers of advanced gas turbine engine components for many reasons. These materials typically have potentially high temperatures of usefulness (up to 1400{degrees}C), are chemically inert, have a relatively low specific gravity (important for inertial effects), and are good thermal conductors (i.e., resistant to thermal shock). In order for manufacturers to take advantage of these inherent properties of silicon nitride, the high-temperature mechanical performance of the material must first be characterized. The mechanical response of silicon nitride to static, dynamic, and cyclic conditions at elevated temperatures, along with reliable and representative data, is critical information that gas turbine engine designers and manufacturers require for the confident insertion of silicon nitride components into gas turbine engines. This final report describes the high-temperature mechanical characterization and analyses that were conducted on a candidate structural silicon nitride ceramic. The high-temperature strength, static fatigue (creep rupture), and dynamic and cyclic fatigue performance were characterized. The efforts put forth were part of Work Breakdown Structure Subelement 3.2.1, {open_quotes}Rotor Data Base Generation.{close_quotes} PY6 is comparable to other hot isostatically pressed (HIPed) silicon nitrides currently being considered for advanced gas turbine engine applications.

  6. Effect of reduced cobalt contents on hot isostatically pressed powder metallurgy U-700 alloys

    NASA Technical Reports Server (NTRS)

    Harf, F. H.

    1982-01-01

    The effect of reducing the cobalt content of prealloyed powders of UDIMET 700 (U-700) alloys to 12.7, 8.6, 4.3, and 0% was examined. The powders were hot isostatically pressed into billets, which were given heat treatments appropriate for turbine disks, namely partial solutioning at temperatures below the gamma prime solvus and four step aging treatments. Chemical analyses, metallographic examinations, and X-ray diffraction measurements were performed on the materials. Minor effects on gamma prime content and on room temperature and 650 C tensile properties were observed. Creep rupture lives at 650 C reached a maximum at the 8.4% concentration, while at 760 C a maximum in life was reached at the 4.3% cobalt level. Minimum creep rates increased with decreasing cobalt content at both test temperatures. Extended exposures at 760 and 815 C resulted in decreased tensile strengths and rupture lives for all alloys. Evidence of sigma phase formation was also found.

  7. The substitution of nickel for cobalt in hot isostatically pressed powder metallurgy UDIMET 700 alloys

    NASA Technical Reports Server (NTRS)

    Harf, F. H.

    1985-01-01

    Nickel was substituted in various proportions for cobalt in a series of five hot-isostatically-pressed powder metallurgy alloys based on the UDIMET 700 composition. These alloys were given 5-step heat treatments appropriate for use in turbine engine disks. The resultant microstructures displayed three distinct sizes of gamma-prime particles in a gamma matrix. The higher cobalt-content alloys contained larger amounts of the finest gamma-prime particles, and had the lowest gamma-gamma-prime lattice mismatch. While all alloys had approximately the same tensile properties at 25 and 650 gamma C, the rupture lives at 650 and 760 C peaked in the alloys with cobalt contents between 12.7 and 4.3 pct. Minimum creep rates increased as cobalt contents were lowered, suggesting their correlation with the gamma-prime particle size distribution and the gamma-gamma-prime mismatch. It was also found that, on overaging at temperatures higher than suitable for turbine disk use, the high cobalt-content alloys were prone to sigma phase formation.

  8. Isostatic Gravity Map with Geology of the Santa Ana 30' x 60' Quadrangle, Southern California

    USGS Publications Warehouse

    Langenheim, V.E.; Lee, Tien-Chang; Biehler, Shawn; Jachens, R.C.; Morton, D.M.

    2006-01-01

    This report presents an updated isostatic gravity map, with an accompanying discussion of the geologic significance of gravity anomalies in the Santa Ana 30 by 60 minute quadrangle, southern California. Comparison and analysis of the gravity field with mapped geology indicates the configuration of structures bounding the Los Angeles Basin, geometry of basins developed within the Elsinore and San Jacinto Fault zones, and a probable Pliocene drainage network carved into the bedrock of the Perris block. Total cumulative horizontal displacement on the Elsinore Fault derived from analysis of the length of strike-slip basins within the fault zone is about 5-12 km and is consistent with previously published estimates derived from other sources of information. This report also presents a map of density variations within pre-Cenozoic metamorphic and igneous basement rocks. Analysis of basement gravity patterns across the Elsinore Fault zone suggests 6-10 km of right-lateral displacement. A high-amplitude basement gravity high is present over the San Joaquin Hills and is most likely caused by Peninsular Ranges gabbro and/or Tertiary mafic intrusion. A major basement gravity gradient coincides with the San Jacinto Fault zone and marked magnetic, seismic-velocity, and isotopic gradients that reflect a discontinuity within the Peninsular Ranges batholith in the northeast corner of the quadrangle.

  9. Hot isostatic pressing of silicon nitride with boron nitride, boron carbide, and carbon additions

    NASA Technical Reports Server (NTRS)

    Mieskowski, Diane M.; Sanders, William A.

    1989-01-01

    Si3N4 test bars containing additions of BN, B4C, and C, were hot isostatically pressed in Ta cladding at 1900 and 2050 C to 98.9 percent to 99.5 percent theoretical density. Room-temperature strength data on specimens containing 2 wt pct BN and 0.5 wt pct C were comparable to data obtained for Si3N4 sintered with Y2O3, Y2O3 and Al2O3, or ZrO2. The 1370 C strengths were less than those obtained for additions of Y2O3 or ZrO2 but greater than those obtained from a combination of Y2O3 and Al2O3. SEM fractography indicated that, as with other types of Si3N4, room-temperature strength was controlled by processing flaws. The decrease in strength at 1370 C was typical of Si3N4 having an amorphous grain-boundary phase. The primary advantage of nonoxide additions appears to be in facilitating specimen removal from the Ta cladding.

  10. Hot isostatic pressing of SiC particulate reinforced metal matrix composites

    SciTech Connect

    Loh, N.L.; Wei, Z.; Xu, Z.

    1996-12-31

    Two as-cast SiC particulate reinforced A359-based composites were hot isostatically pressed for a fixed length of time but at various pressures (in the range 100--150 MPa) and temperatures (in the range 450--550 C). It was found that HIP treatment generally increased the ductility but reduced the yield stress drastically. The improvement of ductility was attributed to a reduction of the porosity levels. Quantitative image analyses showed that the HIP treatment reduced the porosity levels significantly. It is of interest to observe that increasing HIP temperature is more effective than increasing HIP pressure in terms of improvement in strength and ductility. Another interesting observation is that most eutectic Si particles were spheroidized during HIP. The spheroidization of Si was believed to contribute to the improvement of mechanical properties, because fracture initiation of the composites was observed to be related to either the breaking of Si particles or the debonding of Si particles from the nearby SiC particles.

  11. Isostatic Gravity Map of the Battle Mountain 30 x 60 Minute Quadrangle, North Central Nevada

    USGS Publications Warehouse

    Ponce, D.A.; Morin, R.L.

    2000-01-01

    Introduction Gravity investigations of the Battle Mountain 30 x 60 minute quadrangle were begun as part of an interagency effort by the U.S. Geological Survey (USGS) and the Bureau of Land Management to help characterize the geology, mineral resources, hydrology, and ecology of the Humboldt River Basin in north-central Nevada. The Battle Mountain quadrangle is located between 40?30' and 41?N. lat. and 116? and 117?W. long. This isostatic gravity map of the Battle Mountain quadrangle was prepared from data from about 1,180 gravity stations. Most of these data are publicly available on a CD-ROM of gravity data of Nevada (Ponce, 1997) and in a published report (Jewel and others, 1997). Data from about 780 gravity stations were collected by the U.S. Geological Survey since 1996; data from about 245 of these are unpublished (USGS, unpub. data, 1998). Data collected from the 400 gravity stations prior to 1996 are a subset of a gravity data compilation of the Winnemucca 1:250,000-scale quadrangle described in great detail by Wagini (1985) and Sikora (1991). This detailed information includes gravity meters used, dates of collection, sources, descriptions of base stations, plots of data, and a list of principal facts. A digital version of the entire data set for the Battle Mountain quadrangle is available on the World Wide Web at: http://wrgis.wr.usgs.gov/docs/gump/gump.html

  12. Rigidity percolation by next-nearest-neighbor bonds on generic and regular isostatic lattices.

    PubMed

    Zhang, Leyou; Rocklin, D Zeb; Chen, Bryan Gin-ge; Mao, Xiaoming

    2015-03-01

    We study rigidity percolation transitions in two-dimensional central-force isostatic lattices, including the square and the kagome lattices, as next-nearest-neighbor bonds ("braces") are randomly added to the system. In particular, we focus on the differences between regular lattices, which are perfectly periodic, and generic lattices with the same topology of bonds but whose sites are at random positions in space. We find that the regular square and kagome lattices exhibit a rigidity percolation transition when the number of braces is ∼LlnL, where L is the linear size of the lattice. This transition exhibits features of both first-order and second-order transitions: The whole lattice becomes rigid at the transition, and a diverging length scale also exists. In contrast, we find that the rigidity percolation transition in the generic lattices occur when the number of braces is very close to the number obtained from Maxwell's law for floppy modes, which is ∼L. The transition in generic lattices is a very sharp first-order-like transition, at which the addition of one brace connects all small rigid regions in the bulk of the lattice, leaving only floppy modes on the edge. We characterize these transitions using numerical simulations and develop analytic theories capturing each transition. Our results relate to other interesting problems, including jamming and bootstrap percolation. PMID:25871071

  13. Late Stage 5 Glacio-isostatic Sea in the St. Lawrence Valley, Canada and United States

    USGS Publications Warehouse

    Occhietti, S.; Balescu, S.; Lamothe, M.; Clet, M.; Cronin, T.; Ferland, P.; Pichet, P.

    1996-01-01

    Although post-glacial marine sediments of late Wisconsinan and early Holocene age are common in eastern Canada and the northeastern United States, remnants of older Pleistocene marine sediments are scarce. A fossiliferous marine clay that predates the classical Wisconsinan was recently discovered in the St. Lawrence Valley. A dominantly estuarine environment is inferred from the geochemistry of the shells (??18O = -7.1) and from benthic foraminifer and ostracode assemblages. The clay indicates a marine invasion (Cartier Sea) shallower and probably shorter than that during the upper late Wisconsinan Champlain Sea episode (12,000-9,500 yr B.P.). The pollen content shows that regional vegetation during the marine episode began as open tundra, then became a Betula and Alnus crispa forest, reached a climatic optimum with Quercus, Corylus, and Abies, and concluded as a Pinus/Picea boreal forest. A corrected infrared stimulated luminescence age of 98,000 ?? 9000 yr is compatible with the epimerization ratio of shells. The Cartier Sea resulted from a post-glacial glacio-isostatic marine invasion in the St. Lawrence lowlands. It probably occurred during late stage 5 and is tentatively assigned to the transition of oxygen isotope substages 5b/5a. This marine episode dates to stage 5 of the preceding continental glacier which extended to middle latitudes in NE America. ?? 1996 University of Washington.

  14. Evaluation of the strength and creep-fatigue behavior of hot isostatically pressed silicon nitride

    SciTech Connect

    Ferber, M.K.; Jenkins, M.G. )

    1992-09-01

    This paper reports that the strength of a commerically available hot isostatically pressed silicon nitride was measured as a function of temperature. To evaluate long-term mechanical reliability of this material, the tensile creep and fatigue behavior was measured at 1150[degrees], 1260[degrees], and 1370[degrees]C. The stress and temperature sensitivities of the secondary (or minimum) creep strain rate were used to estimate the stress exponent and activation energy associated with the dominant creep mechanism. The fatigue characteristics were evaluated by allowing individual creep tests to continue until specimen failure. The applicability of the four-point load geometry to the study of strength and creep behavior was also determined by conducting a limited number of flexural creep tests. The tensile fatigue data revealed two distinct failure mechanisms. At 1150[degrees]C, failure was controlled by a slow crack growth mechanism. At 1260[degrees] and 1370[degrees]C, the accumulation of creep damage in the form of grain boundary cavities and cracks dominated the fatigue behavior. In this temperature regime, the fatigue life was controlled by the secondary (or minimum) creep strain rate in accordance with the Monkman-Grant relation.

  15. A new Holocene relative sea-level curve for western Brittany (France): Insights on isostatic dynamics along the Atlantic coasts of north-western Europe

    NASA Astrophysics Data System (ADS)

    Goslin, Jérôme; Van Vliet Lanoë, Brigitte; Spada, Giorgio; Bradley, Sarah; Tarasov, Lev; Neill, Simon; Suanez, Serge

    2015-12-01

    This study presents new Relative Sea Level (RSL) data that were obtained in the Finistère region (Western tip of Brittany, France) and the implications those data have for the understanding of the isostatic dynamics across north-western Europe, and more specifically along the Atlantic and Channel coasts. New stratigraphic sequences were obtained and analyzed to derive 24 new Sea-level Index Points, in which 6 are basal. These new data considerably increase the knowledge we have of the RSL evolution along the coasts of Western Brittany since the last 8 kyr B.P. From this new dataset, RSL was estimated to rise continuously over the last 8 kyr with a major inflection at ca. 6 kyr cal. BP. Our results show large vertical discrepancies between the RSL records of Brittany and South-Western UK, with the latter plotting several meters below the new data. From this comparison we suggest that the two regions underwent a very different pattern and/or amplitude of subsidence during the last 8 kyr which has implications for the spatial and temporal pattern of the peripheral bulge of the European ice sheets. We compared our data against predictions from Glacio-Isostatic Adjustment models (GIA models). There are large misfits between RSL observations and the predictions of the global (ICE-5G (VM2a) - Peltier, 2004, GLAC1-b - Tarasov and Peltier, 2002; Tarasov et al., 2012, Briggs et al., 2014) and regional UK models ("BIIS" - Bradley et al., 2009; Bradley et al., 2011; "Kuchar"- Kuchar et al., 2012), which can't be resolved through significant changes to the deglaciation history and size of the British-Irish Ice sheet. Paleo-tidal modelling corrections indicate regional changes in the tidal ranges played a negligible role in the data-model misfits. Hence, we propose that the misfits are due to some combination of: (i) unaccounted mass-loss of far-field ice-sheets (Antarctic ice-Sheet or Laurentide Ice-Sheet), (ii) unresolved differences in the deglaciation history and size of

  16. Holocene relative sea-level change, isostatic subsidence and the radial viscosity structure of the mantle of northwest Europe (Belgium, the Netherlands, Germany, southern North Sea)

    NASA Astrophysics Data System (ADS)

    Vink, Annemiek; Steffen, Holger; Reinhardt, Lutz; Kaufmann, Georg

    2007-12-01

    A comprehensive observational database of Holocene relative sea-level (RSL) index points from northwest Europe (Belgium, the Netherlands, northwest Germany, southern North Sea) has been compiled in order to compare and reassess the data collected from the different countries/regions and by different workers on a common time-depth scale. RSL rise varies in magnitude and form between these regions, revealing a complex pattern of differential crustal movement which cannot be solely attributed to tectonic activity. It clearly contains a non-linear, glacio- and/or hydro-isostatic subsidence component, which is only small on the Belgian coastal plain but increases significantly to a value of ca 7.5 m relative to Belgium since 8 cal. ka BP along the northwest German coast. The subsidence is at least in part related to the Post-Glacial collapse of the so-called peripheral forebulge which developed around the Fennoscandian centre of ice loading during the Last Glacial Maximum. The RSL data have been compared to geodynamic Earth models in order to infer the radial viscosity structure of the Earth's mantle underneath NW Europe (lithosphere thickness, upper- and lower-mantle viscosity), and conversely to predict RSL in regions where we have only few observational data (e.g. in the southern North Sea). A very broad range of Earth parameters fit the Belgian RSL data, suggesting that glacial isostatic adjustment (GIA) only had a minor effect on Belgian crustal dynamics during and after the Last Ice Age. In contrast, a narrow range of Earth parameters define the southern North Sea region, reflecting the greater influence of GIA on these deeper/older samples. Modelled RSL data suggest that the zone of maximum forebulge subsidence runs in a relatively narrow, WNW-ESE trending band connecting the German federal state of Lower Saxony with the Dogger Bank area in the southern North Sea. Identification of the effects of local-scale factors such as past changes in tidal range or tectonic

  17. Fluvial dissection, isostatic uplift, and geomorphological evolution of volcanic islands (Gran Canaria, Canary Islands, Spain)

    NASA Astrophysics Data System (ADS)

    Menéndez, Inmaculada; Silva, Pablo G.; Martín-Betancor, Moises; Pérez-Torrado, Francisco José; Guillou, Hervé; Scaillet, S.

    2008-11-01

    Digital analysis of torrential gullies ('barrancos') deeply incised into the volcanic Island of Gran Canaria (Canary Islands) allows us to extract the longitudinal profiles and pre-incision surfaces for individual basins, from which morphometric parameters (length, elevation, area, slope) have been calculated. Other derived parameters, such as ridgeline profiles, maximum incision values, volume removed by fluvial erosion, geophysical relief and isostatic uplift, have also been computed. Based on K/Ar ages for the island, well-constrained incision-uplift rates have been calculated by means of the combination of different methodological approaches commonly used in orogens and large mountain ranges. The geomorphological and morphometric analyses reveal that the island is clearly divided into four environmental quadrants determined by the combination of a couple of key-factors: the age of the volcanic surfaces and the climatic conditions. These factors determine a young sector covered with Plio-Quaternary platform-forming lavas (finished at 1.9-1.5 Ma) evolving under contrasting wet (NE) to dry (SE) climates, and an older sector, conserving the residual surfaces of the Miocene shield building (14.5-8.7 Ma) at the ridgelines, also subjected to wet (NW) and dry (SW) climates. Incision is related to the age zonation of the island. Maximum incisions (< 1200 m) are logically recorded in the older SW sector of the island, but incision rates are directly related to the climatic zonation, with maximum mean values in the wet Northern quadrants (0.18-0.12 mm/yr). The evaluation of the material removed by fluvial erosion for individual basins allows us to assess the consequent theoretical isostatic response in the different sectors of the island. The obtained uplift rates indicate that water availability (by drainage area and elevation) is a relevant controlling factor: the records from the wet Northern sectors show uplift values of between 0.09 and 0.03 mm/yr, whereas in the

  18. Enhancement of the electrical characteristics of metal-free phthalocyanine films using cold isostatic pressing

    SciTech Connect

    Matsushima, Toshinori E-mail: adachi@cstf.kyushu-u.ac.jp; Adachi, Chihaya E-mail: adachi@cstf.kyushu-u.ac.jp; Esaki, Yu

    2014-12-15

    Spatial gaps between grains and other grains, substrates, or electrodes in organic electronic devices are one of the causes of the reduction in the electrical characteristics. In this study, we demonstrate that cold isostatic pressing (CIP) is an effective method to crush the gaps and enhance the electrical characteristics. CIP of metal-free phthalocyanine (H{sub 2}PC) films induced a decrease in the film thickness by 34%–40% because of the gap crush. The connection of smaller grains into a larger grain and planarization of the film surface were also observed in the CIP film. The crystal axes of the H{sub 2}PC crystallites were rearranged from the a-axis to the c-axis of the α-phase crystal structure in a direction perpendicular to the substrate by CIP, indicating favorable hole injection and transport in this direction because of a better overlap of π orbitals. Thermally stimulated current measurements showed that deep hole traps disappeared and the total hole-trap density decreased after CIP. These CIP-induced changes of the film thicknesses, crystal axes and the hole traps lead to a marked increase in the hole mobility of the H{sub 2}PC films from 2.0 × 10{sup −7} to 4.0 × 10{sup −4} cm{sup 2}/V s by 2000 times in the perpendicular direction. We believe that these findings are important for unveiling the underlying carrier injection and transport mechanisms of organic films and for enhancing the performance of future organic electronic devices.

  19. Multiple Geodetic Observations for Identifying Glacial Isostatic Adjustment and the Causes of Sea-Level Change

    NASA Astrophysics Data System (ADS)

    Tamisiea, M. E.; Williams, S. D. P.; Hughes, C. W.; Bingley, R.; Blewitt, G.; Hammond, W. C.; Kreemer, C.

    2015-12-01

    Understanding the Earth's and ocean's response to past changes in global ice extent and ocean volume, collectively termed glacial isostatic adjustment (GIA), is necessary for interpreting observations of present-day sea level change. GIA has the largest effect on sea-level observations nearest the locations of the former ice sheets. Under the former loading centers, crustal uplift contributes to a local relative sea-level fall while the collapsing forebulge surrounding these centers accentuates a local sea-level rise. Some of the longest tide gauge records are in these regions. However, GIA also causes global deformation and geoid changes that introduce systematic differences between global averages of tide gauge and altimetry observations. Clearly accounting for the GIA contribution to sea-level change while identifying other present-day contributors is greatly assisted by additional geodetic measurements. Time-variable satellite gravity observations highlight the regional GIA signal, on length scales of hundreds of kilometers, while also locating water mass changes on the continents and the oceans. As the spatial density of GNSS observations has increased, it has become easier to discern the regional characteristics of crustal deformation (e.g. Blewitt et al. abstract in U009). Combined, these two observations allow for greater separation of GIA and water mass changes. More importantly for society, though, the regional crustal estimates could be combined with coastal altimetry products to create regional estimates of relative sea-level change, the observation most relevant for coastal planning. In this presentation we discuss how the various geodetic measurements complement each other and allow us to identify various components of sea level change, including GIA. We illustrate how the weakness of any individual observation component can be overcome by comparison with the other components. A sustained and global geodetic observing system is essential for

  20. CuCrZr alloy microstructure and mechanical properties after hot isostatic pressing bonding cycles

    NASA Astrophysics Data System (ADS)

    Frayssines, P.-E.; Gentzbittel, J.-M.; Guilloud, A.; Bucci, P.; Soreau, T.; Francois, N.; Primaux, F.; Heikkinen, S.; Zacchia, F.; Eaton, R.; Barabash, V.; Mitteau, R.

    2014-04-01

    ITER first wall (FW) panels are a layered structure made of the three following materials: 316L(N) austenitic stainless steel, CuCrZr alloy and beryllium. Two hot isostatic pressing (HIP) cycles are included in the reference fabrication route to bond these materials together for the normal heat flux design supplied by the European Union (EU). This reference fabrication route ensures sufficiently good mechanical properties for the materials and joints, which fulfil the ITER mechanical specifications, but often results in a coarse grain size for the CuCrZr alloy, which is not favourable, especially, for the thermal creep properties of the FW panels. To limit the abnormal grain growth of CuCrZr and make the ITER FW fabrication route more reliable, a study began in 2010 in the EU in the frame of an ITER task agreement. Two material fabrication approaches have been investigated. The first one was dedicated to the fabrication of solid CuCrZr alloy in close collaboration with an industrial copper alloys manufacturer. The second approach investigated was the manufacturing of CuCrZr alloy using the powder metallurgy (PM) route and HIP consolidation. This paper presents the main mechanical and microstructural results associated with the two CuCrZr approaches mentioned above. The mechanical properties of solid CuCrZr, PM CuCrZr and joints (solid CuCrZr/solid CuCrZr and solid CuCrZr/316L(N) and PM CuCrZr/316L(N)) are also presented.

  1. Sea level and shoreline reconstructions for the Red Sea: isostatic and tectonic considerations and implications for hominin migration out of Africa

    NASA Astrophysics Data System (ADS)

    Lambeck, Kurt; Purcell, Anthony; Flemming, Nicholas. C.; Vita-Finzi, Claudio; Alsharekh, Abdullah M.; Bailey, Geoffrey N.

    2011-12-01

    The history of sea level within the Red Sea basin impinges on several areas of research. For archaeology and prehistory, past sea levels of the southern sector define possible pathways of human dispersal out of Africa. For tectonics, the interglacial sea levels provide estimates of rates for vertical tectonics. For global sea level studies, the Red Sea sediments contain a significant record of changing water chemistry with implications on the mass exchange between oceans and ice sheets during glacial cycles. And, because of its geometry and location, the Red Sea provides a test laboratory for models of glacio-hydro-isostasy. The Red Sea margins contain incomplete records of sea level for the Late Holocene, for the Last Glacial Maximum, for the Last Interglacial and for earlier interglacials. These are usually interpreted in terms of tectonics and ocean volume changes but it is shown here that the glacio-hydro-isostatic process is an additional important component with characteristic spatial variability. Through an iterative analysis of the Holocene and interglacial evidence a separation of the tectonic, isostatic and eustatic contributions is possible and we present a predictive model for palaeo-shorelines and water depths for a time interval encompassing the period proposed for migrations of modern humans out of Africa. Principal conclusions include the following. (i) Late Holocene sea level signals evolve along the length of the Red Sea, with characteristic mid-Holocene highstands not developing in the central part. (ii) Last Interglacial sea level signals are also location dependent and, in the absence of tectonics, are not predicted to occur more than 1-2 m above present sea level. (iii) For both periods, Red Sea levels at 'expected far-field' elevations are not necessarily indicative of tectonic stability and the evidence points to a long-wavelength tectonic uplift component along both the African and Arabian northern and central sides of the Red Sea. (iv) The

  2. Glacial isostatic adjustment in response to changing Late Holocene behaviour of ice streams on the Siple Coast, West Antarctica

    NASA Astrophysics Data System (ADS)

    Nield, Grace A.; Whitehouse, Pippa L.; King, Matt A.; Clarke, Peter J.

    2016-04-01

    The Siple Coast region of Antarctica contains a number of fast-flowing ice streams, which control the dynamics and mass balance of the region. These ice streams are known to undergo stagnation and reactivation cycles, which lead to ice thickness changes that may be sufficient to excite a viscous solid Earth response (glacial isostatic adjustment; GIA). This study aims to quantify Siple Coast ice thickness changes during the last 2000 yr in order to determine the degree to which they might contribute to GIA and associated present-day bedrock uplift rates. This is important because accurate modelling of GIA is necessary to determine the rate of present-day ice-mass change from satellite gravimetry. Recently-published reconstructions of ice-stream variability were used to create a suite of kinematic models for the stagnation-related thickening of Kamb Ice Stream since ˜1850 AD, and a GIA model was used to predict present-day deformation rates in response to this thickening. A number of longer-term loading scenarios, which include the stagnation and reactivation of ice streams across the Siple Coast over the past 2000 yr, were also constructed, and used to investigate the longer term GIA signal in the region. Uplift rates for each of the ice loading histories, based on a range of earth models, were compared with regional GPS-observed uplift rates and an empirical GIA estimate. We estimate Kamb Ice Stream to have thickened by 70-130 m since stagnation ˜165 years ago. Modelled present-day vertical motion in response to this load increase peaks at -17 mm yr-1 (i.e. 17 mm yr-1 subsidence) for the weakest earth models tested here. Comparison of the solid Earth response to ice load changes throughout the last glacial cycle, including ice stream stagnation and reactivation across the Siple Coast during the last 2000 yr, with an empirical GIA estimate suggests that the upper mantle viscosity of the region is greater than 1 × 1020 Pa s. When upper mantle viscosity values of

  3. Paleogeography and paleoenvironments of southwestern Baffin Island (Nunavut, Canada): post-glacial isostatic uplift and isolation of Nettilling Lake from marine influence

    NASA Astrophysics Data System (ADS)

    Narancic, Biljana; Pienitz, Reinhard; Francus, Pierre; Rolland, Nicolas; Wagner, Anne-Marie

    2013-04-01

    Although signs of recent climate change are more compelling in circumpolar regions, we have limited knowledge of Arctic climates and environments and their past variability. In order to better understand and anticipate the extent and nature of future changes in the Arctic, it is necessary to increase our capacity to model past environmental changes. Instrumental monitoring using high technology in polar regions has been implemented only over recent decades (Pienitz et al., 2004). Hence, to extend in time the climate record, we use a multi-proxy paleolimnological approach to study the sedimentary records preserved in Nettilling Lake located on Baffin Island the largest lake in the Canadian Arctic Archipelago. Nettilling Lake has an area of 5.541 km2 and a maximum depth of 65 m (Oliver, 1964). Its basin has undergone postglacial marine invasion following the last deglaciation due to isostatic subsidence exerted by the Laurentide Ice Sheet. The glacio-isostatic uplift of the region resulted in the establishment of a freshwater lake around 5000 years BP (Jacobs et al., 1997). Nettilling Lake remains a scientific frontier for researchers, mainly due to the inaccessibility of the area and the lack of available data. To date, only one exploratory study by Oliver (1964) has focused on the limnological conditions and bathymetry of the lake, and our research aims at providing deeper insights into the history of paleoenvironmental changes in this remote Arctic region. Biostratigraphical and geochemical analyses were completed on two sediment cores, one from a lagoonal system in the northwestern part of Nettilling Lake and another from the eastern part of the Lake. The sediment cores from the lagoonal system clearly document the marine-lacustrine transition through shifts in paleosalinity inferred from the composition of fossil diatom assemblages. Fossil chironomid larvae first appeared in the record after basin isolation and the establishment of freshwater conditions. Precise

  4. Regional glacial-isostatic adjustment in Antarctica inferred from combining spaceborne geodetic observations (ESA-STSE CryoSat+ Project REGINA)

    NASA Astrophysics Data System (ADS)

    Sasgen, Ingo; Martin, Alba; Horvath, Alexander; Klemann, Volker; Petrie, Elizabeth; Wouters, Bert; Horwath, Martin; Pail, Roland; Bamber, Jonathan; Clarke, Peter J.; Konrad, Hannes; Drinwater, Mark

    2016-04-01

    A major uncertainty in determining the mass balance of the Antarctic ice sheet from satellite gravimetry, and to a lesser extent altimetry, measurements is the poorly known correction for the glacial isostatic adjustment (GIA) of the solid Earth. Although much progress has been made in consistently modelling ice-sheet evolution and related bedrock deformation, predictions of GIA remain ambiguous due to the sparsity of geodetic and geological constraints. Here, we present an improved geodetic GIA estimate based on GRACE, Envisat/ICESat/CryoSat-2 and GPS measurements. Using viscoelastic response functions of the radial displacement and gravity field change to a disc load forcing, we estimate GIA based on multiple space-geodetic observations, making use of their different sensitivities to surface and solid Earth processes. The approach allows us to consider a laterally varying lithosphere thickness and mantle viscosity in Antarctica, and particularly investigate the effect of a low-viscosity asthenosphere and a ductile layer in the elastic lithosphere in West Antarctica. We compare our GIA estimate with published estimates and results from numerical modelling, and evaluate its impact on the determination of ice-mass balance in Antarctica from GRACE and CryoSat-2. The results presented are the final results of the Support To Science Element Project REGINA and its Supplementary Study of the European Space Agency, www.regina-science.eu.

  5. Grain-boundary cavitation and bloating of isostatically hot-pressed magnesia-partially-stabilized zirconia on air annealing

    SciTech Connect

    Hogg, C.L.; Stringer, R.K.; Swain, M.V.

    1986-03-01

    Commercially sintered magnesia-partially-stabilized zirconia was densified to near theoretical density by isostatic hot-pressing at 200 MPa and 1700/sup 0/C in argon. Subsequent air annealing above 1100/sup 0/C resulted in bloating of the material due to grain-boundary cavitation. Mass spectrometry of crushed samples detected the evolution of CO/sub 2/ and possibly CO on annealing; the hot-pressed material showed a sudden gas evolution above 1400/sup 0/C. Preliminary Auger and ESCA analysis identified the presence of carbon as graphite and an undefined carbide in both the sintered and the hot-pressed material.

  6. Microstructural and mechanical characteristics of W-2Ti and W-1TiC processed by hot isostatic pressing

    NASA Astrophysics Data System (ADS)

    Muñoz, A.; Savoini, B.; Tejado, E.; Monge, M. A.; Pastor, J. Y.; Pareja, R.

    2014-12-01

    W-2Ti and W-1TiC alloys were produced by mechanical alloying and consolidation by hot isostatic pressing. The composition and microstructural characteristics of these alloys were studied by X-ray diffraction, energy dispersion spectroscopy and scanning electron microscopy. The mechanical behavior of the consolidated alloys was characterized by microhardness measurements and three point bending tests. The mechanical characteristics of the W-2Ti alloy appear to be related to solution hardening. In W-1TiC, the residual porosity should be responsible for the poor behavior observed in comparison with W-2Ti.

  7. Conductive and ferromagnetic contributions of H in ZnCoO using H2 hot isostatic pressure

    NASA Astrophysics Data System (ADS)

    Chan Cho, Yong; Lee, Seunghun; Hyun Nahm, Ho; Jae Kim, Su; Hong Park, Chul; Yeon Lee, Su; Kim, Sung-Kyu; Ryong Cho, Chae; Koinuma, Hideomi; Jeong, Se-Young

    2012-03-01

    For highly H injected ZnCoO achieved by simultaneous high pressure (1000 bar) and annealing using a hot isostatic pressure (HIP), we report electrical and magnetic properties with first-principles calculation results. The HIP process increased the carrier concentration by ˜103 times and restored the conductivity up to that of H injected ZnO. Interestingly, with maintaining high conductivity, the extended HIP processing time significantly enhanced the short-ranged spin orderings of Co-H-Co complexes. Based on the experimental and theoretical results, we proposed the explanation for the relation magnetic characteristics and the behavior of hydrogen triggering spin ordering for spintronic applications.

  8. Northwest outlet channels of Lake Agassiz, isostatic tilting and a migrating continental drainage divide, Saskatchewan, Canada

    NASA Astrophysics Data System (ADS)

    Fisher, Timothy G.; Souch, Catherine

    1998-10-01

    Lake cores obtained from the northwest outlet of glacial Lake Agassiz in northwest Saskatchewan, Canada, provide a minimum date for the cessation of the flood from the northwest outlet, and a chronology for abandonment of mid-Holocene channels that presently straddle the Mackenzie and Churchill drainage divide. The stratigraphy of a vibracore taken from Long Lake consists of a lower pebble gravel fining to massive sand, silty-clay and then fibrous peat. Wood fragments from the base of the clay yielded an accelerator mass spectrometry (AMS) date of 9120 BP. Because the lake is scour in origin and is in the head of the spillway, the date is considered to be a minimum estimate for cessation of the flood from the northwest outlet at the beginning of the Emerson Phase. A vibracore taken at Haas Lake in an abandoned channel surrounded by muskeg with no influent streams, consists of 0.8 m of stratified, pebble gravel containing abundant shell and wood fragments, overlain by 1.62 m of gyttja with a sharp, conformable lower contact. AMS dates range from 5590 BP from the topmost gravel to 3080 BP within the gyttja. The gravel is interpreted as fluvial, recording a river draining Wasekamio Lake north into the Clearwater River across the present-day drainage divide. Today, a drop of 2 m occurs from Wasekamio Lake southeast to Lac Ile-a-la-Crosse, along 150 km of lake basins parallel to the Cree Lake Moraine. The dates from Haas Lake suggest that before 5200 BP, the drainage divide was about 100 km further southeast, implying that during the Emerson Phase, lake level was controlled by a sill near Flatstone Lake at about 430 m instead of between Wasekamio Lake and the Clearwater River, as was previously proposed. Holocene differential isostatic uplift caused the flow reversal in the upper Churchill basin. Anastomosed channels at the mouth of rivers flowing north into lakes indicate that uplift is still active in the area today.

  9. Quantifying subsidence and isostatic readjustment using sedimentary paleomarkers, example from the Gulf of Lion

    NASA Astrophysics Data System (ADS)

    Rabineau, M.; Leroux, E.; Aslanian, D.; Bache, F.; Gorini, C.; Moulin, M.; Molliex, S.; Droz, L.; dos Reis, A. T.; Rubino, J. L.; Guillocheau, F.; Olivet, J. L.

    2014-02-01

    Passive margins are characterised by an important tectonic and thermal subsidence, which favours a good preservation of sedimentary sequences. This sedimentation in turn enhances the subsidence because of loading effects. We present here a direct method based on sedimentary markers seen on seismic data, to evaluate total subsidence rates from the coast to the outer shelf and to the deep basin in the Gulf of Lion, from the beginning of massive salt deposition up to present day (the last circa 6 Ma) with minimal theoretical assumptions. On the shelf, the Pliocene-Quaternary subsidence shows a seaward tilt reaching a rate of 240 m/Ma (±15 m/Ma) at the shelf break (70 km from the present day coastline) (i.e. a total angle of rotation of 0.88° (0.16°/Ma)). We were also able to measure and quantify for the first time the isostatic rebound of the outer shelf due to the Messinian salinity crisis (MSC). This value is very high and reaches up to 1.3 km of uplift during the crisis around the Herault-Sète canyon heads (around 1.8 km/Ma). On the slope, we also find a seaward tilting subsidence from Km 90 to Km 180 with a measured angle of 1.41°. From 180 km to the deepest part of the basin, the total subsidence is then almost vertical and reaches 960 m/Ma (±40 m/Ma) during the last 5.7 Ma (±0.25 Ma) in the deepest part of the basin. The subsidence is organised in three compartments that seem related to the very deep structure of the margin during the opening of the Liguro-provencal basin. These very high total subsidence rates enable high sedimentation rates along the margin with sediments provided by the Rhône river flowing from the Alps, which in turn enable the detailed record of climate evolution during Pliocene-Quaternary that make of the Gulf of Lion a unique archive.

  10. Microstructure and Mechanical Properties of Al6061-31vol.% B4C Composites Prepared by Hot Isostatic Pressing

    NASA Astrophysics Data System (ADS)

    Xian, Yajiang; Pang, Xiaoxuan; He, Shixiong; Wang, Wei; Wang, Xin; Zhang, Pengcheng

    2015-10-01

    Fabrication of durable and usable composites with high content of B4C (up to 31vol.%) is quite challenging in several aspects including blending, cold isostatic pressing, and hot isostatic pressing (HIP), and especially the optimal HIP process is essential to achieve the metal matrix composite with desirable properties. The microstructure and mechanical properties of Al6061-31vol.% B4C with different particle sizes were investigated by scanning electron microscopy (SEM) and tensile testing, respectively. SEM analysis and quantitative measurements of the particle distribution reveal that B4C particles were uniformly distributed in the matrix without agglomeration when the HIP treatment temperature was about 580 °C, and x-ray diffraction also identified a dispersion of B4C particles as well as reaction products (AlB2 and Al3BC) in the composites. Microhardness of Al6061-31vol.% B4C composites was improved with B4C particle size, and the tensile strength of all the samples declined with an increase in B4C particle size. The contribution from different strengthening mechanisms was also discussed.

  11. Structure and hot hardness of RuAl-based alloys produced by reactive sintering using hot isostatic pressing

    NASA Astrophysics Data System (ADS)

    Povarova, K. B.; Morozov, A. E.; Padalko, A. G.; Drozdov, A. A.

    2008-04-01

    The structure and hot hardness (at temperatures up to 1100°C) of RuAl-based powder alloys with 1 3 at % Ni, Mo, Re, or Ru are studied. The alloys are produced by the reactive sintering of cold-compacted bars and subsequent threefold isostatic pressing with intermediate annealing at 1500°C performed after the first hot isostatic pressing. The samples have a residual pore content of 1 2.5 vol % and are characterized by a micrononuniform distribution of base and alloying elements. The alloys with refractory metals, such as Re, Mo, or Ru, are found to have the maximum hardness at all temperatures under study. At low temperatures, the effect is more substantial; the hardness of the Re-containing alloys exceeds that of the other alloys by a factor of 1.3 3.6. The increase in the hardness related to solid-solution alloying becomes more substantial owing to the microinhomogeneity of the sintered powder alloys and weakens because of microporosity. Recommendations that allow the uniformity of the distribution of the base and alloying elements to be increased are given.

  12. Glacial Isostatic Adjustment as a key to understand the neotectonics of northern Central Europe

    NASA Astrophysics Data System (ADS)

    Brandes, Christian; Steffen, Holger; Wu, Patrick

    2014-05-01

    Northern Central Europe is generally regarded as aseismic, however, several historic earthquakes with intensities of up to VII occurred in this region during the last 1200 years (Leydecker, 2009). In a pilot study we analysed the Osning Thrust, which is a one of the major Mesozoic fault zones in northern Central Europe. Several soft-sediment deformation structures like fault-arrays and a sand volcano developed in aeolian sediments, were caused by earthquakes along the Osning Thrust. The growth-strata of faults was dated with the OSL method and showed that the deformation took place between 15.9 ± 1.6 to 13.1 ± 1.5 ka (Brandes et al., 2012, Brandes & Winsemann, 2013). Numerical simulations support the results regarding the timing of the the seismicity and imply that the Late Pleistocene activity of the Osning Thrust was an effect of glacial isostatic adjustment (Brandes et al., 2012). In a second step we analysed more faults in northern Central Europe. It is evident that the historic seismicity was concentrated along major reverse faults that formerly played an important role during a tectonic contraction phase that effected Central Europe in the Late Cretaceous. Between these faults, the seismic activity was almost absent. Many of the historic earthquakes concentrated for a certain time along one fault and there is even evidence for distinct earthquake clusters in northern Central Europe e.g. along the Osning Thrust, the Aller Valley Fault and the Tornquist Zone. The spatial and temporal distribution of earthquakes (clusters that shift from time to time) implies that northern Central Europe behaves like a typical intraplate tectonic region. To analyse, if the faults that show pronounced historic seismicity are postglacial faults, we used the Fault Stability Margin (FSM), which is described in more detail in Wu & Hasegawa (1996). The Fault Stability Margins for the major reverse faults that showed historic seismicity in northern Central Europe reach the δFSM=0

  13. Hot-isostatic pressing of U-10Zr by grain boundary diffusion and creep cavitation. Part 2: Theory and data analysis

    SciTech Connect

    McDeavitt, S.M.; Solomon, A.A.

    1997-08-01

    Uranium-10 wt % zirconium (U-10Zr) is a fuel alloy that has been used in the Experimental Breeder Reactor-II (EBR-II). The high burnup that was desired in this fuel system made high demands on the mechanical compatibility between fuel and cladding both during normal operation and during safety-related transients when rapid differential expansion may cause high stresses. In general, this mechanical stress can be reduced by cladding deformation if the cladding is sufficiently ductile at high burnup, and/or by fuel hot-pressing. Fortunately, the fuel is very porous when it contacts the cladding, but this porosity gradually fills with solid fission products (primarily lanthanides) that may limit the fuel`s compressibility. If the porosity remains open, gaseous fission products are released and the porous fuel creeps rather than hot-presses under contact stresses. If the pores are closed by sintering or by solid fission products, the porous fuel will hot-isostatic press (HIP), as represented by the models to be discussed. HIP experiments performed at 700 C on U-10Zr samples with different impurity phase contents (Part 1) are analyzed in terms of several creep cavitation models. The coupled diffusion/creep cavitation model of Chen and Argon shows good quantitative agreement with measured HIP rates for hydride- and metal-derived U-10Zr materials, assuming that pores are uniformly distributed on grain boundaries and are of modal size, and that far-field strain rates are negligible. The analysis predicts, for the first time, an asymmetry between HIP and swelling at identical pressure-induced driving forces due to differences in grain boundary stresses. The differences in compressibility of hydride- and metal-derived U-10Zr can be partially explained by differences in pore size and spacing. The relevance of the experiments to description of in-reactor densification under external pressure or contact stress due to fuel/cladding mechanical interaction is discussed.

  14. Influence of surface treatment of yttria-stabilized tetragonal zirconia polycrystal with hot isostatic pressing on cyclic fatigue strength.

    PubMed

    Iijima, Toshihiko; Homma, Shinya; Sekine, Hideshi; Sasaki, Hodaka; Yajima, Yasutomo; Yoshinari, Masao

    2013-01-01

    Hot isostatic pressing processed yttria-stabilized tetragonal zirconia polycrystal (HIP Y-TZP) has the potential for application to implants due to its high mechanical performance. The aim of this study was to investigate the influence of surface treatment of HIP Y-TZP on cyclic fatigue strength. HIP Y-TZP specimens were subjected to different surface treatments. Biaxial flexural strength was determined by both static and cyclic fatigue testing. In the cyclic fatigue test, the load was applied at a frequency of 10 Hz for 10(6) cycles in distilled water at 37°C. The surface morphology, roughness, and crystal phase of the surfaces were also evaluated. The cyclic fatigue strength (888 MPa) of HIP Y-TZP with sandblasting and acid-etching was more than twice that of Y-TZP as specified in ISO 13356 for surgical implants (320 MPa), indicating the clinical potential of this material. PMID:23538763

  15. Verification of the effect of surface preparation on Hot Isostatic Pressing diffusion bonding joints of CLAM steel

    NASA Astrophysics Data System (ADS)

    Zhao, Yanyun; Li, Chunjing; Huang, Bo; Liu, Shaojun; Huang, Qunying

    2014-12-01

    Hot Isostatic Pressing (HIP) diffusion bonding with CLAM steel is the primary candidate fabrication technique for the first wall (FW) of DFLL-TBM. Surface state is one of the key factors for the joints quality. The effect of surface state prepared with grinder and miller on HIP diffusion bonding joints of CLAM steel was investigated. HIP diffusion bonding was performed at 140 MPa and 1373 K within 3 h. The mechanical properties of the joints were investigated with instrumented Charpy V-notch impact tests and the microstructures of the joints were analyzed with scanning electron microscopy (SEM). The results showed that the milled samples with fine surface roughness were more suitable for CLAM steel HIP diffusion bonding.

  16. Experimental and Theoretical Investigations of Hot Isostatically Pressed-Produced Stainless Steel/High Alloy Tool Steel Compound Materials

    NASA Astrophysics Data System (ADS)

    Lindwall, Greta; Flyg, Jesper; Frisk, Karin; Sandberg, Odd

    2011-05-01

    Consolidation of tool steel powders and simultaneous joining to a stainless 316L steel are performed by hot isostatic pressing (HIP). Two tool steel grades are considered: a high vanadium alloyed carbon tool steel, and a high vanadium and chromium alloyed nitrogen tool steel. The boundary layer arising during diffusion bonding is in focus and, in particular, the diffusion of carbon and nitrogen over the joint. Measurements of the elemental concentration profiles and corrosion tests by the double loop-electrochemical potentiokinetic reactivation (DL-EPR) method are performed. Comparative calculations with the DICTRA software are performed and are found to be in agreement with the experimental results. It is found that the carbon tool steel grade has a more critical influence on the corrosion resistance of the stainless 316L steel in comparison to the nitrogen tool steel grade.

  17. HVOF Spraying of Fe-Based MMC Coatings with In Situ Formation of Hard Particles by Hot Isostatic Pressing

    NASA Astrophysics Data System (ADS)

    Röttger, A.; Weber, S. L.; Theisen, W.; Rajasekaran, B.; Vaßen, R.

    2012-03-01

    Thick (2-3 mm) Fe-base coatings with admixed ferrotitanium (Fe30Ti70) were applied to austenitic steel by a high-velocity oxy-fuel process (HVOF). Hot-isostatic pressing (HIP) was carried out to the decrease porosity and to increase the material strength, wear resistance, and adhesive bond strength of the deposited coating to the substrate material. SEM and XRD investigations confirmed the formation of hard titanium carbide (TiC) particles during HIP treatment as a result of strong carbon diffusion out of the metal matrix and into the Fe30Ti70 particles. The mechanical and wear properties of the densified coatings were investigated by means of shear tests, hardness measurements, and abrasive wear tests. A comparison of the coatings in the as-sprayed and the HIPed state showed a large increase in the wear resistance due to in situ TiC formation.

  18. Characterization of hot isostatically pressed Bi-Sr-Ca-Cu-O as a function of consolidation variables

    SciTech Connect

    Goretta, K.C.; Miller, D.J.; Poeppel, R.B. ); Nash, A.S. )

    1991-11-01

    Fully dense, bulk Bi{sub 2}Sr{sub 1.7}CaCu{sub 2}O{sub x} (2212) superconductor pellets were made by hot isostatic pressing in an inert atmosphere. Electron microscopy revealed that rotation and bending of the platelike 2212 grains were responsible for much of the densification. Under processing conditions of 825{degrees}C and 105 MPa, dense pellets were obtained in 15 min. Many dislocations, planar faults, and, perhaps, intergrowths of the Bi{sub 2}Sr{sub 2}CuO{sub x} phase were produced during pressing. The dislocations were largely present in subgrain boundaries when the pressing times were increased to 45--120 min.

  19. Pyrochlore-structured titanate ceramics for immobilisation of actinides: Hot isostatic pressing (HIPing) and stainless steel/waste form interactions

    NASA Astrophysics Data System (ADS)

    Zhang, Yingjie; Li, Huijun; Moricca, Sam

    2008-07-01

    A pyrochlore-structured titanate ceramic has been studied in respect of its overall feasibility for immobilisation of impure actinide-rich radioactive wastes through the hot isostatic pressing (HIPing) technique. The resultant waste form contains mainly pyrochlore (˜70%), rutile (˜14%) as well as perovskite (˜12%), hollandite (˜2%) and brannerite (˜1%). Optical spectroscopy confirms that uranium (used to simulate Pu) exists mainly in the stable pyrochlore-structured phase as tetravalent ions as designed. The stainless steel/waste form interactions under HIPing conditions (1280 °C/100 MPa/3 h) do not seem to change the actinide-bearing phases and therefore should have no detrimental effect on the waste form.

  20. Influence of surface treatment of yttria-stabilized tetragonal zirconia polycrystal with hot isostatic pressing on cyclic fatigue strength.

    PubMed

    Iijima, Toshihiko; Homma, Shinya; Sekine, Hideshi; Sasaki, Hodaka; Yajima, Yasutomo; Yoshinari, Masao

    2013-01-01

    Hot isostatic pressing processed yttria-stabilized tetragonal zirconia polycrystal (HIP Y-TZP) has the potential for application to implants due to its high mechanical performance. The aim of this study was to investigate the influence of surface treatment of HIP Y-TZP on cyclic fatigue strength. HIP Y-TZP specimens were subjected to different surface treatments. Biaxial flexural strength was determined by both static and cyclic fatigue testing. In the cyclic fatigue test, the load was applied at a frequency of 10 Hz for 10(6) cycles in distilled water at 37°C. The surface morphology, roughness, and crystal phase of the surfaces were also evaluated. The cyclic fatigue strength (888 MPa) of HIP Y-TZP with sandblasting and acid-etching was more than twice that of Y-TZP as specified in ISO 13356 for surgical implants (320 MPa), indicating the clinical potential of this material.

  1. Geologic significance of new isostatic gravity and aeromagnetic maps of the Winnemucca 1[degree] by 2[degree] quadrangle, Nevada

    SciTech Connect

    Oliver, H.W.; Sikora, R.F. ); Robbins, S.L. )

    1993-04-01

    Since Wagini's 1986 Bouguer and isostatic gravity compilations of the Winnemucca 1[degree] by 2[degree] quadrangle, R. Sikora has provided an 1991 update that includes 133 new stations obtained in the Sonoma Range, Boulder Valley, and the Battle Mountain areas. Since that 1991 update, 371 additional stations have been obtained by S. Robbins in the Pine and Crescent Valley areas to look for possible gravity signatures of petroleum and gold deposits. All these data have been reduced and incorporated into a new isostatic gravity map of the quadrangle. This new compilation shows that the largest residual low of 32 mGal occurs over petroleum-bearing Pine Valley, although nearly-as-large gravity lows (27--31 mGal) occur over Buena Vista, Pleasant, Reese River, and Grass Valleys. A new aeromagnetic compilation of the Winnemucca quadrangle is continued downward to 300 m above terrain and shows a number of magnetic highs associated with igneous rocks, both intrusive and extrusive. A nearly continuous north-northwest trending magnetic high of about 400 nT, known as the northern Nevada rift, cuts across the quadrangle about 10 km east of Battle Mountain and is associated at some locations with Miocene basaltic and andesitic extrusive rocks. Three Miocene epithermal gold deposits are associated with this magnetic high at Mule Canyon, Fire Creek, and Bluckhorn. A smaller but broader magnetic high of about 200 nT at 300 m above terrain is located over the Tuscarora Mountains about 15 km northwest of Carlin. The maximum horizontal gradient of the pseudogravity transformation of the total magnetic field coincides with a series of ten productive gold mines known as the Carlin trend.

  2. An Overview of Project Planning for Hot-Isostatic Pressure Treatment of High-Level Waste Calcine for the Idaho Cleanup Project - 12289

    SciTech Connect

    Nenni, Joseph A.; Thompson, Theron J.

    2012-07-01

    The Calcine Disposition Project is responsible for retrieval, treatment by hot-isostatic pressure, packaging, and disposal of highly radioactive calcine stored at the Idaho Nuclear Technology and Engineering Center at the Idaho National Laboratory Site in southeast Idaho. In the 2009 Amended Record of Decision: Idaho High-Level Waste and Facilities Disposition Final Environmental Impact Statement the Department of Energy documented the selection of hot-isostatic pressure as the technology to treat the calcine. The Record of Decision specifies that the treatment results in a volume-reduced, monolithic waste form suitable for transport outside of Idaho by a target date of December 31, 2035. That target date is specified in the 1995 Idaho Settlement Agreement to treat and prepare the calcine for transport out of Idaho in exchange for allowing storage of Navy spent nuclear fuel at the INL Site. The project is completing the design of the calcine-treatment process and facility to comply with Record of Decision, Settlement Agreement, Idaho Department of Environmental Quality, and Department of Energy requirements. A systems engineering approach is being used to define the project mission and requirements, manage risks, and establish the safety basis for decision making in compliance with DOE O 413.3B, 'Program and Project Management for the Acquisition of Capital Assets'. The approach draws heavily on 'design-for-quality' tools to systematically add quality, predict design reliability, and manage variation in the earliest possible stages of design when it is most efficient. Use of these tools provides a standardized basis for interfacing systems to interact across system boundaries and promotes system integration on a facility-wide basis. A mass and energy model was developed to assist in the design of process equipment, determine material-flow parameters, and estimate process emissions. Data generated from failure modes and effects analysis and reliability, availability

  3. Effect of cold isostatic pressing on the transport current of filamentary MgB2 wire made by the IMD process

    NASA Astrophysics Data System (ADS)

    Kováč, P.; Hušek, I.; Pachla, W.; Melišek, T.; Kulich, M.; Rosová, A.; Kopera, L.

    2016-07-01

    This work describes the effect of cold isostatic pressing applied to as-drawn filamentary wires in a GlidCop and/or Cu sheath made by the internal magnesium diffusion process. Critical currents of as-drawn and isostatically pressed wires at high pressures up to 2.0 GPa followed by heat treatment at 640 °C for 40 min were measured. The obtained results show an improvement in boron powder density resulting in an increase of the critical current of MgB2 layers. The engineering current density increases by 4–13 times after the high-pressure treatment, and is influenced by the density of the boron powder and by the mechanical strength of the outer sheath.

  4. Effect of cold isostatic pressing on the transport current of filamentary MgB2 wire made by the IMD process

    NASA Astrophysics Data System (ADS)

    Kováč, P.; Hušek, I.; Pachla, W.; Melišek, T.; Kulich, M.; Rosová, A.; Kopera, L.

    2016-07-01

    This work describes the effect of cold isostatic pressing applied to as-drawn filamentary wires in a GlidCop and/or Cu sheath made by the internal magnesium diffusion process. Critical currents of as-drawn and isostatically pressed wires at high pressures up to 2.0 GPa followed by heat treatment at 640 °C for 40 min were measured. The obtained results show an improvement in boron powder density resulting in an increase of the critical current of MgB2 layers. The engineering current density increases by 4-13 times after the high-pressure treatment, and is influenced by the density of the boron powder and by the mechanical strength of the outer sheath.

  5. Tensile properties from room temperature to 1315 C of tungsten-lined tantalum-alloy (T-111) tubing fabricated by hot isostatic pressing

    NASA Technical Reports Server (NTRS)

    Buzzard, R. J.; Metroka, R. R.

    1974-01-01

    The effects were studied of a thin tungsten liner on the tensile properties of T-111 tubing considered for fuel cladding in a space power nuclear reactor concept. The results indicate that the metallurgically bonded liner had no appreciable effects on the properties of the T-111 tubing. A hot isostatic pressing method used to apply the liners is described along with a means for overcoming the possible embrittling effects of hydrogen contamination.

  6. The use of isostatic pressing to improve the strength of TLP diffusion bonds in aluminium-based composites

    SciTech Connect

    Shirzadi, A.A.; Wallach, E.R.

    1996-12-31

    Transient Liquid Phase (TLP) diffusion bonding of aluminium-SiC composites, using copper interlayers, was carried out under low bonding pressure to minimize plastic deformation. This was followed by solid-state diffusion bonding under relatively high pressure as a complementary process to improve joint strength and reliability. In the high pressure stage, plastic deformation was avoided by lateral constraint of the sample in order to build up a hydrostatic stress state, simulating hot isostatic pressing (hipping). The bonding temperature in a TLP process is usually determined by the temperature at which the liquid phase forms, e.g., the Al-Cu eutectic formation temperature in this case. In theory, it should be possible to vary the applied pressure in order to optimize bonding. However, the superplastic behavior of the material used in this work led to excessive deformation at the bonding temperature, with consequent restrictions on the bonding pressure and on the resulting bond strengths. The subsequent use of higher bonding pressures with minimal plastic deformation in the second stage of the process resulted in considerable improvements in bond strength. Bonds with shear strengths as high as 70% and 92% respectively of the shear strengths of two aluminium composites, 8090 Al/SiC and 359 Al/SiC (given the same thermal cycles including post solution treatment and ageing), have been achieved.

  7. Ultrafine-Grained Aluminum Processed by a Combination of Hot Isostatic Pressing and Dynamic Plastic Deformation: Microstructure and Mechanical Properties

    NASA Astrophysics Data System (ADS)

    Dirras, G.; Chauveau, T.; Abdul-Latif, A.; Gubicza, J.; Ramtani, S.; Bui, Q.; Hegedűs, Z.; Bacroix, B.

    2012-04-01

    Commercial-purity (99 wt pct), bulk, ultrafine-grained aluminum samples were produced by a two-step process that combines powder consolidation by hot isostatic pressing and dynamic plastic deformation. The compaction step yielded crystallographic texture-free specimens with an average grain size of approximately 2 μm. Then, some of the consolidated specimens were deformed dynamically at room temperature at an initial strain rate of 370 seconds-1 and up to an axial strain of ɛ = 1.25. After dynamic plastic deformation, the grain size and the dislocation density were approximately 500 nm and 1014 m-2, respectively. The yield strength was approximately 77 MPa for the as-consolidated sample, which increased up to approximately 103 MPa and 120 MPa for the impacted samples along the axial and radial directions, respectively. The compression stress as a function of strain showed saturation behavior for the axially deformed samples, whereas the specimens deformed along the radial direction exhibited significant strain softening. The latter behavior is explained mainly by the weakening of the crystallographic texture that occurred because of the strain-path change along the radial direction.

  8. Thermal Shock and Ablation Behavior of Tungsten Nozzle Produced by Plasma Spray Forming and Hot Isostatic Pressing

    NASA Astrophysics Data System (ADS)

    Wang, Y. M.; Xiong, X.; Zhao, Z. W.; Xie, L.; Min, X. B.; Yan, J. H.; Xia, G. M.; Zheng, F.

    2015-08-01

    Tungsten nozzle was produced by plasma spray forming (PSF, relative density of 86 ± 2%) followed by hot isostatic pressing (HIPing, 97 ± 2%) at 2000 °C and 180 MPa for 180 min. Scanning electron microscope, x-ray diffractometer, Archimedes method, Vickers hardness, and tensile tests have been employed to study microstructure, phase composition, density, micro-hardness, and mechanical properties of the parts. Resistance of thermal shock and ablation behavior of W nozzle were investigated by hot-firing test on solid rocket motor (SRM). Comparing with PSF nozzle, less damage was observed for HIPed sample after SRM test. Linear ablation rate of nozzle made by PSF was (0.120 ± 0.048) mm/s, while that after HIPing reduced to (0.0075 ± 0.0025) mm/s. Three types of ablation mechanisms including mechanical erosion, thermophysical erosion, and thermochemical ablation took place during hot-firing test. The order of degree of ablation was nozzle throat > convergence > dilation inside W nozzle.

  9. Sintering and hot isostatic pressing of Bi2Sr2CaCu2O(x)

    NASA Astrophysics Data System (ADS)

    Nash, A. S.; Nash, P.; Poeppel, R. B.; Goretta, K. C.

    1991-01-01

    The Bi2Sr2CaCu2O(x) phase was synthesized by solid-state reaction of oxides and carbonates. Initial compositions of Bi:Sr:Ca:Cu were 4:3:3:6 and 2:1.7:1:2. Pellets of the pure powder and powder containing 2.5, 5, or 15 wt percent Ag were cold-pressed and either sintered or hot isostatically pressed (HIPped). For HIPping, the pellets were encased in thin Ag sheets, canned in steel, and pressed at 105 MPa in argon at 800 or 850 C. HIPping produced dense specimens, but sintering did not. HIPping induced very little decomposition of the Bi2Sr2CaCu2O(x), but a post-HIP anneal was needed to raise the transition temperature above 80 K. The Ag additions appeared to minimize microcracking during HIPping at 800 C. Little microcracking was evident in any of the specimens HIPped at 850 C.

  10. Properties of Porous TiNbZr Shape Memory Alloy Fabricated by Mechanical Alloying and Hot Isostatic Pressing

    NASA Astrophysics Data System (ADS)

    Ma, L. W.; Chung, C. Y.; Tong, Y. X.; Zheng, Y. F.

    2011-07-01

    In the past decades, systematic researches have been focused on studying Ti-Nb-based SMAs by adding ternary elements, such as Mo, Sn, Zr, etc. However, only arc melting or induction melting methods, with subsequent hot or cold rolling, were used to fabricate these Ni-free SMAs. There is no work related to powder metallurgy and porous structures. This study focuses on the fabrication and characterization of porous Ti-22Nb-6Zr (at.%) shape memory alloys produced using elemental powders by means of mechanical alloying and hot isostatic pressing. It is found that the porous Ti-22Nb-6Zr alloys prepared by the HIP process exhibit a homogenous pore distribution with spherical pores, while the pores have irregular shape in the specimen prepared by conventional sintering. X-ray diffraction analysis showed that the solid solution-treated Ti-22Nb-6Zr alloy consists of both β phase and α″ martensite phase. Morphologies of martensite were observed. Finally, the porous Ti-22Nb-6Zr SMAs produced by both MA and HIP exhibit good mechanical properties, such as superior superelasticity, with maximum recoverable strain of ~3% and high compressive strength.

  11. GPS and Relative Sea-level Constraints on Glacial Isostatic Adjustment in North America

    NASA Astrophysics Data System (ADS)

    James, T. S.; Simon, K.; Henton, J. A.; Craymer, M.

    2015-12-01

    Recently, new GIA models have been developed for the Innuitian Ice Sheet and for the north-central portion of the Laurentide Ice Sheet (Simon, 2014; Simon et al., 2015). This new combined model, herein called Innu-Laur15, was developed from the ICE-5G model and load adjustments were made to improve the fit to relative sea-level observations and to GPS-constrained vertical crustal motion in the Canadian Arctic Archipelago and around Hudson Bay. Here, the predictions of Innu-Laur15 are compared to observations and other GIA models over an extended region comprising much of North America east of the Rocky Mountains. GIA predictions are made using compressible Maxwell Earth models with gravitationally self-consistent ocean loading, changing coastlines, and ocean-water inundation where marine ice retreats or floats. For this study, GPS time series are the NA12 solution (Blewitt et al., 2013) downloaded from http://geodesy.unr.edu/NGLStationPages/GlobalStationList and fit with a linear trend, annual and semi-annual terms, and offsets as indicated by station logs and by inspection of the time series. For example, a comparison of GPS observations of vertical crustal motion from the NA12 solution at 360 sites gives root-mean-square (RMS) residuals of 3.2 mm/yr (null hypothesis), 1.8 mm/yr (Innu-Laur15), and 2.9 mm/yr (ICE-5G) for the VM5a Earth model. Preliminary comparisons with other Earth models give similar patterns where Innu-Laur15 provides a better fit than ICE-5G. Further adjustments to the Innu-Laur15 ice sheet history could improve the fit to GPS rates in other regions of North America.

  12. Isostatic geoid anomalies over mid-plate swells in the Central North Atlantic

    NASA Astrophysics Data System (ADS)

    Grevemeyer, Ingo

    1999-08-01

    The relation of geoid height data from Geosat/ERM altimeter measurements to seafloor topography from recent shipborne data is investigated for eight igneous provinces located in the Central North Atlantic. The long wavelength undulations of the geoid, reflecting deep-seated density anomalies, were removed by subtracting a low degree and order spherical harmonic representation of the geoid. After converting residual geoid heights and topography to anomalies related to the thermal plate model, both maps were low-pass filtered to isolate the signal associated with local compensation from surface loading. Finally, the ratio of geoid height to topography was determined by fitting a straight line to the data. Cape Verde, Bermuda, Canary and Madeira swells exhibit high geoid/topography ratios, which signify reheating of the lower lithosphere. These features were classified as thermal swells. Geoid/topography ratios occurring over the New England, Corner, Azores and Great Meteor seamount chains can be explained by Airy compensation model of crustal thickening. This requires non-hotspot processes to be active within the Azores and Great Meteor seamounts.

  13. Phase Transformation Behavior of Hot Isostatically Pressed NiTi-X (X = Ag, Nb, W) Alloys for Functional Engineering Applications

    NASA Astrophysics Data System (ADS)

    Bitzer, M.; Bram, M.; Buchkremer, H. P.; Stöver, D.

    2012-12-01

    Owing to their unique properties, NiTi-based shape memory alloys (SMAs) are highly attractive candidates for a lot of functional engineering applications like biomedical implants (stents), actuators, or coupling elements. Adding a third element is an effective measure to adjust or stabilize the phase transformation behavior to a certain extent. In this context, addition of alloying elements, which are low soluble or almost insoluble in the NiTi matrix is a promising approach and—with the exception of adding Nb—has rarely been reported in the literature so far, especially if the manufacturing of the net-shaped parts of these alloys is aspired. In the case of addition of elemental Nb, broadening of hysteresis between austenitic and martensitic phase transformation temperatures after plastic deformation of the Nb phase is a well-known effect, which is the key of function of coupling elements already established on the market. In the present study, we replaced Nb with additions of elemental Ag and W, both of which are almost insoluble in the NiTi matrix. Compared with Nb, Ag is characterized by higher ductility in combination with lower melting point, enabling liquid phase sintering already at moderate temperatures. Vice versa, addition of W might act in opposite manner considering its inherent brittleness combined with high melting temperature. In the present study, hot isostatic pressing was used for manufacturing such alloys starting from prealloyed NiTi powder and with the additions of Nb, Ag, and W as elemental powders. Microstructures, interdiffusion phenomena, phase transformation behaviors, and impurity contents were investigated aiming to better understand the influence of insoluble phases on bulk properties of NiTi SMAs.

  14. Isostatic and dynamic support of high topography on a North Atlantic passive margin

    NASA Astrophysics Data System (ADS)

    Pedersen, Vivi K.; Huismans, Ritske S.; Moucha, Robert

    2016-07-01

    Substantial controversy surrounds the origin of high topography along passive continental margins. Here we focus on the well-documented elevated passive margin in southwestern Scandinavia, and quantify the relative contributions of crustal isostasy and dynamic topography in controlling the present topography. We find that majority of the topography is compensated by the crustal structure, suggesting a topographic age that is in accord with the 400 Myr old Caledonian orogenesis. In addition, we propose that dynamic uplift of ∼300 m has rejuvenated existing topography locally in the coastal region over the last 10 Myr. Such uplift, combined with a general sea level fall, can help explain a variety of observations that have traditionally been interpreted in favor of a peneplain uplift model. We conclude that high topography along the Scandinavian margin cannot represent remnants of a peneplain uplifted within the last 20 Myr. The topography must have been high since the Caledonian orogeny.

  15. Deep-burial diagenesis: Its implications for vertical movements of the crust, uplift of the lithosphere and isostatic unroofing—A review

    NASA Astrophysics Data System (ADS)

    Friedman, Gerald M.

    1987-03-01

    Various techniques of study of strata exposed at the surface in undeformed areas of the Appalachian Basin and Ozark Done, imply that these strata have been heated to temperatures that suggest a former great depth of burial. The data reveal that the strata have been much more deeply buried than previously thought. If such former deep burial has taken place, then subsequent uplift and erosion must also have taken place to bring these formerly deeply buried strata to the present land surface. Unexpectedly large amounts of uplift and erosion, ranging from 4.3 to 7 km, have re-exposed these formerly deeply buried rocks. This leads to the surprising conclusion that isostatic unroofing has stripped off thick sections of strata whose presence was previously unsuspected. Therefore, the lithosphere, in its isostatic unroofing of thick sequences of sedimentary strata, has undergone much larger vertical motions than many geologists had previously estimated. Case histories in this review include strata of the Silurian of the Northern Appalachian Basin and of the Ordovician of the Ozark Dome, which reached interpreted maximum burial depths of 5 and 4.3 km, respectively; Devonian strata in the Catskill Mountains of New York imply a former depth of burial of ˜ 6.5 km. Lower Ordovician carbonate sequences of the Northern Appalachian Basin imply a depth of burial in excess of 7 km; Middle Ordovician strata from the same basin signify a depth of burial of approximately 5 km; and Devonian strata, a paleodepth of 4.5-5 km. Such former great depths of burial of undeformed strata, which are now exposed at the surface, reflect large-scale vertical movements of the crust and uplift of the lithosphere. These drastic changes represent isostatic unroofing with widespread implications for paleogeography of a kind unrecognized at present.

  16. MICROSCOPY CHARACTERIZATION OF U-MO BEARING MINI-PLATES FABRICATED BY HOT ISOSTATIC PRESSING (HIPPING) WITH A LONG THERMAL CYCLE

    SciTech Connect

    Jan-Fong Jue

    2007-07-01

    The RERTR Program has formed the Production Development Team to coordinate fabrication efforts to produce the fuel elements for the qualifying irradiation tests. These fuel elements will be fabricated in production facilities. Fabrication development data will be shared with all participants on the development team. The INL has been developing a method of cladding using a Hot Isostatic Press (HIP). The operating parameters were varied to understand the impact of time, pressure and temperature on the reaction between the fuel and the cladding. This report details some of the data produced to date.

  17. Digital Isostatic Gravity Map of the Nevada Test Site and Vicinity, Nye, Lincoln, and Clark Counties, Nevada, and Inyo County, California

    USGS Publications Warehouse

    Ponce, David A.; Mankinen, E.A.; Davidson, J.G.; Morin, R.L.; Blakely, R.J.

    2000-01-01

    An isostatic gravity map of the Nevada Test Site area was prepared from publicly available gravity data (Ponce, 1997) and from gravity data recently collected by the U.S. Geological Survey (Mankinen and others, 1999; Morin and Blakely, 1999). Gravity data were processed using standard gravity data reduction techniques. Southwest Nevada is characterized by gravity anomalies that reflect the distribution of pre-Cenozoic carbonate rocks, thick sequences of volcanic rocks, and thick alluvial basins. In addition, regional gravity data reveal the presence of linear features that reflect large-scale faults whereas detailed gravity data can indicate the presence of smaller-scale faults.

  18. Global recovery of the Moho depths using the latest models of gravity and crust density structures

    NASA Astrophysics Data System (ADS)

    Tenzer, R.

    2013-12-01

    The latest gravity and crust density structure models are used to determine the Moho depths based on applying a newly developed gravimetric-isostatic method. This method utilizes expressions for the gravimetric forward and inverse modeling derived in a frequency domain. Methods for a spectral analysis and synthesis of the gravity field and crust density structures are applied in the gravimetric forward modeling of the consolidated curst-stripped gravity disturbances, which have a maximum correlation with the (a priori) Moho model. These gravity disturbances are obtained from the Earth's gravity disturbances after applying the topographic and stripping gravity corrections of major known anomalous crust density structures; in the absence of a global mantle model, mantle density heterogeneities are disregarded. The isostatic scheme applied is based on a complete compensation of the crust relative to the upper mantle density. The functional relation is established between the (unknown) Moho depths and the complete crust-stripped isostatic gravity disturbances, which according to the adopted isostatic scheme have (theoretically) a minimum correlation with the Moho geometry. The system of observation equations, which describes the relation between spherical functions of the isostatic gravity field and Moho geometry, is defined by means of a linearized Fredholm integral equation of the first kind. The Moho depths are determined based on solving the gravimetric inverse problem. The regularization is applied to stabilize the ill-posed solution. This numerical procedure is utilized to determine the Moho depths globally. The gravimetric result is presented and compared with the seismic CRUST1 Moho model.

  19. Influence of Hot Isostatic Pressing on the Microstructure and Mechanical Properties of a Spray-Formed Al-4.5 wt.% Cu Alloy

    NASA Astrophysics Data System (ADS)

    Devaraj, S.; Sankaran, S.; Kumar, R.; Appa Rao, G.

    2014-04-01

    Al-4.5 wt.% Cu alloy was spray atomized and deposited at varied spray heights ranging from 300 to 390 mm. The average grain sizes decreased from ~ 29 to ~ 18 μm and a concomitant increase in the hardness and the 0.2% yield strength (YS) with increase in the spray height. The respective hardness values of SF-300, SF-340, and SF-390 are 451 ± 59, 530 ± 39, and 726 ± 39 MPa and the YS are 108 ± 7, 115 ± 8, and 159 ± 10 MPa. The transmission electron micrographs revealed the morphological changes of the Al2Cu phase from irregular shaped to small plate-shaped and then subsequently to spheroidal shape due to high undercooling encountered during spray atomization with increase in spray height from 300 to 390 mm. The porosity of the spray formed deposits varied between 5 to 12%. Hot isostatic pressing of spray deposits reduced the porosity to less than 0.5% without any appreciable increase in grain size. A dislocation creep mechanism seems to be operative during the secondary processing. A comparison between as-spray formed and hot isostatically pressed deposits exemplifies improvement in mechanical properties as a result of elimination of porosity without affecting the fine grain sizes achieved during the spray-forming process.

  20. Strength and phase stability of yttria-ceria-doped tetragonal zirconia/alumina composites sintered and hot isostatically pressed in argon-oxygen gas atmosphere

    SciTech Connect

    Hirano, M.; Inada, H. )

    1991-03-01

    Yttria-ceria-doped tetragonal zirconia ((Y,Ce)-TZP)/alumina (Al{sub 2}O{sub 3}) composites were fabricated by hot isostatic pressing at 1400{degrees} to 1450{degrees}C and 196 MPa in an Ar-O{sub 2} atmosphere using the fine powders prepared by hydrolysis of ZrOCl{sub 2} solution. The composites consisting of 25 wt% Al{sub 2}O{sub 3} and tetragonal zirconia with compositions 4 mol% YO{sub 1.5}{minus}4 mol% CeO{sub 2}-ZrO{sub 2} and 2.5 mol% YO{sub 1.5}{minus}5.5 mol% CeO{sub 2}-ZrO{sub 2} exhibited means fracture strength as high as 2000 MPa and were resistant to phase transformation under saturated water vapor pressure at 180{degrees}C (1 MPa). Postsintering hot isostatic pressing of (4Y, 4Ce)-TZP/Al{sub 2}O{sub 3} and (2.5Y, 5.5Ce)-TZP/Al{sub 2}O{sub 3} composites was useful to enhance the phase stability under hydrothermal conditions and strength.

  1. Sea-level history during the Last Interglacial complex on San Nicolas Island, California: implications for glacial isostatic adjustment processes, paleozoogeography and tectonics

    USGS Publications Warehouse

    Muhs, Daniel R.; Simmons, Kathleen R.; Schumann, R. Randall; Groves, Lindsey T.; Mitrovica, Jerry X.; Laurel, Deanna

    2012-01-01

    sea stands on New Guinea and Barbados. Numerical models of the glacial isostatic adjustment (GIA) process presented here demonstrate that these differences in the high stands are expected, given the variable geographic distances between the sites and the former Laurentide and Cordilleran ice sheets. Moreover, the numerical results show that the absolute and differential elevations of the observed high stands provide a potentially important constraint on ice volumes during this time interval and on Earth structure.

  2. The effects of weld-repair and hot isostatic pressing on the fracture properties of Ti-5Al-2.5Sn ELI castings

    NASA Technical Reports Server (NTRS)

    Misra, M. S.; Lemeshewsky, S.; Bolstad, D.

    1982-01-01

    The Ti-5Al-2.5Sn extremely low interstitial alloy employed in the large castings which form the critical attachment fittings of the Space Shuttle External Tank was selected because of its high fracture resistance at cryogenic temperatures. Casting was selected over alternative fabrication methods because of its lower cost and adaptability to design changes, although it was found necessary to weld-repair surface and subsurface casting defects in order to reduce the scrap rate and maintain the inherent cost advantage of the castings. Hot Isostatic Pressing was experimentally found to heal the surface and internal defects of the castings, but did not improve tensile or fracture properties and was therefore rejected as a production technique. Production castings are instead weld-repaired, without any mechanical property degradation.

  3. Effect of hot isostatic pressing on the structure and properties of cast polycrystalline gas-turbine blades made of nickel superalloys

    NASA Astrophysics Data System (ADS)

    Beresnev, A. G.

    2012-05-01

    A concept of a two-stage hot isostatic pressing (HIP) cycle is developed for castings made of nickel superalloys in order to minimize plastic deformation and the recrystallization ability of their structure. At the first stage of the cycle, diffusion pore dissolution is predominant due to the motion of vacancies toward grain boundaries in a polycrystal; at the second stage, retained coarse pores are filled during plastic deformation. The effect of uniform compression pressure during HIP and microstructure defects on the vacancy diffusion in nickel superalloys is estimated. A two-stage HIP regime is developed for processing of cast gas-turbine engine blades made of a ZhS6U alloy in order to substantially decrease the shrinkage porosity and to increase the high-temperature characteristics, including the creep and fatigue resistance.

  4. Synroc-D Type Ceramics Produced by Hot Isostatic Pressing and Cold Crucible Melting for Immobilisation of (Al, U) Rich Nuclear Waste

    SciTech Connect

    Vance, Eric R.; La Robina, Michael; Li, Huijun; Davis, Joel

    2007-07-01

    A synroc-D ceramic consisting mostly of spinel, hollandite, pyrochlore-structured CaUTi{sub 2}O{sub 7}, UO{sub 2}, and Ti-rich regions shows promise for immobilisation of a HLW containing mainly Al and U, together with fission products. Ceramics with virtually zero porosities and waste loadings of 50-60 wt% on an oxide basis were prepared by cold crucible melting (CCM) at {approx}1500 deg. C, and also by subsolidus hot isostatic pressing (HIP) at 1100 deg. C to prevent volatile losses. PCT leaching test values for Cs were < 13 g/L, with all other normalised elemental extractions being well below 1 g/L. (authors)

  5. Understanding the Role of Hot Isostatic Pressing Parameters on the Microstructural Evolution of Ti-6Al-4V and Inconel 718 Fabricated by Electron Beam Melting

    SciTech Connect

    Peter, William H.; Nandwana, Peeyush; Kirka, Michael M.; Dehoff, Ryan R.; Sames, William; Erdman, III, Donald L.; Eklund, Anders; Howard, Ron

    2015-04-01

    In this project, Avure and ORNL evaluated the influence of hot isostatic pressing (HIP) and thermal cycling as standalone post processing techniques on the microstructure of electron beam powder bed deposited Ti-6Al-4V and Inconel 718 alloys. Electron beam powder bed deposition is an effective technology for fabricating complex net shape components that cannot be manufactured with conventional processes. However, material deposited by this technology results in columnar grain growth which is detrimental for many applications. For Ti-6Al-4V, it has been found that thermal cycling alone is not sufficient to breakdown the columnar microstructure that is typical of electron beam powder bed technology. HIP, on the other hand, has the potential to be an effective technique to break down the columnar microstructure of Ti-6Al-4V into a more equiaxed and refined β grain structure, and provide a more homogeneous microstructure compared to the thermally cycled samples. Overall, the project showed that hot isostatic pressing reduced/eliminated porosity in both Ti-6Al-4V and Inconel 718 However, based on the unique thermal cycle and the application of pressure in the HIP vessel, Ti-6Al-4V e-beam deposited microstructures were modified from columnar grain growth to equiaxed microstructures; a significant outcome to this collaboration. Inconel 718, on the other hand, shows no change in the macrostructure as a result of the current HIP cycle based on the thermal history, and would require further investigation. Though the results of HIP cycle were very good at changing the microstructure, further development in optimizing the post heat treatments and HIP cycles is required to improve mechanical properties.

  6. Pressure-induced structural changes in the network-forming isostatic glass GeSe4: An investigation by neutron diffraction and first-principles molecular dynamics

    NASA Astrophysics Data System (ADS)

    Bouzid, Assil; Pizzey, Keiron J.; Zeidler, Anita; Ori, Guido; Boero, Mauro; Massobrio, Carlo; Klotz, Stefan; Fischer, Henry E.; Bull, Craig L.; Salmon, Philip S.

    2016-01-01

    The changes to the topological and chemical ordering in the network-forming isostatic glass GeSe4 are investigated at pressures up to ˜14.4 GPa by using a combination of neutron diffraction and first-principles molecular dynamics. The results show a network built from corner- and edge-sharing Ge(Se1 /2)4 tetrahedra, where linkages by Se2 dimers or longer Sen chains are prevalent. These linkages confer the network with a local flexibility that helps to retain the network connectivity at pressures up to ˜8 GPa, corresponding to a density increase of ˜37 % . The network reorganization at constant topology maintains a mean coordination number n ¯≃2.4 , the value expected from mean-field constraint-counting theory for a rigid stress-free network. Isostatic networks may therefore remain optimally constrained to avoid stress and retain their favorable glass-forming ability over a large density range. As the pressure is increased to around 13 GPa, corresponding to a density increase of ˜49 % , Ge(Se1 /2)4 tetrahedra remain as the predominant structural motifs, but there is an appearance of 5-fold coordinated Ge atoms and homopolar Ge-Ge bonds that accompany an increase in the fraction of 3-fold coordinated Se atoms. The band gap energy decreases with increasing pressure, and midgap states appear at pressures beyond ˜6.7 GPa. The latter originate from undercoordinated Se atoms that terminate broken Sen chains.

  7. Hydro-isostatic deflection and tectonic tilting in the central Andes: Initial results of a GPS survey of Lake Minchin shorelines

    NASA Technical Reports Server (NTRS)

    Bills, Bruce G.; De Silva, Shanaka L.; Currey, Donald R.; Emenger, Robert S.; Lillquist, Karl D.; Donnellan, Andrea; Worden, Bruce

    1994-01-01

    Sufficiently large lake loads provide a means of probing rheological stratification of the crust and upper mantle. Lake Minchin was the largest of the late Pleistocene pluvial lakes in the central Andes. Prominent shorelines, which formed during temporary still-stands in the climatically driven lake level history, preserve records of lateral variations in subsequent net vertical motions. At its maximum extent the lake was 140 m deep and spanned 400 km N-S and 200 km E-R. The load of surficial water contained in Lake Minchin was sufficient to depress the crust and underlying mantle by 20-40 m, depending on the subjacent rheology. Any other differential vertical motions will also be recorded as departures from horizontality of the shorelines. We recently conducted a survey of shoreline elevations of Lake Minchin with the express intent of monitoring the hydro-isostatic deflection and tectonic tilting. Using real-time differential Global Positioning System (GPS), we measured topographic profiles across suites of shorelines at 15 widely separated locations throughout the basin. Horizontal and vertical accuracies attained are roughly 30 and 70 cm, respectively. Geomorphic evidence suggests that the highest shoreline was occupied only briefly (probably less than 200 years) and radiocarbon dates on gastropod shells found in association with the shore deposits constrain the age to roughly 17 kyr. The basin-side pattern of elevations of the highest shoreline is composed of two distinct signals: (27 +/- 1) m of hydro-isostatic deflection due to the lake load, and a planar tilt with east and north components of (6.8 +/- 0.4) 10(exp -5) and 9-5.3 +/- 0.3) 10(exp -5). This rate of tilting is too high to be plausibly attributed to steady tectonism, and presumably reflects some unresolved combination of tectonism plus the effects of oceanic and lacustrine loads on a laterally heterogeneous substrate. The history of lake level fluctuations is still inadequately known to allow

  8. Phase decomposition of γ-U (bcc) in U-10 wt% Mo fuel alloy during hot isostatic pressing of monolithic fuel plate

    NASA Astrophysics Data System (ADS)

    Park, Y.; Eriksson, N.; Newell, R.; Keiser, D. D.; Sohn, Y. H.

    2016-11-01

    Eutectoid decomposition of γ-phase (cI2) into α-phase (oC4) and γ‧-phase (tI6) during the hot isostatic pressing (HIP) of the U-10 wt% Mo (U10Mo) alloy was investigated using monolithic fuel plate samples consisting of U10Mo fuel alloy, Zr diffusion barrier and AA6061 cladding. The decomposition of the γ-phase was observed because the HIP process is carried out near the eutectoid temperature, 555 °C. Initially, a cellular structure, consisting of γ‧-phase surrounded by α-phase, developed from the destabilization of the γ-phase. The cellular structure further developed into an alternating lamellar structure of α- and γ‧-phases. Using scanning electron microscopy and transmission electron microscopy, qualitative and quantitative microstructural analyses were carried out to identify the phase constituents, and elucidate the microstructural development based on time-temperature-transformation diagram of the U10Mo alloy. The destabilization of γ -phase into α- and γ‧-phases would be minimized when HIP process was carried out with rapid ramping/cooling rate and dwell temperature higher than 560 °C.

  9. Effects of long-time elevated temperature exposures on hot-isostatically-pressed power-metallurgy Udimet 700 alloys with reduced cobalt contents

    NASA Technical Reports Server (NTRS)

    Hart, F. H.

    1984-01-01

    Because almost the entire U.S. consumption of cobalt depends on imports, this metal has been designated "strategic'. The role and effectiveness of cobalt is being evaluated in commercial nickel-base superalloys. Udiment 700 type alloys in which the cobalt content was reduced from the normal 17% down to 12.7%, 8.5%, 4.3%, and 0% were prepared by standard powder metallurgy techniques and hot isostatically pressed into billets. Mechanical testing and microstructural investigations were performed. The mechanical properties of alloys with reduced cobalt contents which were heat-treated identically were equal or better than those of the standard alloy, except that creep rates tended to increase as cobalt was reduced. The effects of long time exposures at 760 C on mechanical properties and at 760 C and 845 C on microstructures were determined. Decreased tensile properties and shorter rupture lives with increased creep rates were observed in alloy modifications. The exposures caused gamma prime particle coarsening and formation of sigma phase in the alloys with higher cobalt contents. Exposure at 845 C also reduced the amount of MC carbides.

  10. Effect of Oxygen Content Upon the Microstructural and Mechanical Properties of Type 316L Austenitic Stainless Steel Manufactured by Hot Isostatic Pressing

    NASA Astrophysics Data System (ADS)

    Cooper, Adam J.; Cooper, Norman I.; Dhers, Jean; Sherry, Andrew H.

    2016-09-01

    Although hot isostatic pressing (HIP) has been shown to demonstrate significant advances over more conventional manufacture routes, it is important to appreciate and quantify the detrimental effects of oxygen involvement during the HIP manufacture process on the microstructural and material properties of the resulting component. This paper quantifies the effects of oxygen content on the microstructure and Charpy impact properties of HIP'd austenitic stainless steel, through combination of detailed metallographic examination and mechanical testing on HIP'd Type 316L steel containing different concentrations (100 to 190 ppm) of oxygen. Micron-scale pores were visible in the microstructure of the HIP'd materials postmetallographic preparation, which result from the removal of nonmetallic oxide inclusions during metallographic preparation. The area fraction of the resulting pores is shown to correlate with the oxygen concentration which influences the Charpy impact toughness over the temperature range of 77 K to 573 K (-196 °C to 300 °C), and demonstrates the influence of oxygen involved during the HIP manufacture process on Charpy toughness. The same test procedures and microstructural analyses were performed on commercially available forged 316L. This showed comparatively fewer inclusions and exhibited higher Charpy impact toughness over the tested temperature range.

  11. A Microstructural Study on the Observed Differences in Charpy Impact Behavior Between Hot Isostatically Pressed and Forged 304L and 316L Austenitic Stainless Steel

    NASA Astrophysics Data System (ADS)

    Cooper, Adam J.; Cooper, Norman I.; Bell, Andrew; Dhers, Jean; Sherry, Andrew H.

    2015-11-01

    With near-net shape technology becoming a more desirable route toward component manufacture due to its ability to reduce machining time and associated costs, it is important to demonstrate that components fabricated via Hot Isostatic Pressing (HIP) are able to perform to similar standards as those set by equivalent forged materials. This paper describes the results of a series of Charpy tests from HIP'd and forged 304L and 316L austenitic stainless steel, and assesses the differences in toughness values observed. The pre-test and post-test microstructures were examined to develop an understanding of the underlying reasons for the differences observed. The as-received microstructure of HIP'd material was found to contain micro-pores, which was not observed in the forged material. In tested specimens, martensite was detectable within close proximity to the fracture surface of Charpy specimens tested at 77 K (-196 °C), and not detected in locations remote from the fracture surface, nor was martensite observed in specimens tested at ambient temperatures. The results suggest that the observed changes in the Charpy toughness are most likely to arise due to differences in as-received microstructures of HIP'd vs forged stainless steel.

  12. The Holocene shore displacement of Gästrikland, eastern Sweden: a contribution to the knowledge of Scandinavian glacio-isostatic uplift

    NASA Astrophysics Data System (ADS)

    Berglund, Mikael

    2005-09-01

    The shore displacement in Gästrikland, east-central Sweden, has been investigated by means of AMS radiocarbon dating of sediment cores from isolated basins. Twenty dates from 11 sites are presented. Pollen and diatom analyses, and archive material from the Geological Survey of Sweden, have been used to identify isolation intervals in the cores and as chronological support to the 14C dates. An important pollen stratigraphical time-marker is a distinct mid-Holocene increase in Tilia. For the mid-Holocene, pollen stratigraphy is used rather than the 14C dates for the age determination. The deglaciation of Gästrikland, according to the new 14C dates, took place ca. 11 000 cal. yr BP (ca. 9500 14C yr BP). Through the Holocene the shore displacement is regressive. The regression was initially rapid (on average ca. 3.5 m per 100 yr 11 000-7500 cal. yr BP, probably much more rapid at the earliest stage), then slowed down considerably and was from ca. 5000 cal. yr BP (probably already from 7000 cal. yr BP) relatively constant, ca. 0.8-0.9m per 100yr. There are important differences between the shore level curve from Gästrikland and curves from other areas, indicating some irregularities in the regional glacio-isostatic rebound. Copyright

  13. Role of oxidation in the time-dependent failure behavior of hot isostatically pressed silicon nitride at 1,370 C

    SciTech Connect

    Wereszczak, A.A.; Breder, K.; Ferber, M.K. )

    1993-11-01

    Dynamic fatigue studies were conducted on a hot isostatically pressed silicon nitride in ambient air and inert environments using four-point flexure at 1,370 C. Specimens tested in ambient air exhibited a stressing rate dependence with decreased flexure strength with decreased stressing rates. All fracture surfaces of specimens tested in ambient air possessed a sweeping stress-oxidation damage zone that originated at the tensile side of each bend bar. In addition to this stress-oxidation damage, creep damage was concurrently observed in the specimens tested at the slower stressing rates, which appeared to further weaken the material. However, tests conducted in argon or nitrogen revealed flexure strength to be independent of the stressing rate. Creep damage was present at the slower stressing rates, but no stress-oxidation damage was evident similar to that observed on the specimens tested in ambient air. By decoupling the effects of oxidation and creep, it was evident that the former contributed to the formation of a detrimental stress-oxidation damage zone which significantly reduced the strength of this material at 1,370 C.

  14. The nature of isostasy on the moon - How big a Pratt-fall for Airy models. [crustal density-topographic elevation correlation

    NASA Technical Reports Server (NTRS)

    Solomon, S. C.

    1978-01-01

    The correlation between topographic elevation and the major element chemistry of the lunar surface in non-mare regions suggest that a Pratt-type isostatic mechanism may be important in the lunar highlands. Pratt isostasy involves compensation of greater elevation by lower crustal density. Computation of the bulk density from surface chemistry and normative mineralogy, followed by comparisons between calculated density and surface height, is suggested as a means of testing the applicability of the Pratt isostatic model to the moon. A Pratt-type lunar crustal model requires much smaller variations in lunar crustal thickness than those necessitated by a constant-density (Airy) isostatic model. Mechanisms to produce a crust regionally heterogeneous in composition early in lunar differentiation are also required for Pratt isostasy.

  15. The simplest model of jamming

    NASA Astrophysics Data System (ADS)

    Franz, Silvio; Parisi, Giorgio

    2016-04-01

    We study a well known neural network model—the perceptron—as a simple statistical physics model of jamming of hard objects. We exhibit two regimes: (1) a convex optimization regime where jamming is hypostatic and non-critical; (2) a non-convex optimization regime where jamming is isostatic and critical. We characterize the critical jamming phase through exponents describing the distribution laws of forces and gaps. Surprisingly we find that these exponents coincide with the corresponding ones recently computed in high dimensional hard spheres. In addition, modifying the perceptron to a random linear programming problem, we show that isostaticity is not a sufficient condition for singular force and gap distributions. For that, fragmentation of the space of solutions (replica symmetry breaking) appears to be a crucial ingredient. We hypothesize universality for a large class of non-convex constrained satisfaction problems with continuous variables.

  16. Lake Bonneville - Constraints on lithospheric thickness and upper mantle viscosity from isostatic warping of Bonneville, Provo, and Gilbert stage shorelines

    NASA Technical Reports Server (NTRS)

    Bills, Bruce G.; May, Glenn M.

    1987-01-01

    Data collected from three deformed shorelines of Lake Bonneville (the Bonneville, Provo, and Gilbert shorelines) are used to constrain the effective elastic lithospheric thickness to 23 + or - 2 km, the mantle viscosity to (1.2 + or - 0.2) x 10 to the 20th Pa sec, and the depth to a significant viscosity increase to no less than 300 km. A modification of the earth model of Nakiboglu and Lambeck (1982, 1983) is used for the calculations, and the water load is computed at each time step from a digital terrain model and a specified lake elevation. Differences noted between the observed and computed shoreline elevations indicate a regional tilt down to the NE of about 6 x 10 to the -5th, which is suggested to be due to collapse of the peripheral bulge formed by the Laurentide ice sheet.

  17. Assessment of residual stresses on U10Mo alloy based monolithic mini-plates during Hot Isostatic Pressing

    NASA Astrophysics Data System (ADS)

    Ozaltun, Hakan; Herman Shen, M.-H.; Medvedev, Pavel

    2011-12-01

    This article presents an assessment of the residual stresses in U-10 wt.% Mo (U10Mo) alloy based monolithic fuel plates and the elasto-plastic response to thermo-mechanical processing. Monolithic, plate-type fuel is a new fuel form being developed for research and test reactors to achieve higher uranium densities within the reactor core to allow the use of low-enriched uranium fuel in high-performance reactors. Understanding of the three-dimensional residual stress field is important for understanding the in-reactor performance of these plate-type fuels. To define fuel-cladding stress-strain characteristics, a thermo-mechanical finite element model was developed. During fuel plate fabrication, the hot pressing temperature approaches the melting temperature of the cladding, so that temperature dependent material properties were incorporated to improve the accuracy of the model. By using elasto-thermo-plastic material models, it was determined that the cladding material (Al6061-O) is subjected to tensile stresses that exceed its proportional limits. The fuel foil is subject to compressive stresses and remains below yield. The residual stresses in the plates are significant, and therefore, should not be neglected. In particular, the simulations indicate the presence of high stress gradients at the fuel/cladding interface, thus emphasizing the need for a high quality bond.

  18. ASSESSMENT OF RESIDUAL STRESSES ON U10MO ALLOY BASED MONOLITHIC MINI-PLATES DURING HOT ISOSTATIC PRESSING

    SciTech Connect

    Hakan Ozaltun; M.-H. Herman Shen

    2011-12-01

    This article presents an assessment of the residual stress field on U10Mo alloy based monolithic fuel plates and their elasto-plastic response to the thermo-mechanical fabrication process. Monolithic plate-type fuel for research and test reactors is a new fuel form proposed and developed by Idaho National Laboratory (INL) to accomplish higher uranium densities in the reactor core and allow multi-fold reduction of fuel enrichment. Identification of the 3D residual field is critical for benchmarking the new design and understanding the overall performance of the new plate-type fuels. To define fuel-cladding stress-strain characteristics, a new thermo-mechanical finite element model was developed. Material properties at high temperatures and material plasticity were considered carefully to improve the accuracy as the Hot Pressing temperature reaches the melting temperature of the cladding material. By using elasto-thermo-plastic material models, it was determined that the cladding material (AL6061-TO) is exposed to tensile stress field and exceeds its proportional limits, while the fuel foil (U10Mo) is under compression and remains below its yield limit. It was shown that the residual stresses would govern the overall behavior of the plates, and therefore, should not be neglected. In particular, the simulations have revealed the existence of stress gradients at the fuel/cladding interface, thus emphasizing the necessity of excellent bonding quality at the bond region for mechanical endurance.

  19. Resolving Trends in Antarctic Ice Sheet Mass Loss and Glacio-isostatic Adjustment Through Spatio-temporal Source-separation

    NASA Astrophysics Data System (ADS)

    Bamber, J. L.; Schoen, N.; Zammit-Mangion, A.; Rougier, J.; Flament, T.; Luthcke, S. B.; Petrie, E. J.; Rémy, F.

    2013-12-01

    There remains considerable inconsistency between different methods and approaches for determining ice mass trends for Antarctica from satellite observations. There are three approaches that can provide near global coverage for mass trends: altimetry, gravimetry and mass budget calculations. All three approaches suffer from a source separation problem where other geophysical processes limit the capability of the method to resolve the origin and magnitude of a mass change. A fourth approach, GPS vertical motion, provides localised estimates of mass change due to elastic uplift and an indirect estimate of GIA. Each approach has different source separation issues and different spatio-temporal error characteristics. In principle, it should be possible to combine the data and process covariances to minimize the uncertainty in the solution and to produce robust, posterior errors for the trends. In practice, this is a challenging problem in statistics because of the large number of degrees of freedom, the variable spatial and temporal sampling between the different observations and the fact that some processes remain under-sampled, such as firn compaction. Here, we present a novel solution to this problem using the latest methods in statistical modelling of spatio-temporal processes. We use Bayesian hierarchical modelling and employ stochastic partial differential equations to capture our physical understanding of the key processes that influence our observations. Due to the huge number of observations involved (> 10^8) methods are required to reduce the dimensionality of the problem and care is required in treatment of the observations as they are not independent. Here, we focus mainly on the results rather than the full suite of methods and we present time evolving fields of surface mass balance, ice dynamic-driven mass loss, and firn compaction for the period 2003-2009, derived from a combination of ICESat, ENVISAT, GRACE, InSAR, GPS and regional climate model output

  20. Growth kinetics and microstructural evolution during hot isostatic pressing of U-10 wt.% Mo monolithic fuel plate in AA6061 cladding with Zr diffusion barrier

    SciTech Connect

    Y. Park; J. Yoo; K. Huang; D. D. Keiser, Jr.; J. F. Jue; B. Rabin; G. Moore; Y. H. Sohn

    2014-04-01

    Phase constituents and microstructure changes in RERTR fuel plate assemblies as functions of temperature and duration of hot-isostatic pressing (HIP) during fabrication were examined. The HIP process was carried out as functions of temperature (520, 540, 560 and 580 °C for 90 min) and time (45–345 min at 560 °C) to bond 6061 Al-alloy to the Zr diffusion barrier that had been co-rolled with U-10 wt.% Mo (U10Mo) fuel monolith prior to the HIP process. Scanning and transmission electron microscopies were employed to examine the phase constituents, microstructure and layer thickness of interaction products from interdiffusion. At the interface between the U10Mo and Zr, following the co-rolling, the UZr2 phase was observed to develop adjacent to Zr, and the a-U phase was found between the UZr2 and U10Mo, while the Mo2Zr was found as precipitates mostly within the a-U phase. The phase constituents and thickness of the interaction layer at the U10Mo-Zr interface remained unchanged regardless of HIP processing variation. Observable growth due to HIP was only observed for the (Al,Si)3Zr phase found at the Zr/AA6061 interface, however, with a large activation energy of 457 ± 28 kJ/mole. Thus, HIP can be carried to improve the adhesion quality of fuel plate without concern for the excessive growth of the interaction layer, particularly at the U10Mo-Zr interface with the a-U, Mo2Zr, and UZr2 phases.

  1. Growth kinetics and microstructural evolution during hot isostatic pressing of U-10 wt.% Mo monolithic fuel plate in AA6061 cladding with Zr diffusion barrier

    NASA Astrophysics Data System (ADS)

    Park, Y.; Yoo, J.; Huang, K.; Keiser, D. D.; Jue, J. F.; Rabin, B.; Moore, G.; Sohn, Y. H.

    2014-04-01

    Phase constituents and microstructure changes in RERTR fuel plate assemblies as functions of temperature and duration of hot-isostatic pressing (HIP) during fabrication were examined. The HIP process was carried out as functions of temperature (520, 540, 560 and 580 °C for 90 min) and time (45-345 min at 560 °C) to bond 6061 Al-alloy to the Zr diffusion barrier that had been co-rolled with U-10 wt.% Mo (U10Mo) fuel monolith prior to the HIP process. Scanning and transmission electron microscopies were employed to examine the phase constituents, microstructure and layer thickness of interaction products from interdiffusion. At the interface between the U10Mo and Zr, following the co-rolling, the UZr2 phase was observed to develop adjacent to Zr, and the α-U phase was found between the UZr2 and U10Mo, while the Mo2Zr was found as precipitates mostly within the α-U phase. The phase constituents and thickness of the interaction layer at the U10Mo-Zr interface remained unchanged regardless of HIP processing variation. Observable growth due to HIP was only observed for the (Al,Si)3Zr phase found at the Zr/AA6061 interface, however, with a large activation energy of 457 ± 28 kJ/mole. Thus, HIP can be carried to improve the adhesion quality of fuel plate without concern for the excessive growth of the interaction layer, particularly at the U10Mo-Zr interface with the α-U, Mo2Zr, and UZr2 phases.

  2. Erosional dynamics, flexural isostasy, and long-lived escarpments: A numerical modeling study

    NASA Technical Reports Server (NTRS)

    Tucker, Gregory E.; Slingerland, Rudy L.

    1994-01-01

    Erosional escarpments common features of high-elevation rifted continets. Fission track data suffest that these escarpments form by base level lowering and/or marginal uplift during rifting, followed by lateral retreat of an erosion front across tens to hundreds of kioometers. Previous modeling studies have shown that this characteristic pattern of denudation can have a profound impact upon marginal isostatic uplift and the evolution of offshore sedimentary basins. Yet at present there is only a rudimentary understanding of the geomorphic mechanisms capable of driving such prolonged escarpment retreat. In this study we present a nonlinear, two-dimensional landscape evolution model tha tis used to asses the necessary and sufficient conditions for long-term retreat of a rift-generated escarpment. The model represents topography as a grid of cells, with drainage networkds evolving as water flows across the grid in the direction of steepest descent. The model accounts for sediment production by weathering, fluvial sediment transport, bedrock channel erosion, and hillslope sediment transport by diffusive mechanisms and by mass failure. Numerical experiments presented explore the effects of different combinations of erosion processes and of dynamic coupling between denudation and flexural isostatic uplift. Model results suggest that the necessary and sufficient conditions for long-term escarpment retreat are (1) incising bedrock channels in which the erosion rate increases with increasing drainage area, so that the channels steepen and propagate headward; (2) a low rate of sediment production relative to sediment transport efficiency, which promotes relief-generating processes over diffusive ones; (3) high continental elevation, which allows greater freedom for fluvial dissection; and (4) any process, including flexural isostatic uplift, that helps to maintain a drainage divide near an escarpment crest. Flexural isostatic uplift also facilitates escarpment, thereby

  3. Vacuum isostatic micro/macro molding of PTFE materials for laser beam shaping in environmental applications: large scale UV laser water purification

    NASA Astrophysics Data System (ADS)

    Lizotte, Todd; Ohar, Orest

    2009-08-01

    Accessibility to fresh clean water has determined the location and survival of civilizations throughout the ages [1]. The tangible economic value of water is demonstrated by industry's need for water in fields such as semiconductor, food and pharmaceutical manufacturing. Economic stability for all sectors of industry depends on access to reliable volumes of good quality water. As can be seen on television a nation's economy is seriously affected by water shortages through drought or mismanagement and as such those water resources must therefore be managed both for the public interest and the economic future. For over 50 years ultraviolet water purification has been the mainstay technology for water treatment, killing potential microbiological agents in water for leisure activities such as swimming pools to large scale waste water treatment facilities where the UV light photo-oxidizes various pollutants and contaminants. Well tailored to the task, UV provides a cost effective way to reduce the use of chemicals in sanitization and anti-biological applications. Predominantly based on low pressure Hg UV discharge lamps, the system is plagued with lifetime issues (~1 year normal operation), the last ten years has shown that the technology continues to advance and larger scale systems are turning to more advanced lamp designs and evaluating solidstate UV light sources and more powerful laser sources. One of the issues facing the treatment of water with UV lasers is an appropriate means of delivering laser light efficiently over larger volumes or cross sections of water. This paper examines the potential advantages of laser beam shaping components made from isostatically micro molding microstructured PTFE materials for integration into large scale water purification and sterilization systems, for both lamps and laser sources. Applying a unique patented fabrication method engineers can form micro and macro scale diffractive, holographic and faceted reflective structures

  4. Expressions for the Global Gravimetric Moho Modeling in Spectral Domain

    NASA Astrophysics Data System (ADS)

    Tenzer, Robert; Chen, Wenjin

    2014-08-01

    We apply a newly developed numerical method to improve the Moho geometry by the implementation of gravity data. This method utilizes expressions for the gravimetric forward and inverse modeling derived in a frequency domain. Methods for a spectral analysis and synthesis of the gravity field and crust density structures are applied in the gravimetric forward modeling of the consolidated crust-stripped gravity disturbances, which have a maximum correlation with the (a priori) Moho model. These gravity disturbances are obtained from the Earth's gravity disturbances after applying the topographic and stripping gravity corrections of major known anomalous crust density structures; in the absence of a global mantle model, mantle density heterogeneities are disregarded. The isostatic scheme applied is based on a complete compensation of the crust relative to the upper mantle density. The functional relation is established between the (unknown) Moho depths and the complete crust-stripped isostatic gravity disturbances, which according to the adopted isostatic scheme have (theoretically) a minimum correlation with the Moho geometry. The system of observation equations, which describes the relation between spherical functions of the isostatic gravity field and the Moho geometry, is defined by means of a linearized Fredholm integral equation of the first kind. The Moho depths are determined based on solving the gravimetric inverse problem. The regularization is applied to stabilize the ill-posed solution. This numerical procedure is utilized to determine the Moho depths globally. The gravimetric result is presented and compared with the seismic Moho model. Our gravimetric result has a relatively good agreement with the CRUST2.0 Moho model by means of the RMS of differences (of 3.5 km). However, the gravimetric solution has a systematic bias. We explain this bias between the gravimetric and seismic Moho models by the unmodelled mantle heterogeneities and uncertainties in the

  5. The critical parameters in in-situ MgB2 wires and tapes with ex-situ MgB2 barrier after hot isostatic pressure, cold drawing, cold rolling and doping

    NASA Astrophysics Data System (ADS)

    Gajda, D.; Morawski, A.; Zaleski, A. J.; Häßler, W.; Nenkov, K.; Rindfleisch, M. A.; Żuchowska, E.; Gajda, G.; Czujko, T.; Cetner, T.; Hossain, M. S. A.

    2015-05-01

    MgB2 precursor wires were prepared using powder in tube technique by Institute of High Pressure PAS in Warsaw. All samples were annealed under isostatic pressure generated by liquid Argon in the range from 0.3 GPa to 1 GPa. In this paper, we show the effects of different processing routes, namely, cold drawing (CD), cold rolling (CR), hot isostatic pressure (HIP) and doping on critical current density (Jc), pinning force (Fp), irreversible magnetic-field (Birr), critical temperature (Tc), n value, and dominant pinning mechanism in MgB2/Fe wires with ex situ MgB2 barrier. The results show that medium pressures (˜0.35 GPa) lead to high Jc in low and medium magnetic fields (0 T - 9 T). On the other hand, higher pressures (˜1 GPa) lead to enhanced Jc in high magnetic fields (above 9 T). Transport measurements show that CD, CR, and HIP have small effects on Birr and Tc, but CD, CR, HIP, and doping enhance Jc and Fp in in situ MgB2 wires with ex situ MgB2 barrier. Transport measurements on in situ undoped MgB2 wire with ex situ MgB2 barrier yield a Jc of about 100 A/mm2 at 4.2 K in 6 T, at 10 K in 4 T and at 20 K in 2 T. The results also show that cold drawing causes increase of n value.

  6. Growth and ferroelectric properties of Pb(Zr 0.52Ti 0.48)O 3 thin films crystallized on MgO single-crystal substrates by hot isostatic pressing

    NASA Astrophysics Data System (ADS)

    Kobune, Masafumi; Nishioka, Yusuke; Inoue, Tomoaki; Yazawa, Tetsuo

    2005-02-01

    Pb(Zr 0.52Ti 0.48)O 3 films with highly uniform c-axis orientation were fabricated on PbTiO 3 (PT) /Pt(1 0 0)/MgO(1 0 0) substrates from the amorphous state by hot isostatic pressing (HIP). The seven PZT films HIP-treated by single- and multi-step annealing indicated almost preferential (0 0 1) orientation with the degree of the c-axis orientation, α=0.89-0.99. The PZT films treated according to a one-step (700 °C) annealing program had a good squareness of the hysteresis curves. The PZT capacitors with high initial pulse-derived switchable polarization ( Qsw) and a simple Pt/PZT/PT/Pt/MgO structure fabricated using an HIP technique a one-step (700 °C) annealing program can be expected as high endurance ferroelectric ones for FeRAM applications.

  7. The evolution of impact basins - Viscous relaxation of topographic relief. [for lunar surface modeling

    NASA Technical Reports Server (NTRS)

    Solomon, S. C.; Comer, R. P.; Head, J. W.

    1982-01-01

    A topographic profile of the young large lunar basin, Orientale, is presented in order to examine the effects of viscous relaxation on basin topography. Analytical models for viscous flow are considered, showing a wavelength-dependence of time constants for viscous decay on the decrease in viscosity with depth and on the extent of the isostatic compensation of the initial topography. Lunar rheological models which are developed include a half-space model for uniform Newtonian viscosity, density, and gravitational acceleration, a layer over inviscid half space model with material inviscid over geological time scales, and a layer with isostatic compensation where a uniformly viscous layer overlies an inviscid half space of higher density. Greater roughness is concluded, and has been observed, on the moon's dark side due to continued lower temperatures since the time of heavy bombardment.

  8. Modelling of the Global Geopotential Energy & Stress Field

    NASA Astrophysics Data System (ADS)

    Schiffer, C.; Nielsen, S. B.

    2012-04-01

    Lateral density and topography variations yield in and important contribution to the lithospheric stress field. The leading quantity is the Geopotential Energy, the integrated lithostatic pressure in a rock column. The horizontal gradient of this quantity is related to horizontal stresses through the Equations of equilibrium of stresses. The Geopotential Energy furthermore can be linearly related to the Geoid under assumption of local isostasy. Satellite Geoid measurements contain, however, also non-isostatic deeper mantle responses of long wavelength. Unfortunately, high-pass filtering of the Geoid does not suppress only the deeper sources. The age-dependent signal of the oceanic lithosphere, for instance, is of long wave length and a prominent representative of in-plane stress, derived from the horizontal gradient of isostatic Geoid anomalies and responsible for the ridge push effect. Therefore a global lithospheric density model is required in order to isolate the shallow Geoid signal and calculate the stress pattern from isostatically compensated lithospheric sources. We use a linearized inverse method to fit a lithospheric reference model to observations such as topography and surface heat flow in the presence of local isostasy and a steady state geotherm. Subsequently we use a FEM code to solve the Equations of equilibrium of stresses for a three dimensional elastic shell. The modelled results are shown and compared with the global stress field and other publications.

  9. Geodetic use of global digital terrain and crustal databases in gravity field modeling and interpretation

    NASA Astrophysics Data System (ADS)

    Tsoulis, D.

    2013-03-01

    The release of global digital databases for the description of the Earth's topography and the shape of the Earth's crust in terms of consistency and geometry initiates a new era in the interpretation and analysis of the observed gravity field of our planet. The permanent increase in resolution of these databases permits furthermore the identification of high frequency gravity field components, a feature that is of special interest in applications of local or regional scales. The derivation of topographic/isostatic gravity models is the tool which reveals the gravity content of terrain and crustal databases in the spectral domain. We review the significance of some current global digital models in the frame of this analysis by computing distinct spectral gravity quantities and compare them against the Kaula rule of the gravity signal decay and the recently released reference gravity model EGM2008. The different isostatic hypothesis that can be applied in the derivation of a topographic/isostatic model as well its dependency with the increasing harmonic degree is demonstrated and quantified in terms of geoid heights and gravity anomalies. It is shown that the two fundamental compensation mechanisms, namely Airy and Pratt, act complementary in terms of their compensation effect to the uncompensated topography spectrum. The Airy mechanism reduces the uncompensated topography in the longer and medium wavelength part of the spectrum (up to degree 400), while Pratt acts in a compensating manner only for the high to very high frequencies, from degree 100 and onwards.

  10. An assessment of crustal thickness variations on the lunar near side - Models, uncertainties, and implications for crustal differentiation

    NASA Technical Reports Server (NTRS)

    Thurber, C. H.; Solomon, S. C.

    1978-01-01

    The paper presents a series of models for the structure of lunar nearside crust which are consistent with the observed gravity and topography. Each crustal model is derived subject to a specific set of constraints and assumptions. The assumptions/constraints considered include strict isostatic equilibrium, pure Airy compensation mechanism, pure Pratt compensation mechanism, assignment of assumed fixed values for mare basalt thickness, and attribution of all superisostatic mass in the maria to basalt fill. The resulting models are used to assess the degree and mechanism of isostasy, and to investigate the thickness of the mare basalt. Details of the lateral variations in crustal thickness or density and in the degree of isostatic compensation bear strongly on the mode of early crustal differentiation and on the subsequent thermal history of the moon.

  11. Influence of hot isostatic pressing on the structure and properties of an innovative low-alloy high-strength aluminum cast alloy based on the Al-Zn-Mg-Cu-Ni-Fe system

    NASA Astrophysics Data System (ADS)

    Akopyan, T. K.; Padalko, A. G.; Belov, N. A.

    2015-11-01

    Hot isostatic pressing (HIP) is applied for treatment of castings of innovative low-ally high-strength aluminum alloy, nikalin ATs6N0.5Zh based on the Al-Zn-Mg-Cu-Ni-Fe system. The influence of HIP on the structure and properties of castings is studied by means of three regimes of barometric treatment with different temperatures of isometric holding: t 1 = 505 ± 2°C, p 1 = 100 MPa, τ1 = 3 h (HIP1); t 2 = 525 ± 2°C, p 2 = 100 MPa, τ2 = 3 h (HIP2); and t 3 = 545 ± 2°C, p 3 = 100 MPa, τ3 = 3 h (HIP3). It is established that high-temperature HIP leads to actually complete elimination of porosity and additional improvement of the morphology of second phases. Improved structure after HIP provides improvement properties, especially of plasticity. In particular, after heat treatment according of regime HIP2 + T4 (T4 is natural aging), the alloy plasticity is improved by about two times in comparison with the initial state (from ~6 to 12%). While applying regime HIP3 + T6 (T6 is artificial aging for reaching the maximum strength), the plasticity has improved by more than three times in comparison with the initial state, as after treatment according to regimes HIP1 + T6 and HIP2 + T6 (from ~1.2 to ~5.0%), which are characterized by a lower HIP temperature.

  12. Analysis of gravity and topography in the GLIMPSE study region: Isostatic compensation and uplift of the Sojourn and Hotu Matua Ridge systems

    USGS Publications Warehouse

    Harmon, N.; Forsyth, D.W.; Scheirer, D.S.

    2006-01-01

    The Gravity Lieations Intraplate Melting Petrologic and Seismic Expedition (GLIMPSE) Experiment investigated the formation of a series of non-hot spot, intraplate volcanic ridges in the South Pacific and their relationship to cross-grain gravity lineaments detected by satellite altimetry. Using shipboard gravity measurements and a simple model of surface loading of a thin elastic plate, we estimate effective elastic thicknesses ranging from ???2 km beneath the Sojourn Ridge to a maximum of 10 km beneath the Southern Cross Seamount. These elastic thicknesses are lower than predicted for the 3-9 Ma seafloor on which the volcanoes lie, perhaps due to reheating and thinning of the plate during emplacement. Anomalously low apparent densities estimated for the Matua and Southern Cross seamounts 2050 and 2250 kg m-3, respectively, probably are artifacts caused by the assumption of only surface loading, ignoring the presence of subsurface loading in the form of underplated crust and/or low-density mantle. Using satellite free-air gravity and shipboard bathymetry, we calculate the age-detrended, residual mantle Bouguer anomaly (rMBA). The rMBA corrects the free-air anomaly for the direct effects of topography, including the thickening of the crust beneath the seamounts and volcanic ridges due to surface loading of the volcanic edifices. There are broad, negative rMBA anomalies along the Sojourn and Brown ridges and the Hotu Matua seamount chain that extend nearly to the East Pacific Rise. These negative rMBA anomalies connect to negative free-air anomalies in the western part of the study area that have been recognized previously as the beginnings of the cross-grain gravity lineaments. Subtracting the topographic effects of surface loading by the ridges and seamounts from the observed topography reveals that the ridges are built on broad bands of anomalously elevated seafloor. This swell topography and the negative rMBA anomalies contradict the predictions of lithospheric

  13. Microstructure and Mechanical Properties of Long Ti-6Al-4V Rods Additively Manufactured by Selective Electron Beam Melting Out of a Deep Powder Bed and the Effect of Subsequent Hot Isostatic Pressing

    NASA Astrophysics Data System (ADS)

    Lu, S. L.; Tang, H. P.; Ning, Y. P.; Liu, N.; StJohn, D. H.; Qian, M.

    2015-09-01

    An array of eight long Ti-6Al-4V rods (diameter: 12 mm; height: 300 mm) have been additively manufactured, vertically and perpendicular to the powder bed, by selective electron beam melting (SEBM). The purpose was to identify and understand the challenges of fabricating Ti-6Al-4V samples or parts from a deep powder bed (more than 200-mm deep) by SEBM and the necessity of applying post heat treatment. The resulting microstructure and mechanical properties of these Ti-6Al-4V rods were characterized along their building ( i.e., axial) direction by dividing each rod into three segments (top, middle, and bottom), both before ( i.e., as-built) and after hot isostatic pressing (HIP). The as-built microstructure of each rod was inhomogeneous; it was coarsest in the top segment, which showed a near equilibrium α- β lamellar structure, and finest in the bottom segment, which featured a non-equilibrium mixed structure. The tensile properties varied along the rod axis, especially the ductility, but all tensile properties met the requirements specified by ASTM F3001-14. HIP increased the relative density from 99.03 pct of the theoretical density (TD) to 99.90 pct TD and homogenized the microstructure thereby leading to highly consistent tensile properties along the rod axis. The temperature of the stainless steel substrate used in the powder bed was monitored. The as-built inhomogeneous microstructure is attributed to the temperature gradient in the deep powder bed. Post heat treatment is thus necessary for Ti-6Al-4V samples or parts manufactured from a deep powder bed by SEBM. This differs from the additive manufacturing of small samples or parts from a shallow powder bed (less than 100-mm deep) by SEBM.

  14. Eastern Aleutian volcanic arc digital model - version 1.0

    USGS Publications Warehouse

    Saltus, R.W.; Barnett, Adrienne

    2000-01-01

    A 3-dimensional model (Figure 1) of the interaction of oceanic and continental tectonic plates along the eastern portion of the Aleutian volcanic arc helps in the visualization of basic tectonic, geodetic, and geophysical data in this active plate boundary region. The model is constrained by topographic, bathymetric, and seismic data and by the principle of isostasy. Examination of free-air gravity anomalies over the region indicates where the flexural strength of the down-going oceanic slab disturbs local isostatic balance and where low-density sediments have accumulated in the trench and forearc regions.

  15. Preliminary model of the pre-Tertiary basement rocks beneath Yucca Flat, Nevada Test Site, Nevada, based on analysis of gravity and magnetic data

    SciTech Connect

    Phelps, G.A.; McKee, E.H.; Sweetkind, D.; and Langenheim, V.E.

    2000-04-18

    Structures in the pre-Tertiary basement of Yucca Flat, Nevada Test Site, Nevada, are interpreted using the basement topography and basement gravity anomaly derived from an isostatic gravity inversion model. A new fault is proposed which eliminates some of the Paleozoic carbonate section just west of the Halfpint Range. Proposed faults that offset basement surface correlate closely with magnetic anomalies caused by the offset of Tertiary volcanic rocks.

  16. Microwave combustion and sintering without isostatic pressure

    SciTech Connect

    Ebadian, M.A.

    1998-01-01

    In recent years interest has grown rapidly in the application of microwave energy to the processing of ceramics, composites, polymers, and other materials. Advances in the understanding of microwave/materials interactions will facilitate the production of new ceramic materials with superior mechanical properties. One application of particular interest is the use of microwave energy for the mobilization of uranium for subsequent redeposition. Phase III (FY98) will focus on the microwave assisted chemical vapor infiltration tests for mobilization and redeposition of radioactive species in the mixed sludge waste. Uranium hexachloride and uranium (IV) borohydride are volatile compounds for which the chemical vapor infiltration procedure might be developed for the separation of uranium. Microwave heating characterized by an inverse temperature profile within a preformed ceramic matrix will be utilized for CVI using a carrier gas. Matrix deposition is expected to commence from the inside of the sample where the highest temperature is present. The preform matrix materials, which include aluminosilicate based ceramics and silicon carbide based ceramics, are all amenable to extreme volume reduction, densification, and vitrification. Important parameters of microwave sintering such as frequency, power requirement, soaking temperature, and holding time will be investigated to optimize process conditions for the volatilization of uranyl species using a reactive carrier gas in a microwave chamber.

  17. MICROWAVE COMBUSTION AND SINTERING WITHOUT ISOSTATIC PRESSURE

    SciTech Connect

    M.A. Ebadian, Ph.D.

    1999-01-01

    This project is devoted to the development of an innovative technique for the disposal of mixed waste utilizing microwave energy. Because most uranium and plutonium components as well as most fission products have dielectric properties that allow excellent microwave and high-frequency energy coupling, dielectric heating has the potential for application in many processes for treating hazardous wastes. This technology, whether used on its own or as hybrid in conjunction with a conventional process, has positive features, such as energy efficiency. increased throughput, volume reduction, and reduction of disposal and transportation cost, and provides a technique not feasible by conventional means. The hazardous waste will be converted into a dense, stable, and vitrified form so that it may qualify for eventual off-site disposal. If successful, this program will lead to major cost saving for the DOE system.

  18. Microwave Combustion and Sintering Without Isostatic Pressure

    SciTech Connect

    Ebadian, M.A.; Monroe, N.D.H.

    1998-10-20

    This investigation involves a study of the influence of key processing parameters on the heating of materials using microwave energy. Selective and localized heating characteristics of microwaves will be utilized in the sintering of ceramics without hydrostatic pressure. In addition, combustion synthesis will be studied for the production of powders, carbides, and nitrides by combining two or more solids or a solid and a gas to form new materials. The insight gained from the interaction of microwaves with various materials will be utilized in the mobilization and subsequent redeposition of uranium.

  19. Modeling Late Quaternary discharge of the Mississippi River system

    SciTech Connect

    Craig, R.G.; Orndorff, R. . Dept. of Geology)

    1992-01-01

    The authors estimate discharge in the Mississippi River system during various stages of Lake Agassiz and configurations of the Laurentide Ice Sheet, using a numerical representation of elements defining the hydrologic system. Ice sheet margins and isostatic depression due to ice sheet load are digitized from published maps. Terrain is represented with a digital elevation model (DEM) at 10 km spacing. Drainage, and the positions of ice marginal lakes are computed from the DEM after superposing the ice sheet configuration and isostatic depression. Meltwater supply is computed using the method of Teller (1990). Non-glacial runoff is computed as a constant change (nominally 2x) from published modern values of unit area runoff. Computations are limited to average annual values; short term floods and seasonal variations are not represented. They test the model by comparisons of discharge estimates--using modern drainage configurations and runoff values--to those available from gauging stations. They also compare their estimate of glacial discharge, without increasing modern non-glacial runoff, to that of Teller (1990). Using Laurentide runoff and incremented non-glacial discharge estimates based on paleoclimatic evidence, they compute significantly larger discharges than those reported by Teller (1990). This is primarily due to increased non-glacial runoff. This model provides a basis for pointwise comparisons to field evidence at critical sites.

  20. Lunar mascons - Another model and its implications

    NASA Technical Reports Server (NTRS)

    Kunze, A. W. G.

    1974-01-01

    A mascon model is proposed in which the mass excess of the mare basalts in the circular maria is supported isostatically by mass deficits at depth. The model predicts the observed positive gravity anomalies surrounded by negative ring anomalies and explains the absence of gravity anomalies over the irregular maria. The model implies that mare basalts were derived by partial melting of a source region at depth due to pressure relief resulting from the excavation of the circular mare basins, and that the crystalline residuum in the source region is of lower density than the original source rock. The trace element enrichment and near cotectic character of Apollo 11 and 12 lavas reported by some investigators may be caused by extensive magma fractionation enroute from an origin in the circular maria to the final, distant emplacement sites.

  1. Modeling shear instability and fracture in dynamically deformed Al/W granular composites

    NASA Astrophysics Data System (ADS)

    Olney, Karl; Benson, David; Nesterenko, Vitali F.

    2012-03-01

    Aluminum/Tungsten granular composites are materials which combine high density and strength with bulk distributed fracture of Al matrix into small particles under impact or shock loading. They are processed using cold and hot isostatic pressing of W particles/rods in the matrix of Al powder. Numerical models were used to elucidate the dynamic behavior of these materials under dynamic conditions simulating low velocity high energy impact in drop weight test (10 m/s). It was demonstrated that arrangement of W components and bonding between Al particles dramatically affect the samples shear localization and mode of fracture of the Al matrix in agreement with experiments.

  2. Elastic thickness of the lithosphere and tectonic evolution: implications for GIA models

    NASA Astrophysics Data System (ADS)

    Amantov, Aleksey; Fjeldskaar, Willy

    2015-04-01

    Rheological properties used in GIA models require independent verifications and possible modifications. To estimate the flexural rigidity of the lithosphere in simple platform areas we use peneplain distortion, which enable us to compute isostatic response from sediment load and compare the results with observed changes in geometry. This was done for several different platform regions: - Baltic (Fennoscandian) Shield, including structural elements of the Russian Platform - Barents Sea platform areas - Kara and Western Siberian domain - Eastern Siberian Platform In the East European and East Siberian old cratons we modeled isostatic distortion of Neoproterozoic Ediacaran peneplain and some other relevant surfaces. For the Arctic we used Mid-Late Jurassic surface (JP) as a distinct unconformity and well-traced (by seismic and well data) surface in the Arctic region. The isostatic distortion of peneplains under sediment load / erosion for the old Archean - Proterozoic cratons in general confirms earlier rheology model with the flexural rigidity of the lithosphere around 5x10**23 Nm (effective elastic thickness of 30-40 km), but could be slightly lower in the Barents basins. Deviations are generally relatively small and could be explained by e.g. by averaging over fault-zones, tectonic events, compaction structures and density variations. However, the situation for the Kara-Western Siberian domain is very different, with large deviations between observations and calculations. With a slight reduction of the effective elastic thickness in the Kara Sea to 10-20 km the fit is much better. Based on the results we suggest two different major types of lithosphere rigidity in the area. This seems reasonable because they typify domains with different crustal age. Western Siberian platform, with Kara continuation has much younger basement, in addition to significant magmatic activity and Early Mesosoic extension. The lithosphere rigidity is a function of age and temperature; as

  3. On a spectral method for forward gravity field modelling

    NASA Astrophysics Data System (ADS)

    Root, B. C.; Novák, P.; Dirkx, D.; Kaban, M.; van der Wal, W.; Vermeersen, L. L. A.

    2016-07-01

    This article reviews a spectral forward gravity field modelling method that was initially designed for topographic/isostatic mass reduction of gravity data. The method transforms 3D spherical density models into gravitational potential fields using a spherical harmonic representation. The binomial series approximation in the approach, which is crucial for its computational efficiency, is examined and an error analysis is performed. It is shown that, this method cannot be used for density layers in crustal and upper mantle regions, because it results in large errors in the modelled potential field. Here, a correction is proposed to mitigate this erroneous behaviour. The improved method is benchmarked with a tesseroid gravity field modelling method and is shown to be accurate within ±4 mGal for a layer representing the Moho density interface, which is below other errors in gravity field studies. After the proposed adjustment the method can be used for the global gravity modelling of the complete Earth's density structure.

  4. Moho depth model from GOCE gravity gradient data for the Central Asian Orogenic Belt

    NASA Astrophysics Data System (ADS)

    Guy, Alexandra; Holzrichter, Nils; Ebbing, Jörg

    2016-04-01

    GOCE gravity gradient data are used together with published seismic data to determine the Moho geometry and the isostatic state of the Central Asian Orogenic Belt (CAOB). The CAOB is an accretionary orogen formed during the Palaeozoic at the periphery of the Siberian cratonic nucleus by the successive amalgamation of different types of crust (cratonic, oceanic, passive margin, magmatic arc, back-arc, ophiolites, accretionary wedge) followed by an oroclinal bending during Permian-Triassic times. This large area was and is still of great interest for geoscientific studies mainly because of its potential in mineral and fossil resources and also for its outstanding, but still misunderstood, geodynamic evolution. However, the geophysical investigations remain scarce due to the remoteness of the area. A systematic analysis of the crustal thickness has been omitted yet, although the geometry of the crust-mantle boundary (Moho boundary) provides crucial information on the evolution of the lithosphere and on the coupling between upper mantle and the crust - particularly interesting for oroclinal bending processes. In this study, the gravity gradient data of GOCE are used to investigate the topography of the Moho for Mongolia and its surroundings. In addition, we used inversion of gravity data and calculation of the isostatic Moho from topographic data to the World Gravity Map (WGM) 2012 satellite-terrestrial model of the Earth's gravity anomalies and these results are compared together with those obtained for the GOCE gravity data. The results of the gravity inversion are constrained by the few xenolith studies and the seismic data available: the receiver function seismic method for north and central Mongolia, deep seismic sounding and seismic reflection profiles in northern China; and tomography in southern Siberia. Then, the effects of isostatic compensation are evaluated by the comparison between the results of the gravity inversion and the isostatic Moho. Finally, a 3D

  5. Dynamic topography in subduction zones: insights from laboratory models

    NASA Astrophysics Data System (ADS)

    Bajolet, Flora; Faccenna, Claudio; Funiciello, Francesca

    2014-05-01

    The topography in subduction zones can exhibit very complex patterns due to the variety of forces operating this setting. If we can deduce the theoretical isostatic value from density structure of the lithosphere, the effect of flexural bending and the dynamic component of topography are difficult to quantify. In this work, we attempt to measure and analyze the topography of the overriding plate during subduction compared to a pure shortening setting. We use analog models where the lithospheres are modeled by thin-sheet layers of silicone putty lying on low-viscosity syrup (asthenosphere). The model is shorten by a piston pushing an oceanic plate while a continental plate including a weak zone to localize the deformation is fixed. In one type of experiments, the oceanic plate bends and subducts underneath the continental one; in a second type the two plates are in contact without any trench, and thus simply shorten. The topography evolution is monitored with a laser-scanner. In the shortening model, the elevation increases progressively, especially in the weak zone, and is consistent with expected isostatic values. In the subduction model, the topography is characterized, from the piston to the back-wall, by a low elevation of the dense oceanic plate, a flexural bulge, the trench forming a deep depression, the highly elevated weak zone, and the continental upper plate of intermediate elevation. The topography of the upper plate is consistent with isostatic values for very early stages, but exhibits lower elevations than expected for later stages. For a same amount of shortening of the continental plate, the thickening is the same and the plate should have the same elevation in both types of models. However, comparing the topography at 20, 29 and 39% of shortening, we found that the weak zone is 0.4 to 0.6 mm lower when there is an active subduction. Theses values correspond to 2.6 to 4 km in nature. Although theses values are high, there are of the same order as

  6. Understanding subsidence in the Mississippi Delta region due to sediment, ice, and ocean loading: Insights from geophysical modeling

    NASA Astrophysics Data System (ADS)

    Wolstencroft, Martin; Shen, Zhixiong; Törnqvist, Torbjörn E.; Milne, Glenn A.; Kulp, Mark

    2014-04-01

    The processes responsible for land surface subsidence in the Mississippi Delta (MD) have been vigorously debated. Numerous studies have postulated a dominant role for isostatic subsidence associated with sediment loading. Previous computational modeling of present-day vertical land motion has been carried out in order to understand geodetic data. While the magnitudes of these measured rates have been reproduced, the model parameter values required have often been extreme and, in some cases, unrealistic. In contrast, subsidence rates in the MD on the 103 year timescale due to delta loading estimated from relative sea level reconstructions are an order of magnitude lower. In an attempt to resolve this conflict, a sensitivity analysis was carried out using a spherically symmetric viscoelastic solid Earth deformation model with sediment, ice, and ocean load histories. The model results were compared with geologic and geodetic observations that provide a record of vertical land motion over three distinctly different timescales (past 80 kyr, past 7 kyr, and past ~15 years). It was found that glacial isostatic adjustment is likely to be the dominant contributor to vertical motion of the Pleistocene and underlying basement. Present-day basement subsidence rates solely due to sediment loading are found to be less than ~0.5 mm yr-1. The analysis supports previous suggestions in the literature that Earth rheology parameters are time dependent. Specifically, the effective elastic thickness of the lithosphere may be <50 km on a 105 year timescale, but closer to 100 km over 103 to 104 year timescales.

  7. Flexural and gravity modelling of the Mérida Andes and Barinas Apure Basin, Western Venezuela

    NASA Astrophysics Data System (ADS)

    Chacín, Luis; Jácome, María I.; Izarra, Carlos

    2005-08-01

    The kinematic evolution of the Barinas-Apure Basin and the southern Mérida Andes from Lower Miocene to the Present is numerically modelled using flexural isostatic theory and geophysical and geological data. Two published regional transects are used to build up a reference section, which is then used to constrain important parameters (e.g. shortenings and sedimentary thicknesses) for the flexural modelling. To control the location of the main fault system in the flexural model earthquake information is also used. The estimated flexural elastic thickness of the South American lithosphere beneath the Barinas-Apure Basin and the Mérida Andes Range is 25 km. The value for the final total shortening is 60 km. The flexural isostatic model shows that the Andean uplift has caused the South American lithosphere subsidence and the development of the Barinas-Apure Basin. In addition, gravity modelling was used to understand deep crustal features that could not be predicted by flexural theory. Consequently, the best-fit flexural model is used to build a gravity model across the Mérida Andes and the Barinas-Apure Basin preserving the best-controlled structural features from the flexural modelling (e.g. basin wavelength and depth) and slightly changing the main bodies density values and deep crustal structures. The final gravity model is intended to be representative of the major features affecting the gravity field in the study area. The predicted morphology in the lower crustal level of the final gravity model favours the hypothesis of a present delamination or megathrust of the Maracaibo crust over the South American Shield. This process would use the Conrad discontinuity as a main detachment surface within an incipient NW dipping continental subduction.

  8. Global Dynamic Modeling of Space-Geodetic Data

    NASA Technical Reports Server (NTRS)

    Bird, Peter

    1995-01-01

    The proposal had outlined a year for program conversion, a year for testing and debugging, and two years for numerical experiments. We kept to that schedule. In first (partial) year, author designed a finite element for isostatic thin-shell deformation on a sphere, derived all of its algebraic and stiffness properties, and embedded it in a new finite element code which derives its basic solution strategy (and some critical subroutines) from earlier flat-Earth codes. Also designed and programmed a new fault element to represent faults along plate boundaries. Wrote a preliminary version of a spherical graphics program for the display of output. Tested this new code for accuracy on individual model plates. Made estimates of the computer-time/cost efficiency of the code for whole-earth grids, which were reasonable. Finally, converted an interactive graphical grid-designer program from Cartesian to spherical geometry to permit the beginning of serious modeling. For reasons of cost efficiency, models are isostatic, and do not consider the local effects of unsupported loads or bending stresses. The requirements are: (1) ability to represent rigid rotation on a sphere; (2) ability to represent a spatially uniform strain-rate tensor in the limit of small elements; and (3) continuity of velocity across all element boundaries. Author designed a 3-node triangle shell element which has two different sets of basis functions to represent (vector) velocity and all other (scalar) variables. Such elements can be shown to converge to the formulas for plane triangles in the limit of small size, but can also applied to cover any area smaller than a hemisphere. The difficult volume integrals involved in computing the stiffness of such elements are performed numerically using 7 Gauss integration points on the surface of the sphere, beneath each of which a vertical integral is performed using about 100 points.

  9. Microstructure and mechanical behavior of ODS and non-ODS Fe-14Cr model alloys produced by spark plasma sintering

    NASA Astrophysics Data System (ADS)

    Auger, M. A.; de Castro, V.; Leguey, T.; Muñoz, A.; Pareja, R.

    2013-05-01

    In this work the spark plasma sintering (SPS) technique has been explored as an alternative consolidation route for producing ultra-fine grained Fe-14Cr model alloys containing a dispersion of oxide nanoparticles. Elemental powders of Fe and Cr, and nanosized Y2O3 powder have been mechanically alloyed in a planetary ball mill and rapidly sintered in a spark plasma furnace. Two alloys, with nominal compositions Fe-14%Cr and Fe-14%Cr-0.3%Y2O3 (wt.%), have been fabricated and their microstructure and mechanical properties investigated. The results have been compared with those obtained for other powder metallurgy processed alloys of the same composition but consolidated by hot isostatic pressing. The SPS technique under the present conditions has produced Fe-14Cr materials that apparently exhibit different microstructures yielding inferior mechanical properties than the counterpart material consolidated by hot isostatic pressing. Although the presence of a dispersion of Y-rich particles is evident, the oxide dispersion strengthened (ODS) Fe-14Cr alloy consolidated by SPS exhibits poor tensile properties. The extensive decoration of the powder particle surfaces with Cr-rich precipitates and the residual porosity appear to be responsible for the impaired properties of this ODS alloy consolidated by SPS.

  10. Modeling

    SciTech Connect

    Loth, E.; Tryggvason, G.; Tsuji, Y.; Elghobashi, S. E.; Crowe, Clayton T.; Berlemont, A.; Reeks, M.; Simonin, O.; Frank, Th; Onishi, Yasuo; Van Wachem, B.

    2005-09-01

    Slurry flows occur in many circumstances, including chemical manufacturing processes, pipeline transfer of coal, sand, and minerals; mud flows; and disposal of dredged materials. In this section we discuss slurry flow applications related to radioactive waste management. The Hanford tank waste solids and interstitial liquids will be mixed to form a slurry so it can be pumped out for retrieval and treatment. The waste is very complex chemically and physically. The ARIEL code is used to model the chemical interactions and fluid dynamics of the waste.

  11. Mars gravity field model from Mariner 9, Viking 1 and 2 data

    NASA Technical Reports Server (NTRS)

    Balmino, G.; Moynot, B.; Christensen, E. J.; Roucher, P.; Vales, N.

    1979-01-01

    Earth artificial satellite methods are extended by means of two way Doppler data, to the computation of very accurate orbiter trajectories around another planet, and to the determination of its gravity field. It is reported that in the case of Mars, all observations collected by 10 Deep Space Network stations located at three different sites during the Mariner 9 and Viking 1 and 2 missions have been processed and used to compute a full twelfth degree and order spherical harmonic model of the gravitational potential. It is concluded that the aeroid derived from the model shows very large correlations with the Martian topography, raising questions as to the deep structure of the planet which cannot be interpreted on the basis of topographic and isostatic considerations alone.

  12. Crustal thinning between the Ethiopian and East African Plateaus from modeling Rayleigh wave dispersion

    SciTech Connect

    Benoit, M H; Nyblade, A A; Pasyanos, M E

    2006-01-17

    The East African and Ethiopian Plateaus have long been recognized to be part of a much larger topographic anomaly on the African Plate called the African Superswell. One of the few places within the African Superswell that exhibit elevations of less than 1 km is southeastern Sudan and northern Kenya, an area containing both Mesozoic and Cenozoic rift basins. Crustal structure and uppermost mantle velocities are investigated in this area by modeling Rayleigh wave dispersion. Modeling results indicate an average crustal thickness of 25 {+-} 5 km, some 10-15 km thinner than the crust beneath the adjacent East African and Ethiopian Plateaus. The low elevations can therefore be readily attributed to an isostatic response from crustal thinning. Low Sn velocities of 4.1-4.3 km/s also characterize this region.

  13. Constitutive and life modeling of single crystal blade alloys for root attachment analysis

    NASA Technical Reports Server (NTRS)

    Meyer, T. G.; Mccarthy, G. J.; Favrow, L. H.; Anton, D. L.; Bak, Joe

    1988-01-01

    Work to develop fatigue life prediction and constitutive models for uncoated attachment regions of single crystal gas turbine blades is described. At temperatures relevant to attachment regions, deformation is dominated by slip on crystallographic planes. However, fatigue crack initiation and early crack growth are not always observed to be crystallographic. The influence of natural occurring microporosity will be investigated by testing both hot isostatically pressed and conventionally cast PWA 1480 single crystal specimens. Several differnt specimen configurations and orientations relative to the natural crystal axes are being tested to investigate the influence of notch acuity and the material's anisotropy. Global and slip system stresses in the notched regions were determined from three dimensional stress analyses and will be used to develop fatigue life prediction models consistent with the observed lives and crack characteristics.

  14. Applying modern measurements of Pleistocene loads to model lithospheric rheology

    NASA Astrophysics Data System (ADS)

    Beard, E. P.; Hoggan, J. R.; Lowry, A. R.

    2011-12-01

    The remnant shorelines of Pleistocene Lake Bonneville provide a unique opportunity for building a dataset from which to infer rheological properties of the lower crust and upper mantle. Multiple lakeshores developed over a period of around 30 kyr which record the lithosphere's isostatic response to a well-constrained load history. Bills et al. (1994) utilized a shoreline elevation dataset compiled by Currey (1982) in an attempt to model linear (Maxwell) viscosity as a function of depth beneath the basin. They estimated an effective elastic thickness (Te) for the basin of 20-25 km which differs significantly from the 5-15 km estimates derived from models of loading on geologic timescales (e.g., Lowry and Pérez-Gussinyé, 2011). We propose that the discrepancy in Te modeled by these two approaches may be resolved with dynamical modeling of a common rheology, using a more complete shoreline elevation dataset applied to a spherical Earth model. Where Currey's (1982) dataset was compiled largely from observations of depositional shoreline features, we are developing an algorithm for estimating elevation variations in erosional shorelines based on cross-correlation and stacking techniques similar to those used to automate picking of seismic phase arrival times. Application of this method to digital elevation models (DEMs) will increase the size and accuracy of the shoreline elevation dataset, enabling more robust modeling of the rheological properties driving isostatic response to unloading of Lake Bonneville. Our plan is to model these data and invert for a relatively small number of parameters describing depth- and temperature-dependent power-law rheology of the lower crust and upper mantle. These same parameters also will be used to model topographic and Moho response to estimates of regional mass variation on the longer loading timescales to test for inconsistencies. Bills, B.G., D.R. Currey, and G.A. Marshall, 1994, Viscosity estimates for the crust and upper

  15. Results of intermediate-scale hot isostatic press can experiments

    SciTech Connect

    Nelson, L.O.; Vinjamuri, K.

    1995-05-01

    Radioactive high-level waste (HLW) has been managed at the Idaho Chemical Processing Plant (ICPP) for a number of years. Since 1963, liquid HLW has been solidified into a granular solid (calcine). Presently, over 3,800 m{sup 3} of calcine is stored in partially-underground stainless steel bins. Four intermediate- scale HLW can tests (two 6-in OD {times} 12-in tall and two 4-in OD {times} 7-in tall) are described and compared to small-scale HIP can tests (1- to 3-in OD {times} 1- to 4.5-in tall). The intermediate-scale HIP cans were loaded with a 70/30 calcine/frit blend and HIPped at an off-site facility at 1050{degrees}C; and 20 ksi. The dimensions of two cans (4-in OD {times} 7-in tall) were monitored during the HIP cycle with eddy-current sensors. The sensor measurements indicated that can deformation occurs rapidly at 700{degrees}C; after which, there is little additional can shrinkage. HIP cans were subjected to a number of analyses including calculation of the overall packing efficiency (56 to 59%), measurement of glass-ceramic (3.0 to 3.2 g/cc), 14-day MCC-1 leach testing (total mass loss rates < 1 g/m{sup 2} day), and scanning electron microscopy (SEM). Based on these analyses, the glass-ceramic material produced in intermediate-scale cans is similar to material produced in small-scale cans. No major scale-up problems were indicated. Based on the packing efficiency observed in intermediate- and small-scale tests, the overall packing efficiency of production-scale (24-in OD {times} 36- to 190-in tall) cans would be approximately 64% for a pre-HIP right-circular cylinder geometry. An efficiency of 64% would represent a volume reduction factor of 2.5 over a candidate glass waste prepared at 33 wt% waste loading.

  16. Glacial isostatic stress shadowing by the Antarctic ice sheet

    NASA Technical Reports Server (NTRS)

    Ivins, E. R.; James, T. S.; Klemann, V.

    2005-01-01

    Numerous examples of fault slip that offset late Quaternary glacial deposits and bedrock polish support the idea that the glacial loading cycle causes earthquakes in the upper crust. A semianalytical scheme is presented for quantifying glacial and postglacial lithospheric fault reactivation using contemporary rock fracture prediction methods. It extends previous studies by considering differential Mogi-von Mises stresses, in addition to those resulting from a Coulomb analysis. The approach utilizes gravitational viscoelastodynamic theory and explores the relationships between ice mass history and regional seismicity and faulting in a segment of East Antarctica containing the great Antarctic Plate (Balleny Island) earthquake of 25 March 1998 (Mw 8.1). Predictions of the failure stress fields within the seismogenic crust are generated for differing assumptions about background stress orientation, mantle viscosity, lithospheric thickness, and possible late Holocene deglaciation for the D91 Antarctic ice sheet history. Similar stress fracture fields are predicted by Mogi-von Mises and Coulomb theory, thus validating previous rebound Coulomb analysis. A thick lithosphere, of the order of 150-240 km, augments stress shadowing by a late melting (middle-late Holocene) coastal East Antarctic ice complex and could cause present-day earthquakes many hundreds of kilometers seaward of the former Last Glacial Maximum grounding line.

  17. Self-adjusting, isostatic exoskeleton for the human knee joint.

    PubMed

    Cai, Viet Anh Dung; Bidaud, Philippe; Hayward, Vincent; Gosselin, Florian; Desailly, Eric

    2011-01-01

    A knee-joint exoskeleton design that can apply programmable torques to the articulation and that self-adjusts to its physiological movements is described. Self-adjustment means that the articular torque is automatically produced around the rotational axis of the joint. The requirements are first discussed and the conditions under which the system tracks the spatial relative movements of the limbs are given. If these conditions are met, the torque applied to the joint takes into account the possible relative movements of the limbs without introducing constraints. A prototype was built to demonstrate the applicability of these principles and preliminary tests were carried out to validate the design.

  18. Isostatic gravity map of Yukon Flats, east-central Alaska

    USGS Publications Warehouse

    Morin, Robert L.

    2002-01-01

    The gravity data used to make this map were collected between 1959 and 1984. The data were collected by automobile, aircraft, and watercraft. Most of the data were collected as part of a U.S. Geological Survey (USGS) regional gravity data collection project. Some of the data were collected as part of other USGS local projects. One data set was collected by the NGS (National Geodetic Survey). This map ranges from 65° to 68° N latitude and 141° to 152° W longitude. The names of the 12 1:250,000-scale U.S. Geological Survey quadrangle maps that make up this map are labeled on the map. The western edge of the map is 1 degree of longitude east of the edge of the three most western quadrangles.

  19. Self-adjusting, isostatic exoskeleton for the human knee joint.

    PubMed

    Cai, Viet Anh Dung; Bidaud, Philippe; Hayward, Vincent; Gosselin, Florian; Desailly, Eric

    2011-01-01

    A knee-joint exoskeleton design that can apply programmable torques to the articulation and that self-adjusts to its physiological movements is described. Self-adjustment means that the articular torque is automatically produced around the rotational axis of the joint. The requirements are first discussed and the conditions under which the system tracks the spatial relative movements of the limbs are given. If these conditions are met, the torque applied to the joint takes into account the possible relative movements of the limbs without introducing constraints. A prototype was built to demonstrate the applicability of these principles and preliminary tests were carried out to validate the design. PMID:22254384

  20. Modeling shear instability and fracture in dynamically deformed Al/W granular composites

    NASA Astrophysics Data System (ADS)

    Olney, Karl; Benson, David; Nesterenko, Vitali

    2011-06-01

    Aluminum/Tungsten granular composites are materials which combine high density and strength with bulk distributed fracture of Al matrix into small particles under impact or shock loading. They are processed using cold and hot isostatic pressing of W particles/rods in the matrix of Al powder. The presentation will describe modeling of these materials under dynamic conditions simulating low velocity high energy impact in drop weight test (10 m/s) and also behavior following impact with velocities up to 1200 m/s. It will be demonstrated that morphology of W component and bonding between Al particles dramatically affects their strength, shear localization and mode of fracture of Al matrix. The support for this project provided by the Office of Naval Research Multidisciplinary University Research Initiative Award N00014-07-1-0740 (Program Officer Dr. Clifford Bedford).

  1. A simple model for pediment formation.

    NASA Astrophysics Data System (ADS)

    Mercier, Jonathan; Braun, Jean; Guillocheau, François; Robin, Cecile; Simon, Brendan

    2016-04-01

    Pediments are very flat and smooth erosive surfaces, connected to higher relief by a scarp, that covers up to two thirds of the Earth's surface. A physical mechanism to explain their formation remains elusive. Commonly accepted hypotheses include: (1) the widening of an incised river network (lateral corrasion of Gilbert, 1877), (2) sheetflow erosion, (3) subsurface weathering and exhumation (Strudley et al, 2006) and (4) slope retreat, usually at the base of an escarpment (King, 1949), potentially helped by flexural isostatic rebound (Pelletier, 2010). Here we explore the third hypothesis, which we believe applies mostly in regions characterised by intense rainfall where deep weathering profiles are commonly observed. In this study, using a new coupled model of groundwater flow and surface erosion, we highlight the critical impact of the geometry of the water table and of the unsaturated zone within a weathering profile to explain its evolution through time. The model is calibrated and used to explain the formation of pediments as the product of a dynamical balance between weathering front propagation and surface erosion. We also explore the effects of abrupt changes in rainfall intensity and base level drop on the geometry of the predicted pediments.

  2. The lithospheric-scale 3D structural configuration of the North Alpine Foreland Basin constrained by gravity modelling and the calculation of the 3D load distribution

    NASA Astrophysics Data System (ADS)

    Przybycin, Anna M.; Scheck-Wenderoth, Magdalena; Schneider, Michael

    2014-05-01

    The North Alpine Foreland Basin is situated in the northern front of the European Alps and extends over parts of France, Switzerland, Germany and Austria. It formed as a wedge shaped depression since the Tertiary in consequence of the Euro - Adriatic continental collision and the Alpine orogeny. The basin is filled with clastic sediments, the Molasse, originating from erosional processes of the Alps and underlain by Mesozoic sedimentary successions and a Paleozoic crystalline crust. For our study we have focused on the German part of the basin. To investigate the deep structure, the isostatic state and the load distribution of this region we have constructed a 3D structural model of the basin and the Alpine area using available depth and thickness maps, regional scale 3D structural models as well as seismic and well data for the sedimentary part. The crust (from the top Paleozoic down to the Moho (Grad et al. 2008)) has been considered as two-parted with a lighter upper crust and a denser lower crust; the partition has been calculated following the approach of isostatic equilibrium of Pratt (1855). By implementing a seismic Lithosphere-Asthenosphere-Boundary (LAB) (Tesauro 2009) the crustal scale model has been extended to the lithospheric-scale. The layer geometry and the assigned bulk densities of this starting model have been constrained by means of 3D gravity modelling (BGI, 2012). Afterwards the 3D load distribution has been calculated using a 3D finite element method. Our results show that the North Alpine Foreland Basin is not isostatically balanced and that the configuration of the crystalline crust strongly controls the gravity field in this area. Furthermore, our results show that the basin area is influenced by varying lateral load differences down to a depth of more than 150 km what allows a first order statement of the required compensating horizontal stress needed to prevent gravitational collapse of the system. BGI (2012). The International

  3. New Insights into the Morphology of the Galapagos Platform from Lower Crustal Flow Models

    NASA Astrophysics Data System (ADS)

    Orellana Rovirosa, F.; Richards, M. A.

    2014-12-01

    The volcanically-active Galapagos Islands are constructed upon a broad platform, with the westernmost islands being the most active, marking the present-day position of the Galapagos hotspot (mantle plume). This volcanic platform overlies relatively young oceanic lithosphere (<15 Myr) and exhibits unique morphologic features along its boundaries. The most spectacular of these features is a system of stepped terraces on the southwestern escarpment, with very large vertical relief (>3 km), and contrasting with relatively gentle slopes off the eastern platform edge toward the Carnegie ridge. Considering the horizontal lithostatic pressure differences associated with this bathymetric relief, along with the high temperatures within this young, hotspot-affected oceanic lithosphere and crust; it is likely that lower crustal flow contributes significantly, perhaps even dominantly, to lithospheric and crustal deformation within the Galapagos Platform. Using 2D numerical models that invoke a thin-sheet approximation for the Stokes' equation for a Newtonian fluid with space- and time-dependent viscosity, and assuming isostatic conditions, we show that: (1) the pronounced bathymetric rim along the Eastern platform region (where gravimetric studies indicate Airy isostasy) near Española Island may be the expression of a mature stage of a lower crustal flow front evolving asymptotically during the last ~3 Myr; (2) the spectacular system of stepped terraces along the southwestern edge of the platform may be explained by lower crustal flow-associated backward tilting of the bathymetric surface that, even with small amounts of angular change (~0.1 deg) and potentially occurring in non-isostatic regimes, effectively hinders the horizontal flow of lava. This process of backward-tilting may have been largely restricted to the last ~1 Myr of platform growth, and hence may be a unique event that may involve horizontal extrusion of large lava sheets from within the southwestward

  4. Preliminary gravity inversion model of basins east of Yucca Flat, Nevada Test Site, Nevada.

    SciTech Connect

    Geoffrey A. Phelps; Carter W. Roberts, and Barry C. Moring

    2006-03-17

    The Yucca Flat eastern extension study area, a 14 kilometer by 45 kilometer region contiguous to Yucca Flat on the west and Frenchman Flat on the south, is being studied to expand the boundary of the Yucca Flat hydrogeologic model. The isostatic residual gravity anomaly was inverted to create a model of the depth of the geologic basins within the study area. Such basins typically are floored by dense pre-Tertiary basement rocks and filled with less-dense Tertiary volcanic and sedimentary rocks and Quaternary alluvium, a necessary condition for the use of gravity modeling to predict the depth to the pre-Tertiary basement rocks within the basins. Three models were created: a preferred model to represent the best estimate of depth to pre-Tertiary basement rocks in the study area, and two end-member models to demonstrate the possible range of solutions. The preferred model predicts shallow basins, generally less than 1,000m depth, throughout the study area, with only Emigrant Valley reaching a depth of 1,100m. Plutonium valley and West Fork Scarp Canyon have maximum depths of 800m and 1,000m, respectively. The end-member models indicate that the uncertainty in the preferred model is less than 200m for most of the study area.

  5. A review of analogue modelling of geodynamic processes: Approaches, scaling, materials and quantification, with an application to subduction experiments

    NASA Astrophysics Data System (ADS)

    Schellart, Wouter P.; Strak, Vincent

    2016-10-01

    . In the external approach, all deformation in the system is driven by the externally imposed condition, while in the combined approach, part of the deformation is driven by buoyancy forces internal to the system. In the internal approach, all deformation is driven by buoyancy forces internal to the system and so the system is closed and no energy is added during an experimental run. In the combined approach, the externally imposed force or added energy is generally not quantified nor compared to the internal buoyancy force or potential energy of the system, and so it is not known if these experiments are properly scaled with respect to nature. The scaling theory requires that analogue models are geometrically, kinematically and dynamically similar to the natural prototype. Direct scaling of topography in laboratory models indicates that it is often significantly exaggerated. This can be ascribed to (1) The lack of isostatic compensation, which causes topography to be too high. (2) The lack of erosion, which causes topography to be too high. (3) The incorrect scaling of topography when density contrasts are scaled (rather than densities); In isostatically supported models, scaling of density contrasts requires an adjustment of the scaled topography by applying a topographic correction factor. (4) The incorrect scaling of externally imposed boundary conditions in isostatically supported experiments using the combined approach; When externally imposed forces are too high, this creates topography that is too high. Other processes that also affect surface topography in laboratory models but not in nature (or only in a negligible way) include surface tension (for models using fluids) and shear zone dilatation (for models using granular material), but these will generally only affect the model surface topography on relatively short horizontal length scales of the order of several mm across material boundaries and shear zones, respectively.

  6. Numerical model of the glacially-induced intraplate earthquakes and faults formation

    NASA Astrophysics Data System (ADS)

    Petrunin, Alexey; Schmeling, Harro

    2016-04-01

    According to the plate tectonics, main earthquakes are caused by moving lithospheric plates and are located mainly at plate boundaries. However, some of significant seismic events may be located far away from these active areas. The nature of the intraplate earthquakes remains unclear. It is assumed, that the triggering of seismicity in the eastern Canada and northern Europe might be a result of the glacier retreat during a glacial-interglacial cycle (GIC). Previous numerical models show that the impact of the glacial loading and following isostatic adjustment is able to trigger seismicity in pre-existing faults, especially during deglaciation stage. However this models do not explain strong glaciation-induced historical earthquakes (M5-M7). Moreover, numerous studies report connection of the location and age of major faults in the regions undergone by glaciation during last glacial maximum with the glacier dynamics. This probably imply that the GIC might be a reason for the fault system formation. Our numerical model provides analysis of the strain-stress evolution during the GIC using the finite volume approach realised in the numerical code Lapex 2.5D which is able to operate with large strains and visco-elasto-plastic rheology. To simulate self-organizing faults, the damage rheology model is implemented within the code that makes possible not only visualize faulting but also estimate energy release during the seismic cycle. The modeling domain includes two-layered crust, lithospheric mantle and the asthenosphere that makes possible simulating elasto-plastic response of the lithosphere to the glaciation-induced loading (unloading) and viscous isostatic adjustment. We have considered three scenarios for the model: horizontal extension, compression and fixed boundary conditions. Modeling results generally confirm suppressing seismic activity during glaciation phases whereas retreat of a glacier triggers earthquakes for several thousand years. Tip of the glacier

  7. The role of rheology in extensional basin formation modelling

    NASA Astrophysics Data System (ADS)

    Fernàndez, M.; Ranalli, G.

    1997-12-01

    The rheology of the lithosphere determines its deformation under given initial and boundary conditions. This paper presents a critical discussion on how rheological properties are taken into account in extensional basin modelling. Since strength envelopes are often used in models, we review the uncertainties (in temperature and rheological parameters) and assumptions (in type of rheology and mode of deformation) involved in their construction. Models of extensional basins are classified into three groups: kinematic, kinematic with rheological constraints, and dynamic. Rheology enters kinematic models only implicitly, in the assumption of an isostatic compensation mechanism. We show that there is a critical level of necking that reconciles local isostasy with the finite strength of the lithosphere, which requires a flexural response. Kinematic models with rheological constraints make use of strength envelopes to assess the initial lateral variations of lithospheric strength and its evolution with time at the site of extension. Dynamic models are the only ones to explicitly introduce rheological constitutive equations (usually in plane strain or plane stress). They usually, however, require the presence of an initial perturbation (thickness variations, pre-existing faults, thermal inhomogeneities, rheological inhomogeneities). The mechanical boundary conditions (kinematic and dynamic) and the thermal boundary conditions (constant temperature or constant heat flux at the lower boundary of the lithosphere) may result in negative/positive feedbacks leading to cessation/acceleration of extension. We conclude that, while kinematic models (with rheological constraints if possible) are very successful in accounting for the observed characteristics of sedimentary basins, dynamic models are necessary to gain insight into the physical processes underlying basin formation and evolution.

  8. An improved temperature model of the Antarctic uppermost mantle for the benefit of GIA modelling

    NASA Astrophysics Data System (ADS)

    Stolk, Ward; Kaban, Mikhail; van der Wal, Wouter; Wiens, Doug

    2014-05-01

    Mass changes in Antarctica's ice cap influence the underlying lithosphere and upper mantle. The dynamics of the solid earth are in turn coupled back to the surface and ice dynamics. Furthermore, mass changes due to lithosphere and uppermost mantle dynamics pollute measurements of ice mass change in Antarctica. Thus an improved understanding of temperature, composition and rheology of the Antarctic lithosphere is required, not only to improve geodynamic modelling of the Antarctic continent (e.g. glacial isostatic adjustment (GIA) modelling), but also to improve climate monitoring and research. Recent field studies in Antarctica have generated much new data. These data, especially an improved assessment of crustal thickness and seismic tomography of the upper mantle, now allow for the construction of an improved regional temperature model of the Antarctic uppermost mantle. Even a small improvement in the temperature models for the uppermost mantle could have a significant effect on GIA modelling in Antarctica. Our regional temperature model is based on a joint analysis of a high resolution seismic tomography model (Heeszel et al., forthcoming) and a recent global gravity model (Foerste et al., 2011). The model will be further constrained by additional local data where available. Based on an initial general mantle composition, the temperature and density in the uppermost mantle is modelled, elaborating on the the methodology of Goes et al. (2000) and Cammarano et al. (2003). The gravity signal of the constructed model is obtained using forward gravity modelling. This signal is compared with the observed gravity signal and differences form the basis for the compositional model in the next iteration. The first preliminary results of this study, presented here, will focus on the cratonic areas in East-Antarctica, for which modelling converges after a few iterations. Cammarano, F. and Goes, S. and Vacher, P. and Giardini, D. (2003) Inferring upper-mantle temperatures from

  9. Delft Mass Transport model DMT-2

    NASA Astrophysics Data System (ADS)

    Ditmar, Pavel; Hashemi Farahani, Hassan; Inacio, Pedro; Klees, Roland; Zhao, Qile; Guo, Jing; Liu, Xianglin; Sun, Yu; Riva, Ricardo; Ran, Jiangjun

    2013-04-01

    Gravity Recovery And Climate Experiment (GRACE) satellite mission has enormously extended our knowledge of the Earth's system by allowing natural mass transport of various origin to be quantified. This concerns, in particular, the depletion and replenishment of continental water stocks; shrinking of polar ice sheets; deformation of the Earth's crust triggered by large earthquakes, and isostatic adjustment processes. A number of research centers compute models of temporal gravity field variations and mass transport, using GRACE data as input. One of such models - Delft Mass Transport model - is being produced at the Delft University of Technology in collaboration with the GNSS Research Center of Wuhan University. A new release of this model, DMT-2, has been produced on the basis of a new (second) release of GRACE level-1b data. This model consists of a time-series of monthly solutions spanning a time interval of more than 8 years, starting from Feb. 2003. Each solution consists of spherical harmonic coefficients up to degree 120. Both unconstrained and optimally filtered solutions are obtained. The most essential improvements of the DMT-2 model, as compared to its predecessors (DMT-1 and DMT-1b), are as follows: (i) improved estimation and elimination of low-frequency noise in GRACE data, so that strong mass transport signals are not damped; (ii) computation of accurate stochastic models of data noise for each month individually with a subsequent application of frequency-dependent data weighting, which allows statistically optimal solutions to be compiled even if data noise is colored and gradually changes in time; (iii) optimized estimation of accelerometer calibration parameters; (iv) incorporation of degree 1 coefficients estimated with independent techniques; (v) usage of state-of-the-art background models to de-alias GRACE data from rapid mass transport signals (this includes the EOT11a model of ocean tides and the latest release of the AOD1B product describing

  10. Modeling the thermal deformation of TATB-based explosives. Part 1: Thermal expansion of “neat-pressed” polycrystalline TATB

    SciTech Connect

    Luscher, Darby J.

    2014-05-08

    We detail a modeling approach to simulate the anisotropic thermal expansion of polycrystalline (1,3,5-triamino-2,4,6-trinitrobenzene) TATB-based explosives that utilizes microstructural information including porosity, crystal aspect ratio, and processing-induced texture. This report, the first in a series, focuses on nonlinear thermal expansion of “neat-pressed” polycrystalline TATB specimens which do not contain any binder; additional complexities related to polymeric binder and irreversible ratcheting behavior are briefly discussed, however detailed investigation of these aspects are deferred to subsequent reports. In this work we have, for the first time, developed a mesoscale continuum model relating the thermal expansion of polycrystal TATB specimens to their microstructural characteristics. A self-consistent homogenization procedure is used to relate macroscopic thermoelastic response to the constitutive behavior of single-crystal TATB. The model includes a representation of grain aspect ratio, porosity, and crystallographic texture attributed to the consolidation process. A quantitative model is proposed to describe the evolution of preferred orientation of graphitic planes in TATB during consolidation and an algorithm constructed to develop a discrete representation of the associated orientation distribution function. Analytical and numerical solutions using this model are shown to produce textures consistent with previous measurements and characterization for isostatic and uniaxial “die-pressed” specimens. Predicted thermal strain versus temperature for textured specimens are shown to be in agreement with corresponding experimental measurements. Using the developed modeling approach, several simulations have been run to investigate the influence of microstructure on macroscopic thermal expansion behavior. Results from these simulations are used to identify qualitative trends. Implications of the identified trends are discussed in the context of

  11. Gravity and magnetic anomaly modeling and correlation using the SPHERE program and Magsat data

    NASA Technical Reports Server (NTRS)

    Braile, L. W.; Hinze, W. J. (Principal Investigator); Vonfrese, R. R. B.

    1980-01-01

    The spherical Earth inversion, modeling, and contouring software were tested and modified for processing data in the Southern Hemisphere. Preliminary geologic/tectonic maps and selected cross sections for South and Central America and the Caribbean region are being compiled and as well as gravity and magnetic models for the major geological features of the area. A preliminary gravity model of the Andeas Beniff Zone was constructed so that the density columns east and west of the subducted plates are in approximate isostatic equilibrium. The magnetic anomaly for the corresponding magnetic model of the zone is being computed with the SPHERE program. A test tape containing global magnetic measurements was converted to a tape compatible with Purdue's CDC system. NOO data were screened for periods of high diurnal activity and reduced to anomaly form using the IGS-75 model. Magnetic intensity anomaly profiles were plotted on the conterminous U.S. map using the track lines as the anomaly base level. The transcontinental magnetic high seen in POGO and MAGSAT data is also represented in the NOO data.

  12. Periodicity in a Conceptual Model of Glacial Cycles in the Absence of Milankovitch Forcing

    NASA Astrophysics Data System (ADS)

    Hahn, J.; Walsh, J.; Widiasih, E.; McGehee, R.

    2015-12-01

    Previously, McGehee and Widiasih coupled Budyko's Energy Balance Model with dynamics of a latitudinal ice-line incorporating the albedo feedback effect. They reduced this model to a two-dimensional equation of global mean temperature and a latitudinal ice-line. With this conceptual model, we now include dynamics of the ablation and accumulation of ice, to form a three-dimensional system that partitions the regions of the Earth latitudinally into an accumulation zone, ablation zone, and ice-free zone. Motivated by the findings of Abe-Ouchi et al that the fast retreat of ice-sheets is due to an increased rate of ablation via the effects of delayed isostatic rebound, we incorporate a simple switching mechanism to the model which increases the rate of ablation during periods of glacial retreat. This forms a discontinuous system of the Earth's temperature and ice-volume in which we find a stable periodic orbit. This can be interpreted as a intrinsic cycling of the Earth's climate in the absence of Milankovitch forcing.

  13. End member models for Andean Plateau uplift

    NASA Astrophysics Data System (ADS)

    Barnes, J. B.; Ehlers, T. A.

    2009-12-01

    Diverse techniques have been applied over the past decade to quantify the uplift history of the central Andean Plateau (AP). In this study, opposing models for surface uplift are evaluated including: a rapid rise of ˜ 2.5 km ˜ 10-6 Ma and a slow and steady rise since ˜ 40 Ma. These end member models are evaluated by synthesizing observations of the AP lithosphere and the history of deformation, sedimentation, exhumation, magmatism, uplift, and fluvial incision. Structural and geophysical studies estimate variable shortening magnitudes (˜ 530-150 km) involving cover-to-basement rocks, an isostatically-compensated thick crust (˜ 80-65 km), high heat flow, and zones of variable velocity and attenuation in the crust and mantle. These observations have invoked interpretations such as a hot/weak lithosphere, partial melt, crustal flow, and perhaps current, localized delamination, but do not provide strong support for massive delamination required by the rapid uplift model. Deformation and associated exhumation began ˜ 60-40 Ma and generally migrated eastward with consistent long-term average shortening rates (˜ 12-8 mm/yr) in Bolivia, favoring the slow uplift model. Volcanic and helium isotope evidence show an AP-wide zone of shallow mantle melting and thin lithosphere that has existed since ˜ 25 Ma, which is inconsistent with the rapid rise model that suggests lithospheric thinning occurred 10-6 Ma. Paleoaltimetry data suggest a rapid ˜ 2.5 km elevation gain 10 to 6 Ma, but are equally consistent within error with a linear rise since ≥ 25 Ma. Widespread fluvial incision (2.5-1 km) occurred along the western flank since ˜ 11-8 Ma and may be associated with surface uplift as proposed by the rapid rise model. However, the paleoaltimetry and incision data can also be explained by regional climate change associated with plateau uplift. Implications of these results for reconstructions of AP evolution are that: (1) substantial deformation of a weak lithosphere is

  14. GIA models with composite rheology and 3D viscosity: effect on GRACE mass balance in Antarctica

    NASA Astrophysics Data System (ADS)

    van der Wal, Wouter; Whitehouse, Pippa; Schrama, Ernst

    2014-05-01

    Most Glacial Isostatic Adjustment (GIA) models that have been used to correct GRACE data for the influence of GIA assume a radial stratification of viscosity in the Earth's mantle (1D viscosity). Seismic data in Antarctica indicate that there are large viscosity variations in the horizontal direction (3D viscosity). The purpose of this research is to determine the effect of 3D viscosity on GIA model output, and hence mass balance estimates in Antarctica. We use a GIA model with 3D viscosity and composite rheology in combination with ice loading histories ICE-5G and W12a. From comparisons with uplift and sea-level data in Fennoscandia and North America three preferred viscosity models are selected. For two of the 3D viscosity models the maximum gravity rate due to ICE-5G forcing is located over the Ronne-Filchner ice shelf. This is in contrast with the results obtained using a 1D model, in which the maximum gravity rate due to ICE-5G forcing is always located over the Ross ice shelf. This demonstrates that not all 3D viscosity models can be approximated with a 1D viscosity model. Using CSR release 5 GRACE data from February 2003 to June 2013 mass balance estimates for the three preferred viscosity models are -131 to -171 Gt/year for the ICE-5G model, and -48 to -57 Gt/year for the W12a model. The range due to Earth model uncertainty is larger than the error bar for GRACE (10 Gt/year), but smaller than the range resulting from the difference in ice loading histories.

  15. Modeling lithospheric rheology from modern measurements of Bonneville shoreline deformation

    NASA Astrophysics Data System (ADS)

    Beard, Eric P.

    Here I develop a cross-correlation approach to estimating heights of shoreline features, and apply the new method to paleo-shorelines of Pleistocene Lake Bonneville. I calculaTe 1st-derivative (slope) and 2nd-derivative (curvature) profiles from Digital Elevation Model (DEM) or Global Positioning SysTem Real-Time Kinematic (GPS-RTK) measurements of elevation. I then cross-correla Te pairs of profiles that have been shifT ed by various "lags," or shifts in elevation. The correlation coefficient (a normalized dot-product measure of similarity) is calcula Ted as a function of lag within small (~40 m) windows cenTered at various elevations. The elevation and lag with the greaTest correlation coefficient indicaTes the shoreline elevation at the reference profile and the change in shoreline height for the profile pair. I evalua Te several different algorithms for deriving slope and curvature by examining closure of elevation lags across profile triples. I then model isostatic response to Lake Bonneville loading and unloading. I first model lakeshore uplift response to lake load removal assuming an elastic layer over an inviscid half-space. I obtain a best-fit comparison of predic Ted to observed shoreline heights for the Bonneville level with an elastic layer thickness, Te, of 25±2 km (at 95% confidence) when using only previously published shoreline elevation estimaTes. The best-fit for the Bonneville level when using these estimaTes plus 44 new estima Tes suggests a Te of 26±2 km. The best-fit model for the Provo level suggests Te of 17±3 km. For the Gilbert level, the response is insensitive to the assumed Te. I next model isostatic response to Bonneville loading and unloading

  16. Insight into collision zone dynamics from topography: numerical modelling results and observations

    NASA Astrophysics Data System (ADS)

    Bottrill, A. D.; van Hunen, J.; Allen, M. B.

    2012-11-01

    Dynamic models of subduction and continental collision are used to predict dynamic topography changes on the overriding plate. The modelling results show a distinct evolution of topography on the overriding plate, during subduction, continental collision and slab break-off. A prominent topographic feature is a temporary (few Myrs) basin on the overriding plate after initial collision. This "collisional mantle dynamic basin" (CMDB) is caused by slab steepening drawing, material away from the base of the overriding plate. Also, during this initial collision phase, surface uplift is predicted on the overriding plate between the suture zone and the CMDB, due to the subduction of buoyant continental material and its isostatic compensation. After slab detachment, redistribution of stresses and underplating of the overriding plate cause the uplift to spread further into the overriding plate. This topographic evolution fits the stratigraphy found on the overriding plate of the Arabia-Eurasia collision zone in Iran and south east Turkey. The sedimentary record from the overriding plate contains Upper Oligocene-Lower Miocene marine carbonates deposited between terrestrial clastic sedimentary rocks, in units such as the Qom Formation and its lateral equivalents. This stratigraphy shows that during the Late Oligocene-Early Miocene the surface of the overriding plate sank below sea level before rising back above sea level, without major compressional deformation recorded in the same area. Our modelled topography changes fit well with this observed uplift and subsidence.

  17. Insight into collision zone dynamics from topography: numerical modelling results and observations

    NASA Astrophysics Data System (ADS)

    Bottrill, A. D.; van Hunen, J.; Allen, M. B.

    2012-07-01

    Dynamic models of subduction and continental collision are used to predict dynamic topography changes on the overriding plate. The modelling results show a distinct evolution of topography on the overriding plate, during subduction, continental collision and slab break-off. A prominent topographic feature is a temporary (few Myrs) deepening in the area of the back arc-basin after initial collision. This collisional mantle dynamic basin (CMDB) is caused by slab steepening drawing material away from the base of the overriding plate. Also during this initial collision phase, surface uplift is predicted on the overriding plate between the suture zone and the CMDB, due to the subduction of buoyant continental material and its isostatic compensation. After slab detachment, redistribution of stresses and underplating of the overriding plate causes the uplift to spread further into the overriding plate. This topographic evolution fits the stratigraphy found on the overriding plate of the Arabia-Eurasia collision zone in Iran and south east Turkey. The sedimentary record from the overriding plate contains Upper Oligocene-Lower Miocene marine carbonates deposited between terrestrial clastic sedimentary rocks, in units such as the Qom Formation and its lateral equivalents. This stratigraphy shows that during the Late Oligocene-Early Miocene the surface of the overriding plate sank below sea level before rising back above sea level, without major compressional deformation recorded in the same area. This uplift and subsidence pattern correlates well with our modelled topography changes.

  18. Central South Atlantic kinematics: a 3D ocean basin-scale model of the Walvis Ridge and Rio Grande Rise

    NASA Astrophysics Data System (ADS)

    Bird, D. E.; Hall, S. A.

    2009-12-01

    Prior to the breakup of western Gondwana, ca. 130 Ma, the Tristan da Cuhna mantle plume produced the eastern South American Parana, and western African Etendeka, flood basalts. As the South Atlantic basin opened, the ridge-centered plume produced seaward extending hotspot tracks: Rio Grande Rise on the South American Plate, and Walvis Ridge on the African Plate. Several ocean floor edifices on the hotspot trends appear to produce lower than expected amplitude free air gravity anomalies, suggesting that they are composed of lower density material. We have constructed a 3D gravity model of the South Atlantic basin to examine variations in crustal density associated with the hot spot trends. The model, which encompasses a region that extends from 46°S to 10 °S and from 20°E to 60°W, comprises the following layers: water, sediment, crust, and upper mantle. Variable density sediment and upper mantle layers are incorporated to estimate density changes related to sediment thickness and compaction, and upper mantle temperatures, respectively. The initial Moho horizon is estimated from isostatic equilibrium calculations; however the isostatic effect is scaled away from the seafloor spreading center to simulate the active spreading center. Three open-file grids were used to generate the model: satellite-derived free air gravity, global topography, and sediment thickness of the world. Inverting the model for crustal density reveals a distribution of low-density areas: along the coasts, the seafloor spreading axis, and along the Rio Grande Rise and Walvis Ridge hotspot trends. Coastal and spreading axis low density areas are thought to be related to continental crust and high temperature upper mantle. Hotspot track low density areas might be related to variable densities within the volcanic edifices, variations in their crustal thickness, or upper mantle densities beneath them. Detailed 2D models approximate reasonable density and geometry limits along select transects

  19. Gravity modeling reveals that the "Miocene Pyrenean peneplain" developed at high elevation

    NASA Astrophysics Data System (ADS)

    Bosch, Gemma V.; Van Den Driessche, Jean; Robert, Alexandra; Babault, Julien; Le Carlier, Christian

    2016-04-01

    Geodynamics that shaped the present morphology of the western Mediterranean are mostly linked to the African-Eurasia collision and the extension related to the Mediterranean opening. The Pyrenean chain formed by the collision between the Iberian microplate and the Eurasian plate from the Eocene to the late Oligocene. This resulted in lithosphere thickening especially below the Central Pyrenees that becomes thinner eastwards. Whether the later thinning of the lithosphere in the easternmost Pyrenees involves the removal of the lithospheric mantle or not is debated. This issue joins the problematics about the origin of the high-elevation of the "Miocene Pyrenean peneplain" remnants. Indeed the most striking feature of the Pyrenean morphology is the occurrence of high-elevation, low relief erosional surfaces that are interpreted as the remnants of a Miocene single planation surface, dissected and reworked by Quaternary fluvial and glacial erosion. Two end-member interpretations have proposed to explain the high elevation of this original surface. The first considers that the Miocene Pyrenean peneplain develops near sea-level and was later uplifted, the second claims that the planation surface developed at high elevation in response to the inhibition of erosion consecutively to the progressive rise of the base-level of the Pyrenean drainage network. The first interpretation implies the return to normal crustal thickness by erosion and later uplift by removal of the lithospheric mantle. The second interpretation considers that the mean elevation of the original planation surface matches the thickness of the lithosphere below the chain, taking into account some hundred meters of isostatic rebound due to Quaternary erosion. To test these interpretations, we first restore the Miocene original planation surface by mapping and interpolating the high-elevation, low relief surfaces across the Pyrenees. We then performed 1D and 2D gravity models that we compare with recent

  20. Unraveling topography around subduction zones from laboratory models

    NASA Astrophysics Data System (ADS)

    Husson, Laurent; Guillaume, Benjamin; Funiciello, Francesca; Faccenna, Claudio; Royden, Leigh H.

    2012-03-01

    The relief around subduction zones results from the interplay of dynamic processes that may locally exceed the (iso)static contributions. The viscous dissipation of the energy in and around subduction zones is capable of generating kilometer scale vertical ground movements. In order to evaluate dynamic topography in a self-consistent subduction system, we carried out a set of laboratory experiments, wherein the lithosphere and mantle are simulated by means of Newtonian viscous materials, namely silicone putty and glucose syrup. Models are kept in their most simple form and are made of negative buoyancy plates, of variable width and thickness, freely plunging into the syrup. The surface of the model and the top of the slab are scanned in three dimensions. A forebulge systematically emerges from the bending of the viscous plate, adjacent to the trench. With a large wavelength, dynamic pressure offsets the foreside and backside of the slab by ~ 500 m on average. The suction, that accompanies the vertical descent of the slab depresses the surface on both sides. At a distance equal to the half-width of the slab, the topographic depression amounts to ~ 500 m on average and becomes negligible at a distance that equals the width of the slab. In order to explore the impact of slab rollback on the topography, the trailing edge of the plates is alternatively fixed to (fixed mode) and freed from (free mode) the end wall of the tank. Both the pressure and suction components of the topography are ~ 30% lower in the free mode, indicating that slab rollback fosters the dynamic subsidence of upper plates. Our models are compatible with first order observations of the topography around the East Scotia, Tonga, Kermadec and Banda subduction zones, which exhibit anomalous depths of nearly 1 km as compared to adjacent sea floor of comparable age.

  1. Geophysical modelling of subsidence on the Mississippi Delta

    NASA Astrophysics Data System (ADS)

    Wolstencroft, Martin; Shen, Zhixiong; Törnqvist, Torbjorn; Milne, Glenn; Kulp, Mark

    2014-05-01

    The Mississippi Delta (MD) is experiencing relative sea level rise of approximately 10 mm/yr (Penland and Ramsey, 1990). This rate is caused by a combination of global sea level rise and local subsidence of the land surface. The relative importance of processes thought to be responsible for this subsidence is vigorously debated. Many previous studies have postulated that isostatic subsidence of the Pleistocene basement caused by sediment loading of the MD itself is the major contributor. GPS surveys have produced subsidence rates greater than 5 mm/yr in the MD (e.g. Dokka et al. 2006). Computational modeling studies of vertical land motion on decadal timescales have reproduced these high rates, but required extreme and arguably unrealistic parameter values to do so. Additionally, subsidence rates in the MD on thousand year timescales due to delta loading are found to be an order of magnitude lower than GPS rates (e.g. Törnqvist et al., 2006; Yu et al., 2012). In an attempt to understand the source of this disagreement between data types and better understand the uncertainties in the modelling process, we carried out a sensitivity analysis using a spherically symmetric visco-elastic deformation model. The model included sediment, ice, and ocean load histories from the last 80 kyr. The model results were compared with observations of vertical land motion over three different time scales (past 80 kyr, past 7 kyr, past ~15 years). We found that glacial isostatic adjustment is likely to be the dominant contributor to present-day deformation of the Pleistocene and underlying basement. Basement subsidence rates solely due to sediment loading were found to be less than 0.5 mm/yr. In general, sedimentary processes such as compaction of the Holocene strata appear to contribute more to land surface lowering than subsidence of the basement rock. REFERENCES Dokka, R. K., G. F. Sella, and T. H. Dixon (2006), Tectonic control of subsidence and southward displacement of southeast

  2. Numerical modeling of the late Cenozoic geomorphic evolution of Grand Canyon, Arizona

    NASA Astrophysics Data System (ADS)

    Pelletier, J. D.

    2008-12-01

    The late Cenozoic geomorphic evolution of Grand Canyon has been influenced by three primary tectonic and drainage adjustment events. First, incision into the Paleozoic strata of the southwestern margin of the Colorado Plateau began at 16 Ma in response to relief production along the Grand Wash Fault. Second, the ancestral Upper Colorado River reversed drainage and became integrated with the Lower Colorado River basin through Grand Canyon between 5.5 and 6 Ma. Third, the Colorado River was influenced by Plio- Quaternary normal faulting along the Hurricane and Toroweap Faults. Despite the relatively firm constraints available on the timing of these events, the geomorphic evolution of Grand Canyon is still not well constrained and many questions remain. For example, was there a deeply-incised gorge in western Grand Canyon before Colorado River integration? How and where was the Colorado River integrated? How have incision rates varied in space and time? In this paper, I describe the results of a numerical modeling study designed to address these questions. The model integrates the stream power model for bedrock channel erosion with cliff retreat and the flexural-isostatic response to erosion. The model honors the structural geology of the Grand Canyon region, including the variable erodibility of rocks in the Colorado Plateau and the occurrence of Plio-Quaternary normal faulting along the Hurricane-Toroweap Fault system. We present the results of two models designed to bracket the possible drainage architectures of the southwestern margin of the Colorado Plateau in Miocene time. In the first model, we assume a 13,000 km2 drainage basin primarily sourced from the Hualapai and Coconino Plateaux. The results of this model indicate that relief production along the Grand Wash fault initiated the formation of a large (700 m) knickpoint that migrated headward at a rate of 15 km/Myr prior to drainage integration at 6 Ma to form a deep gorge in western Grand Canyon. This model

  3. A numerical model of continental topographic evolution integrating thin sheet tectonics, river transport, and climate

    NASA Astrophysics Data System (ADS)

    Garcia-Castellanos, D.; Jimenez-Munt, I.

    2013-12-01

    How much does the erosion and sedimentation at the crust's surface influence on the patterns and distribution of tectonic deformation? This question has been mostly addressed from a numerical modelling perspective, at scales ranging from local to orogenic. Here we present a model that aims at constraining this phenomenon at the continental scale. With this purpose, we couple a thin-sheet viscous model of continental deformation with a stream-power surface transport model. The model also incorporates flexural isostatic compensation that permits the formation of large sedimentary foreland basins and a precipitation model that reproduces basic climatic effects such as continentality and orographic rainfall and rain shadow. We quantify the feedbacks between these 4 processes in a synthetic scenario inspired by the India-Asia collision. The model reproduces first-order characteristics of the growth of the Tibetan Plateau as a result of the Indian indentation. A large intramountain basin (comparable to the Tarim Basin) develops when predefining a hard inherited area in the undeformed foreland (Asia). The amount of sediment trapped in it is very sensitive to climatic parameters, particularly to evaporation, because it crucially determines its endorheic/exorheic drainage. We identify some degree of feedback between the deep and the surface processes occurs, leading locally to a <20% increase in deformation rates if orographic precipitation is account for (relative to a reference model with evenly-distributed precipitation). These enhanced thickening of the crust takes place particularly in areas of concentrated precipitation and steep slope, i.e., at the upwind flank of the growing plateau. This effect is particularly enhanced at the corners of the indenter (syntaxes). We hypothesize that this may provide clues for better understanding the mechanisms underlying the intriguing tectonic aneurisms documented in the syntaxes of the Himalayas.

  4. Progress report on the behavior and modeling of copper alloy to stainless steel joints for ITER first wall applications

    SciTech Connect

    Min, J.; Stubbins, J.; Collins, J.; Rowcliffe, A.F.

    1998-09-01

    The stress states that lead to failure of joints between GlidCop{trademark} CuAl25 and 316L SS were examined using finite element modeling techniques to explain experimental observations of behavior of those joints. The joints were formed by hot isostatic pressing (HIP) and bend bar specimens were fabricated with the joint inclined 45{degree} to the major axis of the specimen. The lower surface of the bend bar was notched in order to help induce a precrack for subsequent loading in bending. The precrack was intended to localize a high stress concentration in close proximity to the interface so that its behavior could be examined without complicating factors from the bulk materials and the specimen configuration. Preparatory work to grow acceptable precracks caused the specimen to fail prematurely while the precrack was still progressing into the specimen toward the interface. This prompted the finite element model calculations to help understand the reasons for this behavior from examination of the stress states throughout the specimen. An additional benefit sought from the finite element modeling effort was to understand if the stress states in this non-conventional specimen were representative of those that might be experienced during operation in ITER.

  5. Indenter growth in analogue models of Alpine-type deformation

    NASA Astrophysics Data System (ADS)

    Bonini, Marco; Sokoutis, Dimitrios; Talbot, Christopher J.; Boccaletti, Mario; Milnes, Alan G.

    1999-02-01

    A series of analogue experiments were carried out to simulate continental convergence, as seen in a profile through the Central Alps. A rigid indenter, representing the Adriatic plate, was driven laterally into a sand pack representing the brittle upper crust of Europe, detached and thickening above its subducting ductile lower crust. The rigid indenter advanced at the same steady rate in each experiment, but the dip of its front face was steepened in 15° increments from 15° to 90°. Where the rigid indenter face dipped at 45° or less, a sand wedge rose and was bound by a series of forekinks that nucleated at the toe of the indenter. Where the face of the rigid indenter dipped 60° or more, the wedge was defined by a single forekink and one or more backkinks that nucleated from a point advancing in front of the indenter toe. We interpret these results as indicating that slices of the sand pack and rising wedge are transferred across kink bands to build an "effective" indenter with a frontal dip closer to that dictated by the changing shear strength of the sand pile, which thickens vertically as it shortens laterally. One of our models (with a rigid indenter dipping 75°) simulates most of the major structures shown in recent syntheses of surface geology and deep seismic data in the Central Alps, without the isostatic lithospheric depression. This model accounts for the late collisional stage (Oligocene to Present) complex strain and metamorphic histories in the core of the orogenic wedge, the rapid rise and extrusion of small pips of Alpine eclogites, and the current passivity of the Insubric Line. It also emphasizes that lateral extension along gently dipping "thrusts" (orogen-normal horizontal escape) is confined to the extruded portion of the rising wedge.

  6. Is uplift of volcano clusters in the Tohoku Volcanic Arc, Japan, driven by magma accumulation in hot zones? A geodynamic modeling study

    NASA Astrophysics Data System (ADS)

    George, Ophelia A.; Malservisi, Rocco; Govers, Rob; Connor, Charles B.; Connor, Laura J.

    2016-06-01

    In many volcanic arcs, the rate of tectonic uplift cannot be explained by lithospheric plate motion alone but may be associated with dynamic uplift. Buoyant forces associated with underplated magma bodies lift the upper crust and leads to relatively high rates of topographic change. One such region is northern Honshu, Japan, where Quaternary volcano clusters are spatially associated with uplifted crust and isostatic gravity anomalies. Axisymmetric inversion of Bouguer gravity data for the Sengan volcano cluster shows that these gravity anomalies can be modeled by 30 km radius bodies emplaced at ˜15 km depth. Axisymmetric, finite element models, generated using GTECTON, of a layered Earth representative of the Tohoku crust indicate that the deformation of these midcrustal intrusions produces elevated topography on the surface directly above the intrusion that is bounded by a shallow peripheral trough. The wavelengths of vertical deformation produced by these bodies are sensitive to the thickness of the models' elastic layer and relatively insensitive to the models' rheology. This suggests that the amplitude of the vertical deformation represents a trade-off between the size of the intrusion and the thickness of the elastic layer and is less strongly influenced by the rheology of the lithosphere into which the bodies are emplaced. Our results are consistent with hot zone and hot finger models for the arc and indicate that Tohoku Volcanic Arc features such as gravity anomalies and uplifted basement are related to crustal magma intrusions and hot zones rather than directly related to mantle processes.

  7. Interpretation of geoid anomalies in the contact zone between the East European Craton and the Palaeozoic Platform-II: Modelling of density in the lithospheric mantle

    NASA Astrophysics Data System (ADS)

    Świeczak, M.; Kozlovskaya, E.; Majdański, M.; Grad, M.

    2009-05-01

    We present analysis of lateral variations of density in the upper mantle in the area of contact of the precambrian East European Craton (EEC) and the Palaeozoic Platform (PP) in Poland, obtained by analysis of the gravimetric geoid undulations. A precise 3-D density model of the crust in the study area down to a depth of 50 km, discussed in the first part of this paper (Majdański et al., in press) did not explain all features of the observed geoid. This suggests that these features can be due to density inhomogeneities in the upper mantle. To estimate them, we performed inversion of a residual between the observed geoid and undulations caused by the 3-D density distribution in the crust. Basing on the assumption of local isostatic compensation and Pratt-Hayford isostasy model, the density distribution in the upper mantle was parametrized as a 40-km-thick layer located above the assumed compensation depth of 140 km and subdivided into irregular blocks. The boundaries of the blocks were defined according to boundaries of major tectonic units in the study area and position and shape of the most pronounced anomalies in the residual geoid. A series of sensitivity tests calculated for such density heterogeneities in the upper mantle showed that they can produce geoid undulations of the order of several metres. The density values in each unit were taken as model parameters for the inversion procedure, and inverse problem was solved using global optimization with constraints. The density variations in the upper mantle in the final model correlate well with the surface heat flow. This suggests that these variations can be due to diversity in mantle temperature. The Trans-European Suture Zone (TESZ), which is a major suture separating the EEC from the PP, is not observed as a distinct unit in the mantle. Instead, our study suggests continuation of the lithosphere of the EEC beneath the PP and confirms subdivision of the TESZ into terranes with distinctly different evolution

  8. Incipient mantle delamination, active tectonics and crustal thickening in Northern Morocco: Insights from gravity data and numerical modeling

    NASA Astrophysics Data System (ADS)

    Baratin, Laura-May; Mazzotti, Stéphane; Chéry, Jean; Vernant, Philippe; Tahayt, Abdelilah; Mourabit, Taoufik

    2016-11-01

    The Betic-Rif orocline surrounding the Alboran Sea, the westernmost tip of the Mediterranean Sea, accommodates the NW-SE convergence between the Nubia and Eurasia plates. Recent GPS observations indicate a ∼4 mm/yr SW motion of the Rif Mountains, relative to stable Nubia, incompatible with a simple two-plate model. New gravity data acquired in this study define a pronounced negative Bouguer anomaly south of the Rif, interpreted as a ∼40 km-thick crust in a state of non-isostatic equilibrium. We study the correlation between these present-day kinematic and geodynamic processes using a finite-element code to model in 2-D the first-order behavior of a lithosphere affected by a downward normal traction (representing the pull of a high-density body in the upper mantle). We show that intermediate viscosities for the lower crust and uppermost mantle (1021-1022Pas) allow an efficient coupling between the mantle and the base of the brittle crust, thus enabling (1) the conversion of vertical movement, resulting from the downward traction, to horizontal movement and (2) shortening in the brittle upper crust. Our results show that incipient delamination of the Nubian continental lithosphere, linked to slab pull, can explain the present-day abnormal tectonics, contribute to the gravity anomaly observed in northern Morocco, and give insight into recent tectonics in the Western Mediterranean region.

  9. The post-Triassic evolution of the Sorgenfrei Tornquist Zone — results from thermo-mechanical modelling

    NASA Astrophysics Data System (ADS)

    Hansen, D. L.; Nielsen, S. B.; Lykke-Andersen, H.

    2000-12-01

    The Sorgenfrei-Tornquist Zone (STZ) is part of the Fennoscandian Border Zone separating the Danish Basin from the Fennoscandian Shield. The STZ as a structural element is of Palaeozoic origin and represents the north-westerly segment of the Tornquist-Teisseyre Zone, which separates the younger West European crust from the older East European Platform and extends from the Black Sea to the eastern North Sea area. The STZ was reactivated in Triassic-Jurassic extension and Late Cretaceous and Paleogene compression. This paper investigates the regional geological consequences of the reactivations by quantitative modelling along a profile across the STZ in the Danish area. The numerical model invokes elastic, viscous and plastic deformations of the lithosphere as well as surface processes governed by erosion, sedimentation and lateral transport under the influence of eustatic sea level variations and regional isostatic compensation. Surface processes and lithospheric mechanics are coupled through thermal blanketing effects and loading. The results, in general, address the regional geological consequences of the existence of intracontinental zones of structural weakness. More specifically the results show that the Late Cretaceous and Paleogene chalk depocentres in the Danish Basin are a direct consequence of the inversion of the STZ, and that the STZ inversion together with falling sea level in Cenozoic time are amongst the principal controlling factors in the geological evolution in the eastern North Sea area.

  10. Modeling of Non-Uniform, Late Cenozoic Exhumation of the Laramide Landscape Using Proposed Geophysical and Climatic Forcing Mechanisms

    NASA Astrophysics Data System (ADS)

    Riihimaki, C. A.; Anderson, R. S.; Safran, E. B.

    2001-12-01

    The Laramide ranges and the intervening sedimentary basins stretch across ~300,000 km2 of Wyoming, Colorado, Montana, Utah, and South Dakota, forming some of the most dramatic mountain landscapes of the North American continental interior. Interpretations of the late Cenozoic geophysical and climatic history of the entire western U. S. hinge on assumptions about Laramide landscape evolution, and yet this evolution is ill-understood. The confusion stems from conflicting interpretations of non-uniform erosion rates across the Laramide region, which previous researchers have tried to correlate directly with regional episodes of tectonic or climatic forcing. Erosion in this region is largely driven by downcutting of a fluvial network linking a series of easily eroded sedimentary basins across relatively resistant crystalline cores. It is therefore likely that even a simple climatic or geophysical forcing event may result in a complex temporal and spatial pattern of erosion. We use a two-dimensional numerical model of stream power-based fluvial erosion and the associated flexural isostatic response to test two proposed mechanisms for extensive late Cenozoic exhumation in the Laramide region: regional uplift - for example, uplift driven by the passage of the subducted Farallon slab (e.g., Mitrovica et al., 1989) - which drives changes in stream gradient distributions; and climatic cooling and aridification, which drive changes in the frequency and intensity of floods (e.g., Molnar and England, 1990). We find that four factors dominate the spatial and temporal pattern of sub-regional landscape evolution: 1) the time since the forcing was imposed; 2) the along-drainage distance from baselevel to a basin or range; 3) the distribution of relatively resistant bedrock within the region; and 4) the regionalized pattern of isostatic response to sequential basin exhumation. In particular, we show that each type of forcing produces a predictable, non-uniform pattern of erosion

  11. A gravity model for the Coso geothermal area, California

    SciTech Connect

    Feighner, M.A.; Goldstein, N.E.

    1990-08-01

    Two- and three-dimensional gravity modeling was done using gridded Bouguer gravity data covering a 45 {times} 45 km region over the Coso geothermal area in an effort to identify features related to the heat source and to seek possible evidence for an underlying magma chamber. Isostatic and terrain corrected Bouguer gravity data for about 1300 gravity stations were obtained from the US Geological Survey. After the data were checked, the gravity values were gridded at 1 km centers for the area of interest centered on the Coso volcanic field. Most of the gravity variations can be explained by two lithologic units: (1) low density wedges of Quarternary alluvium with interbedded thin basalts (2.4 g/cm{sup 3}) filling the Rose Valley and Coso Basin/Indian Wells Valley, and (2) low density cover of Tertiary volcanic rocks and intercalated Coso Formation (2.49 g/cm{sup 3}). A 3-D iterative approach was used to find the thicknesses of both units. The gravity anomaly remaining after effects from Units 1 and 2 are removed is a broad north-south-trending low whose major peak lies 5 km north of Sugarloaf Mountain, the largest of the less than 0.3 m.y. old rhyolite domes in the Coso Range. Most of this residual anomaly can be accounted for by a deep, low-density (2.47 g/cm{sup 3}) prismatic body extending from 8 to about 30 km below the surface. While some of this anomaly might be associated with fractured Sierran granitic rocks, its close correlation to a low-velocity zone with comparable geometry suggests that the residual anomaly is probably caused a large zone of partial melt underlying the rhyolite domes of the Coso Range. 12 refs., 9 figs.

  12. Martian sub-crustal stress from gravity and topographic models

    NASA Astrophysics Data System (ADS)

    Tenzer, Robert; Eshagh, Mehdi; Jin, Shuanggen

    2015-09-01

    The latest Martian gravity and topographic models derived from the Mars Orbiter Laser Altimeter and the Mars Global Surveyor spacecraft tracking data are used to compute the sub-crustal stress field on Mars. For this purpose, we apply the method for a simultaneous determination of the horizontal sub-crustal stress component and the crustal thickness based on solving the Navier-Stokes problem and incorporating the Vening Meinesz-Moritz inverse problem of isostasy. Results reveal that most of the Martian sub-crustal stress is concentrated in the Tharsis region, with the most prominent signatures attributed to a formation of Tharsis major volcanoes followed by crustal loading. The stress distribution across the Valles Marineris rift valleys indicates extensional tectonism. This finding agrees with more recent theories of a tectonic origin of Valles Marineris caused, for instance, by a crustal loading of the Tharsis bulge that resulted in a regional trusting and folding. Aside from these features, the Martian stress field is relatively smooth with only a slightly enhanced pattern of major impact basins. The signatures of active global tectonics and polar ice load are absent. Whereas the signature of the hemispheric dichotomy is also missing, the long-wavelength spectrum of the stress field comprises the signature of additional dichotomy attributed to the isostatically uncompensated crustal load of Tharsis volcanic accumulations. These results suggest a different origin of the Earth's and Martian sub-crustal stress. Whereas the former is mainly related to active global tectonics, the latter is generated by a crustal loading and regional tectonism associated with a volcanic evolution on Mars. The additional sub-crustal stress around major impact basins is likely explained by a crustal extrusion after impact followed by a Moho uplift.

  13. Mantle Convection Models Constrained by Seismic Tomography

    NASA Astrophysics Data System (ADS)

    Durbin, C. J.; Shahnas, M.; Peltier, W. R.; Woodhouse, J. H.

    2011-12-01

    Perovskite-post-Perovskite transition (Murakami et al., 2004, Science) that appears to define the D" layer at the base of the mantle. In this initial phase of what will be a longer term project we are assuming that the internal mantle viscosity structure is spherically symmetric and compatible with the recent inferences of Peltier and Drummond (2010, Geophys. Res. Lett.) based upon glacial isostatic adjustment and Earth rotation constraints. The internal density structure inferred from the tomography model is assimilated into the convection model by continuously "nudging" the modification to the input density structure predicted by the convection model back towards the tomographic constraint at the long wavelengths that the tomography specifically resolves, leaving the shorter wavelength structure free to evolve, essentially "slaved" to the large scale structure. We focus upon the ability of the nudged model to explain observed plate velocities, including both their poloidal (divergence related) and toroidal (strike slip fault related) components. The true plate velocity field is then used as an additional field towards which the tomographically constrained solution is nudged.

  14. Investigating feedbacks between surface processes and tectonics in rift settings using numerical models

    NASA Astrophysics Data System (ADS)

    Beucher, Romain; Huismans, Ritske

    2015-04-01

    The Earth's landscape is a product of complex feedbacks between tectonics, driven by plate motion, and climate, which control the erosional processes. Interactions between erosion, tectonics and climate form, modify or destroy geomorphic features while the transfer of mass resulting from erosion and sedimentation affects isostasy and the mechanical behaviour of the lithosphere. Evolution of extensional basins and rifted continental margins creates significant topography, which in turn can change precipitation and erosion patterns. Transfer of sediments from the margins into the basin may change the stress pattern in the crust and thus affect the geometry of the rift. Modelling the complexity of such a system requires an integrated approach looking at interactions between tectonics and surface processes on a range of spatial and temporal scales. We use high-resolution numerical experiments coupling a 2D upper-mantle-scale thermo-mechanical model with a plan-form 2D surface processes model (SPM) to investigate the factors controlling the style of deformation. The experiments consist in simple extension models involving lithosphere with variable thickness (normal-like lithosphere to thick cratonic-like lithosphere) and explore the effects of rheological and compositional variability of the layer components of the crust and the lithosphere. We also explore different values of erosion efficiency together with different pattern of precipitation, including orographic effects. Tomography and geochemistry evidences suggest compositional stratification of the lithosphere. We also explore the effect of a depleted lower lithosphere (compositionally less dense than sublithospheric mantle) on the rift geometry and the effect of the isostatic responses in terms of uplift or subsidence on the surrounding topography. The models provide a basis to discuss the type of interactions between erosion and tectonics in rift settings. Preliminary results show that if erosion does play a

  15. A numerical model of continental-scale topographic evolution integrating thin sheet tectonics, river transport, and orographic precipitation

    NASA Astrophysics Data System (ADS)

    Garcia-Castellanos, Daniel; Jimenez-Munt, Ivone

    2014-05-01

    How much does the erosion and sedimentation at the crust's surface influence on the patterns and distribution of tectonic deformation? This question has been mostly addressed from a numerical modelling perspective, at scales ranging from local to orogenic. Here we present a model that aims at constraining this phenomenon at the continental scale. With this purpose, we couple a thin-sheet viscous model of continental deformation with a stream-power surface transport model. The model also incorporates flexural isostatic compensation that permits the formation of large sedimentary foreland basins and a precipitation model that reproduces basic climatic effects such as continentality and orographic rainfall and rain shadow. We quantify the feedbacks between these 4 processes in a synthetic scenario inspired by the India-Asia collision. The model reproduces first-order characteristics of the growth of the Tibetan Plateau as a result of the Indian indentation. A large intramountain basin (comparable to the Tarim Basin) develops when predefining a hard inherited area in the undeformed foreland (Asia). The amount of sediment trapped in it is very sensitive to climatic parameters, particularly to evaporation, because it crucially determines its endorheic/exorheic drainage. We identify some degree of feedback between the deep and the surface processes occurs, leading locally to a <20% increase in deformation rates if orographic precipitation is account for (relative to a reference model with evenly-distributed precipitation). These enhanced thickening of the crust takes place particularly in areas of concentrated precipitation and steep slope, i.e., at the upwind flank of the growing plateau. This effect is particularly enhanced at the corners of the indenter (syntaxes). We hypothesize that this may provide clues for better understanding the mechanisms underlying the intriguing tectonic aneurisms documented in the syntaxes of the Himalayas.

  16. The Glacial BuzzSaw, Isostasy, and Global Crustal Models

    NASA Astrophysics Data System (ADS)

    Levander, A.; Oncken, O.; Niu, F.

    2015-12-01

    The glacial buzzsaw hypothesis predicts that maximum elevations in orogens at high latitudes are depressed relative to temperate latitudes, as maximum elevation and hypsography of glaciated orogens are functions of the glacial equilibrium line altitude (ELA) and the modern and last glacial maximum (LGM) snowlines. As a consequence crustal thickness, density, or both must change with increasing latitude to maintain isostatic balance. For Airy compensation crustal thickness should decrease toward polar latitudes, whereas for Pratt compensation crustal densities should increase. For similar convergence rates, higher latitude orogens should have higher grade, and presumably higher density rocks in the crustal column due to more efficient glacial erosion. We have examined a number of global and regional crustal models to see if these predictions appear in the models. Crustal thickness is straightforward to examine, crustal density less so. The different crustal models generally agree with one another, but do show some major differences. We used a standard tectonic classification scheme of the crust for data selection. The globally averaged orogens show crustal thicknesses that decrease toward high latitudes, almost reflecting topography, in both the individual crustal models and the models averaged together. The most convincing is the western hemisphere cordillera, where elevations and crustal thicknesses decrease toward the poles, and also toward lower latitudes (the equatorial minimum is at ~12oN). The elevation differences and Airy prediction of crustal thickness changes are in reasonable agreement in the North American Cordillera, but in South America the observed crustal thickness change is larger than the Airy prediction. The Alpine-Himalayan chain shows similar trends, however the strike of the chain makes interpretation ambiguous. We also examined cratons with ice sheets during the last glacial period to see if continental glaciation also thins the crust toward

  17. Neotectonic stresses in Fennoscandia: field observations and modelling

    NASA Astrophysics Data System (ADS)

    Pascal, Christophe

    2013-04-01

    The present-day stress state of Fennoscandia is traditionally viewed as the combination of far field sources and residual glacial loading stresses. Investigations were conducted in different regions of Norway with the purpose of detecting and measuring stress-relief features and to derive from them valuable information on the crustal stress state. Stress-relief features are induced by blasting and sudden rock unloading in road construction and quarrying operations and are common in Norway and very likely in other regions of Fennoscandia. Stress relief at the Earth's surface is diagnostic of anomalously high stress levels at shallow depths in the crust and appears to be a characteristic of the formerly glaciated Baltic and Canadian Precambrian shields. The studied stress-relief features are, in general, indicative of NW-SE compression, suggesting ridge-push as the main source of stress. Our derived stress directions are also in excellent agreement with the ones derived from other kinds of stress indicators, including focal mechanisms from deep earthquakes, demonstrating that stress-relief features are valuable for neotectonic research. As a second step we applied numerical modelling techniques to simulate the neotectonic stress field in Fennoscandia with particular emphasis to southern Norway. A numerical method was used to reconstruct the structure of the Fennoscandian lithosphere. The numerical method involves classical steady-state heat equations to derive lithosphere thickness, geotherm and density distribution and, in addition, requires the studied lithosphere to be isostatically compensated at its base. The a priori crustal structure was derived from previous geophysical studies. Undulations of the geoid were used to calibrate the models. Once the density structure of the Fennoscandian lithosphere is reconstructed it is straightforward to quantify its stress state and compare modelling results with existing stress indicators. The modelling suggests that

  18. Digital elevation model of King Edward VII Peninsula, West Antarctica, from SAR interferometry and ICESat laser altimetry

    USGS Publications Warehouse

    Baek, S.; Kwoun, Oh-Ig; Braun, Andreas; Lu, Zhiming; Shum, C.K.

    2005-01-01

    We present a digital elevation model (DEM) of King Edward VII Peninsula, Sulzberger Bay, West Antarctica, developed using 12 European Remote Sensing (ERS) synthetic aperture radar (SAR) scenes and 24 Ice, Cloud, and land Elevation Satellite (ICESat) laser altimetry profiles. We employ differential interferograms from the ERS tandem mission SAR scenes acquired in the austral fall of 1996, and four selected ICESat laser altimetry profiles acquired in the austral fall of 2004, as ground control points (GCPs) to construct an improved geocentric 60-m resolution DEM over the grounded ice region. We then extend the DEM to include two ice shelves using ICESat profiles via Kriging. Twenty additional ICESat profiles acquired in 2003-2004 are used to assess the accuracy of the DEM. After accounting for radar penetration depth and predicted surface changes, including effects due to ice mass balance, solid Earth tides, and glacial isostatic adjustment, in part to account for the eight-year data acquisition discrepancy, the resulting difference between the DEM and ICESat profiles is -0.57 ?? 5.88 m. After removing the discrepancy between the DEM and ICESat profiles for a final combined DEM using a bicubic spline, the overall difference is 0.05 ?? 1.35 m. ?? 2005 IEEE.

  19. Linking the pressure dependency of elastic and electrical properties of porous rocks by a dual porosity model

    NASA Astrophysics Data System (ADS)

    Han, Tongcheng; Gurevich, Boris; Pervukhina, Marina; Clennell, Michael Ben; Zhang, Junfang

    2016-04-01

    Knowledge about the pressure dependency of elastic and electrical properties is important for a variety of geophysical applications. We present a technique to invert for the stiff and compliant porosity from velocity measurements made as a function of differential pressure on saturated sandstones. A dual porosity concept is used for dry rock compressibility and a squirt model is employed for the pressure and frequency dependent elastic properties of the rocks when saturated. The total porosity obtained from inversion shows satisfactory agreement with experimental results. The electrical cementation factor was determined using the inverted porosity in combination with measured electrical conductivity. It was found that cementation factor increased exponentially with increasing differential pressure during isostatic loading. Elastic compressibility, electrical cementation factor and electrical conductivity of the saturated rocks correlate linearly with compliant porosity, and electrical cementation factor and electrical conductivity exhibit linear correlations with elastic compressibility of the saturated rocks under loading. The results show that the dual porosity concept is sufficient to explain the pressure dependency of elastic, electrical and joint elastic-electrical properties of saturated porous sandstones.

  20. Numerical modelling and comparison of MgB2 bulks fabricated by HIP and infiltration growth

    NASA Astrophysics Data System (ADS)

    Zou, J.; Ainslie, M. D.; Fujishiro, H.; Bhagurkar, A. G.; Naito, T.; Babu, N. Hari; Fagnard, J.-F.; Vanderbemden, P.; Yamamoto, A.

    2015-07-01

    MgB2 in bulk form shows great promise as trapped field magnets (TFMs) as an alternative to bulk (RE)BCO materials to replace permanent magnets in applications such as rotating machines, magnetic bearings and magnetic separation, and the relative ease of fabrication of MgB2 materials has enabled a number of different processing techniques to be developed. In this paper, a comparison is made between bulk MgB2 samples fabricated by the hot isostatic pressing (HIP), with and without Ti-doping, and infiltration growth (IG) methods and the highest trapped field in an IG-processed bulk MgB2 sample, Bz = 2.12 at 5 K and 1.66 T at 15 K, is reported. Since bulk MgB2 has a more homogeneous Jc distribution than (RE)BCO bulks, studies on such systems are made somewhat easier because simplified assumptions regarding the geometry and Jc distribution can be made, and a numerical simulation technique based on the 2D axisymmetric H-formulation is introduced to model the complete process of field cooling (FC) magnetization. As input data for the model, the measured Jc(B,T) characteristics of a single, small specimen taken from each bulk sample are used, in addition to measured specific heat and thermal conductivity data for the materials. The results of the simulation reproduce the experimental results extremely well: (1) indicating the samples have excellent homogeneity, and (2) validating the numerical model as a fast, accurate and powerful tool to investigate the trapped field profile of bulk MgB2 discs of any size accurately, under any specific operating conditions. Finally, the paper is concluded with a numerical analysis of the influence of the dimensions of the bulk sample on the trapped field.

  1. Mantle flow and dynamic topography associated with slab window opening: Insights from laboratory models

    NASA Astrophysics Data System (ADS)

    Guillaume, Benjamin; Moroni, Monica; Funiciello, Francesca; Martinod, Joseph; Faccenna, Claudio

    2010-12-01

    We present dynamically self-consistent mantle-scale laboratory models that have been conducted to improve our understanding of the influence of slab window opening on subduction dynamics, mantle flow and associated dynamic topography over geological time scales. The adopted setup consists of a two-layer linearly viscous system simulating the subduction of a fixed plate of silicone (lithosphere) under negative buoyancy in a viscous layer of glucose syrup (mantle). Our experimental setting is also characterized by a constant-width rectangular window located at the center of a laterally confined slab, modeling the case of the interaction of a trench-parallel spreading ridge with a wide subduction zone. We found that the opening of a slab window does not produce consistent changes of the geometry and the kinematics of the slab. On the contrary, slab-induced mantle circulation, quantified both in the vertical and horizontal sections using the Feature Tracking image analysis technique, is strongly modified. In particular, rollback subduction and the opening of the slab window generate a complex mantle circulation pattern characterized by the presence of poloidal and toroidal components, with the importance of each evolving according to kinematic stages. Mantle coming from the oceanic domain floods through the slab window, indenting the supra-slab mantle zone and producing its deformation without any mixing between mantle portions. The opening of the slab window and the upwelling of sub-slab mantle produce a regional-scale non-isostatic topographic uplift of the overriding plate that would correspond to values ranging between ca. 1 and 5 km in nature. Assuming that our modeling results can be representative of the natural behavior of subduction zones, we compared them to the tectonics and volcanism of the Patagonian subduction zone. We found that the anomalous backarc volcanism that has been developing since the middle Miocene could result from the lateral flow of sub

  2. Hydroclimatic modelling of local sea level rise and its projection in future

    NASA Astrophysics Data System (ADS)

    Naren, A.; Maity, Rajib

    2016-09-01

    Studies on sea level rise (SLR) in the context of climate change are gaining importance in the recent past. Whereas there is some clear evidence of SLR at global scale, its trend varies significantly from location to location. The role of different meteorological variables on sea level change (SLC) is explored. We hypothesise that the role of such variables varies from location to location and modelling of local SLC requires a proper identification of specific role of individual factors. After identifying a group of various local meteorological variables, Supervised Principal Component Analysis (SPCA) is used to develop a location specific Combined Index (CI). The SPCA ensures that the developed CI possesses highest possible association with the historical SLC at that location. Further, using the developed CI, an attempt is made to model the local sea level (LSL) variation in synchronous with the changing climate. The developed approach, termed as hydroclimatic semi-empirical approach, is found to be potential for local SLC at different coastal locations. The validated hydroclimatic approach is used for future projection of SLC at those coastal locations till 2100 for different climate change scenarios, i.e. different Representative Concentration Pathways (RCPs). Future hydrometeorological variables are obtained from Global Climate Models (GCMs) for different such scenarios, i.e. RCP2.6, RCP4.5 and RCP8.5. Effect of glacial isostatic readjustment (GIA) is not included in this study. However, if the reliable information on GIA is available for a location, the same can be arithmetically added to the final outcome of the proposed hydrometeorological approach.

  3. Reconstructions of the Weichselian ice sheet, a comparative study of a thermo-mechanical approach to GIA driven models.

    NASA Astrophysics Data System (ADS)

    Schmidt, Peter; Lund, Björn; Näslund, Jens-Ove; Fastook, James

    2014-05-01

    Observations of glacial isostatic adjustment (GIA) have been used both to study the mechanical properties of the Earth and to invert for Northern Hemisphere palaeo-ice-sheets. This is typically done by solving the sea-level equation using simplified scaling laws to control ice-sheet thickness. However, past ice-sheets can also be reconstructed based on thermo-mechanical modelling driven by palaeo-climate data, invoking simple analytical models to account for the Earth's response. Commonly, both approaches use dated geological markers to constrain the ice-sheet margin location. Irrespective of the approach, the resulting ice-sheet reconstruction depends on the earth response, although the interdependence between the ice model and the earth model differs and therefore the two types of reconstructions could provide complementary information on Earth properties. We compare a thermo-mechanical reconstruction of the Weichselian ice-sheet using the UMISM model (Näslund, 2010) to two GIA driven reconstructions, ANU (Lambeck et al., 2010) and ICE-5G (Peltier & Fairbanks, 2006), commonly used in GIA modelling. We evaluate the three reconstructions both in terms of ice-sheet configurations and predicted Fennoscandian surface deformation ICE-5G comprise the largest reconstructed ice-sheet whereas ANU and UMISM are more similar in volume and areal extent. Significant differences still exists between ANU and UMISM, especially during the final deglaciation phase. Prior to the final retreat of the ice-sheet, ICE-5G is displays a massive and more or less constant ice-sheet configuration, while both ANU and UMISM fluctuates with at times almost ice-free conditions, such as during MIS3. This results in ICE-5G being close to isostatic equilibrium at LGM, whereas ANU and UMISM are not. Hence, the pre-LGM evolution of the Weichselian ice-sheet needs to be considered in GIA studies. For example, perturbing the ANU or UMISM reconstructions we find that changes more recent than 36 kyr BP

  4. Thermal and stress analysis of hot isostatically pressed, alumina ceramic, nuclear waste containers

    SciTech Connect

    Chang, Yun; Hoenig, C.L.

    1990-03-01

    The Yucca Mountain Project is studying design and fabrication options for a safe durable container in which to store nuclear waste underground at Yucca Mountain, Nevada. The ceramic container discussed here is an alternative to using a metal container. This ceramic alternative would be selected if site conditions prove too corrosive to use metals for nuclear waste storage. Some of the engineering problems addressed in this study were: the stress generated in the alumina container by compressive loads when 4000 to 40,000 psi of external pressure is applied; the thermal stress in the container during the heating and cooling processes; the temperature histories of the container in various production scenarios and the power required for typical heaters; the fastest possible turnaround time to heat, seal, and cool the container commensurate with preserving the structural integrity of the ceramic and the closure; the testing of some commercial heating elements to determine the maximum available heat output; and the trade-offs between the minimization in thermal stress and cycle time for closure. 2 refs., 23 figs., 2 tabs.

  5. Structural Behavior of Monolithic Fuel Plates During Hot Isostatic Pressing and Annealing

    SciTech Connect

    Pavel G. Medvedev; Hakan Ozaltun

    2010-03-01

    This paper presents results of the stress analysis in the monolithic fuel plates during thermal transients performed using COMSOL finite element analysis software. Large difference in the thermal expansion between the U-Mo foil and Al cladding is the main load origin during heating and cooling of the fuel plates. In addition, the mechanical behavior of the plate is affected by the difference in yield points between the foil and the cladding. This is manifested by the plastic deformation and permanent strains in the cladding, and elastic deformation of the foil. The results show existence of the critical temperature points at which the stresses change from compressive to tensile. The paper highlights principal differences in mechanical behavior between monolithic and dispersion fuel plates, underlines the need for mechanical property data, especially for the U-Mo alloys, and discusses the methodology for mechanical analysis of the monolithic plates.

  6. Glacio-isostatic crustal movements caused by historical volume change of the Vatnajokull ice cap, Iceland

    NASA Technical Reports Server (NTRS)

    Sigmundsson, Freysteinn; Einarsson, Pall

    1992-01-01

    Measurements of the lake level of Lake Langisjor at the SW edge of the Vatnajokull ice cap indicate a tilt of 0.26 +/- 0.06 microrad/yr away from the ice cap in the years of 1959-1991. The tilt is too large to be explained as an elastic Earth response to ice retreat this century, or to be caused by change in the gravitational pull of the ice cap, but it can be explained by sub-lithospheric viscous adjustment. Regional subsidence in historical times in SE Iceland can similarly be attributed to viscous adjustment resulting from the increased load of Vatnajokull during the Little Ice Age. The inferred sublithospheric viscosity is 1 x 10 exp 18 - 5 x 10 exp 19 Pa s.

  7. Hot isostatically pressed manufacture of high strength MERL 76 disk and seal shapes

    NASA Technical Reports Server (NTRS)

    Evans, D. J.

    1982-01-01

    The performance of a HIP MERL 76 disk installed in an experimental engine and exposed to realistic operating conditions in a 150 hour, 1500 cycle endurance test is examined. Post test analysis, based on visual, fluorescence penetrant and dimensional inspection, indicates that the disk performs satisfactorily.

  8. Manufacture of low carbon astroloy turbine disk shapes by hot isostatic pressing. Volume 2, project 1

    NASA Technical Reports Server (NTRS)

    Eng, R. D.; Evans, D. J.

    1979-01-01

    The performance of a hot isotatic pressed disk installed in an experimental engine and exposed to realistic operating conditions in a 150-hour engine test and a 1000 cycle endurance test is documented. Post test analysis, based on visual, fluorescent penetrant and dimensional inspection, revealed no defects in the disk and indicated that the disk performed satisfactorily.

  9. Hot isostatic pressing of silicon nitride Sisub3n4 containing zircon, or zirconia and silica

    NASA Technical Reports Server (NTRS)

    Somiya, S.; Yoshimura, M.; Suzuki, T.; Nishimura, H.

    1980-01-01

    A hydrothermal synthesis apparatus with a 10 KB cylinder was used to obtain a sintered body of silicon nitride. The sintering auxiliary agents used were zircon (ZrSiO4) and a mixture of zirconia (ZrO2) and silica (SiO2). Experiments were conducted with the amounts of ZrSi04 or ArO2 and SiO2 varying over a wide range and the results compared to discover the quantity of additive which produced sintering in silicon nitride by the hot pressing method.

  10. Neotectonics of northern Central Europe: the legacy of Glacial Isostatic Adjustment

    NASA Astrophysics Data System (ADS)

    Brandes, C.; Steffen, H.; Wu, P. P.

    2013-12-01

    Northern Central Europe is regarded as aseismic, however, several historic earthquakes with intensities of up to VII occurred in this region during the last 1000 years. This historic seismicity is clearly concentrated along major reverse faults that formerly played an important role during a tectonic inversion phase in the Late Cretaceous. Here we show with numerical simulations that large parts of the observed seismicity in northern Central Europe is most likely an effect of stress changes induced by the decay of the Scandinavian ice sheet after the Weichselian glaciation and the interference with the background stress field related to the ongoing convergence of Africa and Europe. Many of the historic earthquakes concentrate for a certain time along one fault and there is even evidence for distinct earthquake clusters in northern Central Europe e.g. along the Osning Thrust or at least along closely spaced faults like in the Gardelegen area. Such a distribution fits the characteristics of other intraplate seismic zones like the eastern United States and requires a re-evaluation of the seismic hazard potential of northern Central Europe, especially in view of the revived search for nuclear waste repositories and ongoing discussions about CO2 sequestration projects in the area.

  11. Characterisation of stainless steel synroc interactions under hot isostatic pressing (HIPing) conditions

    NASA Astrophysics Data System (ADS)

    Li, H.; Zhang, Y.; McGlinn, P. J.; Moricca, S.; Begg, B. D.; Vance, E. R.

    2006-09-01

    Stainless steel/synroc interactions under HIPing conditions (1280 °C/100 MPa/3 h) have been studied. The synroc material was based on the zirconolite-rich ceramic targeted for surplus Pu disposition. A ˜300 mm-thick complex reaction interface with 8 distinct layers has been identified. Although the Fe diffusion controlled interactions have changed the microstructures of the synroc phases at the interface, they do not affect the integrity of synroc and are unlikely to have any detrimental effect on this synroc derivative.

  12. Glacial isostatic adjustment and Earth rotation: Refined constraints on the viscosity of the deepest mantle

    SciTech Connect

    Peltier, W.R.; Jiang, X.

    1996-02-10

    This report explores the use of the present-day rate and direction of polar wander and the magnitude of the nontidal acceleration of the rate of planetary rotation of the earth to contrain the viscosity of the lower regions of the lower mantle.

  13. Role of isostaticity and load-bearing microstructure in the elasticity of yielded colloidal gels.

    PubMed

    Hsiao, Lilian C; Newman, Richmond S; Glotzer, Sharon C; Solomon, Michael J

    2012-10-01

    We report a simple correlation between microstructure and strain-dependent elasticity in colloidal gels by visualizing the evolution of cluster structure in high strain-rate flows. We control the initial gel microstructure by inducing different levels of isotropic depletion attraction between particles suspended in refractive index matched solvents. Contrary to previous ideas from mode coupling and micromechanical treatments, our studies show that bond breakage occurs mainly due to the erosion of rigid clusters that persist far beyond the yield strain. This rigidity contributes to gel elasticity even when the sample is fully fluidized; the origin of the elasticity is the slow Brownian relaxation of rigid, hydrodynamically interacting clusters. We find a power-law scaling of the elastic modulus with the stress-bearing volume fraction that is valid over a range of volume fractions and gelation conditions. These results provide a conceptual framework to quantitatively connect the flow-induced microstructure of soft materials to their nonlinear rheology.

  14. Synthesis of increased-density bismuth-based superconductors with cold isostatic pressing and heat treating

    DOEpatents

    Lanagan, Michael T.; Picciolo, John J.; Dorris, Stephen E.

    1997-01-01

    The present invention is directed to a process for producing high temperature superconducting ceramic materials. More particularly, the present invention is directed to a process that enhances the densification of Bi.sub.1.8 Pb.sub.0.4 Sr.sub.2 Ca.sub.2 Cu.sub.3 O.sub.10 "BSCCO" ceramics.

  15. Reassessing Geophysical Models of the Bushveld Complex in 3D

    NASA Astrophysics Data System (ADS)

    Cole, J.; Webb, S. J.; Finn, C.

    2012-12-01

    Conceptual geophysical models of the Bushveld Igneous Complex show three possible geometries for its mafic component: 1) Separate intrusions with vertical feeders for the eastern and western lobes (Cousins, 1959) 2) Separate dipping sheets for the two lobes (Du Plessis and Kleywegt, 1987) 3) A single saucer-shaped unit connected at depth in the central part between the two lobes (Cawthorn et al, 1998) Model three incorporates isostatic adjustment of the crust in response to the weight of the dense mafic material. The model was corroborated by results of a broadband seismic array over southern Africa, known as the Southern African Seismic Experiment (SASE) (Nguuri, et al, 2001; Webb et al, 2004). This new information about the crustal thickness only became available in the last decade and could not be considered in the earlier models. Nevertheless, there is still on-going debate as to which model is correct. All of the models published up to now have been done in 2 or 2.5 dimensions. This is not well suited to modelling the complex geometry of the Bushveld intrusion. 3D modelling takes into account effects of variations in geometry and geophysical properties of lithologies in a full three dimensional sense and therefore affects the shape and amplitude of calculated fields. The main question is how the new knowledge of the increased crustal thickness, as well as the complexity of the Bushveld Complex, will impact on the gravity fields calculated for the existing conceptual models, when modelling in 3D. The three published geophysical models were remodelled using full 3Dl potential field modelling software, and including crustal thickness obtained from the SASE. The aim was not to construct very detailed models, but to test the existing conceptual models in an equally conceptual way. Firstly a specific 2D model was recreated in 3D, without crustal thickening, to establish the difference between 2D and 3D results. Then the thicker crust was added. Including the less

  16. Horizontal and vertical velocities derived from the IDS contribution to ITRF2014, and comparisons with geophysical models

    NASA Astrophysics Data System (ADS)

    Moreaux, G.; Lemoine, F. G.; Argus, D. F.; Santamaría-Gómez, A.; Willis, P.; Soudarin, L.; Gravelle, M.; Ferrage, P.

    2016-07-01

    In the context of the 2014 realization of the International Terrestrial Reference Frame (ITRF2014), the International DORIS Service (IDS) has delivered to the IERS a set of 1140 weekly SINEX files including station coordinates and Earth orientation parameters, covering the time period from 1993.0 to 2015.0. From this set of weekly SINEX files, the IDS Combination Center estimated a cumulative DORIS position and velocity solution to obtain mean horizontal and vertical motion of 160 stations at 71 DORIS sites. The main objective of this study is to validate the velocities of the DORIS sites by comparison with external models or time series. Horizontal velocities are compared with two recent global plate models (GEODVEL 2010 and NNR-MORVEL56). Prior to the comparisons, DORIS horizontal velocities were corrected for Global Isostatic Adjustment (GIA) from the ICE-6G (VM5a) model. For more than half of the sites, the DORIS horizontal velocities differ from the global plate models by less than 2-3 mm/yr. For five of the sites (Arequipa, Dionysos/Gavdos, Manila, Santiago) with horizontal velocity differences wrt these models larger than 10 mm/yr, comparisons with GNSS estimates show the veracity of the DORIS motions. Vertical motions from the DORIS cumulative solution are compared with the vertical velocities derived from the latest GPS cumulative solution over the time span 1995.0-2014.0 from the University of La Rochelle (ULR6) solution at 31 co-located DORIS-GPS sites. These two sets of vertical velocities show a correlation coefficient of 0.83. Vertical differences are larger than 2 mm/yr at 23 percent of the sites. At Thule the disagreement is explained by fine-tuned DORIS discontinuities in line with the mass variations of outlet glaciers. Furthermore, the time evolution of the vertical time series from the DORIS station in Thule show similar trends to the GRACE equivalent water height.

  17. An interdisciplinary approach to constructing models of the lithosphere and asthenosphere of Antarctica

    NASA Astrophysics Data System (ADS)

    Reading, Anya; Halpin, Jacqueline; Cracknell, Matthew

    2015-04-01

    In this contribution, we aim to draw on the wealth of information that now exists across several Earth Sciences disciplines and relates to the structure of the lithosphere and asthenosphere of Antarctica. Geological terranes that are well constrained in continents that were neighbours of Antarctica prior to the break-up of Gondwana (South America, Africa, India and Australia) are represented in three dimensions. Extrapolation into the interior of Antarctica is constrained by extensive remote sensing and geophysical datasets. We also incorporate direct information on the Antarctic continent which has substantially improved in both quality and coverage following extensive field programs of several nations in association with the 2007-2008 International Polar Year. Where several contrasting models remain possible, we construct multiple models that allow such alternatives to be readily compared. The models that we construct are of an appropriate resolution for continent scale rheological and seismological simulations. They consist of spatial coordinates including depth, material property values, and also metadata which provide for nominal uncertainty estimates and provenance information for the model values. This approach enables a variety of information to be included in a single model, and well and less-well constrained parts of the model to be handled with rigor. The combination of multiple models, and model uncertainty metadata, into model suites is a liberating one. We maximise the inclusion of information across the disciplines of geoscience such that inaccurate, insufficient and inconsistent data may be evaluated. Applications of the new models include large-scale ice sheet modelling, including glacial isostatic adjustment studies. They can also be applied to sensitivity testing with respect to new instrumental deployments in Antarctica such as large scale passive seismic experiments. As the international community progresses from reconnaissance studies to

  18. Exploiting sedimentation datasets to model the impact of sediment loading on sea level at the Yellow River Delta

    NASA Astrophysics Data System (ADS)

    Pico, T.; Mitrovica, J. X.; Ferrier, K.

    2015-12-01

    In order to accurately depict glacial isostatic adjustment (GIA) of the solid Earth and consequent sea level, it is necessary to incorporate the loading and unloading of the crust occurring over glacial cycles in the form of sediment erosion and deposition. The inclusion of sediment loading in GIA models becomes even more imperative when studying sea level at densely populated centers along coastlines, many of which are located at large river deltas. Sediment deposition at deltas influences sea level by introducing a load, which in turn alters crustal elevation and perturbs the gravitational field. These sediment loads vary in space and time over glacial cycles, as deltas prograde during sea-level highstands and shelves are exposed during lowstands. The Yellow River serves as an archetypical case study of fluvial response to glacial cycles. Draining the highly erodible, glacially derived Loess Plateau, the Yellow River's sediment flux is the 2nd highest in the world. This site provides an ideal location for modeling sediment loads in order to investigate how glacial cycles control sedimentation history and regional sea level. This study employs datasets constraining deposition and erosion that are physically recorded in dated sediment cores, seismic sections, and river flux measurements. These sedimentary datasets elucidate how loading varies spatially and with time in the basin, but also, importantly, data of fossil-bearing cores act to constrain sea level history during this period. Thus, we utilize physical sedimentary data as both an input to our model and a check on the predicted local sea level. Our gravitationally self-consistent global model is then capable of exploring and constraining how evolving sediment loads and migrating depositional centers impact local predicted crustal deformation, and therefore sea-level, over glacial timescales.

  19. Leadership Models.

    ERIC Educational Resources Information Center

    Freeman, Thomas J.

    This paper discusses six different models of organizational structure and leadership, including the scalar chain or pyramid model, the continuum model, the grid model, the linking pin model, the contingency model, and the circle or democratic model. Each model is examined in a separate section that describes the model and its development, lists…

  20. The Lithosphere of The East African Rift System: Insights From Three-Dimensional Density Modelling

    NASA Astrophysics Data System (ADS)

    Woldetinsae, G.; Götze, H. J.

    2004-12-01

    We use the gravity data that cover the large part of the Afro-Arabian rift system, the eastern branch (Ethiopia-Afar and northern Kenya), in order to produce a regional density model. In an earlier work the new and old gravity data were compiled, evaluated and homogenised using a consistent data reduction procedures. Three basic constraints widely spaced over a 1500 km rift length have been generated between 1969 and 2003 by an international consortium with information from isostatic models, global tomography, geological, geochemical evidences, and petrological and experimental results. These are integrated and applied to the model to constrain upper and lower crustal structures underneath the Rift and Plateau areas. New crustal thickness estimations (Dugda et al., 2004 in press) and inferences from recent velocity models along the axis of the Main Ethiopian Rift (Keller et al., 2004) are added to the density model. Thirty parallel planes cutting across the entire plateau region and Rift system (Afar-Ethiopia-Kenya) are interactively modelled using a starting geometry that invoke asthenospheric upwelling. Densities for the upper crust are calculated using Nafe Drake method, averaged from earlier interpretation and measured ones from the Geological Survey of Ethiopia database (e.g. Geothermal project, GSE petrophysical laboratory, pers. communication). Densities for lower crust are estimated using the approach by Sobolov and Babyko (1994). We used also lower crustal densities calculated by (Simyu and Keller, 1997) for the northern part of Kenya rift. The preliminary model offers a possibility to quantify depth, thickness and volumes of different geological interfaces and bodies. As for example, the estimation of the volume of volcanic constructs on the western plateau of Ethiopia is relatively larger than the eastern plateau. The load map derived from the model indicated maximum crustal loads at the crust/mantle interface (ca. 40km) on the eastern and western flanks

  1. Modeling Sea-Level Change using Errors-in-Variables Integrated Gaussian Processes

    NASA Astrophysics Data System (ADS)

    Cahill, Niamh; Parnell, Andrew; Kemp, Andrew; Horton, Benjamin

    2014-05-01

    We perform Bayesian inference on historical and late Holocene (last 2000 years) rates of sea-level change. The data that form the input to our model are tide-gauge measurements and proxy reconstructions from cores of coastal sediment. To accurately estimate rates of sea-level change and reliably compare tide-gauge compilations with proxy reconstructions it is necessary to account for the uncertainties that characterize each dataset. Many previous studies used simple linear regression models (most commonly polynomial regression) resulting in overly precise rate estimates. The model we propose uses an integrated Gaussian process approach, where a Gaussian process prior is placed on the rate of sea-level change and the data itself is modeled as the integral of this rate process. The non-parametric Gaussian process model is known to be well suited to modeling time series data. The advantage of using an integrated Gaussian process is that it allows for the direct estimation of the derivative of a one dimensional curve. The derivative at a particular time point will be representative of the rate of sea level change at that time point. The tide gauge and proxy data are complicated by multiple sources of uncertainty, some of which arise as part of the data collection exercise. Most notably, the proxy reconstructions include temporal uncertainty from dating of the sediment core using techniques such as radiocarbon. As a result of this, the integrated Gaussian process model is set in an errors-in-variables (EIV) framework so as to take account of this temporal uncertainty. The data must be corrected for land-level change known as glacio-isostatic adjustment (GIA) as it is important to isolate the climate-related sea-level signal. The correction for GIA introduces covariance between individual age and sea level observations into the model. The proposed integrated Gaussian process model allows for the estimation of instantaneous rates of sea-level change and accounts for all

  2. Effect of GIA models with 3D composite mantle viscosity on GRACE mass balance estimates for Antarctica

    NASA Astrophysics Data System (ADS)

    van der Wal, Wouter; Whitehouse, Pippa L.; Schrama, Ernst J. O.

    2015-03-01

    Seismic data indicate that there are large viscosity variations in the mantle beneath Antarctica. Consideration of such variations would affect predictions of models of Glacial Isostatic Adjustment (GIA), which are used to correct satellite measurements of ice mass change. However, most GIA models used for that purpose have assumed the mantle to be uniformly stratified in terms of viscosity. The goal of this study is to estimate the effect of lateral variations in viscosity on Antarctic mass balance estimates derived from the Gravity Recovery and Climate Experiment (GRACE) data. To this end, recently-developed global GIA models based on lateral variations in mantle temperature are tuned to fit constraints in the northern hemisphere and then compared to GPS-derived uplift rates in Antarctica. We find that these models can provide a better fit to GPS uplift rates in Antarctica than existing GIA models with a radially-varying (1D) rheology. When 3D viscosity models in combination with specific ice loading histories are used to correct GRACE measurements, mass loss in Antarctica is smaller than previously found for the same ice loading histories and their preferred 1D viscosity profiles. The variation in mass balance estimates arising from using different plausible realizations of 3D viscosity amounts to 20 Gt/yr for the ICE-5G ice model and 16 Gt/yr for the W12a ice model; these values are larger than the GRACE measurement error, but smaller than the variation arising from unknown ice history. While there exist 1D Earth models that can reproduce the total mass balance estimates derived using 3D Earth models, the spatial pattern of gravity rates can be significantly affected by 3D viscosity in a way that cannot be reproduced by GIA models with 1D viscosity. As an example, models with 1D viscosity always predict maximum gravity rates in the Ross Sea for the ICE-5G ice model, however, for one of the three preferred 3D models the maximum (for the same ice model) is found

  3. A new estimate of the effective elastic thickness of the Canadian shield from admittance analyses using the wavelet transform, and models of flexure and mantle convection

    NASA Astrophysics Data System (ADS)

    Kirby, J. F.; Swain, C. J.

    2013-12-01

    The flexural rigidity of the Earth's cratonic regions is a topic of much controversy. While many studies have suggested that cratons possess high elastic strength, others maintain that the continental lithosphere is everywhere weak. In this study we focus on the Canadian shield, and show that perceived evidence for weak cratonic lithosphere is compromised by shortcomings of the spectral analysis technique. Here we compare estimates of the admittance between free-air gravity and topography in the spectral domain from wavelet and multitaper methods. We apply particular attention to their long wavelength values, since it is here that the signals from mantle convection, glacial isostatic adjustment (GIA) and flexure are often present together. Our results show that, when used with certain parameter values, the multitaper method has a comparatively poor resolution at long wavelengths, and hence is not always able to distinguish between the harmonics due to convection and flexural processes. This renders it unreliable for estimating the flexural rigidity. We then show that the wavelet method does have the requisite properties to make this distinction, since it is able to correctly resolve a low-admittance dip at long wavelengths in both synthetic and real data. When the observed wavelet admittance of the Canadian shield is inverted against the predictions of a combined flexural, convection and GIA model, we find that the shield possesses a core of high effective elastic thickness (Te), greater than 118 km to 95% confidence, located to the immediate south-west of Hudson Bay.

  4. Models and role models.

    PubMed

    ten Cate, Jacob M

    2015-01-01

    Developing experimental models to understand dental caries has been the theme in our research group. Our first, the pH-cycling model, was developed to investigate the chemical reactions in enamel or dentine, which lead to dental caries. It aimed to leverage our understanding of the fluoride mode of action and was also utilized for the formulation of oral care products. In addition, we made use of intra-oral (in situ) models to study other features of the oral environment that drive the de/remineralization balance in individual patients. This model addressed basic questions, such as how enamel and dentine are affected by challenges in the oral cavity, as well as practical issues related to fluoride toothpaste efficacy. The observation that perhaps fluoride is not sufficiently potent to reduce dental caries in the present-day society triggered us to expand our knowledge in the bacterial aetiology of dental caries. For this we developed the Amsterdam Active Attachment biofilm model. Different from studies on planktonic ('single') bacteria, this biofilm model captures bacteria in a habitat similar to dental plaque. With data from the combination of these models, it should be possible to study separate processes which together may lead to dental caries. Also products and novel agents could be evaluated that interfere with either of the processes. Having these separate models in place, a suggestion is made to design computer models to encompass the available information. Models but also role models are of the utmost importance in bringing and guiding research and researchers. PMID:25871413

  5. Models, Fiction, and Fictional Models

    NASA Astrophysics Data System (ADS)

    Liu, Chuang

    2014-03-01

    The following sections are included: * Introduction * Why Most Models in Science Are Not Fictional * Typically Fictional Models in Science * Modeling the Unobservable * Fictional Models for the Unobservable? * References

  6. Space-geodetic Constraints on GIA Models with 3D Viscosity

    NASA Astrophysics Data System (ADS)

    Van Der Wal, W.; Xu, Z.

    2012-12-01

    Models for Glacial Isostatic Adjustment (GIA) are an important correction to observations of mass change in the polar regions. Inputs for GIA models include past ice thickness and deformation parameters of the Earth's mantle, both of which are imperfectly known. Here we focus on the latter by investigating GIA models with 3D viscosity and composite (linear and non-linear) flow laws. It was found recently that GIA models with a composite flow law result in a better fit to historic sea level data, but they predict too low present-day uplift rates and gravity rates. Here GIA models are fit to space-geodetic constraints in Fennoscandia and North America. The preferred models are used to calculate the magnitude of the GIA correction on mass change estimates in Greenland and Antarctica. The observations used are GRACE Release 4 solutions from CSR and GFZ and published GPS solutions for North America and Fennoscandia, as well as historic sea level data. The GIA simulations are performed with a finite element model of a spherical, self-gravitating, incompressible Earth with 2x2 degree elements. Parameters in the flow laws are taken from seismology, heatflow measurements and experimental constraints and the ice loading history is prescribed by ICE-5G. It was found that GRACE and GPS derived uplift rates agree at the level of 1 mm/year in North America and at a level of 0.5 mm/year in Fennoscandia, the difference between the two regions being due to larger GPS errors and under sampling in North America. It can be concluded that both GPS and GRACE see the same process and the effects of filtering, noise and non-GIA processes such as land hydrology are likely to be small. Two GIA models are found that bring present-day uplift rate close to observed values in North America and Fennoscandia. These models result in a GIA correction of -17 Gt/year and -26 Gt/year on Greenland mass balance estimates from GRACE.

  7. Structural and stratigraphic evolution of the Iberia-Newfoundland margin: A quantitative modeling approach

    NASA Astrophysics Data System (ADS)

    Karner, Garry; Johnson, Christopher; Mohn, Geoffroy; Manatschal, Gianreto

    2013-04-01

    Passive margins develop by extension and rupture of continental lithosphere. In general, the structure of a passive margin depends on a number of fundamental parameters, including the inherited rheology, rheological evolution during extension, magmatism, relative plate motions and the thermal properties of the continental crust and mantle before, during, and after rifting. These parameters determine the style, distribution and rate of extension, as well as the amount of syn- and post-rift accommodation and magmatism. In this presentation, we will investigate the paleo-water depths developed during hyper-extension of the Iberian-Newfoundland margin lithosphere by applying a process-oriented integration procedure that simulates the preserved margin stratigraphy using a model for deformation of the lithosphere and flexural isostasy. Seismic reflection and refraction data, gravity, and ODP drilling of the Iberian-Newfoundland margin are used as constraints. Manatschal et al., (2007) structurally reconstructed the Iberia margin to a 6-8 km pre-rift crustal thickness capped by shallow water Tithonian carbonates, suggesting an initial relief near sea-level. For reasonable crustal and mantle densities, this is difficult to achieve isostatically. Re-examining the evidence for shallow water sediments from Well 1069A (Leg 173 1069A16R3 127-130) suggests an environment of deposition consistent with a slope setting. The large organic content within the 1069A samples is dominated by woody and coaly particles, suggesting that this depositional package is part of a debris flow rapidly deposited in water depths of 500-1000 m from the laterally adjacent, shallow Galicia Bank to the north. We have applied the Quantitative Basin Analysis (QBA) to integrate seismic stratigraphic interpretations of two representative sections across the northern and southern Iberian margin and Newfoundland margin (Sutra & Manatschal, in press) to model the thinning of the lithosphere and the respective

  8. Integrated geophysical-petrological modelling of the Trans-European Suture Zone along the TOR-profile

    NASA Astrophysics Data System (ADS)

    Pappa, Folker; Ebbing, Jörg; Rabbel, Wolfgang

    2014-05-01

    We apply the integrated geophysical-petrological software package LitMod3D to study the effect of changes in thickness and composition associated with the Sorgenfrei-Tornquist-Zone as part of the Transeuropean Suture Zone (TESZ). Results of the TOR-project (Teleseismic Tomography TORnquist) show a P wave velocity anomaly that indicates an abrupt step in the base lithosphere between southern Sweden and Northern Germany. From a depth of ~300 km beneath the proto-Proterozoic Baltic shield the base lithosphere increases to less than 100 km beneath the Phanerozoic terranes in the southwest. However, this significant change in lithospheric thickness is not expressed by significant changes in the gravity field or topography. Hence, some form of isostatic compensation must be achieved by changes in the composition or thermal structure of the crust or upper mantle. First sensitivity tests were performed to show that the most important parameters to explain seismic upper mantle velocities, gravity and topography. These are, in addition to lithospheric thickness, the densities and thermal conductivity in the crust and the amount of depletion of the subcontinental lithospheric mantle (SCLM). When applying a simple geometry with steps at the Moho and base lithosphere, the TOR results could be reproduced to a large degree when applying different compositions for the SCLM beneath the Proterozoic and Phanerozoic domains. To address the gravity field and topography as well, we present two alternative models for the TOR-profile. In the first model, the gravity field and topography is explained by dividing the Phanerozoic SCLM in a refertilized upper and more depleted lower part. This model leads to a deeper base lithosphere (130 km), but does not provide a very good fit to the P wave velocities. In the second alternative, the thermal conductivity of the Phanerozoic crust and for the sediments has been increased within reasonable parameters. This leads to a shallower LAB ~100 km and

  9. The role of mechanical heterogeneities during continental breakup: a 3D lithospheric-scale modelling approach

    NASA Astrophysics Data System (ADS)

    Duclaux, Guillaume; Huismans, Ritske S.; May, Dave

    2015-04-01

    olivine for the mantle. A constant extension rate is imposed on two opposite walls in the horizontal direction; the model' surface evolves freely; an isostatic boundary condition is imposed on the bottom wall. We explore a range of weak notches geometries, as well as the presence of random noise across a central region of the model. We compare the evolution of the geometry of the surface rift segments, their linkage and faults propagation during ongoing extension. These models allow us to assess the importance of mechanical heterogeneities for controlling passive margin geometries, and to precise the underlying physics governing continental breakup.

  10. A crust-scale 3D structural model of the Beaufort-Mackenzie Basin (Arctic Canada)

    NASA Astrophysics Data System (ADS)

    Sippel, Judith; Scheck-Wenderoth, Magdalena; Lewerenz, Björn; Kroeger, Karsten Friedrich

    2013-04-01

    The Beaufort-Mackenzie Basin was initiated in the Early Jurassic as part of an Arctic rifted passive continental margin which soon after became overprinted by Cordilleran foreland tectonics. Decades of industrial exploration and scientific research in this petroliferous region have produced a wide spectrum of geological and geophysical data as well as geoscientific knowledge. We have integrated available grids of sedimentary horizons, well data, seismic reflection and refraction data, and the observed regional gravity field into the first crust-scale 3D structural model of the Beaufort-Mackenzie Basin. Many characteristics of this model reflect the complex geodynamic and tectonostratigraphic history of the basin. The Mesozoic-Cenozoic sedimentary part of the model comprises seven clastic units (predominantly sandy shales) of which the modelled thickness distributions allow to retrace the well-established history of the basin comprising a gradual north(east)ward shift of the main depocentres as well as diverse phases of localised erosion. As a result of this development, the present-day configuration of the basin reveals that the sedimentary units tend to be younger, more porous, and thus less dense towards the north at a constant depth level. By integrating three refraction seismic profiles and performing combined isostatic and 3D gravity modelling, we have modelled the sub-sedimentary basement of the Beaufort-Mackenzie Basin. The continental basement spans from unstretched domains (as thick as about 42 km) in the south to extremely thinned domains (of less than 5 km thickness) in the north where it probably represents transitional crust attached to the oceanic crust of the Canada Basin. The uppermost parts of the continental crust are less dense (ρ = 2710 kg/m3) and most probably made up by pre-Mesozoic meta-sediments overlying a heavier igneous and metamorphic crust (ρ = 2850 kg/m3). The presented crust-scale 3D structural model shows that the greatest

  11. Constrained potential field modeling of the crustal architecture of the Musgrave Province in central Australia: Evidence for lithospheric strengthening due to crust-mantle boundary uplift

    NASA Astrophysics Data System (ADS)

    Aitken, Alan R. A.; Betts, Peter G.; Weinberg, Roberto F.; Gray, Daniel

    2009-12-01

    We image the crustal architecture of the Musgrave Province with petrophysically constrained forward models of new potential field data. These models image divergent shallow-dipping crustal scale thrusts that, at depth, link with an axial zone defined by steeper, lithospheric scale transpressional shear zones. They also show that to permit a near-surface density distribution that is consistent with petrophysical and geological observations, approximately 15-20 km of crust-mantle boundary uplift is necessary beneath the axial zone. The long-term preservation of this crust-mantle boundary offset implies a change from relatively weak lithosphere to relatively strong lithosphere during the intraplate Petermann Orogeny. To explain this, we propose a model in which uplift of the axial zone of the orogen leads to local lithospheric strengthening as a result of the uplift of mantle rocks into the lower crust, coupled with long-term lithospheric cooling due to the erosion of a radioactive upper crust. Brace-Goetze lithospheric strength models suggest that these processes may have increased the integrated strength of the lithosphere by a factor of 1.4-2.8. Because of this strengthening, this system is self-limiting, and activity will cease when lithospheric strength is sufficient to resist external forces and support isostatic imbalances. A simple force-balance model demonstrates that the force required to uplift the axial zone is tectonically reasonable and that the system can subsequently withstand significant tensional forces. This example shows that crust-mantle boundary uplift coupled with reduced crustal heat production can profoundly affect the long-term strength of the continental lithosphere and may be a critical process in the tectonic stabilization of intraplate regions.

  12. Rheological variations across an active rift system -- results from lithosphere-scale 3D gravity and thermal models of the Kenya Rift

    NASA Astrophysics Data System (ADS)

    Meeßen, Christian; Sippel, Judith; Cacace, Mauro; Scheck-Wenderoth, Magdalena; Fishwick, Stewart; Heine, Christian; Strecker, Manfred R.

    2015-04-01

    Due to its tectono-volcanic activity and economic (geothermal and petroleum) potential, the eastern branch of the East African Rift System (EARS) is one of the best studied extensional systems worldwide and an important natural laboratory for the development of geodynamic concepts on rifting and nascent continental break-up. The Kenya Rift, an integral part of the eastern branch of the EARS, has formed in the area of weak Proterozoic crust of the Mozambique mobile belt adjacent to the rheologically stronger Archean Tanzania craton. To assess the variations in lithospheric strength between different tectonic domains and their influence on the tectonic evolution of the region, we developed a set of structural, density, thermal and rheological 3D models. For these models we integrated multi-disciplinary information, such as published geological field data, sediment thicknesses, well information, existing structural models, seismic refraction and reflection data, seismic tomography, gravity and heat-flow data. Our main approach focused on combined 3D isostatic and gravity modelling. The resulting lithosphere-scale 3D density model provides new insights into the depth distribution of the crust-mantle boundary and thickness variations of different crustal density domains. The latter further facilitate interpretations of variations of lithologies and related physical rock properties. By considering lithology-dependent heat production and thermal conductivity, we calculate the conductive thermal field across the region of the greater Kenya Rift. Finally, the assessed variations in lithology and temperature allow deriving differences in the integrated strength of the lithosphere across the different tectonic domains.

  13. Quaternary Morphodynamics of Fluvial Dispersal Systems Revealed: The Fly River, PNG, and the Sunda Shelf, SE Asia, simulated with the Massively Parallel GPU-based Model 'GULLEM'

    NASA Astrophysics Data System (ADS)

    Aalto, R. E.; Lauer, J. W.; Darby, S. E.; Best, J.; Dietrich, W. E.

    2015-12-01

    During glacial-marine transgressions vast volumes of sediment are deposited due to the infilling of lowland fluvial systems and shallow shelves, material that is removed during ensuing regressions. Modelling these processes would illuminate system morphodynamics, fluxes, and 'complexity' in response to base level change, yet such problems are computationally formidable. Environmental systems are characterized by strong interconnectivity, yet traditional supercomputers have slow inter-node communication -- whereas rapidly advancing Graphics Processing Unit (GPU) technology offers vastly higher (>100x) bandwidths. GULLEM (GpU-accelerated Lowland Landscape Evolution Model) employs massively parallel code to simulate coupled fluvial-landscape evolution for complex lowland river systems over large temporal and spatial scales. GULLEM models the accommodation space carved/infilled by representing a range of geomorphic processes, including: river & tributary incision within a multi-directional flow regime, non-linear diffusion, glacial-isostatic flexure, hydraulic geometry, tectonic deformation, sediment production, transport & deposition, and full 3D tracking of all resulting stratigraphy. Model results concur with the Holocene dynamics of the Fly River, PNG -- as documented with dated cores, sonar imaging of floodbasin stratigraphy, and the observations of topographic remnants from LGM conditions. Other supporting research was conducted along the Mekong River, the largest fluvial system of the Sunda Shelf. These and other field data provide tantalizing empirical glimpses into the lowland landscapes of large rivers during glacial-interglacial transitions, observations that can be explored with this powerful numerical model. GULLEM affords estimates for the timing and flux budgets within the Fly and Sunda Systems, illustrating complex internal system responses to the external forcing of sea level and climate. Furthermore, GULLEM can be applied to most ANY fluvial system to

  14. 3D structural model of the North Alpine Foreland Basin, Bavarian Part

    NASA Astrophysics Data System (ADS)

    Przybycin, Anna M.; Scheck-Wenderoth, Magdalena; Schneider, Michael

    2013-04-01

    The continental collision of Europe and Africa leads to the rise of the European Alps, which gave way to the formation of the North Alpine Foreland Basin, also referred to as the Molasse Basin, since the Tertiary. This typically wedge formed "foredeep" basin is filled with predominantly clastic sediments originating from erosional processes of the Alps which overly a southward dipping Mesozoic and Paleozoic succession. With our project we want to contribute to the understanding of the structure and subsequently of the thermal configuration of the Molasse Basin and its underlying deposits on a basin wide scale. We constructed a 3D structural model of the basin down to the crust-mantle-boundary, beginning with the Bavarian part. Therefore we used an approach of already existing local to midscale 2D and 3D structural models (e.g. Lüschen et al. 2006) as well as surface maps, seismic, well and gravity data. This 3D structural model resolves 5 sedimentary layers of the Mesozoic, including the geothermally utilized carbonate Malm aquifer (e.g. Birner et al. 2011), as well as the combined Paleozoic basement. Assuming isostatic equilibrium of the system a lithosphere-asthenosphere-boundary (LAB) has been calculated and compared to other published LABs of the region. Subsequently the model has been further constrained by 3D gravity modeling. The outcomes show that Cretaceous sediments are restricted to a small region in the central to eastern model area and are mostly overlain by the Tertiary Molasse sediments. The Triassic sediments occur in the northern and western part of the model area and do not continue far under the Molasse basin proper, while the Jurassic can be tracked as far south as beneath the Alps. The evaluation of the gravity indicates that the crystalline crust consists of a lighter upper crust and a denser lower crust. Our final LAB is shallowest under the Triassic subbasin, descending below the Bohemian Massif and the Molasse Basin proper and rising again

  15. ICE-6G models of postglacial relative sea-level history applied to Holocene coral reef and mangrove records of the western Caribbean

    NASA Astrophysics Data System (ADS)

    Toscano, M. A.; Peltier, W. R.; Drummond, R.; Gonzalez, J.

    2012-12-01

    Fossil coral reefs and mangrove peat accumulations at western Caribbean sites along a latitudinal gradient from the Florida Keys through Belize and Panama provide dated and interpreted 8,000 year Holocene sea-level records for comparison with RSL predictions of the ICE-6G (VM5A, VM5B; L90) models of glacio-hydro-isostatic adjustment, with and without rotational feedback. These presumably passive continental margin sites provide the means to establish a N-S spatial trend in the varying influences of GIA, eustatic components of Holocene sea level, extent of forebulge collapse and influence of rotational feedback over a 20° latitudinal range. Previous ICE6G (VM5A) model-coral data comparisons for St Croix, USVI, Antigua, Martinique and Barbados (Toscano, Peltier and Drummond, 2011, QSR) along the eastern Caribbean plate and island arc illustrated the close model-data compatibility, the influence of rotational feedback acting as a significant factor in reducing misfits, and the need for high quality in situ data to confirm the extension of the proglacial forebulge into tropical latitudes. The gradient of western Caribbean continental shelf sites comprises a much more varied range of model-data relationships based on extensive combined Acropora palmata (reef crest coral) and Rhizophora mangle (microtidal mangrove) peat datasets in all cases. Starting at the northernmost region with the Florida Keys, there exist negative model misfits to the data, suggesting the possibility of a positive tectonic overprint upon expectations related to the glacial isostatic adjustment process acting alone, even though this region is normally believed to be tectonically stable. The largest multi-proxy database from Belize supports the likelihood of increasing rates of subsidence from north to south in the Belize Lagoon, which may account for numerous positive GIA model-data misfits. The southernmost site at Panama is most similar to Belize in the possible nature of tectonic influences on

  16. A 70th Degree Lunar Gravity Model (GLGM-2) from Clementine and other tracking data

    NASA Technical Reports Server (NTRS)

    Lemonie, Frank G. R.; Smith, David E.; Zuber, Maria T.; Neumann, Gregory A.

    1997-01-01

    A spherical harmonic model of the lunar gravity field complete to degree and order 70 has been developed from S band Doppler tracking data from the Clementine mission, as well as historical tracking data from Lunar Orbiters 1-5 and the Apollo 15 and 16 subsatellites. The model combines 361,000 Doppler observations from Clementine with 347,000 historical observations. The historical data consist of mostly 60-s Doppler with a noise of 0.25 to several mm/s. The Clementine data consist of mostly 10-s Doppler data, with a data noise of 0.25 mm/s for the observations from the Deep Space Network, and 2.5 mm/s for the data from a naval tracking station at Pomonkey, Maryland. Observations provided Clementine, provide the strongest satellite constraint on the Moon's low-degree field. In contrast the historical data, collected by spacecraft that had lower periapsis altitudes, provide distributed regions of high-resolution coverage within +/- 29 deg of the nearside lunar equator. To obtain the solution for a high-degree field in the absence of a uniform distribution of observations, we applied an a priori power law constraint of the form 15 x 10(exp -5)/sq l which had the effect of limiting the gravitational power and noise at short wavelengths. Coefficients through degree and order 18 are not significantly affected by the constraint, and so the model permits geophysical analysis of effects of the major basins at degrees 10-12. The GLGM-2 model confirms major features of the lunar gravity field shown in previous gravitational field models but also reveals significantly more detail, particularly at intermediate wavelengths (10(exp 3) km). Free-air gravity anomaly maps derived from the new model show the nearside and farside highlands to be gravitationally smooth, reflecting a state of isostatic compensation. Mascon basins (including Imbrium, Serenitatis, Crisium, Smythii, and Humorum) are denoted by gravity highs first recognized from Lunar Orbiter tracking. All of the major

  17. Geodynamic evolution of the lithosphere beneath the Eastern Anatolia region: Constraints from geodynamic modeling

    NASA Astrophysics Data System (ADS)

    Memis, Caner; Hakan Gogus, Oguz; Pysklywec, Russell; Keskin, Mehmet; Celal Sengor, A. M.; Topuz, Gultekin

    2016-04-01

    The east Anatolian orogenic plateau is characterized by an average elevation of 2 km, and is delimited by the Bitlis-Zagros collision zone to the south and the Pontide arc to the north. Stratigraphic evidence suggests that the high plateau attained its current elevation since the Serravallian (about 12 million years ago), but probably did not reach its present height until at least the latest Pliocene. While the crustal shortening following the Arabia-Eurasia collision in the south enabled its relatively rapid rise and regional tectonic evolution, the presumed removal of the downgoing slab beneath east Anatolia has potentially played a significant role in this geodynamic configuration. According to the proposed scenario, the northward subducting slab of Neo-Tethys peels away from the overlying crust similar to the lithospheric delamination model. In this work, we performed a series of lithospheric removal models by varying rheological, physical and mechanical properties by using 2D numerical geodynamic experiments, (e.g. plate convergence rate, crustal thickness, mantle lithosphere yield-stress). Our model results show that the average amount of delamination hinge motion is maximum (18 km/my) when the lower crustal rheology is felsic granulite. The slab break-off only occurs at lower convergence rates (≤ 2 cm/yr), and is imposed on the margin of delaminating mantle lithosphere. The surface uplift takes place above the asthenospheric column (or plateau gap) through isostatic and thermal support of asthenospheric upwelling, and varies dependent on the width of the asthenospheric column. However; with higher plate convergence rates (≥3 cm/yr), the asthenospheric column does not widen enough and the continental collision occurs rather than delamination/peeling away. In this case, the average uplift appears in the central section of the crust, and this exceeds a surface elevation of 3 km. All model results are consistent with the observations from the Eastern

  18. Sea-level and solid-Earth deformation feedbacks in ice sheet modelling

    NASA Astrophysics Data System (ADS)

    Konrad, Hannes; Sasgen, Ingo; Klemann, Volker; Thoma, Malte; Grosfeld, Klaus; Martinec, Zdeněk

    2014-05-01

    The interactions of ice sheets with the sea level and the solid Earth are important factors for the stability of the ice shelves and the tributary inland ice (e.g. Thomas and Bentley, 1978; Gomez et al, 2012). First, changes in ice extent and ice thickness induce viscoelastic deformation of the Earth surface and Earth's gravity field. In turn, global and local changes in sea level and bathymetry affect the grounding line and, subsequently, alter the ice dynamic behaviour. Here, we investigate these feedbacks for a synthetic ice sheet configuration as well as for the Antarctic ice sheet using a three-dimensional thermomechanical ice sheet and shelf model, coupled to a viscoelastic solid-Earth and gravitationally self-consistent sea-level model. The respective ice sheet undergoes a forcing from rising sea level, warming ocean, and/or changing surface mass balance. The coupling is realized by exchanging ice thickness, Earth surface deformation and sea level periodically. We apply several sets of viscoelastic Earth parameters to our coupled model, e.g. simulating a low-viscous upper mantle present at the Antarctic Peninsula (Ivins et al., 2011). Special focus of our study lies on the evolution of Earth surface deformation and local sea level changes, as well as on the accompanying grounding line evolution. N. Gomez, D. Pollard, J. X. Mitrovica, P. Huybers, and P. U. Clark 2012. Evolution of a coupled marine ice sheet-sea level model, J. Geophys. Res., 117, F01013, doi:10.1029/2011JF002128. E. R. Ivins, M. M. Watkins, D.-N. Yuan, R. Dietrich, G. Casassa, and A. Rülke 2011. On-land ice loss and glacial isostatic adjustment at the Drake Passage: 2003-2009, J. Geophys. Res. 116, B02403, doi: 10.1029/2010JB007607 R. H. Thomas and C. R. Bentley 1978. A model for Holocene retreat of the West Antarctic Ice Sheet, Quaternary Research, 10 (2), pages 150-170, doi: 10.1016/0033-5894(78)90098-4.

  19. Geomorphology: Tales of topography

    NASA Astrophysics Data System (ADS)

    Flowers, Rebecca M.

    2014-07-01

    The origins of topographic relief are challenging to disentangle. Modelling shows that differential isostatic rebound due to erosion of rocks of variable density may influence topography, inspiring a fresh look at topographic highs in landscapes.

  20. Preliminary model of the pre-Tertiary basement rocks beneath Yucca Flat, Nevada Test Site, Nevada, based on analysis of gravity and magnetic data

    USGS Publications Warehouse

    Phelps, Geoffrey A.; McKee, Edwin H.; Sweetkind, D.; Langenheim, V.E.

    2000-01-01

    The Environmental Restoration Program of the U.S. Department of Energy, Nevada Operations Office, was developed to investigate the possible consequences to the environment of 40 years of nuclear testing on the Nevada Test Site. The majority of the tests were detonated underground, introducing contaminants into the ground-water system (Laczniak and others, 1996). An understanding of the ground-water flow paths is necessary to evaluate the extent of ground-water contamination. This report provides information specific to Yucca Flat on the Nevada Test Site. Critical to understanding the ground-water flow beneath Yucca Flat is an understanding of the subsurface geology, particularly the structure and distribution of the pre-Tertiary rocks, which comprise both the major regional aquifer and aquitard sequences (Winograd and Thordarson, 1975; Laczniak and others, 1996). Because the pre-Tertiary rocks are not exposed at the surface of Yucca Flat their distribution must be determined through well logs and less direct geophysical methods such as potential field studies. In previous studies (Phelps and others, 1999; Phelps and Mckee, 1999) developed a model of the basement surface of the Paleozoic rocks beneath Yucca Flat and a series of normal faults that create topographic relief on the basement surface. In this study the basement rocks and structure of Yucca Flat are examined in more detail using the basement gravity anomaly derived from the isostatic gravity inversion model of Phelps and others (1999) and high-resolution magnetic data, as part of an effort to gain a better understanding of the Paleozoic rocks beneath Yucca Flat in support of groundwater modeling.

  1. Tracer-aided modelling using long-term and high resolution data to assess non-stationarity in stream water age

    NASA Astrophysics Data System (ADS)

    Soulsby, C.; Birkel, C.; Tetzlaff, D.

    2015-12-01

    Understanding how water and solutes move through watersheds and the associated travel times remains a key research frontier in hydrology. Here we integrate long-term data (6 years of weekly isotope measurements in rainfall and runoff) into a tracer-aided conceptual modelling approach to provide fresh insights into the complex interrelationships between catchment storage dynamics, hydrological connectivity and resulting non-stationary stream water ages. We show that in a wet Scottish upland catchment dominated by runoff generation from riparian peats (histosols) with high water storage capacity, the storage dynamics of different landscape units (e.g. hillslope vs. riparian zones) regulate both mixing processes and the strength of hydrological connectivity that govern water and solute fluxes and determine catchment travel times. We also found that the frequency and longevity of hydrological connectivity and the associated relative importance of dynamic flow paths control the contribution of younger (< 1 month) or older (>4 years) waters to the stream. Water and solute transport is mainly facilitated by overland flow from saturated histosols connected to the stream network even during smaller events. However, during prolonged dry periods, near-surface runoff "switches off" and stream water is dominated by older groundwater. The saturated riparian soils represent large mixing zones that buffer the time variance of water age and act as "isostats" damping variable inputs. These zones also integrate catchment-scale partial mixing processes. Although simulations depend on model performance, which is influenced by stochastic variation in isotope inputs, a longer-term storage analysis using this tracer-aided model allowed us to examine the sensitivity of the catchment response and transit times to extreme hydroclimatic variability. These insights were validated using a more recent high resolution dataset (3 years of daily isotope data) which also improved constraints on

  2. Investigating the relation between the geometric properties of river basins and the filtering parameters for regional land hydrology applications using GRACE models

    NASA Astrophysics Data System (ADS)

    Piretzidis, Dimitrios; Sideris, Michael G.

    2016-04-01

    This study investigates the possibilities of local hydrology signal extraction using GRACE data and conventional filtering techniques. The impact of the basin shape has also been studied in order to derive empirical rules for tuning the GRACE filter parameters. GRACE CSR Release 05 monthly solutions were used from April 2002 to August 2015 (161 monthly solutions in total). SLR data were also used to replace the GRACE C2,0 coefficient, and a de-correlation filter with optimal parameters for CSR Release 05 data was applied to attenuate the correlation errors of monthly mass differences. For basins located at higher latitudes, the effect of Glacial Isostatic Adjustment (GIA) was taken into account using the ICE-6G model. The study focuses on three geometric properties, i.e., the area, the convexity and the width in the longitudinal direction, of 100 basins with global distribution. Two experiments have been performed. The first one deals with the determination of the Gaussian smoothing radius that minimizes the gaussianity of GRACE equivalent water height (EWH) over the selected basins. The EWH kurtosis was selected as a metric of gaussianity. The second experiment focuses on the derivation of the Gaussian smoothing radius that minimizes the RMS difference between GRACE data and a hydrology model. The GLDAS 1.0 Noah hydrology model was chosen, which shows good agreement with GRACE data according to previous studies. Early results show that there is an apparent relation between the geometric attributes of the basins examined and the Gaussian radius derived from the two experiments. The kurtosis analysis experiment tends to underestimate the optimal Gaussian radius, which is close to 200-300 km in many cases. Empirical rules for the selection of the Gaussian radius have been also developed for sub-regional scale basins.

  3. Coherency strain and its effect on ionic conductivity and diffusion in solid electrolytes--an improved model for nanocrystalline thin films and a review of experimental data.

    PubMed

    Korte, C; Keppner, J; Peters, A; Schichtel, N; Aydin, H; Janek, J

    2014-11-28

    A phenomenological and analytical model for the influence of strain effects on atomic transport in columnar thin films is presented. A model system consisting of two types of crystalline thin films with coherent interfaces is assumed. Biaxial mechanical strain ε0 is caused by lattice misfit of the two phases. The conjoined films consist of columnar crystallites with a small diameter l. Strain relaxation by local elastic deformation, parallel to the hetero-interface, is possible along the columnar grain boundaries. The spatial extent δ0 of the strained hetero-interface regions can be calculated, assuming an exponential decay of the deformation-forces. The effect of the strain field on the local ionic transport in a thin film is then calculated by using the thermodynamic relation between (isostatic) pressure and free activation enthalpy ΔG(#). An expression describing the total ionic transport relative to bulk transport of a thin film or a multilayer as a function of the layer thickness is obtained as an integral average over strained and unstrained regions. The expression depends only on known material constants such as Young modulus Y, Poisson ratio ν and activation volume ΔV(#), which can be combined as dimensionless parameters. The model is successfully used to describe own experimental data from conductivity and diffusion studies. In the second part of the paper a comprehensive literature overview of experimental studies on (fast) ion transport in thin films and multilayers along solid-solid hetero-interfaces is presented. By comparing and reviewing the data the observed interface effects can be classified into three groups: (i) transport along interfaces between extrinsic ionic conductors (and insulator), (ii) transport along an open surface of an extrinsic ionic conductor and (iii) transport along interfaces between intrinsic ionic conductors. The observed effects in these groups differ by about five orders of magnitude in a very consistent way. The

  4. Comparing the effects of rheology on the dynamics and topography of 3D subduction-collision models

    NASA Astrophysics Data System (ADS)

    Pusok, Adina E.; Kaus, Boris; Popov, Anton

    2015-04-01

    Most of the major mountain belts and orogenic plateaus are found within the overlying plate of active or fossil subduction and/or collision zones. It is well known that they evolve differently from one another as the result of specific combinations of surface and mantle processes. The differences among the structures and evolutions of mountain belts arise for several reasons, such as different strengths of materials, different amounts of regional isostatic compensation, and different mechanisms by which forces are applied to the convergence plates. All these possible controlling factors can change with space and time. Of all the mountain belts and orogenic plateaus, the most striking example is the India-Asia collision zone, which gave rise to the Himalayas and the Tibetan Plateau, the largest region of elevated topography and anomalously thick crust on Earth. Understanding the formation and evolution of such a highly elevated region has been the focus of many tectonic and numerical models. While some of these models (i.e. thin sheet model) have successfully illustrated some of the basic physics of continental collision, none can simultaneously represent active processes such as subduction, underthrusting, channel flow or extrusion, for which fully 3D models are required. Here, we employed the 3D code LaMEM to investigate the role that subduction, continental collision and indentation play on lithosphere dynamics at convergent margins, and the implications they have for the Asian tectonics. Our model setup resembles a simplified tectonic map of the India-Asia collision zone and we performed long-term 3D simulations to analyse the dynamics and the conditions under which large topographic plateaus, such as the Tibetan Plateau can form in an integrated lithospheric and upper-mantle scale model. Results of models with linear viscous rheologies show different modes between the oceanic subduction side (continuous subduction, trench retreat and slab roll-back) and the

  5. Lithospheric velocity model across the Southern Central Iberian Zone (Variscan Iberian Massif): The ALCUDIA wide-angle seismic reflection transect

    NASA Astrophysics Data System (ADS)

    Ehsan, Siddique Akhtar; Carbonell, Ramon; Ayarza, Puy; Martí, David; Martínez Poyatos, David; Simancas, José Fernando; Azor, Antonio; Ayala, Concepción; Torné, Montserrat; Pérez-Estaún, Andrés.

    2015-03-01

    A P wave seismic velocity model has been obtained for the Central Iberian Zone, the largest continental fragment of the Iberian Variscan Belt. The spatially dense, high-resolution, wide-angle seismic reflection experiment, ALCUDIA-WA, was acquired in 2012 across central Iberia, aiming to constrain the lithospheric structure and resolve the physical properties of the crust and upper mantle. The seismic transect, ~310 km long, crossed the Central Iberian Zone from its suture with the Ossa-Morena Zone to the southern limit of the Central System mountain range. The energy generated by five shots was recorded by ~900 seismic stations. High-amplitude phases were identified in every shot gather for the upper crust (Pg and PiP) and Moho (PmP and Pn). In the upper crust, the P wave velocities increase beneath the Cenozoic Tajo Basin. The base of the upper crust varies from ~13 km to ~20 km between the southernmost Central Iberian Zone and the Tajo Basin. Lower crustal velocities are more homogeneous. From SW-NE, the traveltime of PmP arrivals varies from ~10.5 s to ~11.8 s, indicating lateral variations in the P wave velocity and the crustal thickness, reflecting an increase toward the north related with alpine tectonics and the isostatic response of the crust to the orogenic load. The results suggest that the high velocities of the upper crust near the Central System might correspond to igneous rocks and/or high-grade metamorphic rocks. The contrasting lithologies and the increase in the Moho depth to the north evidence differences in the Variscan evolution.

  6. Inelastic models of lithospheric stress - II. Implications for outer-rise seismicity and dynamics

    USGS Publications Warehouse

    Mueller, S.; Spence, W.; Choy, G.L.

    1996-01-01

    Outer-rise seismicity and dynamics are examined using inelastic models of lithospheric deformation, which allow a more realistic characterization of stress distributions and failure behaviour. We conclude that thrust- and normal-faulting outer-rise earthquakes represent substantially different states of stress within the oceanic lithosphere. Specifically, the normal-faulting events occur in response to downward plate bending, which establishes the 'standard', bending-dominated state of outer-rise stress, and the thrust-faulting events occur in response to an elevated level of in-plane compression, which develops only in response to exceptional circumstances. This interpretation accounts for the observation that normal-faulting outer-rise earthquakes occur more frequently and are more widely distributed than their thrust-faulting counterparts, an observation for which the simple bending model offers no explanation. In addition, attributing both thrust- and normal-faulting outer-rise earthquakes to plate bending implies that both classes of events should occur within relatively close lateral proximity to one another because both are allegedly a manifestation of the same bending-dominated stress distribution, whereas, in reality, this is not observed. We propose that the tendency for thrust-faulting outer-rise earthquakes to exhibit greater source depths than their normal-faulting counterparts (an observation that is frequently cited in support of the bending interpretation of the former) is merely a consequence of the fact that bending-induced tension is confined to the upper lithosphere. Our model predicts that outer-rise in-plane-force variations may promote thrust-faulting outer-rise activity prior to an underthrusting interplate subduction earthquake and normal-faulting outer-rise activity following such an earthquake, but that both forms of outer-rise activity are unlikely to be associated with the same subduction earthquake. A corollary implication of our model

  7. Refined models of gravitational potential energy compared with stress and strain rate patterns in Iberia

    NASA Astrophysics Data System (ADS)

    Neves, Maria C.; Fernandes, Rui M.; Adam, Claudia

    2014-11-01

    This study examines the role of gravitational potential energy (GPE) in generating second-order (spatial scale ∼102 km) variations in the Iberia stress and strain-rate patterns. We present a new map of present-day strain rate field derived from the secular velocity field computed using all available continuously operating Global Navigation Satellite Systems (GNSS) stations in Iberia. The estimated strain rate field is generally consistent with the tectonic framework of the Iberian region, even though sporadic sharp local variations downgrade its correlation with the regional stress patterns. Many of the sharp spatial variations in the strain rate map are consistent with local changes of deformation style determined by prevailing faults. To obtain a more accurate estimate of GPE we use new data on the structure of the crust and apply a thin sheet approach using a 3-D definition of deviatoric stress. The GPE is derived from two isostatically compensated models (GPEd and GPEe compensated by density and elevation adjustment, respectively) and from the truncated geoid (GPEg). The GPE stresses are then summed with the first-order stress field due to the Eurasia-Nubia (EU-NU) convergence and the results compared with both the stress and strain rate data. In agreement with previous studies, we find that the GPE does not significantly change the NW-SE average direction of the most compressive stress (SHmax) imposed by the EU-NU collision, its main effect being to cause spatially changing stress regimes. From the analysis of the different GPE models we find: (1) in the Pyrenees, the tectonic forces have a secondary role when compared to the GPE. In this region, the model that best correlates with observations is the one emphasizing the role of surface elevation as a source of GPE (GPEe); (2) in the Iberian Chain and the Betics, the GPE imposes NE-SW extension consistent with a strike-slip regime and is equally (GPEe) or more (GPEg) important than the tectonic forces. In

  8. Investigating the Uplift of Southern Africa Using Coupled Thermo-mechanical and Surface Processes Models

    NASA Astrophysics Data System (ADS)

    Beucher, R.; Huismans, R. S.; Brown, R. W.; Robin, C.

    2014-12-01

    The topography of southern and eastern Africa (referred to as the African Superswell by Nyblade and Robinson, 1994) is anomalously high (> 900m) relative to central and west Africa, and also to other continents. The southern tip of Africa is surrounded by passive margins and mid ocean ridges as a result of continental rifting (early Jurassic in the east, late Jurassic in the west) and Gondwana break up. Recent studies have also identified the Earth's largest low seismic velocity anomaly in the mid-lower mantle beneath southern Africa and catalysed interest in the role the interactions between surface and deep processes play in generating large scale topography. Understanding how the relief evolved since rifting onset is fundamental to advancing knowledge about the coupling between deep tectonics and dynamic topography. Such a large scale topographic feature may also have important impact on atmosphere circulation and precipitations patterns. The complexity of such a system requires an integrated approach looking at interactions between tectonics and surface processes on a range of spatial and temporal scales. We use high-resolution numerical experiments coupling a 2D upper-mantle-scale thermo-mechanical model with a plan-form 2D surface processes model (SPM) to investigate the factors controlling the style of deformation. The experiments consist in simple extension models involving lithosphere with variable thickness (normal-like lithosphere to thick cratonic-like lithosphere) and explore the effects of rheological and compositional variability of the layer components of the crust and the lithosphere. Tomography and geochemistry evidences suggest a possible counterflow in the lower lithosphere in parts of the African western margins. We discuss the effect of a gravitationally driven lithospheric counterflow of depleted lower lithosphere (compositionally less dense than sublithospheric mantle) on the rift geometry and the effect of the isostatic responses in terms

  9. Normal fault growth above pre-existing structures: insights from discrete element modelling

    NASA Astrophysics Data System (ADS)

    Wrona, Thilo; Finch, Emma; Bell, Rebecca; Jackson, Christopher; Gawthorpe, Robert; Phillips, Thomas

    2016-04-01

    In extensional systems, pre-existing structures such as shear zones may affect the growth, geometry and location of normal faults. Recent seismic reflection-based observations from the North Sea suggest that shear zones not only localise deformation in the host rock, but also in the overlying sedimentary succession. While pre-existing weaknesses are known to localise deformation in the host rock, their effect on deformation in the overlying succession is less well understood. Here, we use 3-D discrete element modelling to determine if and how kilometre-scale shear zones affect normal fault growth in the overlying succession. Discrete element models use a large number of interacting particles to describe the dynamic evolution of complex systems. The technique has therefore been applied to describe fault and fracture growth in a variety of geological settings. We model normal faulting by extending a 60×60×30 km crustal rift-basin model including brittle and ductile interactions and gravitation and isostatic forces by 30%. An inclined plane of weakness which represents a pre-existing shear zone is introduced in the lower section of the upper brittle layer at the start of the experiment. The length, width, orientation and dip of the weak zone are systematically varied between experiments to test how these parameters control the geometric and kinematic development of overlying normal fault systems. Consistent with our seismic reflection-based observations, our results show that strain is indeed localised in and above these weak zones. In the lower brittle layer, normal faults nucleate, as expected, within the zone of weakness and control the initiation and propagation of neighbouring faults. Above this, normal faults nucleate throughout the overlying strata where their orientations are strongly influenced by the underlying zone of weakness. These results challenge the notion that overburden normal faults simply form due to reactivation and upwards propagation of pre

  10. Lithosphere-scale 3D gravity modelling of the Barents Sea and Kara Sea

    NASA Astrophysics Data System (ADS)

    Klitzke, P.; Faleide, J.; Sippel, J.; Scheck-Wenderoth, M.

    2013-12-01

    The Barents - Kara Sea region covers the major part of the European Arctic shelf. Its northern and western boundaries are young passive margins which originate from early Paleocene-Eocene opening of the Eurasia Basin and the Norwegian-Greenland Sea. In contrast, the basement of the Barents and Kara shelves has been consolidated much earlier, during three major late Precambrian to Permian orogenies. Additionally, the shelf experienced multiple episodes of localised subsidence which resulted in the formation of ultra-deep sedimentary basins varying strongly in their geometry between different subregions. Consequently, the preserved sedimentary record is interrupted by major megasequence boundaries that are well-described in the western Barents Sea. Using this subdivision for the sedimentary record, we traced four major megasequence boundaries across the Barents and Kara shelves by analysing interpreted seismic refraction and reflection data, geological maps and previously published 3D-models. We integrate this shallow information into a 3D geological model and complement the latter downward with the top crystalline crust, the Moho and a new lithosphere-asthenosphere boundary. The sedimentary units have been assigned physical properties considering the respective lithology to calculate a depth-dependent density distribution. Thereby, the obtained bulk densities also account for late Cenozoic uplift/erosion and the maximum Pleistocene ice sheet thickness. For the lithospheric mantle, the density distribution is constrained by an earlier published velocity model (Levshin et al., 2007). On the base of isostatic calculations and 3D gravity modelling the density configuration of the crystalline crust and the geometry of potential high-density bodies is investigated. Finally, we correlate preserved sediment maxima and reconstructed erosion maps with subsedimentary velocity and density variations to gain new insights into the development of Barents and Kara Sea basins

  11. Escarpment evolution on high-elevation rifted margins: Insights derived from a surface processes model that combines diffusion, advection and reaction

    NASA Technical Reports Server (NTRS)

    Kooi, Henk; Beaumont, Christopher

    1994-01-01

    Experiments with a surface processes model of large-scale (1-1000 km) long-term (1-100 m.y.) erosional denudation are used to establish the controls on the evolution of a model escarpment that is related to the rifting of a continent. The mdoel describes changes in topographic form as a result of sumultaneous short- and long-range mass transport representing hillslope (diffusive) processes and fluvial transport (advection), repsectively. Fluvial entrainment is modeled as a first-order kinetic reaction which reflects the erodibility of the substrate, and therefore the fluvial system is not necessarily carrying at capacity. One dimensional and planform models demonstrate that the principal controls on the evolution of an initially steep model escarpment are (1) antecedent topography/drainage; (2) the timesale (or equivalently a length scale) in the fluvial entrainment reaction; (3) the flexural response of the lithosphere to denudation; and (4) the relative efficiencies of the short- and long-range transport processes. When rainfall and substrate lithology are uniform, a significant amount of discharge draining over the escarpment top causes it to degrade. Only when the top of the model escarpment coincides with a drainage divide can escarpment retreat occur for these conditions. An additional requirement for retreat of a model escarpment without decline is a long reaction time scale for fluvial entrainment. This corresponds to a substrate that is hard to detach by flucial erosion, and therefore to fluvial erosion that is not transport limited. Coninuous backtilting of an escarpment due ot flexural isostatic uplift in response to denudational unloading helps maintain the scarp top as a divide. It is essntial if the escarpment gradient is to be preserved during retreat in a uniform lithology. Low flexural rigidieties propote steep and slowly retreating escarpments. For given rainfall and substrate conditions, the morphology of a retraeating model escarpment is

  12. Climate Interpretations of GRACE Gravity Field Data: Implications of the Accuracy of the ICE- 5G(VM2)GIA Model for the Inference of Mass Loss from the Antarctic Ice Sheet

    NASA Astrophysics Data System (ADS)

    Drummond, R.; Peltier, W. R.

    2007-12-01

    Application of the ICE-5G(VM2)GIA model to the interpretation of RL04 GRACE data from the CSR demonstrates that this model delivers a highly accurate prediction of the time dependent gravity field over the North American continent. In this region the signal is dominated by the contribution of the ongoing process of glacial isostatic adjustment to the removal of the ancient Laurentide ice-sheet that once covered the region. When the GRACE field is filtered by the removal of the ICE-5G(VM2) prediction, significant residuals exist over both Greenland and Alaska that must be attributed to the melt-back of land ice from these regions due to high latitude climate warming. The corrections in these regions due to Late PLeistocene deglaciation are small. For Antarctica, however, the inferred rate of mass loss depends entirely upon the GIA correction, with a state of near modern day mass balance being inferred in the absence of the application of a GIA correction and a significant rate of mass loss being implied when such a correction is applied to the raw data. Using the latest masscon solutions for the inference of the rate of surface mass loss from Antarctica (Luthcke et al., personal communication), corrected for the influence of GIA using the ICE-5G(VM2) model, one infers a rate of mass loss from Antarctica of approximately 105 Gt/annum. The issue of the accuracy of the ICE-5G(VM2) model for Antarctic applications is therefor extremely important.The presentation will address this issue in detail.

  13. Models, Part IV: Inquiry Models.

    ERIC Educational Resources Information Center

    Callison, Daniel

    2002-01-01

    Discusses models for information skills that include inquiry-oriented activities. Highlights include WebQuest, which uses Internet resources supplemented with videoconferencing; Minnesota's Inquiry Process based on the Big Six model for information problem-solving; Indiana's Student Inquiry Model; constructivist learning models for inquiry; and…

  14. Layer-Based Modelling of the Earth's Gravitational Potential up to 10-km Scale in Spherical Harmonics in Spherical and Ellipsoidal Approximation

    NASA Astrophysics Data System (ADS)

    Rexer, Moritz; Hirt, Christian; Claessens, Sten; Tenzer, Robert

    2016-08-01

    Global forward modelling of the Earth's gravitational potential, a classical problem in geophysics and geodesy, is relevant for a range of applications such as gravity interpretation, isostatic hypothesis testing or combined gravity field modelling with high and ultra-high resolution. This study presents spectral forward modelling with volumetric mass layers to degree 2190 for the first time based on two different levels of approximation. In spherical approximation, the mass layers are referred to a sphere, yielding the spherical topographic potential. In ellipsoidal approximation where an ellipsoid of revolution provides the reference, the ellipsoidal topographic potential (ETP) is obtained. For both types of approximation, we derive a mass layer concept and study it with layered data from the Earth2014 topography model at 5-arc-min resolution. We show that the layer concept can be applied with either actual layer density or density contrasts w.r.t. a reference density, without discernible differences in the computed gravity functionals. To avoid aliasing and truncation errors, we carefully account for increased sampling requirements due to the exponentiation of the boundary functions and consider all numerically relevant terms of the involved binominal series expansions. The main outcome of our work is a set of new spectral models of the Earth's topographic potential relying on mass layer modelling in spherical and in ellipsoidal approximation. We compare both levels of approximations geometrically, spectrally and numerically and quantify the benefits over the frequently used rock-equivalent topography (RET) method. We show that by using the ETP it is possible to avoid any displacement of masses and quantify also the benefit of mapping-free modelling. The layer-based forward modelling is corroborated by GOCE satellite gradiometry, by in-situ gravity observations from recently released Antarctic gravity anomaly grids and degree correlations with spectral models of

  15. Supermatrix models

    SciTech Connect

    Yost, S.A.

    1991-05-01

    Radom matrix models based on an integral over supermatrices are proposed as a natural extension of bosonic matrix models. The subtle nature of superspace integration allows these models to have very different properties from the analogous bosonic models. Two choices of integration slice are investigated. One leads to a perturbative structure which is reminiscent of, and perhaps identical to, the usual Hermitian matrix models. Another leads to an eigenvalue reduction which can be described by a two component plasma in one dimension. A stationary point of the model is described.

  16. Supermatrix models

    SciTech Connect

    Yost, S.A. . Dept. of Physics and Astronomy)

    1992-09-30

    In this paper, random matrix models based on an integral over supermatrices are proposed as a natural extension of bosonic matrix models. The subtle nature of superspace integration allows these models to have very different properties from the analogous bosonic models. Two choices of integration slice are investigated. One leads to a perturbative structure which is reminiscent of, and perhaps identical to, the usual Hermitian matrix models. Another leads to an eigenvalue reduction which can be described by a two-component plasma in one dimension. A stationary point of the model is described.

  17. Tides and lake-level variations in the great Patagonian lakes: Observations, modelling and geophysical implications.

    NASA Astrophysics Data System (ADS)

    Marderwald, Eric; Richter, Andreas; Horwath, Martin; Hormaechea, Jose Luis; Groh, Andreas

    2016-04-01

    In Patagonia, the glacial-isostatic adjustment (GIA) to past ice-mass changes (Ivins & James 2004; Klemann et al. 2007) is of particular interest in the context of the determination of the complex regional rheology related to plate subduction in a triple-junction constellation. To further complicate the situation, GIA is overlaid with load deformation not only due to present ice mass changes but also due to water-level changes in the lakes surrounding the icefields and the ocean surrounding Patagonia. These elastic deformations affect the determination of glacial-isostatic uplift rates from GPS observations (Dietrich et al. 2010; Lange et al. 2014). Observations of lake tides and their comparison with the theoretical tidal signal have been used previously to validate predictions of ocean tidal loading and have revealed regional deviations from conventional global elastic earth models (Richter et al. 2009). In this work we investigate the tides and lake-level variations in Lago Argentino, Lago Viedma, Lago San Martín/O'Higgins and Lago Buenos Aires/General Carrera. This allows us to test, among other things, the validity of tidal loading models. We present pressure tide-gauge records from two sites in Lago Argentino extending over 2.5 years (Richter et al. 2015). These observations are complemented by lake-level records provided by the Argentine National Hydrometeorological Network. Based on these lake-level time series the principal processes affecting the lake level are identified and quantified. Lake-level changes reflecting variations in lake volume are dominated by a seasonal cycle exceeding 1 m in amplitude. Lake-volume changes occur in addition with a daily period in response to melt water influx from surrounding glaciers. In Lago Argentino sporadic lake-volume jumps are caused by bursting of the ice dam of Perito Moreno glacier. Water movements in these lakes are dominated by surface seiches reaching 20 cm in amplitude. A harmonic tidal analysis of the lake

  18. Collisional plateaus. [in earth and Venus lithospheres

    NASA Technical Reports Server (NTRS)

    Morgan, P.; Burke, K.

    1985-01-01

    Aspects of the geology of collisional plateaus formed by the thickening of continental crust are briefly reviewed. The history of studies of collisional plateaus is summarized, and igneous activity in collisional plateaus is discussed. Isostatic considerations pertaining to these plateaus are addressed, developing models of isostatic support of topography which illustrate the importance of compressional tectonics in the creation of high altitude plateaus. Possible analogous environments on Venus are considered. Finally, the paradox of extension associated with compression in the plateaus is discussed.

  19. Conserving mass and energy in cooling models of oceanic lithosphere requires upper mantle origins for trends in subsidence and heat flux and indicates global power of 30 TW

    NASA Astrophysics Data System (ADS)

    Criss, R. E.; Hofmeister, A. M.; Hamza, V. N.

    2008-12-01

    One-dimensional conductive cooling models of ocean lithosphere fail to predict the lateral variation in oceanic heat flux and provide problematic calculations of subsidence, for reasons enumerated below. Our new model follows conservation laws and shows that bathymetric trends are tied to upper mantle temperature variations, given realistic values for thermal expansivity. Heat flux increases towards mid-ocean ridges due to (1) flux varying across upper mantle convection cells and (2) redistribution of mantle heat (Qmtl) by moving magma, and also by (3) hydrothermal circulation. Foremost, widespread, lateral, uptake of Qmtl as latent heat occurs during deep lithospheric melting but this energy is released near ridges through dike emplacement during seafloor spreading. Redistribution and energy conservation account for the local heat flux maximum near x=1200 km, heretofore unexplained. We show that the trend Qmtl(x) far from the ridge is consistent with behavior near the ridge and measured global power of <30 TW , which is compatible with quasi-steady-state conditions and an enstatite chondrite model for the Earth. Observables, such as the pattern of mid-ocean ridges on the globe, point to layered convection and lack of vigor, and gross characteristics of the Earth are supported by an enstatite chondrite model. Our analysis circumvents problems associated with 1-d conductive cooling models of the lithosphere: (1) Existing models replaced conservation of rock-mass with isostatic balance, which unwittingly created subsidence by converting lithosphere to ocean. (2) Half-space models incorrectly cancelled infinities. (3) Plate models omitted latent heat which is immense. (4) 1-d models only permit vertical contraction. These faulty constructs fitted seafloor depths through erroneous use of volumetric (αV=3αL) thermal expansivity coupled with great leeway in cross-multiplied parameters. The underlying premise that thermal aspects of lithosphere can be separately

  20. Turbulence modeling

    NASA Technical Reports Server (NTRS)

    Rubesin, Morris W.

    1987-01-01

    Recent developments at several levels of statistical turbulence modeling applicable to aerodynamics are briefly surveyed. Emphasis is on examples of model improvements for transonic, two-dimensional flows. Experience with the development of these improved models is cited to suggest methods of accelerating the modeling process necessary to keep abreast of the rapid movement of computational fluid dynamics into the computation of complex three-dimensional flows.

  1. Architectural Models

    ERIC Educational Resources Information Center

    Levenson, Harold E.; Hurni, Andre

    1978-01-01

    Suggests building models as a way to reinforce and enhance related subjects such as architectural drafting, structural carpentry, etc., and discusses time, materials, scales, tools or equipment needed, how to achieve realistic special effects, and the types of projects that can be built (model of complete building, a panoramic model, and model…

  2. Radiation Models

    ERIC Educational Resources Information Center

    James, W. G. G.

    1970-01-01

    Discusses the historical development of both the wave and the corpuscular photon model of light. Suggests that students should be informed that the two models are complementary and that each model successfully describes a wide range of radiation phenomena. Cites 19 references which might be of interest to physics teachers and students. (LC)

  3. Constraining age and rate of deformation in the northern Bolivian Andes from cross sections, cooling ages, and thermokinematic modeling

    NASA Astrophysics Data System (ADS)

    McQuarrie, N.; Ehlers, T. A.; Rak, A. J.

    2015-12-01

    A critical component in assessing the viability of proposed plate tectonic or geodynamic processes in regions of convergence is the expected or predicted age and rate of deformation in the overriding plate. Commonly, age of deformation is inferred through geochronology of foreland basin and wedge-top sedimentary rocks and bedrock thermochronometer cooling signals. In Bolivia the original pulse of deformation of the fold-thrust belt is argue to be as young as 38-25 Ma based on the age of synorogenic strata or as old as 65-45 Ma due to proposed foreland basin rocks deposited in the Bolivian Altiplano. The large discrepancies in proposed age, rate and magnitude of deformation through the Bolivian Andes limit our ability to relate age and rate of shortening to internal geodynamic or external plate tectonic processes. We evaluate permissible ranges in age of initiation and rate of deformation through a forward kinematic model of the northern Bolivian fold-thrust belt. Each step of deformation accounts for isostatic loading from thrust faults and subsequent erosional of structural highs. The kinematic model predicts an evolution of flexural basins into which synorogenic sediments are deposited allowing us to fully integrate age of exhumation and deposition to age and magnitude of deformation. By assigning an age to each deformation step, we create a range of velocity vectors that are input into the thermokinematic model Pecube, which predicts thermochronometer cooling histories based on kinematics, topography, thermal parameters and shortening rates. We match the pattern of predicted ages with the across strike pattern of measured zircon fission track, apatite fission track and apatite (U-Th)/ He cooling ages. The sensitivity of modeled thermochronologic data to the age at which deformation initiates indicate that northern Bolivian EC started deforming at 50 Ma and may have begun as early as 55 Ma. The acceptable velocity envelope for the modeled section permits either a

  4. Horizontal and vertical velocities derived from the IDS contribution to ITRF2014, and comparisons with geophysical models

    NASA Astrophysics Data System (ADS)

    Moreaux, G.; Lemoine, F. G.; Argus, D. F.; Santamaría-Gómez, A.; Willis, P.; Soudarin, L.; Gravelle, M.; Ferrage, P.

    2016-10-01

    In the context of the 2014 realization of the International Terrestrial Reference Frame, the International DORIS (Doppler Orbitography Radiopositioning Integrated by Satellite) Service (IDS) has delivered to the IERS a set of 1140 weekly SINEX files including station coordinates and Earth orientation parameters, covering the time period from 1993.0 to 2015.0. From this set of weekly SINEX files, the IDS combination centre estimated a cumulative DORIS position and velocity solution to obtain mean horizontal and vertical motion of 160 stations at 71 DORIS sites. The main objective of this study is to validate the velocities of the DORIS sites by comparison with external models or time-series. Horizontal velocities are compared with two recent global plate models (GEODVEL 2010 and NNR-MORVEL56). Prior to the comparisons, DORIS horizontal velocities were corrected for Global Isostatic Adjustment from the ICE-6G (VM5a) model. For more than half of the sites, the DORIS horizontal velocities differ from the global plate models by less than 2-3 mm yr-1. For five of the sites (Arequipa, Dionysos/Gavdos, Manila and Santiago) with horizontal velocity differences with respect to these models larger than 10 mm yr-1, comparisons with GNSS estimates show the veracity of the DORIS motions. Vertical motions from the DORIS cumulative solution are compared with the vertical velocities derived from the latest GPS cumulative solution over the time span 1995.0-2014.0 from the University of La Rochelle solution at 31 co-located DORIS-GPS sites. These two sets of vertical velocities show a correlation coefficient of 0.83. Vertical differences are larger than 2 mm yr-1 at 23 percent of the sites. At Thule, the disagreement is explained by fine-tuned DORIS discontinuities in line with the mass variations of outlet glaciers. Furthermore, the time evolution of the vertical time-series from the DORIS station in Thule show similar trends to the GRACE equivalent water height.

  5. The Laurentide Ice Sheet at LGM: Space Geodetic and Absolute Gravity Observations Require a Multi-domed Model

    NASA Astrophysics Data System (ADS)

    Peltier, W. R.

    2002-05-01

    Although surface geomorphological evidence has continued to suggest that the LGM form of the LIS was multi-domed, both explicit ice-mechanics based reconstructions such as that produced in the CLIMAP project, and models based upon the inversion of relative sea level observations such as ICE-4G(VM2), have led to the inference of single domed structures. Three recent sets of observations related to the isostatic adjustment process require that these single domed reconstructions be abandoned. The first of these consists of the VLBI based measurement of the rate of present day vertical motion at Yellowknife in the Northwest Territories of Canada, demonstrating that the rate predicted by the ICE-4G(VM2) model is more than a factor of two less than observed(Argus et al., 1999). The second consists of absolute gravity measurements on a traverse south from Churchill on Hudson Bay across the southern margin of the former LIS into the United States(Lambert et al., 2001). Finally there is the recent demonstration that the ICE-4G reconstruction of the process of post-LGM deglaciation has too little LGM mass (Peltier,2002). Analyses to be presented in this paper show that the additional LGM ice required by the latter analysis very precisely suffices to reconcile the misfits to the first two sets of observations when it is placed in a Keewatin Dome centred over the Yellowknife region. The resulting model of the LGM form of the LIS is then very close to that originally suggested by Dyke and Prest (1987). This modified form of the ICE-4G model is viable if and only if the depth dependence of mantle viscosity is very close to VM2. Models with higher viscosity in the lower mantle are ruled out by the data as they overpredict both the space geodetic and absolute gravity observations when ice thickness over Keewatin is significantly increased so as to satisfy far field requirements concerning the eustatic sea level depression at LGM.

  6. The effect of rheological approximations on the dynamics and topography in 3D subduction-collision models

    NASA Astrophysics Data System (ADS)

    Pusok, Adina E.; Kaus, Boris J. P.; Popov, Anton A.

    2016-04-01

    Most of the major mountain belts and orogenic plateaus are found within the overlying plate of active or fossil subduction and/or collision zones. Moreover, they evolve differently from one another as the result of specific combinations of surface and mantle processes. These differences arise for several reasons, such as different rheological properties, different amounts of regional isostatic compensation, and different mechanisms by which forces are applied to the convergent plates. Previous 3D geodynamic models of subduction/collision processes have used various rheological approximations, making numerical results difficult to compare, since there is no clear image on the extent of these approximations on the dynamics. Here, we employ the code LaMEM to perform high-resolution long-term 3D simulations of subduction/continental collision in an integrated lithospheric and upper-mantle scale model. We test the effect of rheological approximations on mantle and lithosphere dynamics in a geometrically simplified model setup that resembles a tectonic map of the India-Asia collision zone. We use the "sticky-air" approach to allow for the development of topography and the dynamics of subduction and collision is entirely driven by slab-pull (i.e. "free subduction"). The models exhibit a wide range of behaviours depending on the rheological law employed: from linear to temperature-dependent visco-elasto-plastic rheology that takes into account both diffusion and dislocation creep. For example, we find that slab dynamics varies drastically between end member models: in viscous approximations, slab detachment is slow following a viscous thinning, while for a non-linear visco-elasto-plastic rheology, slab detachment is relatively fast, inducing strong mantle flow in the slab window. We also examine the stress states in the subducting and overriding plates and topography evolution in the upper plate, and we discuss the implications on lithosphere dynamics at convergent margins

  7. Tides and lake-level variations in the great Patagonian lakes: Observations, modelling and geophysical implications.

    NASA Astrophysics Data System (ADS)

    Marderwald, Eric; Richter, Andreas; Horwath, Martin; Hormaechea, Jose Luis; Groh, Andreas

    2016-04-01

    In Patagonia, the glacial-isostatic adjustment (GIA) to past ice-mass changes (Ivins & James 2004; Klemann et al. 2007) is of particular interest in the context of the determination of the complex regional rheology related to plate subduction in a triple-junction constellation. To further complicate the situation, GIA is overlaid with load deformation not only due to present ice mass changes but also due to water-level changes in the lakes surrounding the icefields and the ocean surrounding Patagonia. These elastic deformations affect the determination of glacial-isostatic uplift rates from GPS observations (Dietrich et al. 2010; Lange et al. 2014). Observations of lake tides and their comparison with the theoretical tidal signal have been used previously to validate predictions of ocean tidal loading and have revealed regional deviations from conventional global elastic earth models (Richter et al. 2009). In this work we investigate the tides and lake-level variations in Lago Argentino, Lago Viedma, Lago San Martín/O'Higgins and Lago Buenos Aires/General Carrera. This allows us to test, among other things, the validity of tidal loading models. We present pressure tide-gauge records from two sites in Lago Argentino extending over 2.5 years (Richter et al. 2015). These observations are complemented by lake-level records provided by the Argentine National Hydrometeorological Network. Based on these lake-level time series the principal processes affecting the lake level are identified and quantified. Lake-level changes reflecting variations in lake volume are dominated by a seasonal cycle exceeding 1 m in amplitude. Lake-volume changes occur in addition with a daily period in response to melt water influx from surrounding glaciers. In Lago Argentino sporadic lake-volume jumps are caused by bursting of the ice dam of Perito Moreno glacier. Water movements in these lakes are dominated by surface seiches reaching 20 cm in amplitude. A harmonic tidal analysis of the lake

  8. Hydrological models are mediating models

    NASA Astrophysics Data System (ADS)

    Babel, L. V.; Karssenberg, D.

    2013-08-01

    Despite the increasing role of models in hydrological research and decision-making processes, only few accounts of the nature and function of models exist in hydrology. Earlier considerations have traditionally been conducted while making a clear distinction between physically-based and conceptual models. A new philosophical account, primarily based on the fields of physics and economics, transcends classes of models and scientific disciplines by considering models as "mediators" between theory and observations. The core of this approach lies in identifying models as (1) being only partially dependent on theory and observations, (2) integrating non-deductive elements in their construction, and (3) carrying the role of instruments of scientific enquiry about both theory and the world. The applicability of this approach to hydrology is evaluated in the present article. Three widely used hydrological models, each showing a different degree of apparent physicality, are confronted to the main characteristics of the "mediating models" concept. We argue that irrespective of their kind, hydrological models depend on both theory and observations, rather than merely on one of these two domains. Their construction is additionally involving a large number of miscellaneous, external ingredients, such as past experiences, model objectives, knowledge and preferences of the modeller, as well as hardware and software resources. We show that hydrological models convey the role of instruments in scientific practice by mediating between theory and the world. It results from these considerations that the traditional distinction between physically-based and conceptual models is necessarily too simplistic and refers at best to the stage at which theory and observations are steering model construction. The large variety of ingredients involved in model construction would deserve closer attention, for being rarely explicitly presented in peer-reviewed literature. We believe that devoting

  9. Model Experiments and Model Descriptions

    NASA Technical Reports Server (NTRS)

    Jackman, Charles H.; Ko, Malcolm K. W.; Weisenstein, Debra; Scott, Courtney J.; Shia, Run-Lie; Rodriguez, Jose; Sze, N. D.; Vohralik, Peter; Randeniya, Lakshman; Plumb, Ian

    1999-01-01

    The Second Workshop on Stratospheric Models and Measurements Workshop (M&M II) is the continuation of the effort previously started in the first Workshop (M&M I, Prather and Remsberg [1993]) held in 1992. As originally stated, the aim of M&M is to provide a foundation for establishing the credibility of stratospheric models used in environmental assessments of the ozone response to chlorofluorocarbons, aircraft emissions, and other climate-chemistry interactions. To accomplish this, a set of measurements of the present day atmosphere was selected. The intent was that successful simulations of the set of measurements should become the prerequisite for the acceptance of these models as having a reliable prediction for future ozone behavior. This section is divided into two: model experiment and model descriptions. In the model experiment, participant were given the charge to design a number of experiments that would use observations to test whether models are using the correct mechanisms to simulate the distributions of ozone and other trace gases in the atmosphere. The purpose is closely tied to the needs to reduce the uncertainties in the model predicted responses of stratospheric ozone to perturbations. The specifications for the experiments were sent out to the modeling community in June 1997. Twenty eight modeling groups responded to the requests for input. The first part of this section discusses the different modeling group, along with the experiments performed. Part two of this section, gives brief descriptions of each model as provided by the individual modeling groups.

  10. Glacial landscape evolution and sediment export: insights from digital topographic analyses and numerical modelling (Invited)

    NASA Astrophysics Data System (ADS)

    Brocklehurst, S. H.; MacGregor, K. R.

    2013-12-01

    Sediment accumulation rates in the Gulf of Alaska and low-temperature thermochronology from the European Alps, amongst other lines of evidence, indicate accelerated glacial incision and sediment export associated with the Middle Pleistocene Transition (MPT), ~1 Ma. At this time, the change from symmetrical 40-kyr temperature cycles to larger amplitude, asymmetric 100-kyr cycles would have allowed larger, longer lived glaciers to develop, which is inferred as a key contributor to accelerated glacial erosion. Digital topographic analyses comparing glaciated drainage basins of different sizes in the Southern Alps, New Zealand, and Teton Range, western US, amongst others, indicate the importance of scale in glacial landscape development. In smaller drainage basins, or those at the limit of glaciation, landscape modification is primarily restricted to carving characteristic cirques at the heads of valleys. Glaciers may have occasionally spilled from these to carve U-shaped cross-sections downvalley, but without substantial vertical incision. In larger drainage basins with a longer history of glacial occupation, glacial incision has produced shallower downvalley profiles with characteristic glacial steps, presumably accompanied by greater sediment export. A numerical glacial longitudinal profile evolution model, driven by temperature cycles representing either side of the MPT, is used to compare glacial erosion and sediment export from initial Pleistocene glaciations with post-MPT behaviour. The modelled landscape response to the MPT is strongly dependent on the tectonic setting and the behaviour of the fluvial system downstream of the glacier. With no imposed tectonic rock uplift, the major change in the landscape is the carving of cirque forms and glacial longitudinal profiles at the start of the Pleistocene; the MPT would have had little impact on landscape morphology or sediment export. Imposing tectonic as well as isostatic rock uplift, alongside inefficient fluvial

  11. Analytical Models

    NASA Technical Reports Server (NTRS)

    1984-01-01

    A system-level design and analysis model was developed. This model was conceived to have several key elements: a solar pond thermodynamic performance model, a power generation subsystem model, and an economic analysis element. The basic approach was to create these elements or modules and refine them on an individual basis yet retain the capability to easily couple them into a full system design model. This building block approach allows for maximum flexibility and substitution of refined descriptions as the technology develops. A general overview of interconnecting these subsystem models is presented. The primary program control element will perform the administrative functions of data input, data output, information storage and transfer, and sequential calling of the subsystem models. From the point of view of the requirements of a system design model, a power conversion subsystem model was developed. The goal of the effort was a preliminary subsystem model compatible with the solar pond subsystem model so that a first order system simulation analysis could be performed.

  12. Modeling Pharmacokinetics.

    PubMed

    Bois, Frederic Y; Brochot, Céline

    2016-01-01

    Pharmacokinetics is the study of the fate of xenobiotics in a living organism. Physiologically based pharmacokinetic (PBPK) models provide realistic descriptions of xenobiotics' absorption, distribution, metabolism, and excretion processes. They model the body as a set of homogeneous compartments representing organs, and their parameters refer to anatomical, physiological, biochemical, and physicochemical entities. They offer a quantitative mechanistic framework to understand and simulate the time-course of the concentration of a substance in various organs and body fluids. These models are well suited for performing extrapolations inherent to toxicology and pharmacology (e.g., between species or doses) and for integrating data obtained from various sources (e.g., in vitro or in vivo experiments, structure-activity models). In this chapter, we describe the practical development and basic use of a PBPK model from model building to model simulations, through implementation with an easily accessible free software. PMID:27311461

  13. ICRF modelling

    SciTech Connect

    Phillips, C.K.

    1985-12-01

    This lecture provides a survey of the methods used to model fast magnetosonic wave coupling, propagation, and absorption in tokamaks. The validity and limitations of three distinct types of modelling codes, which will be contrasted, include discrete models which utilize ray tracing techniques, approximate continuous field models based on a parabolic approximation of the wave equation, and full field models derived using finite difference techniques. Inclusion of mode conversion effects in these models and modification of the minority distribution function will also be discussed. The lecture will conclude with a presentation of time-dependent global transport simulations of ICRF-heated tokamak discharges obtained in conjunction with the ICRF modelling codes. 52 refs., 15 figs.

  14. Ventilation Model

    SciTech Connect

    H. Yang

    1999-11-04

    The purpose of this analysis and model report (AMR) for the Ventilation Model is to analyze the effects of pre-closure continuous ventilation in the Engineered Barrier System (EBS) emplacement drifts and provide heat removal data to support EBS design. It will also provide input data (initial conditions, and time varying boundary conditions) for the EBS post-closure performance assessment and the EBS Water Distribution and Removal Process Model. The objective of the analysis is to develop, describe, and apply calculation methods and models that can be used to predict thermal conditions within emplacement drifts under forced ventilation during the pre-closure period. The scope of this analysis includes: (1) Provide a general description of effects and heat transfer process of emplacement drift ventilation. (2) Develop a modeling approach to simulate the impacts of pre-closure ventilation on the thermal conditions in emplacement drifts. (3) Identify and document inputs to be used for modeling emplacement ventilation. (4) Perform calculations of temperatures and heat removal in the emplacement drift. (5) Address general considerations of the effect of water/moisture removal by ventilation on the repository thermal conditions. The numerical modeling in this document will be limited to heat-only modeling and calculations. Only a preliminary assessment of the heat/moisture ventilation effects and modeling method will be performed in this revision. Modeling of moisture effects on heat removal and emplacement drift temperature may be performed in the future.

  15. Climate Models

    NASA Technical Reports Server (NTRS)

    Druyan, Leonard M.

    2012-01-01

    Climate models is a very broad topic, so a single volume can only offer a small sampling of relevant research activities. This volume of 14 chapters includes descriptions of a variety of modeling studies for a variety of geographic regions by an international roster of authors. The climate research community generally uses the rubric climate models to refer to organized sets of computer instructions that produce simulations of climate evolution. The code is based on physical relationships that describe the shared variability of meteorological parameters such as temperature, humidity, precipitation rate, circulation, radiation fluxes, etc. Three-dimensional climate models are integrated over time in order to compute the temporal and spatial variations of these parameters. Model domains can be global or regional and the horizontal and vertical resolutions of the computational grid vary from model to model. Considering the entire climate system requires accounting for interactions between solar insolation, atmospheric, oceanic and continental processes, the latter including land hydrology and vegetation. Model simulations may concentrate on one or more of these components, but the most sophisticated models will estimate the mutual interactions of all of these environments. Advances in computer technology have prompted investments in more complex model configurations that consider more phenomena interactions than were possible with yesterday s computers. However, not every attempt to add to the computational layers is rewarded by better model performance. Extensive research is required to test and document any advantages gained by greater sophistication in model formulation. One purpose for publishing climate model research results is to present purported advances for evaluation by the scientific community.

  16. Phenomenological models

    SciTech Connect

    Braby, L.A.

    1990-09-01

    The biological effects of ionizing radiation exposure are the result of a complex sequence of physical, chemical, biochemical, and physiological interactions. One way to begin a search for an understanding of health effects of radiation is through the development of phenomenological models of the response. Many models have been presented and tested in the slowly evolving process of characterizing cellular response. A range of models covering different endpoints and phenomena has developed in parallel. Many of these models employ similar assumptions about some underlying processes while differing about the nature of others. An attempt is made to organize many of the models into groups with similar features and to compare the consequences of those features with the actual experimental observations. It is assumed that by showing that some assumptions are inconsistent with experimental observations, the job of devising and testing mechanistic models can be simplified. 43 refs., 13 figs.

  17. Microstructural anomalies in hot-isostatic pressed U–10wt.% Mo fuel plates with Zr diffusion barrier

    SciTech Connect

    Park, Y.; Eriksson, N.; Keiser, D. D.; Jue, J.; Rabin, B.; Moore, G.; Sohn, Y. H.

    2015-05-01

    Microstructural anomalies in the co-rolled-and-HIP'ed U–10 wt.% Mo (U10Mo) metallic fuel plate with Zr diffusion barrier assembly were examined as a function of HIP temperature (from 520 to 580 °C) and duration (45, 60, 90, 180 and 345 min) by scanning and transmission electron microscopy. The anomalies observed in this study are carbide/oxide inclusions within the U10Mo fuel alloy, and regions of limited interaction between the U10Mo alloy and Zr barrier, frequently associated with carbide/oxide inclusions. In the U10Mo alloy, the cF8, Fm3m (225) UC phase (a=4.955 Å) and cF12, Fm3m (225) UO2 phase (a=5.467 Å) were observed throughout the U10Mo alloy with an approximate volume percent of 0.5 to 1.8. The volume percent of the UC–UO2 inclusions within the U10Mo alloy did not change as functions of HIP temperature and time. These inclusion phases, located near the surface of the U10Mo alloy, were frequently observed to impede the development of interdiffusion and reaction between the U10Mo alloy and Zr diffusion barrier. The regions of limited interaction between the U10Mo and Zr barrier decreased with an increase in HIP temperature, however no noticeable trend was observed with an increase in HIP duration at constant temperature of 560 °C.

  18. The Manufacture of W-UO2 Fuel Elements for NTP Using the Hot Isostatic Pressing Consolidation Process

    NASA Technical Reports Server (NTRS)

    Broadway, Jeramie; Hickman, Robert; Mireles, Omar

    2012-01-01

    NTP is attractive for space exploration because: (1) Higher Isp than traditional chemical rockets (2)Shorter trip times (3) Reduced propellant mass (4) Increased payload. Lack of qualified fuel material is a key risk (cost, schedule, and performance). Development of stable fuel form is a critical path, long lead activity. Goals of this project are: Mature CERMET and Graphite based fuel materials and Develop and demonstrate critical technologies and capabilities.

  19. Isostatic gravity map and principal facts for 694 gravity stations in Yellowstone National Park and vicinity, Wyoming, Montana, and Idaho

    USGS Publications Warehouse

    Carle, S.F.; Glen, J.M.; Langenheim, V.E.; Smith, R.B.; Oliver, H.W.

    1990-01-01

    The report presents the principal facts for gravity stations compiled for Yellowstone National Park and vicinity. The gravity data were compiled from three sources: Defense Mapping Agency, University of Utah, and U.S. Geological Survey. Part A of the report is a paper copy describing how the compilation was done and presenting the data in tabular format as well as a map; part B is a 5-1/4 inch floppy diskette containing only the data files in ASCII format. Requirements for part B: IBM PC or compatible, DOS v. 2.0 or higher. Files contained on this diskette: DOD.ISO -- File containing the principal facts of the 514 gravity stations obtained from the Defense Mapping Agency. The data are in Plouff format* (see file PFTAB.TEX). UTAH.ISO -- File containing the principal facts of 153 gravity stations obtained from the University of Utah. Data are in Plouff format. USGS.ISO -- File containing the principal facts of 27 gravity stations collected by the U.S. Geological Survey in July 1987. Data are in Plouff format. PFTAB.TXT -- File containing explanation of principal fact format. ACC.TXT -- File containing explanation of accuracy codes.

  20. Vertical movements of crust, uplift of lithosphere, and isostatic unroofing: case histories from the Ozark dome and northern Appalachians

    SciTech Connect

    Friedman, G.M.

    1987-05-01

    Evidence of former deep burial of Ordovician to Devonian strata of the Ozark dome and northern Appalachians has been obtained from petrographic and geochemical studies of carbonates and coal-bearing rocks. In diagenetic minerals of the carbonate rocks, fluid inclusion homogenization temperatures and delta/sup 18/O values indicate paleotemperatures of 100 to 200/sup 0/C. The geothermometers used also include vitrinite reflectance, level of organic metamorphism (LOM), Staplin kerogen alteration index, and conodont alteration index (CAI). Maximum depths of burial were calculated from the estimated paleotemperatures assuming a geothermal gradient of about 25/sup 0/C/km. Strata of the Silurian of the northern Appalachian basin and of the Ordovician of the Ozark dome are interpreted to have reached maximum burial depths of 5 and 4.3 km, respectively; Devonian strata in the Catskill Mountains of New York had former burial depths of about 6.5 km; Lower Ordovician carbonate sequences of the northern Appalachian basin were buried to more than 7 km; Middle Ordovician strata from the same basin had paleodepths of approximately 5 km, and Devonian strata, 4.5 to 5 km. If these strata were formerly buried much more deeply than previously thought, then unexpectedly large amounts of uplift and erosion, ranging from 4.3 to 7 km, must also have occurred to bring these strata to the present land surface. The occurrence of such large-scale vertical movements of the crust and lithosphere needs to be recognized in paleogeographic reconstructions.

  1. Ag-doped FeSe0.94 polycrystalline samples obtained through hot isostatic pressing with improved grain connectivity

    NASA Astrophysics Data System (ADS)

    Gajda, G.; Morawski, A.; Rogacki, K.; Cetner, T.; Zaleski, A. J.; Buchkov, K.; Nazarova, E.; Balchev, N.; Hossain, M. S. A.; Diduszko, R.; Gruszka, K.; Przysłupski, P.; Fajfrowski, Ł.; Gajda, D.

    2016-09-01

    We evaluate the effects of high pressure during annealing on the structural and superconducting properties of Ag-doped FeSe bulks. The results obtained in this work indicate that the annealing at high pressure increases the critical temperature, upper critical field and irreversibility field due to the improved uniformity and grain connectivity.

  2. Building models

    SciTech Connect

    Burr, M.T.

    1995-04-01

    As developers make progress on independent power projects around the world, models for success are beginning to emerge. Different models are evolving to create ownership structures that accomoate a complex system of regulatory requirements. Other frameworks make use of previously untapped fuel resources, or establish new sources of financing; however, not all models may be applied to a given project. This article explores how developers are finding new alternatives for overcoming development challenges that are common to projects in many countries.

  3. Calorimetry modeling

    SciTech Connect

    Robinson, C.E.

    1990-01-01

    A heat-flow calorimeter has been modeled on a Compaq PC, using the Algor Heat Transfer Modeling and Analysis Program, Algor Interactive Systems, Inc., Pittsburgh, PA. Employed in this application of the Algor finite element analysis program are two-dimensional axisymmetric thermal conductivity elements. The development of a computer calorimeter modeling program allows for the testing of new materials and techniques without actual fabrication of the calorimeter. 2 figs.

  4. Cloud Modeling

    NASA Technical Reports Server (NTRS)

    Tao, Wei-Kuo; Moncrieff, Mitchell; Einaud, Franco (Technical Monitor)

    2001-01-01

    Numerical cloud models have been developed and applied extensively to study cloud-scale and mesoscale processes during the past four decades. The distinctive aspect of these cloud models is their ability to treat explicitly (or resolve) cloud-scale dynamics. This requires the cloud models to be formulated from the non-hydrostatic equations of motion that explicitly include the vertical acceleration terms since the vertical and horizontal scales of convection are similar. Such models are also necessary in order to allow gravity waves, such as those triggered by clouds, to be resolved explicitly. In contrast, the hydrostatic approximation, usually applied in global or regional models, does allow the presence of gravity waves. In addition, the availability of exponentially increasing computer capabilities has resulted in time integrations increasing from hours to days, domain grids boxes (points) increasing from less than 2000 to more than 2,500,000 grid points with 500 to 1000 m resolution, and 3-D models becoming increasingly prevalent. The cloud resolving model is now at a stage where it can provide reasonably accurate statistical information of the sub-grid, cloud-resolving processes poorly parameterized in climate models and numerical prediction models.

  5. Ventilation Model

    SciTech Connect

    V. Chipman

    2002-10-05

    The purpose of the Ventilation Model is to simulate the heat transfer processes in and around waste emplacement drifts during periods of forced ventilation. The model evaluates the effects of emplacement drift ventilation on the thermal conditions in the emplacement drifts and surrounding rock mass, and calculates the heat removal by ventilation as a measure of the viability of ventilation to delay the onset of peak repository temperature and reduce its magnitude. The heat removal by ventilation is temporally and spatially dependent, and is expressed as the fraction of heat carried away by the ventilation air compared to the fraction of heat produced by radionuclide decay. One minus the heat removal is called the wall heat fraction, or the remaining amount of heat that is transferred via conduction to the surrounding rock mass. Downstream models, such as the ''Multiscale Thermohydrologic Model'' (BSC 2001), use the wall heat fractions as outputted from the Ventilation Model to initialize their post-closure analyses. The Ventilation Model report was initially developed to analyze the effects of preclosure continuous ventilation in the Engineered Barrier System (EBS) emplacement drifts, and to provide heat removal data to support EBS design. Revision 00 of the Ventilation Model included documentation of the modeling results from the ANSYS-based heat transfer model. The purposes of Revision 01 of the Ventilation Model are: (1) To validate the conceptual model for preclosure ventilation of emplacement drifts and verify its numerical application in accordance with new procedural requirements as outlined in AP-SIII-10Q, Models (Section 7.0). (2) To satisfy technical issues posed in KTI agreement RDTME 3.14 (Reamer and Williams 2001a). Specifically to demonstrate, with respect to the ANSYS ventilation model, the adequacy of the discretization (Section 6.2.3.1), and the downstream applicability of the model results (i.e. wall heat fractions) to initialize post

  6. Model Selection for Geostatistical Models

    SciTech Connect

    Hoeting, Jennifer A.; Davis, Richard A.; Merton, Andrew A.; Thompson, Sandra E.

    2006-02-01

    We consider the problem of model selection for geospatial data. Spatial correlation is typically ignored in the selection of explanatory variables and this can influence model selection results. For example, the inclusion or exclusion of particular explanatory variables may not be apparent when spatial correlation is ignored. To address this problem, we consider the Akaike Information Criterion (AIC) as applied to a geostatistical model. We offer a heuristic derivation of the AIC in this context and provide simulation results that show that using AIC for a geostatistical model is superior to the often used approach of ignoring spatial correlation in the selection of explanatory variables. These ideas are further demonstrated via a model for lizard abundance. We also employ the principle of minimum description length (MDL) to variable selection for the geostatistical model. The effect of sampling design on the selection of explanatory covariates is also explored.

  7. Turbulence modeling

    NASA Technical Reports Server (NTRS)

    Bardina, Jorge E.

    1995-01-01

    The objective of this work is to develop, verify, and incorporate the baseline two-equation turbulence models which account for the effects of compressibility into the three-dimensional Reynolds averaged Navier-Stokes (RANS) code and to provide documented descriptions of the models and their numerical procedures so that they can be implemented into 3-D CFD codes for engineering applications.

  8. Dispersion Modeling.

    ERIC Educational Resources Information Center

    Budiansky, Stephen

    1980-01-01

    This article discusses the need for more accurate and complete input data and field verification of the various models of air pollutant dispension. Consideration should be given to changing the form of air quality standards based on enhanced dispersion modeling techniques. (Author/RE)

  9. Modeling Sunspots

    ERIC Educational Resources Information Center

    Oh, Phil Seok; Oh, Sung Jin

    2013-01-01

    Modeling in science has been studied by education researchers for decades and is now being applied broadly in school. It is among the scientific practices featured in the "Next Generation Science Standards" ("NGSS") (Achieve Inc. 2013). This article describes modeling activities in an extracurricular science club in a high…

  10. Phonological Models.

    ERIC Educational Resources Information Center

    Ballard, W.L.

    1968-01-01

    The article discusses models of synchronic and diachronic phonology and suggests changes in them. The basic generative model of phonology is outlined with the author's reinterpretations. The systematic phonemic level is questioned in terms of its unreality with respect to linguistic performance and its lack of validity with respect to historical…

  11. Student Modelers.

    ERIC Educational Resources Information Center

    Confrey, Jere; Doerr, Helen M.

    1994-01-01

    Presents an argument for learner-centered modeling tools and approaches that take into account students' conceptions. Based on a theoretical argument for the interplay of grounded activity and systematic inquiry, the article reports on a study of an integrated science and mathematics high school class that investigated modeling activities.…

  12. Protein structure modeling with MODELLER.

    PubMed

    Webb, Benjamin; Sali, Andrej

    2014-01-01

    Genome sequencing projects have resulted in a rapid increase in the number of known protein sequences. In contrast, only about one-hundredth of these sequences have been characterized at atomic resolution using experimental structure determination methods. Computational protein structure modeling techniques have the potential to bridge this sequence-structure gap. In this chapter, we present an example that illustrates the use of MODELLER to construct a comparative model for a protein with unknown structure. Automation of a similar protocol has resulted in models of useful accuracy for domains in more than half of all known protein sequences.

  13. Linguistic models and linguistic modeling.

    PubMed

    Pedryez, W; Vasilakos, A V

    1999-01-01

    The study is concerned with a linguistic approach to the design of a new category of fuzzy (granular) models. In contrast to numerically driven identification techniques, we concentrate on budding meaningful linguistic labels (granules) in the space of experimental data and forming the ensuing model as a web of associations between such granules. As such models are designed at the level of information granules and generate results in the same granular rather than pure numeric format, we refer to them as linguistic models. Furthermore, as there are no detailed numeric estimation procedures involved in the construction of the linguistic models carried out in this way, their design mode can be viewed as that of a rapid prototyping. The underlying algorithm used in the development of the models utilizes an augmented version of the clustering technique (context-based clustering) that is centered around a notion of linguistic contexts-a collection of fuzzy sets or fuzzy relations defined in the data space (more precisely a space of input variables). The detailed design algorithm is provided and contrasted with the standard modeling approaches commonly encountered in the literature. The usefulness of the linguistic mode of system modeling is discussed and illustrated with the aid of numeric studies including both synthetic data as well as some time series dealing with modeling traffic intensity over a broadband telecommunication network.

  14. OSPREY Model

    SciTech Connect

    Veronica J. Rutledge

    2013-01-01

    The absence of industrial scale nuclear fuel reprocessing in the U.S. has precluded the necessary driver for developing the advanced simulation capability now prevalent in so many other countries. Thus, it is essential to model complex series of unit operations to simulate, understand, and predict inherent transient behavior and feedback loops. A capability of accurately simulating the dynamic behavior of advanced fuel cycle separation processes will provide substantial cost savings and many technical benefits. The specific fuel cycle separation process discussed in this report is the off-gas treatment system. The off-gas separation consists of a series of scrubbers and adsorption beds to capture constituents of interest. Dynamic models are being developed to simulate each unit operation involved so each unit operation can be used as a stand-alone model and in series with multiple others. Currently, an adsorption model has been developed within Multi-physics Object Oriented Simulation Environment (MOOSE) developed at the Idaho National Laboratory (INL). Off-gas Separation and REcoverY (OSPREY) models the adsorption of off-gas constituents for dispersed plug flow in a packed bed under non-isothermal and non-isobaric conditions. Inputs to the model include gas, sorbent, and column properties, equilibrium and kinetic data, and inlet conditions. The simulation outputs component concentrations along the column length as a function of time from which breakthrough data is obtained. The breakthrough data can be used to determine bed capacity, which in turn can be used to size columns. It also outputs temperature along the column length as a function of time and pressure drop along the column length. Experimental data and parameters were input into the adsorption model to develop models specific for krypton adsorption. The same can be done for iodine, xenon, and tritium. The model will be validated with experimental breakthrough curves. Customers will be given access to

  15. Model hydrographs

    USGS Publications Warehouse

    Mitchell, W.D.

    1972-01-01

    Model hydrographs are composed of pairs of dimensionless ratios, arrayed in tabular form, which, when modified by the appropriate values of rainfall exceed and by the time and areal characteristics of the drainage basin, satisfactorily represent the flood hydrograph for the basin. Model bydrographs are developed from a dimensionless translation hydrograph, having a time base of T hours and appropriately modified for storm duration by routing through reservoir storage, S=kOx. Models fall into two distinct classes: (1) those for which the value of x is unity and which have all the characteristics of true unit hydrographs and (2) those for which the value of x is other than unity and to which the unit-hydrograph principles of proportionality and superposition do not apply. Twenty-six families of linear models and eight families of nonlinear models in tabular form from the principal subject of this report. Supplemental discussions describe the development of the models and illustrate their application. Other sections of the report, supplemental to the tables, describe methods of determining the hydrograph characteristics, T, k, and x, both from observed hydrograph and from the physical characteristics of the drainage basin. Five illustrative examples of use show that the models, when properly converted to incorporate actual rainfall excess and the time and areal characteristics of the drainage basins, do indeed satisfactorily represent the observed flood hydrographs for the basins.

  16. Stereometric Modelling

    NASA Astrophysics Data System (ADS)

    Grimaldi, P.

    2012-07-01

    These mandatory guidelines are provided for preparation of papers accepted for publication in the series of Volumes of The The stereometric modelling means modelling achieved with : - the use of a pair of virtual cameras, with parallel axes and positioned at a mutual distance average of 1/10 of the distance camera-object (in practice the realization and use of a stereometric camera in the modeling program); - the shot visualization in two distinct windows - the stereoscopic viewing of the shot while modelling. Since the definition of "3D vision" is inaccurately referred to as the simple perspective of an object, it is required to add the word stereo so that "3D stereo vision " shall stand for "three-dimensional view" and ,therefore, measure the width, height and depth of the surveyed image. Thanks to the development of a stereo metric model , either real or virtual, through the "materialization", either real or virtual, of the optical-stereo metric model made visible with a stereoscope. It is feasible a continuous on line updating of the cultural heritage with the help of photogrammetry and stereometric modelling. The catalogue of the Architectonic Photogrammetry Laboratory of Politecnico di Bari is available on line at: http://rappresentazione.stereofot.it:591/StereoFot/FMPro?-db=StereoFot.fp5&-lay=Scheda&-format=cerca.htm&-view

  17. Phenomenological models.

    PubMed

    Braby, L A

    1991-01-01

    The biological effects of ionizing radiation exposure are the result of a complex sequence of physical, chemical, biochemical, and physiological interactions which are modified by characteristics of the radiation, the timing of its administration, the chemical and physical environment, and the nature of the biological system. However, it is generally agreed that the health effects in animals originate from changes in individual cells, or possibly small groups of cells, and that these cellular changes are initiated by ionizations and excitations produced by the passage of charged particles through the cells. One way to begin a search for an understanding of health effects of radiation is through the development of phenomenological models of the response. Many models have been presented and tested in the slowly evolving process of characterizing cellular response. Different phenomena (LET dependence, dose rate effect, oxygen effect etc.) and different end points (cell survival, aberration formation, transformation, etc.) have been observed, and no single model has been developed to cover all of them. Instead, a range of models covering different end points and phenomena have developed in parallel. Many of these models employ similar assumptions about some underlying processes while differing about the nature of others. An attempt is made to organize many of the models into groups with similar features and to compare the consequences of those features with the actual experimental observations. It is assumed that by showing that some assumptions are inconsistent with experimental observations, the job of devising and testing mechanistic models can be simplified. PMID:1811477

  18. Phenomenological models.

    PubMed

    Braby, L A

    1991-01-01

    The biological effects of ionizing radiation exposure are the result of a complex sequence of physical, chemical, biochemical, and physiological interactions which are modified by characteristics of the radiation, the timing of its administration, the chemical and physical environment, and the nature of the biological system. However, it is generally agreed that the health effects in animals originate from changes in individual cells, or possibly small groups of cells, and that these cellular changes are initiated by ionizations and excitations produced by the passage of charged particles through the cells. One way to begin a search for an understanding of health effects of radiation is through the development of phenomenological models of the response. Many models have been presented and tested in the slowly evolving process of characterizing cellular response. Different phenomena (LET dependence, dose rate effect, oxygen effect etc.) and different end points (cell survival, aberration formation, transformation, etc.) have been observed, and no single model has been developed to cover all of them. Instead, a range of models covering different end points and phenomena have developed in parallel. Many of these models employ similar assumptions about some underlying processes while differing about the nature of others. An attempt is made to organize many of the models into groups with similar features and to compare the consequences of those features with the actual experimental observations. It is assumed that by showing that some assumptions are inconsistent with experimental observations, the job of devising and testing mechanistic models can be simplified.

  19. Modular Modeling System Model Builder

    SciTech Connect

    McKim, C.S.; Matthews, M.T.

    1996-12-31

    The latest release of the Modular Modeling System (MMS) Model Builder adds still more time-saving features to an already powerful MMS dynamic-simulation tool set. The Model Builder takes advantage of 32-bit architecture within the Microsoft Windows 95/NT{trademark} Operating Systems to better integrate a mature library of power-plant components. In addition, the MMS Library of components can now be modified and extended with a new tool named MMS CompGen{trademark}. The MMS Model Builder allows the user to quickly build a graphical schematic representation for a plant by selecting from a library of predefined power plant components to dynamically simulate their operation. In addition, each component has a calculation subroutine stored in a dynamic-link library (DLL), which facilitates the determination of a steady-state condition and performance of routine calculations for the component. These calculations, termed auto-parameterization, help avoid repetitive and often tedious hand calculations for model initialization. In striving to meet the needs for large models and increase user productivity, the MMS Model Builder has been completely revamped to make power plant model creation and maintainability easier and more efficient.

  20. A Model for Math Modeling

    ERIC Educational Resources Information Center

    Lin, Tony; Erfan, Sasan

    2016-01-01

    Mathematical modeling is an open-ended research subject where no definite answers exist for any problem. Math modeling enables thinking outside the box to connect different fields of studies together including statistics, algebra, calculus, matrices, programming and scientific writing. As an integral part of society, it is the foundation for many…

  1. Energy Models

    EPA Science Inventory

    Energy models characterize the energy system, its evolution, and its interactions with the broader economy. The energy system consists of primary resources, including both fossil fuels and renewables; power plants, refineries, and other technologies to process and convert these r...

  2. Modeling Arcs

    SciTech Connect

    Insepov, Z.; Norem, J.; Vetizer, S.; Mahalingam, S.

    2011-12-23

    Although vacuum arcs were first identified over 110 years ago, they are not yet well understood. We have since developed a model of breakdown and gradient limits that tries to explain, in a self-consistent way: arc triggering, plasma initiation, plasma evolution, surface damage and gradient limits. We use simple PIC codes for modeling plasmas, molecular dynamics for modeling surface breakdown, and surface damage, and mesoscale surface thermodynamics and finite element electrostatic codes for to evaluate surface properties. Since any given experiment seems to have more variables than data points, we have tried to consider a wide variety of arcing (rf structures, e beam welding, laser ablation, etc.) to help constrain the problem, and concentrate on common mechanisms. While the mechanisms can be comparatively simple, modeling can be challenging.

  3. Programming models

    SciTech Connect

    Daniel, David J; Mc Pherson, Allen; Thorp, John R; Barrett, Richard; Clay, Robert; De Supinski, Bronis; Dube, Evi; Heroux, Mike; Janssen, Curtis; Langer, Steve; Laros, Jim

    2011-01-14

    A programming model is a set of software technologies that support the expression of algorithms and provide applications with an abstract representation of the capabilities of the underlying hardware architecture. The primary goals are productivity, portability and performance.

  4. PREDICTIVE MODELS

    SciTech Connect

    Ray, R.M. )

    1986-12-01

    PREDICTIVE MODELS is a collection of five models - CFPM, CO2PM, ICPM, PFPM, and SFPM - used in the 1982-1984 National Petroleum Council study of enhanced oil recovery (EOR) potential. Each pertains to a specific EOR process designed to squeeze additional oil from aging or spent oil fields. The processes are: 1) chemical flooding, where soap-like surfactants are injected into the reservoir to wash out the oil; 2) carbon dioxide miscible flooding, where carbon dioxide mixes with the lighter hydrocarbons making the oil easier to displace; 3) in-situ combustion, which uses the heat from burning some of the underground oil to thin the product; 4) polymer flooding, where thick, cohesive material is pumped into a reservoir to push the oil through the underground rock; and 5) steamflood, where pressurized steam is injected underground to thin the oil. CFPM, the Chemical Flood Predictive Model, models micellar (surfactant)-polymer floods in reservoirs, which have been previously waterflooded to residual oil saturation. Thus, only true tertiary floods are considered. An option allows a rough estimate of oil recovery by caustic or caustic-polymer processes. CO2PM, the Carbon Dioxide miscible flooding Predictive Model, is applicable to both secondary (mobile oil) and tertiary (residual oil) floods, and to either continuous CO2 injection or water-alternating gas processes. ICPM, the In-situ Combustion Predictive Model, computes the recovery and profitability of an in-situ combustion project from generalized performance predictive algorithms. PFPM, the Polymer Flood Predictive Model, is switch-selectable for either polymer or waterflooding, and an option allows the calculation of the incremental oil recovery and economics of polymer relative to waterflooding. SFPM, the Steamflood Predictive Model, is applicable to the steam drive process, but not to cyclic steam injection (steam soak) processes.

  5. Sensitivity of grounding line dynamics to viscoelastic deformation of the solid Earth: Inferences from a fully coupled ice sheet - solid Earth model

    NASA Astrophysics Data System (ADS)

    Konrad, H.; Sasgen, I.; Thoma, M.; Klemann, V.; Grosfeld, K.; Martinec, Z.

    2013-12-01

    The interactions of ice sheets with the sea level and the solid Earth are important factors for the stability of the ice shelves and the tributary inland ice (e.g. Thomas and Bentley, 1978; Gomez et al, 2012). First, changes in ice extent and ice thickness induce viscoelastic deformation of the Earth surface and Earth's gravity field. In turn, global and local changes in sea level and bathymetry affect the grounding line and, subsequently, alter the ice dynamic behaviour. Here, we investigate these feedbacks for a synthetic ice sheet configuration as well as for the Antarctic ice sheet using a three-dimensional thermomechanical ice sheet and shelf model, coupled to a viscoelastic solid-Earth and gravitationally self-consistent sea-level model. The respective ice sheet undergoes a forcing from rising sea level, warming ocean, and/or changing surface mass balance. The coupling is realized by exchanging ice thickness, Earth surface deformation, and sea level periodically. We apply several sets of viscoelastic Earth parameters to our coupled model, e.g. simulating a low-viscous upper mantle present at the Antarctic Peninsula (Ivins et al., 2011). Special focus of our study lies on the evolution of Earth surface deformation and local sea level changes, as well as on the accompanying grounding line evolution. N. Gomez, D. Pollard, J. X. Mitrovica, P. Huybers, and P. U. Clark 2012. Evolution of a coupled marine ice sheet-sea level model, J. Geophys. Res., 117, F01013, doi:10.1029/2011JF002128. E. R. Ivins, M. M. Watkins, D.-N. Yuan, R. Dietrich, G. Casassa, and A. Rülke 2011. On-land ice loss and glacial isostatic adjustment at the Drake Passage: 2003-2009, J. Geophys. Res. 116, B02403, doi: 10.1029/2010JB007607 R. H. Thomas and C. R. Bentley 1978. A model for Holocene retreat of the West Antarctic Ice Sheet, Quaternary Research, 10 (2), pages 150-170, doi: 10.1016/0033-5894(78)90098-4.

  6. Mechanistic models

    SciTech Connect

    Curtis, S.B.

    1990-09-01

    Several models and theories are reviewed that incorporate the idea of radiation-induced lesions (repairable and/or irreparable) that can be related to molecular lesions in the DNA molecule. Usually the DNA double-strand or chromatin break is suggested as the critical lesion. In the models, the shoulder on the low-LET survival curve is hypothesized as being due to one (or more) of the following three mechanisms: (1) interaction'' of lesions produced by statistically independent particle tracks; (2) nonlinear (i.e., linear-quadratic) increase in the yield of initial lesions, and (3) saturation of repair processes at high dose. Comparisons are made between the various approaches. Several significant advances in model development are discussed; in particular, a description of the matrix formulation of the Markov versions of the RMR and LPL models is given. The more advanced theories have incorporated statistical fluctuations in various aspects of the energy-loss and lesion-formation process. An important direction is the inclusion of physical and chemical processes into the formulations by incorporating relevant track structure theory (Monte Carlo track simulations) and chemical reactions of radiation-induced radicals. At the biological end, identification of repair genes and how they operate as well as a better understanding of how DNA misjoinings lead to lethal chromosome aberrations are needed for appropriate inclusion into the theories. More effort is necessary to model the complex end point of radiation-induced carcinogenesis.

  7. Mechanistic models

    SciTech Connect

    Curtis, S.B.

    1990-09-01

    Several models and theories are reviewed that incorporate the idea of radiation-induced lesions (repairable and/or irreparable) that can be related to molecular lesions in the DNA molecule. Usually the DNA double-strand or chromatin break is suggested as the critical lesion. In the models, the shoulder on the low-LET survival curve is hypothesized as being due to one (or more) of the following three mechanisms: (1) ``interaction`` of lesions produced by statistically independent particle tracks; (2) nonlinear (i.e., linear-quadratic) increase in the yield of initial lesions, and (3) saturation of repair processes at high dose. Comparisons are made between the various approaches. Several significant advances in model development are discussed; in particular, a description of the matrix formulation of the Markov versions of the RMR and LPL models is given. The more advanced theories have incorporated statistical fluctuations in various aspects of the energy-loss and lesion-formation process. An important direction is the inclusion of physical and chemical processes into the formulations by incorporating relevant track structure theory (Monte Carlo track simulations) and chemical reactions of radiation-induced radicals. At the biological end, identification of repair genes and how they operate as well as a better understanding of how DNA misjoinings lead to lethal chromosome aberrations are needed for appropriate inclusion into the theories. More effort is necessary to model the complex end point of radiation-induced carcinogenesis.

  8. Modelling sea-level data from China and Malay-Thai Peninsula to infer Holocene eustatic sea-level change

    NASA Astrophysics Data System (ADS)

    Bradley, S.; Milne, G.; Zong, Y.; Horton, B.

    2008-12-01

    Late Devensian relative sea-level observations record changes in global sea level driven by a complex interplay between tectonic, isostatic and climatic processes, and as such have been adopted in many previous modelling studies to provide information on spatial and temporal ice sheet history, rheological earth properties, and global meltwater signals. In regions distant from previously glaciated areas (so-called 'far- field sites'), sea-level observations have been used to constrain the rate and magnitude of the global eustatic sea level change, as these data are primarily sensitive to changes in the global meltwater flux (Clark et al. 1978) Constraining the eustatic component of sea level change is useful since it provides a direct measure of past continental ice volume that can be compared to results obtained from oxygen isotope methods. A second application, which is the primary focus of this study, is the inference of eustatic change during the mid-to-late Holocene. Constraining the eustaic signal provides information on both: (i) the rate and timing of major ice melting at the end of the last deglaciation and (ii) the magnitude of melting during the late Holocene. The latter is an important baseline that can be compared to estimates of global sea-level rise in the 20th century. The typical sea-level pattern at far-field locations is characterized by a steady rise to a mid- Holocene highstand, followed by a slow monotonic fall to present day levels. Previous studies have examined the spatial and temporal variations in the Holocene highstand to arrive at estimates of eustatic change in the mid-to-late Holocene (Nadaka and Lambeck 1989; Flemming et al. 1998; Lambeck 2002; Peltier 2002). While the results of these studies are broadly compatible, there remain significant discrepancies and so it is important to consider additional data to improve constraints on the eustatic signal. This study addresses this aim by considering previously un-modelled Holocene sea

  9. Modeling reality

    NASA Technical Reports Server (NTRS)

    Denning, Peter J.

    1990-01-01

    Although powerful computers have allowed complex physical and manmade hardware systems to be modeled successfully, we have encountered persistent problems with the reliability of computer models for systems involving human learning, human action, and human organizations. This is not a misfortune; unlike physical and manmade systems, human systems do not operate under a fixed set of laws. The rules governing the actions allowable in the system can be changed without warning at any moment, and can evolve over time. That the governing laws are inherently unpredictable raises serious questions about the reliability of models when applied to human situations. In these domains, computers are better used, not for prediction and planning, but for aiding humans. Examples are systems that help humans speculate about possible futures, offer advice about possible actions in a domain, systems that gather information from the networks, and systems that track and support work flows in organizations.

  10. Supernova models

    SciTech Connect

    Woosley, S.E.; Weaver, T.A.

    1980-01-01

    Recent progress in understanding the observed properties of Type I supernovae as a consequence of the thermonuclear detonation of white dwarf stars and the ensuing decay of the /sup 56/Ni produced therein is reviewed. Within the context of this model for Type I explosions and the 1978 model for Type II explosions, the expected nucleosynthesis and gamma-line spectra from both kinds of supernovae are presented. Finally, a qualitatively new approach to the problem of massive star death and Type II supernovae based upon a combination of rotation and thermonuclear burning is discussed.

  11. Orogenic evolution of the External Dinarides in the NE Adriatic region: a model constrained by tectonostratigraphy of Upper Cretaceous to Paleogene carbonates

    NASA Astrophysics Data System (ADS)

    Korbar, Tvrtko

    2009-11-01

    Mesozoic to Cenozoic evolution of the central part of the Adriatic plate (External Dinarides and Adriatic foreland) is still a matter of debate. This is expressed by opposing paleogeographic models: single carbonate platform (Adriatic or Adriatic-Dinaridic) versus two carbonate platforms (Adriatic and Dinaridic) separated by the inter-platform Budva-Cukali basin. Estimates of shortening during Adria NE subduction, that resulted in the development of the Dinaric Alps, differ substantially. The single-platform model involves minor shortening achieved by folding and faulting along steep reverse faults. The two-platform model involves significant shortening achieved mainly by thrust stacking, which resulted in almost complete underthrusting of the intervening basinal deposits. Analysis of Upper Cretaceous to Paleogene stratigraphical data from both outcrops and boreholes allows regional correlation and the interpretation of major lithostratigraphic units. As a result, a few tectonostratigraphic units are recognized. The tectonostratigraphy is used as a basis for a new model on the late Mesozoic to Cenozoic evolution of the region. Generally, Adriatic and Dinaridic segments acted as major regional crustal entities of Adria. The upper portions of the sedimentary cover were differentially affected by progressive, southwestward verging thin-skinned deformations during the Paleocene to Eocene (Miocene?). The Adriatic foreland stayed out of the deformations, and is characterized predominantly by wrench and salt tectonics. The regional tectonic map shows arcuate thrust fronts of the External Dinarides. They could be a consequence of both, differential propagation of early-orogenic thin-skinned deformations over crustal fragments separated by transversal faults, and/or differential (isostatic?) movements of the fragments. The collision zone of the Adriatic and Dinaridic segments is characterized by late-orogenic (Oligocene to Miocene) thick-skinned compressional uplift

  12. Painting models

    NASA Astrophysics Data System (ADS)

    Baart, F.; Donchyts, G.; van Dam, A.; Plieger, M.

    2015-12-01

    The emergence of interactive art has blurred the line between electronic, computer graphics and art. Here we apply this art form to numerical models. Here we show how the transformation of a numerical model into an interactive painting can both provide insights and solve real world problems. The cases that are used as an example include forensic reconstructions, dredging optimization, barrier design. The system can be fed using any source of time varying vector fields, such as hydrodynamic models. The cases used here, the Indian Ocean (HYCOM), the Wadden Sea (Delft3D Curvilinear), San Francisco Bay (3Di subgrid and Delft3D Flexible Mesh), show that the method used is suitable for different time and spatial scales. High resolution numerical models become interactive paintings by exchanging their velocity fields with a high resolution (>=1M cells) image based flow visualization that runs in a html5 compatible web browser. The image based flow visualization combines three images into a new image: the current image, a drawing, and a uv + mask field. The advection scheme that computes the resultant image is executed in the graphics card using WebGL, allowing for 1M grid cells at 60Hz performance on mediocre graphic cards. The software is provided as open source software. By using different sources for a drawing one can gain insight into several aspects of the velocity fields. These aspects include not only the commonly represented magnitude and direction, but also divergence, topology and turbulence .

  13. Atmospheric Modeling

    EPA Science Inventory

    Although air quality models have been applied historically to address issues specific to ambient air quality standards (i.e., one criteria pollutant at a time) or welfare (e.g.. acid deposition or visibility impairment). they are inherently multipollutant based. Therefore. in pri...

  14. Modeling Muscles

    ERIC Educational Resources Information Center

    Goodwyn, Lauren; Salm, Sarah

    2007-01-01

    Teaching the anatomy of the muscle system to high school students can be challenging. Students often learn about muscle anatomy by memorizing information from textbooks or by observing plastic, inflexible models. Although these mediums help students learn about muscle placement, the mediums do not facilitate understanding regarding integration of…

  15. Modeling Convection

    ERIC Educational Resources Information Center

    Ebert, James R.; Elliott, Nancy A.; Hurteau, Laura; Schulz, Amanda

    2004-01-01

    Students must understand the fundamental process of convection before they can grasp a wide variety of Earth processes, many of which may seem abstract because of the scales on which they operate. Presentation of a very visual, concrete model prior to instruction on these topics may facilitate students' understanding of processes that are largely…

  16. Ensemble Models

    EPA Science Inventory

    Ensemble forecasting has been used for operational numerical weather prediction in the United States and Europe since the early 1990s. An ensemble of weather or climate forecasts is used to characterize the two main sources of uncertainty in computer models of physical systems: ...

  17. Criticality Model

    SciTech Connect

    A. Alsaed

    2004-09-14

    The ''Disposal Criticality Analysis Methodology Topical Report'' (YMP 2003) presents the methodology for evaluating potential criticality situations in the monitored geologic repository. As stated in the referenced Topical Report, the detailed methodology for performing the disposal criticality analyses will be documented in model reports. Many of the models developed in support of the Topical Report differ from the definition of models as given in the Office of Civilian Radioactive Waste Management procedure AP-SIII.10Q, ''Models'', in that they are procedural, rather than mathematical. These model reports document the detailed methodology necessary to implement the approach presented in the Disposal Criticality Analysis Methodology Topical Report and provide calculations utilizing the methodology. Thus, the governing procedure for this type of report is AP-3.12Q, ''Design Calculations and Analyses''. The ''Criticality Model'' is of this latter type, providing a process evaluating the criticality potential of in-package and external configurations. The purpose of this analysis is to layout the process for calculating the criticality potential for various in-package and external configurations and to calculate lower-bound tolerance limit (LBTL) values and determine range of applicability (ROA) parameters. The LBTL calculations and the ROA determinations are performed using selected benchmark experiments that are applicable to various waste forms and various in-package and external configurations. The waste forms considered in this calculation are pressurized water reactor (PWR), boiling water reactor (BWR), Fast Flux Test Facility (FFTF), Training Research Isotope General Atomic (TRIGA), Enrico Fermi, Shippingport pressurized water reactor, Shippingport light water breeder reactor (LWBR), N-Reactor, Melt and Dilute, and Fort Saint Vrain Reactor spent nuclear fuel (SNF). The scope of this analysis is to document the criticality computational method. The criticality

  18. Models, Part V: Composition Models.

    ERIC Educational Resources Information Center

    Callison, Daniel

    2003-01-01

    Describes four models: The Authoring Cycle, a whole language approach that reflects the inquiry process; I-Search, an approach to research that uses the power of student interests; Cultural Celebration, using local heritage topics; and Science Lab Report, for the composition of a lab report. (LRW)

  19. Modeling Molecules

    NASA Technical Reports Server (NTRS)

    2000-01-01

    The molecule modeling method known as Multibody Order (N) Dynamics, or MBO(N)D, was developed by Moldyn, Inc. at Goddard Space Flight Center through funding provided by the SBIR program. The software can model the dynamics of molecules through technology which stimulates low-frequency molecular motions and properties, such as movements among a molecule's constituent parts. With MBO(N)D, a molecule is substructured into a set of interconnected rigid and flexible bodies. These bodies replace the computation burden of mapping individual atoms. Moldyn's technology cuts computation time while increasing accuracy. The MBO(N)D technology is available as Insight II 97.0 from Molecular Simulations, Inc. Currently the technology is used to account for forces on spacecraft parts and to perform molecular analyses for pharmaceutical purposes. It permits the solution of molecular dynamics problems on a moderate workstation, as opposed to on a supercomputer.

  20. Dendrite Model

    NASA Technical Reports Server (NTRS)

    1999-01-01

    Dr. Donald Gilles, the Discipline Scientist for Materials Science in NASA's Microgravity Materials Science and Applications Department, demonstrates to Carl Dohrman a model of dendrites, the branch-like structures found in many metals and alloys. Dohrman was recently selected by the American Society for Metals International as their 1999 ASM International Foundation National Merit Scholar. The University of Illinois at Urbana-Champaign freshman recently toured NASA's materials science facilities at the Marshall Space Flight Center.

  1. Modeling biomembranes.

    SciTech Connect

    Plimpton, Steven James; Heffernan, Julieanne; Sasaki, Darryl Yoshio; Frischknecht, Amalie Lucile; Stevens, Mark Jackson; Frink, Laura J. Douglas

    2005-11-01

    Understanding the properties and behavior of biomembranes is fundamental to many biological processes and technologies. Microdomains in biomembranes or ''lipid rafts'' are now known to be an integral part of cell signaling, vesicle formation, fusion processes, protein trafficking, and viral and toxin infection processes. Understanding how microdomains form, how they depend on membrane constituents, and how they act not only has biological implications, but also will impact Sandia's effort in development of membranes that structurally adapt to their environment in a controlled manner. To provide such understanding, we created physically-based models of biomembranes. Molecular dynamics (MD) simulations and classical density functional theory (DFT) calculations using these models were applied to phenomena such as microdomain formation, membrane fusion, pattern formation, and protein insertion. Because lipid dynamics and self-organization in membranes occur on length and time scales beyond atomistic MD, we used coarse-grained models of double tail lipid molecules that spontaneously self-assemble into bilayers. DFT provided equilibrium information on membrane structure. Experimental work was performed to further help elucidate the fundamental membrane organization principles.

  2. Model checking

    NASA Technical Reports Server (NTRS)

    Dill, David L.

    1995-01-01

    Automatic formal verification methods for finite-state systems, also known as model-checking, successfully reduce labor costs since they are mostly automatic. Model checkers explicitly or implicitly enumerate the reachable state space of a system, whose behavior is described implicitly, perhaps by a program or a collection of finite automata. Simple properties, such as mutual exclusion or absence of deadlock, can be checked by inspecting individual states. More complex properties, such as lack of starvation, require search for cycles in the state graph with particular properties. Specifications to be checked may consist of built-in properties, such as deadlock or 'unspecified receptions' of messages, another program or implicit description, to be compared with a simulation, bisimulation, or language inclusion relation, or an assertion in one of several temporal logics. Finite-state verification tools are beginning to have a significant impact in commercial designs. There are many success stories of verification tools finding bugs in protocols or hardware controllers. In some cases, these tools have been incorporated into design methodology. Research in finite-state verification has been advancing rapidly, and is showing no signs of slowing down. Recent results include probabilistic algorithms for verification, exploitation of symmetry and independent events, and the use symbolic representations for Boolean functions and systems of linear inequalities. One of the most exciting areas for further research is the combination of model-checking with theorem-proving methods.

  3. Upper mantle viscosity and lithospheric thickness under Iceland determined from a microphysical modelling approach of mantle rheology

    NASA Astrophysics Data System (ADS)

    Barnhoorn, A.; van der Wal, W.; Drury, M. R.

    2012-04-01

    The Vatnajökull glacier, located in the south-east of Iceland is the largest ice cap of Iceland having a mean radius of ~50 km covering an area of ˜8100 km2. The Vatnajökull glacier is situated directly on top of the spreading axis in the eastern volcanic zone (EVZ) of the Icelandic mid-ocean ridge and near the inferred center of the Icelandic hotspot. Due to the vicinity of the glacier to the active tectonic area, the response of the solid earth to melting of the ice cap is strongly controlled by the properties of the hot newly formed upper mantle underneath the mid-ocean ridge. The relatively high temperatures in the mantle during rifting result in relatively low upper mantle viscosities and fast relaxation times in comparison with tectonically inactive glaciated areas such as in. In this study, estimates for lithospheric thickness and upper mantle viscosity under Iceland are produced by a microphysical modelling approach using the theoretical temperature distribution under mid-ocean ridges combined with olivine diffusion and dislocation creep flow laws. Large lateral variations in upper mantle viscosity and especially lithospheric thickness are expected for Iceland perpendicular to the ridge axis due to the large changes in temperatures away from the ridge axis. The lithospheric thickness (27-40 km) and upper mantle viscosity (2 × 1018-1019 Pa s) outcomes for the recent glaciation are consistent with previous reports of viscosity and lithospheric thickness from glacial isostatic adjustment studies. A combination of a 40 km thick elastic lithosphere and an average upper mantle viscosity of 5 × 1018 Pa s would suggest that the upper mantle under Iceland is most likely dry. Also, the results indicate that the presence of a plume under Iceland cannot explain the recent low viscosity values reported for Iceland. Using a larger extent and larger thickness of the Icelandic icecap during the Weichselian glaciation event (˜10,000 BP) this study predicts that during

  4. Coherency strain and its effect on ionic conductivity and diffusion in solid electrolytes--an improved model for nanocrystalline thin films and a review of experimental data.

    PubMed

    Korte, C; Keppner, J; Peters, A; Schichtel, N; Aydin, H; Janek, J

    2014-11-28

    A phenomenological and analytical model for the influence of strain effects on atomic transport in columnar thin films is presented. A model system consisting of two types of crystalline thin films with coherent interfaces is assumed. Biaxial mechanical strain ε0 is caused by lattice misfit of the two phases. The conjoined films consist of columnar crystallites with a small diameter l. Strain relaxation by local elastic deformation, parallel to the hetero-interface, is possible along the columnar grain boundaries. The spatial extent δ0 of the strained hetero-interface regions can be calculated, assuming an exponential decay of the deformation-forces. The effect of the strain field on the local ionic transport in a thin film is then calculated by using the thermodynamic relation between (isostatic) pressure and free activation enthalpy ΔG(#). An expression describing the total ionic transport relative to bulk transport of a thin film or a multilayer as a function of the layer thickness is obtained as an integral average over strained and unstrained regions. The expression depends only on known material constants such as Young modulus Y, Poisson ratio ν and activation volume ΔV(#), which can be combined as dimensionless parameters. The model is successfully used to describe own experimental data from conductivity and diffusion studies. In the second part of the paper a comprehensive literature overview of experimental studies on (fast) ion transport in thin films and multilayers along solid-solid hetero-interfaces is presented. By comparing and reviewing the data the observed interface effects can be classified into three groups: (i) transport along interfaces between extrinsic ionic conductors (and insulator), (ii) transport along an open surface of an extrinsic ionic conductor and (iii) transport along interfaces between intrinsic ionic conductors. The observed effects in these groups differ by about five orders of magnitude in a very consistent way. The

  5. EARA2014 (East Asia Radially Anisotropic Model Based on Adjoint Tomography) and its Interpretations: Insights to the Formation of the Hangai Dome and the Tibetan Plateau

    NASA Astrophysics Data System (ADS)

    Chen, M.; Niu, F.; Liu, Q.; Tromp, J.

    2015-12-01

    EARA2014 -a 3-D radially anisotropic model of the crust and mantle beneath East Asia down to 900 km depth- is developed by adjoint tomography based on a spectral element method. The data set used for the inversion comprises 1.7 million frequency-dependent traveltime measurements from waveforms of 227 earthquakes recorded by 1869 stations. After 20 iterations, the new model (named EARA2014) exhibits sharp and detailed wave speed anomalies with improved correlations with surface tectonic units compared to previous models. As part of tectonic interpretations of EARA2014, we investigated the seismic wavespeed anomalies beneath two prominent uplifted regions in East Asia: (1) Hangai Dome, an intra-continental low-relief surface with more than 2 km elevation in central Mongolia, and (2) Tibetan Plateau, a vast continental-margin surface with an average elevation of 4.5 km in west China. We discover beneath Hangai Dome a deep low shear wavespeed (low-V) conduit indicating a slightly warmer (54 K-127 K) upwelling from the transition zone. We propose that the mantle upwelling induced decompression melting in the uppermost mantle and that excess heat associated with melt transport modified the lithosphere that isostatically compensates the surface uplift of Hangai Dome at upper mantle depths (> 80 km). On the other hand, we observe no discernable focused deep mantle upwelling directly beneath Tibetan Plateau, which is instead dominated by a strong high-V structure, appearing below 100 km depth and extending to the bottom of the mantle transition zone. However, we find a very strong and localized low-V anomaly beneath the Tibetan Plateau in the crust and uppermost mantle (at depths of ~50 km and 100 km) mainly confined within the Songpan Ganzi Fold Belt and the northern Qiangtang Block. This low-V anomaly is spatially linked to a low-V anomaly beneath the Chuandian Block in the same depth range, which is fed by a deep mantle upwelling directly beneath Hainan Volcano in south

  6. Contribution of Regional Climate Drivers to Future Winter Sea-Level Changes in the Baltic Sea Estimated by Statistical Methods and Simulations of Climate Models

    NASA Astrophysics Data System (ADS)

    Hünicke, B.; Zorita, E.

    2008-12-01

    A statistical downscaling approach is applied to the output of different global climate model simulations driven by SRES A2 future scenarios of greenhouse gas concentrations to estimate the contribution of changes in the atmospheric circulation and in precipitation to regional future winter sea-level changes. The method is based on observed statistical relationships between Sea level as predictand and large-scale climate fields as predictors. The approach is applied to the Baltic Sea as it is one of the largest brackish seas in the world and a clear example for a complex coupled ocean-atmosphere land system with a complex coastline and bathymetry. Recent studies indicated that Baltic Sea level variations on decadal and longer time scales are strongly influenced by atmospheric forcings, but the influence of different large-scale forcing factors on sea level vary geographically. While the decadal sea level variations in the northern and eastern Baltic gauges are strongly influenced by the atmospheric circulation, the decadal variations in the southern Baltic Sea can be (statistically) better explained by area-averaged precipitation. The results indicate that future trends in sea-level rise caused by these forcing are larger than the past variability. Using sea level pressure as predictor for the central and eastern Baltic Sea level stations, three climate models lead to 21st century future trends in the range of the order of 1 to 2 mm/year. Using precipitation as predictor for the stations in the Southern Baltic Coast all five models lead to significant trends with a range of the order of 0.4 mm/year. These numbers are smaller, but of the order of magnitude as the predicted future global sea level rise. Nevertheless, these estimations comprise only a partial contribution of selected large-scale regional predictors and an estimation of the total regional sea-level rise has to consider other regional factors such as the isostatic contribution to relative sea

  7. Molecular Modeling

    NASA Astrophysics Data System (ADS)

    Holmes, Jon L.

    1999-06-01

    Molecular modeling has trickled down from the realm of pharmaceutical and research laboratories into the realm of undergraduate chemistry instruction. It has opened avenues for the visualization of chemical concepts that previously were difficult or impossible to convey. I am sure that many of you have developed exercises using the various molecular modeling tools. It is the desire of this Journal to become an avenue for you to share these exercises among your colleagues. It is to this end that Ron Starkey has agreed to edit such a column and to publish not only the description of such exercises, but also the software documents they use. The WWW is the obvious medium to distribute this combination and so accepted submissions will appear online as a feature of JCE Internet. Typical molecular modeling exercise: finding conformation energies. Molecular Modeling Exercises and Experiments is the latest feature column of JCE Internet, joining Conceptual Questions and Challenge Problems, Hal's Picks, and Mathcad in the Chemistry Curriculum. JCE Internet continues to seek submissions in these areas of interest and submissions of general interest. If you have developed materials and would like to submit them, please see our Guide to Submissions for more information. The Chemical Education Resource Shelf, Equipment Buyers Guide, and WWW Site Review would also like to hear about chemistry textbooks and software, equipment, and WWW sites, respectively. Please consult JCE Internet Features to learn more about these resources at JCE Online. Email Announcements Would you like to be informed by email when the latest issue of the Journal is available online? when a new JCE Software title is shipping? when a new JCE Internet article has been published or is available for Open Review? when your subscription is about to expire? A new feature of JCE Online makes this possible. Visit our Guestbook to learn how. When

  8. Students' Models of Curve Fitting: A Models and Modeling Perspective

    ERIC Educational Resources Information Center

    Gupta, Shweta

    2010-01-01

    The Models and Modeling Perspectives (MMP) has evolved out of research that began 26 years ago. MMP researchers use Model Eliciting Activities (MEAs) to elicit students' mental models. In this study MMP was used as the conceptual framework to investigate the nature of students' models of curve fitting in a problem-solving environment consisting of…

  9. 10. MOVABLE BED SEDIMENTATION MODELS. DOGTOOTH BEND MODEL (MODEL SCALE: ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    10. MOVABLE BED SEDIMENTATION MODELS. DOGTOOTH BEND MODEL (MODEL SCALE: 1' = 400' HORIZONTAL, 1' = 100' VERTICAL), AND GREENVILLE BRIDGE MODEL (MODEL SCALE: 1' = 360' HORIZONTAL, 1' = 100' VERTICAL). - Waterways Experiment Station, Hydraulics Laboratory, Halls Ferry Road, 2 miles south of I-20, Vicksburg, Warren County, MS

  10. Biomimetic modelling.

    PubMed Central

    Vincent, Julian F V

    2003-01-01

    Biomimetics is seen as a path from biology to engineering. The only path from engineering to biology in current use is the application of engineering concepts and models to biological systems. However, there is another pathway: the verification of biological mechanisms by manufacture, leading to an iterative process between biology and engineering in which the new understanding that the engineering implementation of a biological system can bring is fed back into biology, allowing a more complete and certain understanding and the possibility of further revelations for application in engineering. This is a pathway as yet unformalized, and one that offers the possibility that engineers can also be scientists. PMID:14561351

  11. The origin of the non-mare mascon gravity anomalies in lunar basins

    NASA Astrophysics Data System (ADS)

    Andrews-Hanna, Jeffrey C.

    2013-01-01

    Many lunar basins are characterized by prominent positive gravity anomalies over the basin interiors, referred to as mass concentrations or mascons. While a significant fraction of some near-side mascon anomalies can be explained as a result of the flexural support of the mare basalts within the basins, a number of basins, including Orientale, exhibit mascons in excess of those that can be plausibly ascribed to the mare. Some basins exhibit mascons but lack mare altogether. Lunar gravity and topography data are used to map the isostatic anomaly, or the height of the surface above or below its isostatic level. Orientale is representative of the majority of lunar basins, in which the super-isostatic basin center is surrounded by a sub-isostatic annulus of comparable magnitude but greater area. The basin structure as a whole is found to be strongly sub-isostatic. High-resolution crustal thickness models of Orientale confirm that it is surrounded by an annulus of thickened but sub-isostatic crust. It is proposed that the flexural uplift of the annulus causes the uplift and positive gravity anomalies within the basin center. Finite element models are used to examine the flexural uplift of the sub-isostatic annulus and the basin center for a range of lithosphere thicknesses both outside the basin and in the basin interior. The uplift of the basin center can exceed 2 km, increasing the central gravity anomaly by ˜200 mGal. This annular uplift explains a significant fraction of the Orientale mascon, and is likely a dominant cause of non-mare mascons globally.

  12. Postglacial Rebound Model ICE-6G_C (VM5a) Constrained by Geodetic and Geologic Observations

    NASA Astrophysics Data System (ADS)

    Peltier, W. R.; Argus, D. F.; Drummond, R.

    2014-12-01

    We fit the revised global model of glacial isostatic adjustment ICE-6G_C (VM5a) to all available data, consisting of several hundred GPS uplift rates, a similar number of 14C dated relative sea level histories, and 62 geologic estimates of changes in Antarctic ice thickness. The mantle viscosity profile, VM5a is a simple multi-layer fit to prior model VM2 of Peltier (1996, Science). However, the revised deglaciation history, ICE-6G (VM5a), differs significantly from previous models in the Toronto series. (1) In North America, GPS observations of vertical uplift of Earth's surface from the Canadian Base Network require the thickness of the Laurentide ice sheet at Last Glacial Maximum to be significantly revised. At Last Glacial Maximum the new model ICE-6G_C in this region, relative to ICE-5G, roughly 50 percent thicker east of Hudson Bay (in and northern Quebec and Labrador region) and roughly 30 percent thinner west of Hudson Bay (in Manitoba, Saskatchewan, and the Northwest Territories).the net change in mass, however, is small. We find that rates of gravity change determined by GRACE when corrected for the predictions of ICE-6G_C (VM5a) are significantly smaller than residuals determined on the basis of earlier models. (2) In Antarctica, we fit GPS uplift rates, geologic estimates of changes in ice thickness, and geologic constraints on the timing of ice loss. The resulting deglaciation history also differs significantly from prior models. The contribution of Antarctic ice loss to global sea level rise since Last Glacial Maximum in ICE-6G_C is 13.6 meters, less than in ICE-5G (17.5 m), but significantly larger than in both the W12A model of Whitehouse et al. [2012] (8 m) and the IJ05 R02 model of Ivins et al. [2013] (7.5 m). In ICE-6G_C rapid ice loss occurs in Antarctica from 11.5 to 8 thousands years ago, with a rapid onset at 11.5 ka thereby contributing significantly to Meltwater Pulse 1B. In ICE-6G_C (VM5a), viscous uplift of Antarctica is increasing

  13. Atmosphere model on the area of GBAS system for real-time GNSS and meteorological applications

    NASA Astrophysics Data System (ADS)

    Bosy, J.; Rohm, W.; Kaplon, J.; Sierny, J.; IGG WUE & LS; GNSS Meteorology Team

    2011-12-01

    of the coast north of the MTJ in Oregon and Washington has the opposite sign (uplift) and varies with distance between the coast and the trench, as may be expected from elastic strain accumulation at the locked subduction zone, coupled with a contrast in rheological structure affecting GIA. In terms of LSL and hence societal impact, our measured mean California subsidence of 0.5 mm/yr approximately cancels with GIA models of global GSL lowering at a similar rate. This GSL lowering is caused by the increasing volume of ocean basins as the mantle flows away from under the oceans in isostatic response to >100 m of sea level rise following Pleistocene deglaciation. So the net LSL in California caused by coastal VLM plus GSL lowering by GIA is ~0.5 mm/yr LSL rise to the north, and ~0.5 mm/yr lowering to the south. Since our VLM estimates do not account for large earthquakes, the trends in LSL over geological time could look quite different. Given that our GPS time series are selected from a globally consistent set from >11,000 stations, we note that similar studies could be applied using our dataset in a seamless way over coastlines across the globe, depending on available station coverage.

  14. Fault models

    NASA Astrophysics Data System (ADS)

    Sayah, H. R.; Buehler, M. G.

    1985-06-01

    A major problem in the qualification of integrated circuit cells and in the development of adequate tests for the circuits is to lack of information on the nature and density of fault models. Some of this information is being obtained from the test structures. In particular, the Pinhole Array Capacitor is providing values for the resistance of gate oxide shorts, and the Addressable Inverter Matrix is providing values for parameter distributions such as noise margins. Another CMOS fault mode, that of the open-gated transistor, is examined and the state of the transistors assessed. Preliminary results are described for a number of open-gated structures such as transistors, inverters, and NAND gates. Resistor faults are applied to various CMOS gates and the time responses are noted. The critical value for the resistive short to upset the gate response was determined.

  15. Joint Inversion and Forward Modeling of Gravity and Magnetic Data in the Ismenius Region of Mars

    NASA Technical Reports Server (NTRS)

    Milbury, C. A.; Raymond, C. A.; Jewell, J. B.; Smrekar, S. E.; Schubert, G.

    2005-01-01

    The unexpected discovery of remanent crustal magnetism on Mars was one of the most intriguing results from the Mars Global Surveyor mission. The origin of the pattern of magnetization remains elusive. Correlations with gravity and geology have been examined to better understand the nature of the magnetic anomalies. In the area of the Martian dichotomy between 50 and 90 degrees E (here referred to as the Ismenius Area), we find that both the Bouguer and the isostatic gravity anomalies appear to correlate with the magnetic anomalies and a buried fault, and allow for a better constraint on the magnetized crust].

  16. Modeling uncertainty: quicksand for water temperature modeling

    USGS Publications Warehouse

    Bartholow, John M.

    2003-01-01

    Uncertainty has been a hot topic relative to science generally, and modeling specifically. Modeling uncertainty comes in various forms: measured data, limited model domain, model parameter estimation, model structure, sensitivity to inputs, modelers themselves, and users of the results. This paper will address important components of uncertainty in modeling water temperatures, and discuss several areas that need attention as the modeling community grapples with how to incorporate uncertainty into modeling without getting stuck in the quicksand that prevents constructive contributions to policy making. The material, and in particular the reference, are meant to supplement the presentation given at this conference.

  17. Pre-Modeling Ensures Accurate Solid Models

    ERIC Educational Resources Information Center

    Gow, George

    2010-01-01

    Successful solid modeling requires a well-organized design tree. The design tree is a list of all the object's features and the sequential order in which they are modeled. The solid-modeling process is faster and less prone to modeling errors when the design tree is a simple and geometrically logical definition of the modeled object. Few high…

  18. The role of topography in geodetic gravity field modelling

    NASA Technical Reports Server (NTRS)

    Forsberg, R.; Sideris, M. G.

    1989-01-01

    Masses associated with the topography, bathymetry, and its isostatic compensation are a dominant source of gravity field variations, especially at shorter wavelengths. On global scales the topographic/isostatic effects are also significant, except for the lowest harmonics. In practice, though, global effects need not be taken into account as such effects are included in the coefficients of the geopotential reference fields. On local scales, the short-wavelength gravity variations due to the topography may, in rugged terrain, be an order of magnitude larger than other effects. In such cases, explicit or implicit terrain reduction procedures are mandatory in order to obtain good prediction results. Such effects may be computed by space-domain integration or by fast Fourier transformation (FFT) methods. Numerical examples are given for areas of the Canadian Rockies. In principle, good knowledge of the topographic densities is required to produce the smoothest residual field. Densities may be determined from sample measurements or by gravimetric means, but both are somewhat troublesome methods in practice. The use of a standard density, e.g., 2.67 g/cu cm, may often yield satisfactory results and may be put within a consistent theoretical framework. The independence of density assumptions is the key point of the classical Molodensky approach to the geodetic boundary value problem. The Molodensky solutions take into account that land gravity field observations are done on a non-level surface. Molodensky's problem may be solved by integral expansions or more effective FFT methods, but the solution should not be intermixed with the use of terrain reductions. The methods are actually complimentary and may both be required in order to obtain the smoothest possible signal, least prone to aliasing and other effects coming from sparse data coverage, typical of rugged topography.

  19. CISNET lung models: Comparison of model assumptions and model structures

    PubMed Central

    McMahon, Pamela M.; Hazelton, William; Kimmel, Marek; Clarke, Lauren

    2012-01-01

    Sophisticated modeling techniques can be powerful tools to help us understand the effects of cancer control interventions on population trends in cancer incidence and mortality. Readers of journal articles are however rarely supplied with modeling details. Six modeling groups collaborated as part of the National Cancer Institute’s Cancer Intervention and Surveillance Modeling Network (CISNET) to investigate the contribution of US tobacco control efforts towards reducing lung cancer deaths over the period 1975 to 2000. The models included in this monograph were developed independently and use distinct, complementary approaches towards modeling the natural history of lung cancer. The models used the same data for inputs and agreed on the design of the analysis and the outcome measures. This article highlights aspects of the models that are most relevant to similarities of or differences between the results. Structured comparisons can increase the transparency of these complex models. PMID:22882887

  20. Building Mental Models by Dissecting Physical Models

    ERIC Educational Resources Information Center

    Srivastava, Anveshna

    2016-01-01

    When students build physical models from prefabricated components to learn about model systems, there is an implicit trade-off between the physical degrees of freedom in building the model and the intensity of instructor supervision needed. Models that are too flexible, permitting multiple possible constructions require greater supervision to…

  1. I&C Modeling in SPAR Models

    SciTech Connect

    John A. Schroeder

    2012-06-01

    The Standardized Plant Analysis Risk (SPAR) models for the U.S. commercial nuclear power plants currently have very limited instrumentation and control (I&C) modeling [1]. Most of the I&C components in the operating plant SPAR models are related to the reactor protection system. This was identified as a finding during the industry peer review of SPAR models. While the Emergency Safeguard Features (ESF) actuation and control system was incorporated into the Peach Bottom Unit 2 SPAR model in a recent effort [2], various approaches to expend resources for detailed I&C modeling in other SPAR models are investigated.

  2. Comparative Protein Structure Modeling Using MODELLER.

    PubMed

    Webb, Benjamin; Sali, Andrej

    2014-09-08

    Functional characterization of a protein sequence is one of the most frequent problems in biology. This task is usually facilitated by accurate three-dimensional (3-D) structure of the studied protein. In the absence of an experimentally determined structure, comparative or homology modeling can sometimes provide a useful 3-D model for a protein that is related to at least one known protein structure. Comparative modeling predicts the 3-D structure of a given protein sequence (target) based primarily on its alignment to one or more proteins of known structure (templates). The prediction process consists of fold assignment, target-template alignment, model building, and model evaluation. This unit describes how to calculate comparative models using the program MODELLER and discusses all four steps of comparative modeling, frequently observed errors, and some applications. Modeling lactate dehydrogenase from Trichomonas vaginalis (TvLDH) is described as an example. The download and installation of the MODELLER software is also described.

  3. Stress transmission and incipient yield flow in dense granular materials

    NASA Astrophysics Data System (ADS)

    Blumenfeld, Raphael

    2010-05-01

    Jammed granular matter transmits stresses non-uniformly like no conventional solid, especially when it is on the verge of failure. Jamming is caused by self-organization of granular matter under external loads, often giving rise to networks of force chains that support the loads non-uniformly. An ongoing debate in the literature concerns the correct way to model the static stress field in such media: good old elasticity theory or newcomer isostaticity theory. The two differ significantly and, in particular in 2D, isostaticity theory leads naturally to force chain solutions. More recently, it has been proposed that real granular materials are made of mixtures of regions, some behaving elastically and some isostatically. The theory to describe these systems has been named stato-elasticity. In this paper, I first present the rationale for stato-elasticity theory. An important step towards the construction of this theory is a good understanding of stress transmission in the regions of pure isostatic states. A brief description is given of recently derived general solutions for 2D isostatic regions with nonuniform structures, which go well beyond the over-simplistic picture of force chains. I then show how the static stress equations are related directly to incipient yield flow and derive the equations that govern yield and creep rheology of dense granular matter at the initial stages of failure. These equations are general and describe strains in granular materials of both rigid and compliant particles.

  4. Modeling of 3d Space-time Surface of Potential Fields and Hydrogeologic Modeling of Nuclear Waste Disposal Sites

    NASA Astrophysics Data System (ADS)

    Shestopalov, V.; Bondarenko, Y.; Zayonts, I.; Rudenko, Y.

    Introduction After the Chernobyl Nuclear Power Plant (CNPP) disaster (04.26.1986) a huge amount (over 2000 sq. km) of nuclear wastes appeared within so-called "Cher- nobyl Exclusion Zone" (CEZ). At present there are not enough storage facilities in the Ukraine for safe disposal of nuclear wastes and hazardous chemical wastes. The urgent problem now is safe isolation of these dangerous wastes. According to the developed state program of radioactive waste management, the construction of a na- tional storage facility of nuclear wastes is planned. It is also possible to create regional storage facilities for hazardous chemical wastes. The region of our exploration cov- ers the eastern part of the Korosten Plutone and its slope, reaching the CNPP. 3D Space-Time Surface Imaging of Geophysical Fields. There are only three direct meth- ods of stress field reconstruction in present practice, namely the field investigations based on the large-scale fracturing tests, petrotectonic and optical polarization meth- ods. Unfortunately, all these methods are extremely laborious and need the regular field tests, which is difficult to conduct in the areas of anisotropic rock outcrops. A compilation of magnetic and gravity data covering the CNPP area was carried out as a prelude to an interpretation study. More than thirty map products were generated from magnetic, gravity and geodesy data to prepare the 3D Space-Time Surface Images (3D STSI). Multi-layer topography and geophysic surfaces included: total magnetic intensity, isostatically-corrected Bouguer gravity, aspect and slope, first and second derivatives, vertical and horizontal curvature, histogram characteristics and space cor- relation coefficients between the gradient fields. Many maps shows the first and sec- ond derivatives of the potential fields, with the results of lineament (edge) structure detection superimposed. The lineament or edges of the potential fields are located from maximal gradient in many directions

  5. Comparative Protein Structure Modeling Using MODELLER.

    PubMed

    Webb, Benjamin; Sali, Andrej

    2016-01-01

    Comparative protein structure modeling predicts the three-dimensional structure of a given protein sequence (target) based primarily on its alignment to one or more proteins of known structure (templates). The prediction process consists of fold assignment, target-template alignment, model building, and model evaluation. This unit describes how to calculate comparative models using the program MODELLER and how to use the ModBase database of such models, and discusses all four steps of comparative modeling, frequently observed errors, and some applications. Modeling lactate dehydrogenase from Trichomonas vaginalis (TvLDH) is described as an example. The download and installation of the MODELLER software is also described. © 2016 by John Wiley & Sons, Inc. PMID:27322406

  6. Comparative Protein Structure Modeling Using MODELLER.

    PubMed

    Webb, Benjamin; Sali, Andrej

    2016-06-20

    Comparative protein structure modeling predicts the three-dimensional structure of a given protein sequence (target) based primarily on its alignment to one or more proteins of known structure (templates). The prediction process consists of fold assignment, target-template alignment, model building, and model evaluation. This unit describes how to calculate comparative models using the program MODELLER and how to use the ModBase database of such models, and discusses all four steps of comparative modeling, frequently observed errors, and some applications. Modeling lactate dehydrogenase from Trichomonas vaginalis (TvLDH) is described as an example. The download and installation of the MODELLER software is also described. © 2016 by John Wiley & Sons, Inc.

  7. An extended cure model and model selection.

    PubMed

    Peng, Yingwei; Xu, Jianfeng

    2012-04-01

    We propose a novel interpretation for a recently proposed Box-Cox transformation cure model, which leads to a natural extension of the cure model. Based on the extended model, we consider an important issue of model selection between the mixture cure model and the bounded cumulative hazard cure model via the likelihood ratio test, score test and Akaike's Information Criterion (AIC). Our empirical study shows that AIC is informative and both the score test and the likelihood ratio test have adequate power to differentiate between the mixture cure model and the bounded cumulative hazard cure model when the sample size is large. We apply the tests and AIC methods to leukemia and colon cancer data to examine the appropriateness of the cure models considered for them in the literature.

  8. Earth rheology in Iceland: new constraints from InSAR observations and models of crustal deformation induced by glacial surge and GIA

    NASA Astrophysics Data System (ADS)

    Auriac, Amandine; Sigmundsson, Freysteinn; Hooper, Andy; Spaans, Karsten; Björnsson, Helgi; Pálsson, Finnur; Pinel, Virginie; Feigl, Kurt L.

    2014-05-01

    About 11% of Iceland is covered by glaciers. The largest ice cap, Vatnajökull, has an area of ~8100 km² with an average ice thickness of ~380 m. Climate changes since the late 19th century has induced significant ice loss at Icelandic glaciers, resulting in a broad Glacial Isostatic Adjustment (GIA) uplift signal in the country. Furthermore, many of the major outlets from Icelandic ice caps are known to surge with a quiescent period of a few to up to ~10 decades. During a surge (lasting only a few months) large quantities of ice are transported to the glacier and terminal region from the interior zone of the ice caps. Due to this large scale mass transport, a surge implies a local crustal subsidence. In 1993 to 1995, the major outlets from SW-Vatnajökull surged. Deformation due both to GIA and the surges was observed and used to infer the properties of the crust and mantle beneath Iceland through modelling. Interferometric Synthetic Aperture Radar (InSAR) data from 1992-2002, providing high resolution ground observations, were used to measure the GIA uplift and surge-induced subsidence with mm to cm accuracy. InSAR time series and velocity estimates reveal a GIA signal of up to 25-28 mm/yr close to the ice cap. We disentangled the near instantaneous surge-induced crustal signal from the long-term GIA by inverting for a step function at the time of the surge, superimposed on the assumed linear GIA deformation rate. This yielded a surge-induced deformation signal reaching up to 75 mm at the ice edge. Finite element modelling is performed to reproduce each signal and infer some of the Earth properties. Each model is compared to the observations and a probability distribution of our free parameters is obtained using a Bayesian approach. For the surge-induced deformation, we use elastic modelling with one or two elastic layers and a digital map of the ice mass distribution after the surge, created from surface elevation measurements and glacier surface DEMs prior to

  9. Calculation of the 3D density model of the Earth

    NASA Astrophysics Data System (ADS)

    Piskarev, A.; Butsenko, V.; Poselov, V.; Savin, V.

    2009-04-01

    The study of the Earth's crust is a part of investigation aimed at extension of the Russian Federation continental shelf in the Sea of Okhotsk Gathered data allow to consider the Sea of Okhotsk' area located outside the exclusive economic zone of the Russian Federation as the natural continuation of Russian territory. The Sea of Okhotsk is an Epi-Mesozoic platform with Pre-Cenozoic heterogeneous folded basement of polycyclic development and sediment cover mainly composed of Paleocene - Neocene - Quaternary deposits. Results of processing and complex interpretation of seismic, gravity, and aeromagnetic data along profile 2-DV-M, as well as analysis of available geological and geophysical information on the Sea of Okhotsk region, allowed to calculate of the Earth crust model. 4 layers stand out (bottom-up) in structure of the Earth crust: granulite-basic (density 2.90 g/cm3), granite-gneiss (limits of density 2.60-2.76 g/cm3), volcanogenic-sedimentary (2.45 g/cm3) and sedimentary (density 2.10 g/cm3). The last one is absent on the continent; it is observed only on the water area. Density of the upper mantle is taken as 3.30 g/cm3. The observed gravity anomalies are mostly related to the surface relief of the above mentioned layers or to the density variations of the granite-metamorphic basement. So outlining of the basement blocks of different constitution preceded to the modeling. This operation is executed after Double Fourier Spectrum analysis of the gravity and magnetic anomalies and following compilation of the synthetic anomaly maps, related to the basement density and magnetic heterogeneity. According to bathymetry data, the Sea of Okhotsk can be subdivided at three mega-blocks. Taking in consideration that central Sea of Okhotsk area is aseismatic, i.e. isostatic compensated, it is obvious that Earth crust structure of these three blocks is different. The South-Okhotsk depression is characteristics by 3200-3300 m of sea depths. Moho surface in this area is at

  10. Model selection for logistic regression models

    NASA Astrophysics Data System (ADS)

    Duller, Christine

    2012-09-01

    Model selection for logistic regression models decides which of some given potential regressors have an effect and hence should be included in the final model. The second interesting question is whether a certain factor is heterogeneous among some subsets, i.e. whether the model should include a random intercept or not. In this paper these questions will be answered with classical as well as with Bayesian methods. The application show some results of recent research projects in medicine and business administration.

  11. Multilevel Model Prediction

    ERIC Educational Resources Information Center

    Frees, Edward W.; Kim, Jee-Seon

    2006-01-01

    Multilevel models are proven tools in social research for modeling complex, hierarchical systems. In multilevel modeling, statistical inference is based largely on quantification of random variables. This paper distinguishes among three types of random variables in multilevel modeling--model disturbances, random coefficients, and future response…

  12. "Bohr's Atomic Model."

    ERIC Educational Resources Information Center

    Willden, Jeff

    2001-01-01

    "Bohr's Atomic Model" is a small interactive multimedia program that introduces the viewer to a simplified model of the atom. This interactive simulation lets students build an atom using an atomic construction set. The underlying design methodology for "Bohr's Atomic Model" is model-centered instruction, which means the central model of the…