Generating A Strobed Laser Light Sheet

NASA Technical Reports Server (NTRS)

Leighty, Bradley D.; Franke, John M.; Rhodes, David B.; Jones, Stephen B.

1994-01-01

An optoelectronic system generating synchronous, strobed sheet of laser light developed for use in making visible flow of air about model helicopter rotor. Used in wind-tunnel tests to determine actual locations of vortices for comparison with locations predicted by mathematical models to validate models. Each blade tip produces vortex. By establishing successive vortex locations, researcher determines trajectory of vortex pattern. Light-sheet strobe circuits provide selection of blade positions, strobe-pulse durations, and multiple pulses per revolution for rotors having two to nine blades. To make flow visible, vaporizing propylene glycol injected upstream of model. System also provides calibrated trigger delay of strobe pulses, adjustable strobe-pulse durations, selectable number of blades, and slip-sync mode to make flow visible as though in slow motion.

A Model Based Approach to Increase the Part Accuracy in Robot Based Incremental Sheet Metal Forming

DOE Office of Scientific and Technical Information (OSTI.GOV)

Meier, Horst; Laurischkat, Roman; Zhu Junhong

One main influence on the dimensional accuracy in robot based incremental sheet metal forming results from the compliance of the involved robot structures. Compared to conventional machine tools the low stiffness of the robot's kinematic results in a significant deviation of the planned tool path and therefore in a shape of insufficient quality. To predict and compensate these deviations offline, a model based approach, consisting of a finite element approach, to simulate the sheet forming, and a multi body system, modeling the compliant robot structure, has been developed. This paper describes the implementation and experimental verification of the multi bodymore » system model and its included compensation method.« less

AN INTEGRAL EQUATION REPRESENTATION OF WIDE-BAND ELECTROMAGNETIC SCATTERING BY THIN SHEETS

EPA Science Inventory

An efficient, accurate numerical modeling scheme has been developed, based on the integral equation solution to compute electromagnetic (EM) responses of thin sheets over a wide frequency band. The thin-sheet approach is useful for simulating the EM response of a fracture system ...

Modelling water flow under glaciers and ice sheets

PubMed Central

Flowers, Gwenn E.

2015-01-01

Recent observations of dynamic water systems beneath the Greenland and Antarctic ice sheets have sparked renewed interest in modelling subglacial drainage. The foundations of today's models were laid decades ago, inspired by measurements from mountain glaciers, discovery of the modern ice streams and the study of landscapes evacuated by former ice sheets. Models have progressed from strict adherence to the principles of groundwater flow, to the incorporation of flow ‘elements’ specific to the subglacial environment, to sophisticated two-dimensional representations of interacting distributed and channelized drainage. Although presently in a state of rapid development, subglacial drainage models, when coupled to models of ice flow, are now able to reproduce many of the canonical phenomena that characterize this coupled system. Model calibration remains generally out of reach, whereas widespread application of these models to large problems and real geometries awaits the next level of development. PMID:27547082

Modelling water flow under glaciers and ice sheets.

PubMed

Flowers, Gwenn E

2015-04-08

Recent observations of dynamic water systems beneath the Greenland and Antarctic ice sheets have sparked renewed interest in modelling subglacial drainage. The foundations of today's models were laid decades ago, inspired by measurements from mountain glaciers, discovery of the modern ice streams and the study of landscapes evacuated by former ice sheets. Models have progressed from strict adherence to the principles of groundwater flow, to the incorporation of flow 'elements' specific to the subglacial environment, to sophisticated two-dimensional representations of interacting distributed and channelized drainage. Although presently in a state of rapid development, subglacial drainage models, when coupled to models of ice flow, are now able to reproduce many of the canonical phenomena that characterize this coupled system. Model calibration remains generally out of reach, whereas widespread application of these models to large problems and real geometries awaits the next level of development.

Computer-aided light sheet flow visualization using photogrammetry

NASA Technical Reports Server (NTRS)

Stacy, Kathryn; Severance, Kurt; Childers, Brooks A.

1994-01-01

A computer-aided flow visualization process has been developed to analyze video images acquired from rotating and translating light sheet visualization systems. The computer process integrates a mathematical model for image reconstruction, advanced computer graphics concepts, and digital image processing to provide a quantitative and a visual analysis capability. The image reconstruction model, based on photogrammetry, uses knowledge of the camera and light sheet locations and orientations to project two-dimensional light sheet video images into three-dimensional space. A sophisticated computer visualization package, commonly used to analyze computational fluid dynamics (CFD) results, was chosen to interactively display the reconstructed light sheet images with the numerical surface geometry for the model or aircraft under study. The photogrammetric reconstruction technique and the image processing and computer graphics techniques and equipment are described. Results of the computer-aided process applied to both a wind tunnel translating light sheet experiment and an in-flight rotating light sheet experiment are presented. The capability to compare reconstructed experimental light sheet images with CFD solutions in the same graphics environment is also demonstrated.

Computer-Aided Light Sheet Flow Visualization

NASA Technical Reports Server (NTRS)

Stacy, Kathryn; Severance, Kurt; Childers, Brooks A.

1993-01-01

A computer-aided flow visualization process has been developed to analyze video images acquired from rotating and translating light sheet visualization systems. The computer process integrates a mathematical model for image reconstruction, advanced computer graphics concepts, and digital image processing to provide a quantitative and visual analysis capability. The image reconstruction model, based on photogrammetry, uses knowledge of the camera and light sheet locations and orientations to project two-dimensional light sheet video images into three-dimensional space. A sophisticated computer visualization package, commonly used to analyze computational fluid dynamics (CFD) data sets, was chosen to interactively display the reconstructed light sheet images, along with the numerical surface geometry for the model or aircraft under study. A description is provided of the photogrammetric reconstruction technique, and the image processing and computer graphics techniques and equipment. Results of the computer aided process applied to both a wind tunnel translating light sheet experiment and an in-flight rotating light sheet experiment are presented. The capability to compare reconstructed experimental light sheet images and CFD solutions in the same graphics environment is also demonstrated.

Computer-aided light sheet flow visualization

NASA Technical Reports Server (NTRS)

Stacy, Kathryn; Severance, Kurt; Childers, Brooks A.

1993-01-01

A computer-aided flow visualization process has been developed to analyze video images acquired from rotating and translating light sheet visualization systems. The computer process integrates a mathematical model for image reconstruction, advanced computer graphics concepts, and digital image processing to provide a quantitative and visual analysis capability. The image reconstruction model, based on photogrammetry, uses knowledge of the camera and light sheet locations and orientations to project two-dimensional light sheet video images into three-dimensional space. A sophisticated computer visualization package, commonly used to analyze computational fluid dynamics (CFD) data sets, was chosen to interactively display the reconstructed light sheet images, along with the numerical surface geometry for the model or aircraft under study. A description is provided of the photogrammetric reconstruction technique, and the image processing and computer graphics techniques and equipment. Results of the computer aided process applied to both a wind tunnel translating light sheet experiment and an in-flight rotating light sheet experiment are presented. The capability to compare reconstructed experimental light sheet images and CFD solutions in the same graphics environment is also demonstrated.

Coupled ice sheet-ocean modelling to investigate ocean driven melting of marine ice sheets in Antarctica

NASA Astrophysics Data System (ADS)

Jong, Lenneke; Gladstone, Rupert; Galton-Fenzi, Ben

2017-04-01

Ocean induced melting below the ice shelves of marine ice sheets is a major source of uncertainty for predictions of ice mass loss and Antarctica's resultant contribution to future sea level rise. The floating ice shelves provide a buttressing force against the flow of ice across the grounding line into the ocean. Thinning of these ice shelves due to an increase in melting reduces this force and can lead to an increase in the discharge of grounded ice. Fully coupled modelling of ice sheet-ocean interactions is key to improving understanding the influence of the Southern ocean on the evolution of the Antarctic ice sheet, and to predicting its future behaviour under changing climate conditions. Coupling of ocean and ice sheet models is needed to provide more realistic melt rates at the base of ice shelves and hence make better predictions of the behaviour of the grounding line and the shape of the ice-shelf cavity as the ice sheet evolves. The Framework for Ice Sheet - Ocean Coupling (FISOC) has been developed to provide a flexible platform for performing coupled ice sheet - ocean modelling experiments. We present preliminary results using FISOC to couple the Regional Ocean Modelling System (ROMS) with Elmer/Ice in idealised experiments Marine Ice Sheet-Ocean Model Intercomparison Project (MISOMIP). These experiments use an idealised geometry motivated by that of Pine Island glacier and the adjacent Amundsen Sea in West Antarctica, a region which has shown shown signs of thinning ice and grounding line retreat.

The response of grounded ice to ocean temperature forcing in a coupled ice sheet-ice shelf-ocean cavity model

NASA Astrophysics Data System (ADS)

Goldberg, D. N.; Little, C. M.; Sergienko, O. V.; Gnanadesikan, A.

2010-12-01

Ice shelves provide a pathway for the heat content of the ocean to influence continental ice sheets. Changes in the rate or location of basal melting can alter their geometry and effect changes in stress conditions at the grounding line, leading to a grounded ice response. Recent observations of ice streams and ice shelves in the Amundsen Sea sector of West Antarctica have been consistent with this story. On the other hand, ice dynamics in the grounding zone control flux into the shelf and thus ice shelf geometry, which has a strong influence on the circulation in the cavity beneath the shelf. Thus the coupling between the two systems, ocean and ice sheet-ice shelf, can be quite strong. We examine the response of the ice sheet-ice shelf-ocean cavity system to changes in ocean temperature using a recently developed coupled model. The coupled model consists a 3-D ocean model (GFDL's Generalized Ocean Layered Dynamics model, or GOLD) to a two-dimensional ice sheet-ice shelf model (Goldberg et al, 2009), and allows for changing cavity geometry and a migrating grounding line. Steady states of the coupled system are found even under considerable forcing. The ice shelf morphology and basal melt rate patterns of the steady states exhibit detailed structure, and furthermore seem to be unique and robust. The relationship between temperature forcing and area-averaged melt rate is influenced by the response of ice shelf morphology to thermal forcing, and is found to be sublinear in the range of forcing considered. However, results suggest that area-averaged melt rate is not the best predictor of overall system response, as grounding line stability depends on local aspects of the basal melt field. Goldberg, D N, D M Holland and C G Schoof, 2009. Grounding line movement and ice shelf buttressing in marine ice sheets, Journal of Geophysical Research-Earth Surfaces, 114, F04026.

Toward more accurate basal boundary conditions: a new 2-D model of distributed and channelised subglacial drainage

NASA Astrophysics Data System (ADS)

Werder, M. A.; Hewitt, I. J.; Schoof, C.; Flowers, G. E.

2012-04-01

Basal boundary conditions are one of the least constrained components of today's ice sheet models. To get at these one needs to know the distributed basal water pressure. We present a new glacier drainage system model to contribute to this missing piece of the puzzle. This two dimensional mathematical/numerical model combines distributed and channelised drainage at the ice-bed interface coupled to a water storage component. Notably the model determines the location of the channels as part of the solution. This is achieved by allowing channels (modelled as R-channels) to form on any of the edges of the unstructured triangular grid used to discretise the model. The distributed system is represented by a water sheet which is a continuum description of a linked-cavity system and exchanges water with the channels along their length. Water storage is parameterised as a function of the subglacial water pressure, which can be interpreted as storage in an englacial aquifer or due to elastic processes. The parabolic equation that determines the water pressure is solved using finite elements, the time evolution of the water sheet thickness and channel diameter are governed by local differential equations that are integrated using explicit methods. To explore the model's properties, we apply it to synthetic ice sheet catchments with areas up to 3000km2. We present steady state drainage system configurations and evaluate their channel-network properties (fractal dimensions, channel spacing). We find that an arborescent channel network forms whose density depends on the water sheet conductivity relative to water input. As a further experiment, we force the model with a seasonally and diurnally varying melt water input to investigate how the modelled drainage system evolves on these time scales: a channelised system grows up glacier as meltwater is delivered to the bed in spring and collapses in autumn. Water pressure is highest just before the formation of channels and then drops. Conversely, the diurnal variations in discharge affect the drainage system morphology only slightly. Instead they lead to large water pressure variations which lag meltwater input and coincide with changes in the volume of stored water. By incorporating an evolving R-channel network within a continuum model of distributed water drainage and storage, this 2-D model succeeds in qualitatively reproducing many of the observed and postulated features of the glacier drainage system.

A Statistical Model of the Magnetotail Neutral Sheet

NASA Astrophysics Data System (ADS)

Xiao, Sudong; Zhang, Tielong; Baumjohann, Wolfgang; Nakamura, Rumi; Ge, Yasong; Du, Aimin; Wang, Guoqiang; Lu, Quanming

2015-04-01

The neutral sheet of the magnetotail is characterized by weak magnetic field, strong cross tail current, and a reversal of the magnetic field direction across it. The dynamics of the earth's magnetosphere is greatly influenced by physical processes that occur near the neutral sheet. However, the exact position of the neutral sheet is variable in time. It is therefore essential to have a reliable estimate of the average position of the neutral sheet. Magnetic field data from ten years of Cluster, nineteen years of Geotail, four years of TC 1, and seven years of THEMIS observations have been incorporated to obtain a model of the magnetotail neutral sheet. All data in aberrated GSM (Geocentric Solar Magnetospheric) coordinate system are normalized to the same solar wind pressure condition. The shape and position of the neutral sheet, illustrated directly by the separator of positive and negative Bx on the YZ cross sections, are fitted with a displaced ellipse model. It is consistent with previous studies that the neutral sheet becomes curvier in the YZ cross section when the dipole tilt increases, yet our model shows the curviest neutral sheet compared with previous models. The new model reveals a hinging distance very close to 10 RE at a reference solar wind dynamic pressure of 2 nPa. We find that the earth dipole tilt angle not only affects the neutral sheet configuration in the YZ cross section but also in the XZ cross section. The neutral sheet becomes more tilting in the XZ cross section when the dipole tilt increases. The effect of an interplanetary magnetic field (IMF) penetration is studied, and an IMF By-related twisting of about 3° is found. Anticlockwise twisting of the neutral sheet is observed, looking along the downtail direction, for a positive IMF By, and clockwise twisting of the neutral sheet for a negative IMF By.

VESL: The Virtual Earth Sheet Laboratory for Ice Sheet Modeling and Visualization

NASA Astrophysics Data System (ADS)

Cheng, D. L. C.; Larour, E. Y.; Quinn, J. D.; Halkides, D. J.

2016-12-01

We introduce the Virtual Earth System Laboratory (VESL), a scientific modeling and visualization tool delivered through an integrated web portal for dissemination of data, simulation of physical processes, and promotion of climate literacy. The current prototype leverages NASA's Ice Sheet System Model (ISSM), a state-of-the-art polar ice sheet dynamics model developed at the Jet Propulsion Lab and UC Irvine. We utilize the Emscripten source-to-source compiler to convert the C/C++ ISSM engine core to JavaScript, and bundled pre/post-processing JS scripts to be compatible with the existing ISSM Python/Matlab API. Researchers using VESL will be able to effectively present their work for public dissemination with little-to-no additional post-processing. This will allow for faster publication in peer-reviewed journals and adaption of results for educational applications. Through future application of this concept to multiple aspects of the Earth System, VESL has the potential to broaden data applications in the geosciences and beyond. At this stage, we seek feedback from the greater scientific and public outreach communities regarding the ease of use and feature set of VESL, as we plan its expansion, and aim to achieve more rapid communication and presentation of scientific results.

Energized Oxygen : Speiser Current Sheet Bifurcation

NASA Astrophysics Data System (ADS)

George, D. E.; Jahn, J. M.

2017-12-01

A single population of energized Oxygen (O+) is shown to produce a cross-tail bifurcated current sheet in 2.5D PIC simulations of the magnetotail without the influence of magnetic reconnection. Treatment of oxygen in simulations of space plasmas, specifically a magnetotail current sheet, has been limited to thermal energies despite observations of and mechanisms which explain energized ions. We performed simulations of a homogeneous oxygen background, that has been energized in a physically appropriate manner, to study the behavior of current sheets and magnetic reconnection, specifically their bifurcation. This work uses a 2.5D explicit Particle-In-a-Cell (PIC) code to investigate the dynamics of energized heavy ions as they stream Dawn-to-Dusk in the magnetotail current sheet. We present a simulation study dealing with the response of a current sheet system to energized oxygen ions. We establish a, well known and studied, 2-species GEM Challenge Harris current sheet as a starting point. This system is known to eventually evolve and produce magnetic reconnection upon thinning of the current sheet. We added a uniform distribution of thermal O+ to the background. This 3-species system is also known to eventually evolve and produce magnetic reconnection. We add one additional variable to the system by providing an initial duskward velocity to energize the O+. We also traced individual particle motion within the PIC simulation. Three main results are shown. First, energized dawn- dusk streaming ions are clearly seen to exhibit sustained Speiser motion. Second, a single population of heavy ions clearly produces a stable bifurcated current sheet. Third, magnetic reconnection is not required to produce the bifurcated current sheet. Finally a bifurcated current sheet is compatible with the Harris current sheet model. This work is the first step in a series of investigations aimed at studying the effects of energized heavy ions on magnetic reconnection. This work differs significantly from previous investigations involving heavy ions in that they are energized as opposed to being simply thermal. This is a variation based firmly on published in-situ measurements. It also differs in that a complete population is used as opposed to simply test particles in a magnetic field model.

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

NASA Astrophysics Data System (ADS)

Rybak, Oleg; Volodin, Evgeny; Huybrechts, Philippe

2016-04-01

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

Ice sheets play important role in climate change

NASA Astrophysics Data System (ADS)

Clark, Peter U.; MacAyeal, Douglas R.; Andrews, John T.; Bartlein, Patrick J.

Ice sheets once were viewed as passive elements in the climate system enslaved to orbitally generated variations in solar radiation. Today, modeling results and new geologic records suggest that ice sheets actively participated in late-Pleistocene climate change, amplifying or driving significant variability at millennial as well as orbital timescales. Although large changes in global ice volume were ultimately caused by orbital variations (the Milankovitch hypothesis), once in existence, the former ice sheets behaved dynamically and strongly influenced regional and perhaps even global climate by altering atmospheric and oceanic circulation and temperature.Experiments with General Circulation Models (GCMs) yielded the first inklings of ice sheets' climatic significance. Manabe and Broccoli [1985], for example, found that the topographic and albedo effects of ice sheets alone explain much of the Northern Hemisphere cooling identified in paleoclimatic records of the last glacial maximum (˜21 ka).

The influence of atmospheric grid resolution in a climate model-forced ice sheet simulation

NASA Astrophysics Data System (ADS)

Lofverstrom, Marcus; Liakka, Johan

2018-04-01

Coupled climate-ice sheet simulations have been growing in popularity in recent years. Experiments of this type are however challenging as ice sheets evolve over multi-millennial timescales, which is beyond the practical integration limit of most Earth system models. A common method to increase model throughput is to trade resolution for computational efficiency (compromise accuracy for speed). Here we analyze how the resolution of an atmospheric general circulation model (AGCM) influences the simulation quality in a stand-alone ice sheet model. Four identical AGCM simulations of the Last Glacial Maximum (LGM) were run at different horizontal resolutions: T85 (1.4°), T42 (2.8°), T31 (3.8°), and T21 (5.6°). These simulations were subsequently used as forcing of an ice sheet model. While the T85 climate forcing reproduces the LGM ice sheets to a high accuracy, the intermediate resolution cases (T42 and T31) fail to build the Eurasian ice sheet. The T21 case fails in both Eurasia and North America. Sensitivity experiments using different surface mass balance parameterizations improve the simulations of the Eurasian ice sheet in the T42 case, but the compromise is a substantial ice buildup in Siberia. The T31 and T21 cases do not improve in the same way in Eurasia, though the latter simulates the continent-wide Laurentide ice sheet in North America. The difficulty to reproduce the LGM ice sheets in the T21 case is in broad agreement with previous studies using low-resolution atmospheric models, and is caused by a substantial deterioration of the model climate between the T31 and T21 resolutions. It is speculated that this deficiency may demonstrate a fundamental problem with using low-resolution atmospheric models in these types of experiments.

The Potsdam Parallel Ice Sheet Model (PISM-PIK) - Part 2: Dynamic equilibrium simulation of the Antarctic ice sheet

NASA Astrophysics Data System (ADS)

Martin, M. A.; Winkelmann, R.; Haseloff, M.; Albrecht, T.; Bueler, E.; Khroulev, C.; Levermann, A.

2010-08-01

We present a dynamic equilibrium simulation of the ice sheet-shelf system on Antarctica with the Potsdam Parallel Ice Sheet Model (PISM-PIK). The simulation is initialized with present-day conditions for topography and ice thickness and then run to steady state with constant present-day surface mass balance. Surface temperature and basal melt distribution are parameterized. Grounding lines and calving fronts are free to evolve, and their modeled equilibrium state is compared to observational data. A physically-motivated dynamic calving law based on horizontal spreading rates allows for realistic calving fronts for various types of shelves. Steady-state dynamics including surface velocity and ice flux are analyzed for whole Antarctica and the Ronne-Filchner and Ross ice shelf areas in particular. The results show that the different flow regimes in sheet and shelves, and the transition zone between them, are captured reasonably well, supporting the approach of superposition of SIA and SSA for the representation of fast motion of grounded ice. This approach also leads to a natural emergence of streams in this new 3-D marine ice sheet model.

Outreach/education interface for Cryosphere models using the Virtual Ice Sheet Laboratory

NASA Astrophysics Data System (ADS)

Larour, E. Y.; Halkides, D. J.; Romero, V.; Cheng, D. L.; Perez, G.

2014-12-01

In the past decade, great strides have been made in the development of models capable of projecting the future evolution of glaciers and the polar ice sheets in a changing climate. These models are now capable of replicating some of the trends apparent in satellite observations. However, because this field is just now maturing, very few efforts have been dedicated to adapting these capabilities to education. Technologies that have been used in outreach efforts in Atmospheric and Oceanic sciences still have not been extended to Cryospheric Science. We present a cutting-edge, technologically driven virtual laboratory, geared towards outreach and k-12 education, dedicated to the polar ice sheets on Antarctica and Greenland, and their role as major contributors to sea level rise in coming decades. VISL (Virtual Ice Sheet Laboratory) relies on state-of-the art Web GL rendering of polar ice sheets, Android/iPhone and web portability using Javascript, as well as C++ simulations (back-end) based on the Ice Sheet System Model, the NASA model for simulating the evolution of polar ice sheets. Using VISL, educators and students can have an immersive experience into the world of polar ice sheets, while at the same exercising the capabilities of a state-of-the-art climate model, all of it embedded into an education experience that follows the new STEM standards for education.This work was performed at the California Institute of Technology's Jet Propulsion Laboratory under a contract with the National Aeronautics and Space Administration's Cryosphere Science Program.

Modeling North American Ice Sheet Response to Changes in Precession and Obliquity

NASA Astrophysics Data System (ADS)

Tabor, C.; Poulsen, C. J.; Pollard, D.

2012-12-01

Milankovitch theory proposes that changes in insolation due to orbital perturbations dictate the waxing and waning of the ice sheets (Hays et al., 1976). However, variations in solar forcing alone are insufficient to produce the glacial oscillations observed in the climate record. Non-linear feedbacks in the Earth system likely work in concert with the orbital cycles to produce a modified signal (e.g. Berger and Loutre, 1996), but the nature of these feedbacks remain poorly understood. To gain a better understand of the ice dynamics and climate feedbacks associated with changes in orbital configuration, we use a complex Earth system model consisting of the GENESIS GCM and land surface model (Pollard and Thompson, 1997), the Pennsylvania State University ice sheet model (Pollard and DeConto, 2009), and the BIOME vegetation model (Kaplan et al., 2001). We began this study by investigating ice sheet sensitivity to a range of commonly used ice sheet model parameters, including mass balance and albedo, to optimize simulations for Pleistocene orbital cycles. Our tests indicate that choice of mass balance and albedo parameterizations can lead to significant differences in ice sheet behavior and volume. For instance, use of an insolation-temperature mass balance scheme (van den Berg, 2008) allows for a larger ice sheet response to orbital changes than the commonly employed positive degree-day method. Inclusion of a large temperature dependent ice albedo, representing phenomena such as melt ponds and dirty ice, also enhances ice sheet sensitivity. Careful tuning of mass balance and albedo parameterizations can help alleviate the problem of insufficient ice sheet retreat during periods of high summer insolation (Horton and Poulsen, 2007) while still accurately replicating the modern climate. Using our optimized configuration, we conducted a series of experiments with idealized transient orbits in an asynchronous coupling scheme to investigate the influence of obliquity and precession on the Laurentide and Cordillera ice sheets of North America. Preliminary model results show that the ice sheet response to changes in obliquity are larger than for precession despite providing a smaller direct insolation variation in the Northern Hemisphere high latitudes. A combination of enhanced Northern Hemisphere mid-latitude temperature gradient and longer cycle duration allow for a larger ice sheet response to obliquity than would be expected from insolation forcing alone. Conversely, a shorter duration dampens the ice sheet response to precession. Nevertheless, the precession cycle does cause significant changes in ice volume, a feature not observed in the Early Pleistocene δ18O records (Raymo and Nisancioglu, 2003). Future work will examine the climate response to an idealized transient orbit that includes concurrent variations in obliquity, precession, and eccentricity.

Landform Formation Under Ice Sheets

NASA Astrophysics Data System (ADS)

Schoof, C. G.; Ng, F. S.; Hallet, B.

2004-12-01

We present a new mathematical model for the formation of subglacial landforms such as drumlins under a warm-based, soft-bedded ice sheet. At the heart of the model is a channelized drainage system in which smaller channels grow at the expense of larger ones, leading to the continuous creation and extinction of drainage paths, and to a spatially distributed imprint on the landscape. We demonstrate how interactions between such a drainage system, bed topography and ice flow can lead to the spontaneous formation of subglacial landforms, and discuss the effect of different sediment transport characteristics in the drainage system on the shape and migration of these landforms. This mathematical model is the first component of a study of landscape/ice-sheet self-organization, which is inspired and guided, in part, by new digital topographic data (LIDAR) that are revealing with unprecedented detail the striking grain of glacially scoured topography on length scales ranging from 0.5 to 20 km.

Ardnamurchan 3D cone-sheet architecture explained by a single elongate magma chamber

PubMed Central

Burchardt, Steffi; Troll, Valentin R.; Mathieu, Lucie; Emeleus, Henry C.; Donaldson, Colin H.

2013-01-01

The Palaeogene Ardnamurchan central igneous complex, NW Scotland, was a defining place for the development of the classic concepts of cone-sheet and ring-dyke emplacement and has thus fundamentally influenced our thinking on subvolcanic structures. We have used the available structural information on Ardnamurchan to project the underlying three-dimensional (3D) cone-sheet structure. Here we show that a single elongate magma chamber likely acted as the source of the cone-sheet swarm(s) instead of the traditionally accepted model of three successive centres. This proposal is supported by the ridge-like morphology of the Ardnamurchan volcano and is consistent with the depth and elongation of the gravity anomaly underlying the peninsula. Our model challenges the traditional model of cone-sheet emplacement at Ardnamurchan that involves successive but independent centres in favour of a more dynamical one that involves a single, but elongate and progressively evolving magma chamber system. PMID:24100542

Ardnamurchan 3D cone-sheet architecture explained by a single elongate magma chamber.

PubMed

Burchardt, Steffi; Troll, Valentin R; Mathieu, Lucie; Emeleus, Henry C; Donaldson, Colin H

2013-10-08

The Palaeogene Ardnamurchan central igneous complex, NW Scotland, was a defining place for the development of the classic concepts of cone-sheet and ring-dyke emplacement and has thus fundamentally influenced our thinking on subvolcanic structures. We have used the available structural information on Ardnamurchan to project the underlying three-dimensional (3D) cone-sheet structure. Here we show that a single elongate magma chamber likely acted as the source of the cone-sheet swarm(s) instead of the traditionally accepted model of three successive centres. This proposal is supported by the ridge-like morphology of the Ardnamurchan volcano and is consistent with the depth and elongation of the gravity anomaly underlying the peninsula. Our model challenges the traditional model of cone-sheet emplacement at Ardnamurchan that involves successive but independent centres in favour of a more dynamical one that involves a single, but elongate and progressively evolving magma chamber system.

Leveraging Cloud Technology to Provide a Responsive, Reliable and Scalable Backend for the Virtual Ice Sheet Laboratory Using the Ice Sheet System Model and Amazon's Elastic Compute Cloud

NASA Astrophysics Data System (ADS)

Perez, G. L.; Larour, E. Y.; Halkides, D. J.; Cheng, D. L. C.

2015-12-01

The Virtual Ice Sheet Laboratory(VISL) is a Cryosphere outreach effort byscientists at the Jet Propulsion Laboratory(JPL) in Pasadena, CA, Earth and SpaceResearch(ESR) in Seattle, WA, and the University of California at Irvine (UCI), with the goal of providing interactive lessons for K-12 and college level students,while conforming to STEM guidelines. At the core of VISL is the Ice Sheet System Model(ISSM), an open-source project developed jointlyat JPL and UCI whose main purpose is to model the evolution of the polar ice caps in Greenland and Antarctica. By using ISSM, VISL students have access tostate-of-the-art modeling software that is being used to conduct scientificresearch by users all over the world. However, providing this functionality isby no means simple. The modeling of ice sheets in response to sea and atmospheric temperatures, among many other possible parameters, requiressignificant computational resources. Furthermore, this service needs to beresponsive and capable of handling burst requests produced by classrooms ofstudents. Cloud computing providers represent a burgeoning industry. With majorinvestments by tech giants like Amazon, Google and Microsoft, it has never beeneasier or more affordable to deploy computational elements on-demand. This isexactly what VISL needs and ISSM is capable of. Moreover, this is a promisingalternative to investing in expensive and rapidly devaluing hardware.

Planetary period modulations of Saturn's magnetotail current sheet: A simple illustrative mathematical model

NASA Astrophysics Data System (ADS)

Cowley, S. W. H.; Provan, G.; Hunt, G. J.; Jackman, C. M.

2017-01-01

We mathematically model the modulation effects on Saturn's equatorial magnetotail and magnetodisk current sheet produced by the combined magnetic field perturbations of the northern and southern planetary period oscillation (PPO) systems, specifically north-south displacements associated with the radial perturbation field and thickness modulations associated with the colatitudinal perturbation field. Since the phasing of the two PPO systems is taken to be related to the radial field perturbations, while the relative phasing of the colatitudinal perturbations is opposite for the two systems, the north-south oscillations reinforce when the two PPO systems are in phase, while the thickening-thinning effects reinforce when they are in antiphase. For intermediate relative phases we show that when the northern PPO system leads the southern the sheet is thicker when moving south to north than when moving north to south, while when the northern PPO system lags the southern the sheet is thicker when moving north to south than when moving south to north, thus leading to sawtooth profiles in the radial field for near-equatorial observers, of opposite senses in the two cases. Given empirically determined modulation amplitudes, the maximum sawtooth effect is found to be small when one system dominates the other, but becomes clear when the amplitude of one system lies within a factor of 2 of the other.

Surface Mass Balance of the Greenland Ice Sheet Derived from Paleoclimate Reanalysis

NASA Astrophysics Data System (ADS)

Badgeley, J.; Steig, E. J.; Hakim, G. J.; Anderson, J.; Tardif, R.

2017-12-01

Modeling past ice-sheet behavior requires independent knowledge of past surface mass balance. Though models provide useful insight into ice-sheet response to climate forcing, if past climate is unknown, then ascertaining the rate and extent of past ice-sheet change is limited to geological and geophysical constraints. We use a novel data-assimilation framework developed under the Last Millennium Reanalysis Project (Hakim et al., 2016) to reconstruct past climate over ice sheets with the intent of creating an independent surface mass balance record for paleo ice-sheet modeling. Paleoclimate data assimilation combines the physics of climate models and the time series evidence of proxy records in an offline, ensemble-based approach. This framework allows for the assimilation of numerous proxy records and archive types while maintaining spatial consistency with known climate dynamics and physics captured by the models. In our reconstruction, we use the Community Climate System Model version 4, CMIP5 last millennium simulation (Taylor et al., 2012; Landrum et al., 2013) and a nearly complete database of ice core oxygen isotope records to reconstruct Holocene surface temperature and precipitation over the Greenland Ice Sheet on a decadal timescale. By applying a seasonality to this reconstruction (from the TraCE-21ka simulation; Liu et al., 2009), our reanalysis can be used in seasonally-based surface mass balance models. Here we discuss the methods behind our reanalysis and the performance of our reconstruction through prediction of unassimilated proxy records and comparison to paleoclimate reconstructions and reanalysis products.

Understanding Greenland ice sheet hydrology using an integrated multi-scale approach

NASA Astrophysics Data System (ADS)

Rennermalm, A. K.; Moustafa, S. E.; Mioduszewski, J.; Chu, V. W.; Forster, R. R.; Hagedorn, B.; Harper, J. T.; Mote, T. L.; Robinson, D. A.; Shuman, C. A.; Smith, L. C.; Tedesco, M.

2013-03-01

Improved understanding of Greenland ice sheet hydrology is critically important for assessing its impact on current and future ice sheet dynamics and global sea level rise. This has motivated the collection and integration of in situ observations, model development, and remote sensing efforts to quantify meltwater production, as well as its phase changes, transport, and export. Particularly urgent is a better understanding of albedo feedbacks leading to enhanced surface melt, potential positive feedbacks between ice sheet hydrology and dynamics, and meltwater retention in firn. These processes are not isolated, but must be understood as part of a continuum of processes within an integrated system. This letter describes a systems approach to the study of Greenland ice sheet hydrology, emphasizing component interconnections and feedbacks, and highlighting research and observational needs.

Reconstructing the last Irish Ice Sheet 2: a geomorphologically-driven model of ice sheet growth, retreat and dynamics

NASA Astrophysics Data System (ADS)

Greenwood, Sarah L.; Clark, Chris D.

2009-12-01

The ice sheet that once covered Ireland has a long history of investigation. Much prior work focussed on localised evidence-based reconstructions and ice-marginal dynamics and chronologies, with less attention paid to an ice sheet wide view of the first order properties of the ice sheet: centres of mass, ice divide structure, ice flow geometry and behaviour and changes thereof. In this paper we focus on the latter aspect and use our new, countrywide glacial geomorphological mapping of the Irish landscape (>39 000 landforms), and our analysis of the palaeo-glaciological significance of observed landform assemblages (article Part 1), to build an ice sheet reconstruction yielding these fundamental ice sheet properties. We present a seven stage model of ice sheet evolution, from initiation to demise, in the form of palaeo-geographic maps. An early incursion of ice from Scotland likely coalesced with local ice caps and spread in a south-westerly direction 200 km across Ireland. A semi-independent Irish Ice Sheet was then established during ice sheet growth, with a branching ice divide structure whose main axis migrated up to 140 km from the west coast towards the east. Ice stream systems converging on Donegal Bay in the west and funnelling through the North Channel and Irish Sea Basin in the east emerge as major flow components of the maximum stages of glaciation. Ice cover is reconstructed as extending to the continental shelf break. The Irish Ice Sheet became autonomous (i.e. separate from the British Ice Sheet) during deglaciation and fragmented into multiple ice masses, each decaying towards the west. Final sites of demise were likely over the mountains of Donegal, Leitrim and Connemara. Patterns of growth and decay of the ice sheet are shown to be radically different: asynchronous and asymmetric in both spatial and temporal domains. We implicate collapse of the ice stream system in the North Channel - Irish Sea Basin in driving such asymmetry, since rapid collapse would sever the ties between the British and Irish Ice Sheets and drive flow configuration changes in response. Enhanced calving and flow acceleration in response to rising relative sea level is speculated to have undermined the integrity of the ice stream system, precipitating its collapse and driving the reconstructed pattern of ice sheet evolution.

Automated Rapid Prototyping of 3D Ceramic Parts

NASA Technical Reports Server (NTRS)

McMillin, Scott G.; Griffin, Eugene A.; Griffin, Curtis W.; Coles, Peter W. H.; Engle, James D.

2005-01-01

An automated system of manufacturing equipment produces three-dimensional (3D) ceramic parts specified by computational models of the parts. The system implements an advanced, automated version of a generic rapid-prototyping process in which the fabrication of an object having a possibly complex 3D shape includes stacking of thin sheets, the outlines of which closely approximate the horizontal cross sections of the object at their respective heights. In this process, the thin sheets are made of a ceramic precursor material, and the stack is subsequently heated to transform it into a unitary ceramic object. In addition to the computer used to generate the computational model of the part to be fabricated, the equipment used in this process includes: 1) A commercially available laminated-object-manufacturing machine that was originally designed for building woodlike 3D objects from paper and was modified to accept sheets of ceramic precursor material, and 2) A machine designed specifically to feed single sheets of ceramic precursor material to the laminated-object-manufacturing machine. Like other rapid-prototyping processes that utilize stacking of thin sheets, this process begins with generation of the computational model of the part to be fabricated, followed by computational sectioning of the part into layers of predetermined thickness that collectively define the shape of the part. Information about each layer is transmitted to rapid-prototyping equipment, where the part is built layer by layer. What distinguishes this process from other rapid-prototyping processes that utilize stacking of thin sheets are the details of the machines and the actions that they perform. In this process, flexible sheets of ceramic precursor material (called "green" ceramic sheets) suitable for lamination are produced by tape casting. The binder used in the tape casting is specially formulated to enable lamination of layers with little or no applied heat or pressure. The tape is cut into individual sheets, which are stacked in the sheet-feeding machine until used. The sheet-feeding machine can hold enough sheets for about 8 hours of continuous operation.

Pleistocene hydrology of North America: The role of ice sheets in reorganizing groundwater flow systems

NASA Astrophysics Data System (ADS)

Person, Mark; McIntosh, Jennifer; Bense, Victor; Remenda, V. H.

2007-09-01

While the geomorphic consequences of Pleistocene megafloods have been known for some time, it has been only in the past 2 decades that hydrogeologists and glaciologists alike have begun to appreciate the important impact that ice sheet-aquifer interactions have had in controlling subsurface flow patterns, recharge rates, and the distribution of fresh water in confined aquifer systems across North America. In this paper, we document the numerous lines of geochemical, isotopic, and geomechanical evidence of ice sheet hydrogeology across North America. We also review the mechanical, thermal, and hydrologic processes that control subsurface fluid migration beneath ice sheets. Finite element models of subsurface fluid flow, permafrost formation, and ice sheet loading are presented to investigate the coupled nature of transport processes during glaciation/deglaciation. These indicate that recharge rates as high as 10 times modern values occurred as the Laurentide Ice Sheet overran the margins of sedimentary basins. The effects of ice sheet loading and permafrost formation result in complex transient flow patterns within aquifers and confining units alike. Using geochemical and environmental isotopic data, we estimate that the volume of glacial meltwater emplaced at the margins of sedimentary basins overrun by the Laurentide Ice Sheet totals about 3.7 × 104 km3, which is about 0.2% of the volume of the Laurentide Ice Sheet. Subglacial infiltration estimates based on continental-scale hydrologic models are even higher (5-10% of meltwater generated). These studies in sum call into question the widely held notion that groundwater flow patterns within confined aquifer systems are controlled primarily by the water table configuration during the Pleistocene. Rather, groundwater flow patterns were likely much more complex and transient in nature than has previously been thought. Because Pleistocene recharge rates are believed to be highly variable, these studies have profound implications for water resource managers charged with determining sustainable pumping rates from confined aquifers that host ice sheet meltwater.

VESL: The Virtual Earth Sheet Laboratory for Ice Sheet Modeling and Visualization

NASA Astrophysics Data System (ADS)

Cheng, D. L. C.; Larour, E. Y.; Quinn, J. D.; Halkides, D. J.

2017-12-01

We present the Virtual Earth System Laboratory (VESL), a scientific modeling and visualization tool delivered through an integrated web portal. This allows for the dissemination of data, simulation of physical processes, and promotion of climate literacy. The current iteration leverages NASA's Ice Sheet System Model (ISSM), a state-of-the-art polar ice sheet dynamics model developed at the Jet Propulsion Lab and UC Irvine. We utilize the Emscripten source-to-source compiler to convert the C/C++ ISSM engine core to JavaScript, and bundled pre/post-processing JS scripts to be compatible with the existing ISSM Python/Matlab API. Researchers using VESL will be able to effectively present their work for public dissemination with little-to-no additional post-processing. Moreover, the portal allows for real time visualization and editing of models, cloud based computational simulation, and downloads of relevant data. This allows for faster publication in peer-reviewed journals and adaption of results for educational applications. Through application of this concept to multiple aspects of the Earth System, VESL is able to broaden data applications in the geosciences and beyond. At this stage, we still seek feedback from the greater scientific and public outreach communities regarding the ease of use and feature set of VESL. As we plan its expansion, we aim to achieve more rapid communication and presentation of scientific results.

The Potsdam Parallel Ice Sheet Model (PISM-PIK) - Part 2: Dynamic equilibrium simulation of the Antarctic ice sheet

NASA Astrophysics Data System (ADS)

Martin, M. A.; Winkelmann, R.; Haseloff, M.; Albrecht, T.; Bueler, E.; Khroulev, C.; Levermann, A.

2011-09-01

We present a dynamic equilibrium simulation of the ice sheet-shelf system on Antarctica with the Potsdam Parallel Ice Sheet Model (PISM-PIK). The simulation is initialized with present-day conditions for bed topography and ice thickness and then run to steady state with constant present-day surface mass balance. Surface temperature and sub-shelf basal melt distribution are parameterized. Grounding lines and calving fronts are free to evolve, and their modeled equilibrium state is compared to observational data. A physically-motivated calving law based on horizontal spreading rates allows for realistic calving fronts for various types of shelves. Steady-state dynamics including surface velocity and ice flux are analyzed for whole Antarctica and the Ronne-Filchner and Ross ice shelf areas in particular. The results show that the different flow regimes in sheet and shelves, and the transition zone between them, are captured reasonably well, supporting the approach of superposition of SIA and SSA for the representation of fast motion of grounded ice. This approach also leads to a natural emergence of sliding-dominated flow in stream-like features in this new 3-D marine ice sheet model.

Using paleoclimate data to improve models of the Antarctic Ice Sheet

NASA Astrophysics Data System (ADS)

King, M. A.; Phipps, S. J.; Roberts, J. L.; White, D.

2016-12-01

Ice sheet models are the most descriptive tools available to simulate the future evolution of the Antarctic Ice Sheet (AIS), including its contribution towards changes in global sea level. However, our knowledge of the dynamics of the coupled ice-ocean-lithosphere system is inevitably limited, in part due to a lack of observations. Furthemore, to build computationally efficient models that can be run for multiple millennia, it is necessary to use simplified descriptions of ice dynamics. Ice sheet modeling is therefore an inherently uncertain exercise. The past evolution of the AIS provides an opportunity to constrain the description of physical processes within ice sheet models and, therefore, to constrain our understanding of the role of the AIS in driving changes in global sea level. We use the Parallel Ice Sheet Model (PISM) to demonstrate how paleoclimate data can improve our ability to predict the future evolution of the AIS. A large, perturbed-physics ensemble is generated, spanning uncertainty in the parameterizations of four key physical processes within ice sheet models: ice rheology, ice shelf calving, and the stress balances within ice sheets and ice shelves. A Latin hypercube approach is used to optimally sample the range of uncertainty in parameter values. This perturbed-physics ensemble is used to simulate the evolution of the AIS from the Last Glacial Maximum ( 21,000 years ago) to present. Paleoclimate records are then used to determine which ensemble members are the most realistic. This allows us to use data on past climates to directly constrain our understanding of the past contribution of the AIS towards changes in global sea level. Critically, it also allows us to determine which ensemble members are likely to generate the most realistic projections of the future evolution of the AIS.

Modelling seasonal meltwater forcing of the velocity of land-terminating margins of the Greenland Ice Sheet

NASA Astrophysics Data System (ADS)

Koziol, Conrad P.; Arnold, Neil

2018-03-01

Surface runoff at the margin of the Greenland Ice Sheet (GrIS) drains to the ice-sheet bed, leading to enhanced summer ice flow. Ice velocities show a pattern of early summer acceleration followed by mid-summer deceleration due to evolution of the subglacial hydrology system in response to meltwater forcing. Modelling the integrated hydrological-ice dynamics system to reproduce measured velocities at the ice margin remains a key challenge for validating the present understanding of the system and constraining the impact of increasing surface runoff rates on dynamic ice mass loss from the GrIS. Here we show that a multi-component model incorporating supraglacial, subglacial, and ice dynamic components applied to a land-terminating catchment in western Greenland produces modelled velocities which are in reasonable agreement with those observed in GPS records for three melt seasons of varying melt intensities. This provides numerical support for the hypothesis that the subglacial system develops analogously to alpine glaciers and supports recent model formulations capturing the transition between distributed and channelized states. The model shows the growth of efficient conduit-based drainage up-glacier from the ice sheet margin, which develops more extensively, and further inland, as melt intensity increases. This suggests current trends of decadal-timescale slowdown of ice velocities in the ablation zone may continue in the near future. The model results also show a strong scaling between average summer velocities and melt season intensity, particularly in the upper ablation area. Assuming winter velocities are not impacted by channelization, our model suggests an upper bound of a 25 % increase in annual surface velocities as surface melt increases to 4 × present levels.

Possible contribution of ice-sheet/lithosphere interactions to past glaciological changes in Greenland

NASA Astrophysics Data System (ADS)

Alley, R. B.; Parizek, B. R.; Anandakrishnan, S.; Pollard, D.; Stevens, N. T.; Pourpoint, M.

2017-12-01

Ice-lithosphere interactions may have influenced the history of ice-sheet sensitivity to climate change. The Greenland ice sheet (GIS) is sensitive to warming, and is likely to be largely removed if subjected to relatively small additional temperature increases. The recent report (Schaefer et al., 2016, Nature) of near-complete GIS removal under modest Pleistocene forcing suggests that GIS sensitivity may be even greater than generally modeled, but lack of major Holocene retreat is more consistent with existing models. As shown by Stevens et al. (2016, JGR), peak lithospheric flexural stresses associated with ice-age GIS cycling are of the same order as dike-driving stresses in plutonic systems, and migrate over ice-age cycles. The full analysis by Stevens et al. suggests the possibility that the onset of cyclic ice-sheet loading allowed deep melt associated with the passage of the Icelandic hot spot beneath Greenland to work up though the crust to or near the base of the ice sheet, helping explain the anomalous geothermal heat fluxes observed at the head of the Northeast Greenland Ice Stream and elsewhere in the northern part of GIS. If ice-age cycling aided extraction of an existing reservoir of melted rock, then geothermal heat flux would have risen with the onset of extraction and migration, but with a subsequent fall associated with reservoir depletion. Simple parameterized flow-model simulations confirm intuition that a higher geothermal flux makes deglaciation easier, with the northern part of the ice sheet especially important. Large uncertainties remain in quantification, but we suggest the hypothesis that, following the onset of ice-age cycling, deglaciation of the GIS first became easier and then more difficult in response to feedbacks involving the ice sheet and the geological system beneath. In turn, this suggests that evidence of past deglaciation under moderate forcing is consistent with existing ice-sheet models.

Glaciological constraints on current ice mass changes from modelling the ice sheets over the glacial cycles

NASA Astrophysics Data System (ADS)

Huybrechts, P.

2003-04-01

The evolution of continental ice sheets introduces a long time scale in the climate system. Large ice sheets have a memory of millenia, hence the present-day ice sheets of Greenland and Antarctica are still adjusting to climatic variations extending back to the last glacial period. This trend is separate from the direct response to mass-balance changes on decadal time scales and needs to be correctly accounted for when assessing current and future contributions to sea level. One way to obtain estimates of current ice mass changes is to model the past history of the ice sheets and their underlying beds over the glacial cycles. Such calculations assist to distinguish between the longer-term ice-dynamic evolution and short-term mass-balance changes when interpreting altimetry data, and are helpful to isolate the effects of postglacial rebound from gravity and altimetry trends. The presentation will discuss results obtained from 3-D thermomechanical ice-sheet/lithosphere/bedrock models applied to the Antarctic and Greenland ice sheets. The simulations are forced by time-dependent boundary conditions derived from sediment and ice core records and are constrained by geomorphological and glacial-geological data of past ice sheet and sea-level stands. Current simulations suggest that the Greenland ice sheet is close to balance, while the Antarctic ice sheet is still losing mass, mainly due to incomplete grounding-line retreat of the West Antarctic ice sheet since the LGM. The results indicate that altimetry trends are likely dominated by ice thickness changes but that the gravitational signal mainly reflects postglacial rebound.

Stacked endoplasmic reticulum sheets are connected by helicoidal membrane motifs

PubMed Central

Terasaki, Mark; Shemesh, Tom; Kasthuri, Narayanan; Klemm, Robin W.; Schalek, Richard; Hayworth, Kenneth J.; Hand, Arthur R.; Yankova, Maya; Huber, Greg; Lichtman, Jeff W.; Rapoport, Tom A.; Kozlov, Michael M.

2013-01-01

The endoplasmic reticulum (ER) often forms stacked membrane sheets, an arrangement that is likely required to accommodate a maximum of membrane-bound polysomes for secretory protein synthesis. How sheets are stacked is unknown. Here, we used novel staining and automated ultra-thin sectioning electron microscopy methods to analyze stacked ER sheets in neuronal cells and secretory salivary gland cells of mice. Our results show that stacked ER sheets form a continuous membrane system in which the sheets are connected by twisted membrane surfaces with helical edges of left- or right-handedness. The three-dimensional structure of tightly stacked ER sheets resembles a parking garage, in which the different levels are connected by helicoidal ramps. A theoretical model explains the experimental observations and indicates that the structure corresponds to a minimum of elastic energy of sheet edges and surfaces. The structure allows the dense packing of ER sheets in the restricted space of a cell. PMID:23870120

Multi-millennia simulation of Greenland deglaciation from the Max-Plank-Institute Model (MPI-ISM) 2xCO2 simulation

NASA Astrophysics Data System (ADS)

Cabot, Vincent; Vizcaino, Miren; Mikolajewicz, Uwe

2016-04-01

Long-term ice sheet and climate coupled simulations are of great interest since they assess how the Greenland Ice Sheet (GrIS) will respond to global warming and how GrIS changes will impact on the climate system. We have run the Max-Plank-Institute Earth System Model coupled with an Ice Sheet Model (SICOPOLIS) over a time period of 10500 years under two times CO2 forcing. This is a coupled atmosphere (ECHAM5T31), ocean (MPI-OM), dynamic vegetation (LPJ), and ice sheet (SICOPOLIS, 10 km horizontal resolution) model. Given the multi-millennia simulation, the horizontal spatial resolution of the atmospheric component is relatively coarse (3.75°). A time-saving technique (asynchronous coupling) is used once the global climate reaches quasi-equilibrium. In our doubling-CO2 simulation, the GrIS is expected to break up into two pieces (one ice cap in the far north on one ice sheet in the south and east) after 3000 years. During the first 500 simulation years, the GrIS climate and surface mass balance (SMB) are mainly affected by the greenhouse effect-forced climate change. After the simulated year 500, the global climate reaches quasi-equilibrium. Henceforth Greenland climate change is mainly due to ice sheet decay. GrIS albedo reduction enhances melt and acts as a powerful feedback for deglaciation. Due to increased cloudiness in the Arctic region as a result of global climate change, summer incoming shortwave radiation is substantially reduced over Greenland, reducing deglaciation rates. At the end of the simulation, Greenland becomes green with forest growing over the newly deglaciated regions. References: Helsen, M. M., van de Berg, W. J., van de Wal, R. S. W., van den Broeke, M. R., and Oerlemans, J. (2013), Coupled regional climate-ice-sheet simulation shows limited Greenland ice loss during the Eemian, Climate of the Past, 9, 1773-1788, doi: 10.5194/cp-9-1773-2013 Helsen, M. M., van de Wal, R. S. W., van den Broeke, M. R., van de Berg, W. J., and Oerlemans, J. (2015), Coupling of climate models and ice sheet models by the surface mass balance gradients: application to the Greenland Ice Sheet, The Cryosphere, 6, 255-272, doi: 10.5194/tc-6-255-2012 Robinson, A., Calov, R., and Ganopolski, A. (2011), Greenland ice sheet model parameters constrained using simulations of the Eemian Interglacial, Climate of the Past, 7, 381-396, doi: 10.5194/cp-7-381-2011 Vizcaino, M., Mikolajewicz, U., Ziemen, F., Rodehacke, C. B., Greve, R., and van den Broeke, M. R. (2015), Coupled simulations of Greenland Ice Sheet and climate change up to A.D. 2300, Geophysical Research Letters, 42, doi: 10.1002/2014GL061142

Implementation of higher-order vertical finite elements in ISSM v4.13 for improved ice sheet flow modeling over paleoclimate timescales

NASA Astrophysics Data System (ADS)

Cuzzone, Joshua K.; Morlighem, Mathieu; Larour, Eric; Schlegel, Nicole; Seroussi, Helene

2018-05-01

Paleoclimate proxies are being used in conjunction with ice sheet modeling experiments to determine how the Greenland ice sheet responded to past changes, particularly during the last deglaciation. Although these comparisons have been a critical component in our understanding of the Greenland ice sheet sensitivity to past warming, they often rely on modeling experiments that favor minimizing computational expense over increased model physics. Over Paleoclimate timescales, simulating the thermal structure of the ice sheet has large implications on the modeled ice viscosity, which can feedback onto the basal sliding and ice flow. To accurately capture the thermal field, models often require a high number of vertical layers. This is not the case for the stress balance computation, however, where a high vertical resolution is not necessary. Consequently, since stress balance and thermal equations are generally performed on the same mesh, more time is spent on the stress balance computation than is otherwise necessary. For these reasons, running a higher-order ice sheet model (e.g., Blatter-Pattyn) over timescales equivalent to the paleoclimate record has not been possible without incurring a large computational expense. To mitigate this issue, we propose a method that can be implemented within ice sheet models, whereby the vertical interpolation along the z axis relies on higher-order polynomials, rather than the traditional linear interpolation. This method is tested within the Ice Sheet System Model (ISSM) using quadratic and cubic finite elements for the vertical interpolation on an idealized case and a realistic Greenland configuration. A transient experiment for the ice thickness evolution of a single-dome ice sheet demonstrates improved accuracy using the higher-order vertical interpolation compared to models using the linear vertical interpolation, despite having fewer degrees of freedom. This method is also shown to improve a model's ability to capture sharp thermal gradients in an ice sheet particularly close to the bed, when compared to models using a linear vertical interpolation. This is corroborated in a thermal steady-state simulation of the Greenland ice sheet using a higher-order model. In general, we find that using a higher-order vertical interpolation decreases the need for a high number of vertical layers, while dramatically reducing model runtime for transient simulations. Results indicate that when using a higher-order vertical interpolation, runtimes for a transient ice sheet relaxation are upwards of 5 to 7 times faster than using a model which has a linear vertical interpolation, and this thus requires a higher number of vertical layers to achieve a similar result in simulated ice volume, basal temperature, and ice divide thickness. The findings suggest that this method will allow higher-order models to be used in studies investigating ice sheet behavior over paleoclimate timescales at a fraction of the computational cost than would otherwise be needed for a model using a linear vertical interpolation.

Using an extreme bony prominence anatomical model to examine the influence of bed sheet materials and bed making methods on the distribution of pressure on the support surface.

PubMed

Iuchi, Terumi; Nakajima, Yukari; Fukuda, Moriyoshi; Matsuo, Junko; Okamoto, Hiroyuki; Sanada, Hiromi; Sugama, Junko

2014-05-01

Bed sheets generate high surface tension across the support surface and increase pressure to the body through a process known as the hammock effect. Using an anatomical model and a loading device characterized by extreme bony prominences, the present study compared pressure distributions on support surfaces across different bed making methods and bed sheet materials to determine the factors that influence pressure distribution. The model was placed on a pressure mapping system (CONFORMat; NITTA Corp., Osaka, Japan), and interface pressure was measured. Bed sheet elasticity and friction between the support surface and the bed sheets were also measured. For maximum interface pressure, the relative values of the following methods were higher than those of the control method, which did not use any bed sheets: cotton sheets with hospital corners (1.28, p = 0.02), polyester with no corners (1.29, p = 0.01), cotton with no corners (1.31, p = 0.003), and fitted polyester sheets (1.35, p = 0.002). Stepwise multiple regression analysis indicated that maximum interface pressure was negatively correlated with bed sheet elasticity (R(2) = 0.74). A statistically significant negative correlation was observed between maximum interface pressure and immersion depth, which was measured using the loading device (r = -0.40 and p = 0.04). We found that several combinations of bed making methods and bed sheet materials induced maximum interface pressures greater than those observed for the control method. Bed sheet materials influenced maximum interface pressure, and bed sheet elasticity was particularly important in reducing maximum interface pressure. Copyright © 2014 Tissue Viability Society. Published by Elsevier Ltd. All rights reserved.

Effect of en-glacial water on ice sheet temperatures in a warming climate - a model approach

NASA Astrophysics Data System (ADS)

Phillips, T. P.; Rajaram, H.; Steffen, K.

2009-12-01

Each summer, significant amount of melt is generated in the ablation zones of large glaciers and ice sheets. This melt does not run off on the surface of the glacier or ice sheet. In fact a significant fraction enters the glacier and flows through en-glacial and sub-glacial hydrologic systems. Correspondingly, the en-glacial and sub-glacial hydrologic systems are brought to a temperature close to the pressure melting point of ice. The thermal influence of these hydrologic processes is seldom incorporated in heat transfer models for glaciers and ice sheets. In a warming climate, as melt water generation is amplified, en-glacial and sub-glacial hydrologic processes can influence the thermal dynamics of an ice sheet significantly, a feedback which is missed in current models. Although the role of refreezing melt water in the firn of the accumulation zone is often accounted for to explain warmer near-surface temperatures, the role of melt water flow within a glacier is not considered in large ice sheet models. We propose a simple parameterization of the influence of en-glacial and sub-glacial hydrology on the thermal dynamics of ice sheets, in the form of a dual-column model. Our model basically modifies the classical Budd column model for temperature variations in ice sheets by introducing an interaction with an en-glacial column, where the temperature is brought to the melting point during the melt season, and winter-time refreezing is influenced by latent heat effects associated with water retained within the en-glacial and sub-glacial systems. A cryo-hydraulic heat exchange coefficient ς is defined, as a parameter that quantifies this interaction. The parameter ς is related to k/R^2, where R is the characteristic spacing between en-glacial passages. The general behavior of the dual-column model is influenced by the competition between cooling by horizontal advection and warming by cryo-hydraulic exchange. We present a dimensionless parameter to quantify this competition. Model simulations indicate that the combination of en-glacial water flow and winter snow cover can warm the ice and produce a higher steady state en-glacial temperature. Transient simulations indicate a spin-up period of approximately 10 years until the new steady state is attained. The en-glacially trapped water prevents the ice from cooling as the Arctic winter approaches. As the water refreezes in the shallow ice, the snow cover reaches a thickness that insulates the ice and slows further cooling. The en-glacial temperature is highly dependent on the magnitude of the cryo-hydraulic term (warming) and the magnitude of the horizontal advection term (cooling) which control the newly reached balance. The dual-column model was applied to analyze deep borehole temperature profiles from five sites on Dead Glacier in western Greenland north of Jakobshavn Glacier. The model was able to explain some features of the borehole temperatures that cannot be explained by the conventional single column model.

Simulating the impact of glaciations on continental groundwater flow systems: 1. Relevant processes and model formulation

NASA Astrophysics Data System (ADS)

Lemieux, J.-M.; Sudicky, E. A.; Peltier, W. R.; Tarasov, L.

2008-09-01

In the recent literature, it has been shown that Pleistocene glaciations had a large impact on North American regional groundwater flow systems. Because of the myriad of complex processes and large spatial scales involved during periods of glaciation, numerical models have become powerful tools to examine how ice sheets control subsurface flow systems. In this paper, the key processes that must be represented in a continental-scale 3-D numerical model of groundwater flow during a glaciation are reviewed, including subglacial infiltration, density-dependent (i.e., high-salinity) groundwater flow, permafrost evolution, isostasy, sea level changes, and ice sheet loading. One-dimensional hydromechanical coupling associated with ice loading and brine generation were included in the numerical model HydroGeoSphere and tested against newly developed exact analytical solutions to verify their implementation. Other processes such as subglacial infiltration, permafrost evolution, and isostasy were explicitly added to HydroGeoSphere. A specified flux constrained by the ice sheet thickness was found to be the most appropriate boundary condition in the subglacial environment. For the permafrost, frozen and unfrozen elements can be selected at every time step with specified hydraulic conductivities. For the isostatic adjustment, the elevations of all the grid nodes in each vertical grid column below the ice sheet are adjusted uniformly to account for the Earth's crust depression and rebound. In a companion paper, the model is applied to the Wisconsinian glaciation over the Canadian landscape in order to illustrate the concepts developed in this paper and to better understand the impact of glaciation on 3-D continental groundwater flow systems.

Spontaneous bending of pre-stretched bilayers.

PubMed

DeSimone, Antonio

2018-01-01

We discuss spontaneously bent configurations of pre-stretched bilayer sheets that can be obtained by tuning the pre-stretches in the two layers. The two-dimensional nonlinear plate model we use for this purpose is an adaptation of the one recently obtained for thin sheets of nematic elastomers, by means of a rigorous dimensional reduction argument based on the theory of Gamma-convergence (Agostiniani and DeSimone in Meccanica. doi:10.1007/s11012-017-0630-4, 2017, Math Mech Solids. doi:10.1177/1081286517699991, arXiv:1509.07003, 2017). We argue that pre-stretched bilayer sheets provide us with an interesting model system to study shape programming and morphing of surfaces in other, more complex systems, where spontaneous deformations are induced by swelling due to the absorption of a liquid, phase transformations, thermal or electro-magnetic stimuli. These include bio-mimetic structures inspired by biological systems from both the plant and the animal kingdoms.

A Hybrid Vortex Sheet / Point Vortex Model for Unsteady Separated Flows

NASA Astrophysics Data System (ADS)

Darakananda, Darwin; Eldredge, Jeff D.; Colonius, Tim; Williams, David R.

2015-11-01

The control of separated flow over an airfoil is essential for obtaining lift enhancement, drag reduction, and the overall ability to perform high agility maneuvers. In order to develop reliable flight control systems capable of realizing agile maneuvers, we need a low-order aerodynamics model that can accurately predict the force response of an airfoil to arbitrary disturbances and/or actuation. In the present work, we integrate vortex sheets and variable strength point vortices into a method that is able to capture the formation of coherent vortex structures while remaining computationally tractable for control purposes. The role of the vortex sheet is limited to tracking the dynamics of the shear layer immediately behind the airfoil. When parts of the sheet develop into large scale structures, those sections are replaced by variable strength point vortices. We prevent the vortex sheets from growing indefinitely by truncating the tips of the sheets and transfering their circulation into nearby point vortices whenever the length of sheet exceeds a threshold. We demonstrate the model on a variety of canonical problems, including pitch-up and impulse translation of an airfoil at various angles of attack. Support by the U.S. Air Force Office of Scientific Research (FA9550-14-1-0328) with program manager Dr. Douglas Smith is gratefully acknowledged.

Hybrid simulations of magnetic reconnection with kinetic ions and fluid electron pressure anisotropy

DOE PAGES

Le, A.; Daughton, W.; Karimabadi, H.; ...

2016-03-16

We present the first hybrid simulations with kinetic ions and recently developed equations of state for the electron fluid appropriate for reconnection with a guide field. The equations of state account for the main anisotropy of the electron pressure tensor.Magnetic reconnection is studied in two systems, an initially force-free current sheet and a Harris sheet. The hybrid model with the equations of state is compared to two other models, hybrid simulations with isothermal electrons and fully kinetic simulations. Including the anisotropicequations of state in the hybrid model provides a better match to the fully kinetic model. In agreement with fullymore » kinetic results, the main feature captured is the formation of an electron current sheet that extends several ion inertial lengths. This electron current sheet modifies the Hall magnetic field structure near the X-line, and it is not observed in the standard hybrid model with isotropic electrons. The saturated reconnection rate in this regime nevertheless remains similar in all three models. Here, implications for global modeling are discussed.« less

46 CFR 160.060-1 - Incorporation by reference.

Code of Federal Regulations, 2010 CFR

2010-10-01

...-1: Sheet 1—Cutting Pattern and General Arrangement, Model AY. Sheet 2—Cutting Pattern and General Arrangement, Model CYM. Sheet 3—Cutting Pattern and General Arrangement, Model CYS. Sheet 4—Insert Pattern, Model AY. Sheet 5—Insert Pattern, Model CYM. Sheet 6—Insert Pattern, Model CYS. (c) Copies on file...

The dynamics of climate-induced deglacial ice stream acceleration

NASA Astrophysics Data System (ADS)

Robel, A.; Tziperman, E.

2015-12-01

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

Time Evolution of the Macroscopic Characteristics of a Thin Current Sheet in the Course of Its Formation in the Earth's Magnetotail

NASA Astrophysics Data System (ADS)

Domrin, V. I.; Malova, H. V.; Popov, V. Yu.

2018-04-01

A numerical model is developed that allows tracing the time evolution of a current sheet from a relatively thick current configuration with isotropic distributions of the pressure and temperature in an extremely thin current sheet, which plays a key role in geomagnetic processes. Such a configuration is observed in the Earth's magnetotail in the stage preceding a large-scale geomagnetic disturbance (substorm). Thin current sheets are reservoirs of the free energy released during geomagnetic disturbances. The time evolution of the components of the pressure tensor caused by changes in the structure of the current sheet is investigated. It is shown that the pressure tensor in the current sheet evolves in two stages. In the first stage, a current sheet with a thickness of eight to ten proton Larmor radii forms. This stage is characterized by the plasma drift toward the current sheet and the Earth and can be described in terms of the Chu-Goldberger-Low approximation. In the second stage, an extremely thin current sheet with an anisotropic plasma pressure tensor forms, due to which the system is maintained in an equilibrium state. Estimates of the characteristic time of the system evolution agree with available experimental data.

Using palaeoclimate data to improve models of the Antarctic Ice Sheet

NASA Astrophysics Data System (ADS)

Phipps, Steven; King, Matt; Roberts, Jason; White, Duanne

2017-04-01

Ice sheet models are the most descriptive tools available to simulate the future evolution of the Antarctic Ice Sheet (AIS), including its contribution towards changes in global sea level. However, our knowledge of the dynamics of the coupled ice-ocean-lithosphere system is inevitably limited, in part due to a lack of observations. Furthemore, to build computationally efficient models that can be run for multiple millennia, it is necessary to use simplified descriptions of ice dynamics. Ice sheet modelling is therefore an inherently uncertain exercise. The past evolution of the AIS provides an opportunity to constrain the description of physical processes within ice sheet models and, therefore, to constrain our understanding of the role of the AIS in driving changes in global sea level. We use the Parallel Ice Sheet Model (PISM) to demonstrate how palaeoclimate data can improve our ability to predict the future evolution of the AIS. A 50-member perturbed-physics ensemble is generated, spanning uncertainty in the parameterisations of three key physical processes within the model: (i) the stress balance within the ice sheet, (ii) basal sliding and (iii) calving of ice shelves. A Latin hypercube approach is used to optimally sample the range of uncertainty in parameter values. This perturbed-physics ensemble is used to simulate the evolution of the AIS from the Last Glacial Maximum ( 21,000 years ago) to present. Palaeoclimate records are then used to determine which ensemble members are the most realistic. This allows us to use data on past climates to directly constrain our understanding of the past contribution of the AIS towards changes in global sea level. Critically, it also allows us to determine which ensemble members are likely to generate the most realistic projections of the future evolution of the AIS.

A New Ice-sheet / Ocean Interaction Model for Greenland Fjords using High-Order Discontinuous Galerkin Methods

NASA Astrophysics Data System (ADS)

Kopera, M. A.; Maslowski, W.; Giraldo, F.

2015-12-01

One of the key outstanding challenges in modeling of climate change and sea-level rise is the ice-sheet/ocean interaction in narrow, elongated and geometrically complicated fjords around Greenland. To address this challenge we propose a new approach, a separate fjord model using discontinuous Galerkin (DG) methods, or FDG. The goal of this project is to build a separate, high-resolution module for use in Earth System Models (ESMs) to realistically represent the fjord bathymetry, coastlines, exchanges with the outside ocean, circulation and fine-scale processes occurring within the fjord and interactions at the ice shelf interface. FDG is currently at the first stage of development. The DG method provides FDG with high-order accuracy as well as geometrical flexibility, including the capacity to handle non-conforming adaptive mesh refinement to resolve the processes occurring near the ice-sheet/ocean interface without introducing prohibitive computational costs. Another benefit of this method is its excellent performance on multi- and many-core architectures, which allows for utilizing modern high performance computing systems for high-resolution simulations. The non-hydrostatic model of the incompressible Navier-Stokes equation will account for the stationary ice-shelf with sub-shelf ocean interaction, basal melting and subglacial meltwater influx and with boundary conditions at the surface to account for floating sea ice. The boundary conditions will be provided to FDG via a flux coupler to emulate the integration with an ESM. Initially, FDG will be tested for the Sermilik Fjord settings, using real bathymetry, boundary and initial conditions, and evaluated against available observations and other model results for this fjord. The overarching goal of the project is to be able to resolve the ice-sheet/ocean interactions around the entire coast of Greenland and two-way coupling with regional and global climate models such as the Regional Arctic System Model (RASM), Community Earth System Model (CESM) or Advanced Climate Model for Energy (ACME).

High-resolution coupled ice sheet-ocean modeling using the POPSICLES model

NASA Astrophysics Data System (ADS)

Ng, E. G.; Martin, D. F.; Asay-Davis, X.; Price, S. F.; Collins, W.

2014-12-01

It is expected that a primary driver of future change of the Antarctic ice sheet will be changes in submarine melting driven by incursions of warm ocean water into sub-ice shelf cavities. Correctly modeling this response on a continental scale will require high-resolution modeling of the coupled ice-ocean system. We describe the computational and modeling challenges in our simulations of the full Southern Ocean coupled to a continental-scale Antarctic ice sheet model at unprecedented spatial resolutions (0.1 degree for the ocean model and adaptive mesh refinement down to 500m in the ice sheet model). The POPSICLES model couples the POP2x ocean model, a modified version of the Parallel Ocean Program (Smith and Gent, 2002), with the BISICLES ice-sheet model (Cornford et al., 2012) using a synchronous offline-coupling scheme. Part of the PISCEES SciDAC project and built on the Chombo framework, BISICLES makes use of adaptive mesh refinement to fully resolve dynamically-important regions like grounding lines and employs a momentum balance similar to the vertically-integrated formulation of Schoof and Hindmarsh (2009). Results of BISICLES simulations have compared favorably to comparable simulations with a Stokes momentum balance in both idealized tests like MISMIP3D (Pattyn et al., 2013) and realistic configurations (Favier et al. 2014). POP2x includes sub-ice-shelf circulation using partial top cells (Losch, 2008) and boundary layer physics following Holland and Jenkins (1999), Jenkins (2001), and Jenkins et al. (2010). Standalone POP2x output compares well with standard ice-ocean test cases (e.g., ISOMIP; Losch, 2008) and other continental-scale simulations and melt-rate observations (Kimura et al., 2013; Rignot et al., 2013). For the POPSICLES Antarctic-Southern Ocean simulations, ice sheet and ocean models communicate at one-month coupling intervals.

Using artificial neural networks to model aluminium based sheet forming processes and tools details

NASA Astrophysics Data System (ADS)

Mekras, N.

2017-09-01

In this paper, a methodology and a software system will be presented concerning the use of Artificial Neural Networks (ANNs) for modeling aluminium based sheet forming processes. ANNs models’ creation is based on the training of the ANNs using experimental, trial and historical data records of processes’ inputs and outputs. ANNs models are useful in cases that processes’ mathematical models are not accurate enough, are not well defined or are missing e.g. in cases of complex product shapes, new material alloys, new process requirements, micro-scale products, etc. Usually, after the design and modeling of the forming tools (die, punch, etc.) and before mass production, a set of trials takes place at the shop floor for finalizing processes and tools details concerning e.g. tools’ minimum radii, die/punch clearance, press speed, process temperature, etc. and in relation with the material type, the sheet thickness and the quality achieved from the trials. Using data from the shop floor trials and forming theory data, ANNs models can be trained and created, and can be used to estimate processes and tools final details, hence supporting efficient set-up of processes and tools before mass production starts. The proposed ANNs methodology and the respective software system are implemented within the EU H2020 project LoCoMaTech for the aluminium-based sheet forming process HFQ (solution Heat treatment, cold die Forming and Quenching).

The Potsdam Parallel Ice Sheet Model (PISM-PIK) - Part 1: Model description

NASA Astrophysics Data System (ADS)

Winkelmann, R.; Martin, M. A.; Haseloff, M.; Albrecht, T.; Bueler, E.; Khroulev, C.; Levermann, A.

2011-09-01

We present the Potsdam Parallel Ice Sheet Model (PISM-PIK), developed at the Potsdam Institute for Climate Impact Research to be used for simulations of large-scale ice sheet-shelf systems. It is derived from the Parallel Ice Sheet Model (Bueler and Brown, 2009). Velocities are calculated by superposition of two shallow stress balance approximations within the entire ice covered region: the shallow ice approximation (SIA) is dominant in grounded regions and accounts for shear deformation parallel to the geoid. The plug-flow type shallow shelf approximation (SSA) dominates the velocity field in ice shelf regions and serves as a basal sliding velocity in grounded regions. Ice streams can be identified diagnostically as regions with a significant contribution of membrane stresses to the local momentum balance. All lateral boundaries in PISM-PIK are free to evolve, including the grounding line and ice fronts. Ice shelf margins in particular are modeled using Neumann boundary conditions for the SSA equations, reflecting a hydrostatic stress imbalance along the vertical calving face. The ice front position is modeled using a subgrid-scale representation of calving front motion (Albrecht et al., 2011) and a physically-motivated calving law based on horizontal spreading rates. The model is tested in experiments from the Marine Ice Sheet Model Intercomparison Project (MISMIP). A dynamic equilibrium simulation of Antarctica under present-day conditions is presented in Martin et al. (2011).

Stacked endoplasmic reticulum sheets are connected by helicoidal membrane motifs.

PubMed

Terasaki, Mark; Shemesh, Tom; Kasthuri, Narayanan; Klemm, Robin W; Schalek, Richard; Hayworth, Kenneth J; Hand, Arthur R; Yankova, Maya; Huber, Greg; Lichtman, Jeff W; Rapoport, Tom A; Kozlov, Michael M

2013-07-18

The endoplasmic reticulum (ER) often forms stacked membrane sheets, an arrangement that is likely required to accommodate a maximum of membrane-bound polysomes for secretory protein synthesis. How sheets are stacked is unknown. Here, we used improved staining and automated ultrathin sectioning electron microscopy methods to analyze stacked ER sheets in neuronal cells and secretory salivary gland cells of mice. Our results show that stacked ER sheets form a continuous membrane system in which the sheets are connected by twisted membrane surfaces with helical edges of left- or right-handedness. The three-dimensional structure of tightly stacked ER sheets resembles a parking garage, in which the different levels are connected by helicoidal ramps. A theoretical model explains the experimental observations and indicates that the structure corresponds to a minimum of elastic energy of sheet edges and surfaces. The structure allows the dense packing of ER sheets in the restricted space of a cell. Copyright © 2013 Elsevier Inc. All rights reserved.

A new research project on the interaction of the solid Earth and the Antarctic Ice Sheet

NASA Astrophysics Data System (ADS)

Fukuda, Y.; Nishijima, J.; Kazama, T.; Nakamura, K.; Doi, K.; Suganuma, Y.; Okuno, J.; Araya, A.; Kaneda, H.; Aoyama, Y.

2017-12-01

A new research project of "Grant-in-Aid for Scientific Research on Innovative Areas" funded by JSPS (Japan Society for the Promotion of Science) has recently been launched. The title of the project is "Giant reservoirs of heat/water/material: Global environmental changes driven by Southern Ocean and Antarctic Ice Sheet", and as a five years project, is aiming to establish a new research area for Antarctic environmental system science. The project consists of 7 research topics, including Antarctic ice sheet and Southern ocean sciences, new observation methodology, modeling and other interdisciplinary topics, and we are involved in the topic A02-2, "Interaction of the solid Earth and the Antarctic Ice Sheet". The Antarctic ice sheet, which relates to the global climate changes through the sea level rise and ocean circulation, is an essential element of the Earth system for predicting the future environment changes. Thus many studies of the ice sheet changes have been conducted by means of geomorphological, geological, geodetic surveys, as well as satellite gravimetry and satellite altimetry. For these studies, one of the largest uncertainties is the effects of GIA. Therefore, GIA as a key to investigate the interaction between the solid Earth and the ice sheet changes, we plan to conduct geomorphological, geological and geodetic surveys in the inland mountain areas and the coastal areas including the surrounding areas of a Japanese station Syowa in East Antarctica, where the in-situ data for constraining GIA models are very few. Combining these new observations with other in-site data, various satellite data and numerical modeling, we aim to estimating a precise GIA model, constructing a reliable ice melting history after the last glacial maximum and obtaining the viscoelastic structure of the Earth's interior. In the presentation, we also show the five years research plans as well. This study was partially supported by JSPS KAKENHI Grant No. 17H06321.

Century/millennium internal climate oscillations in an ocean-atmosphere-continental ice sheet model

NASA Technical Reports Server (NTRS)

Birchfield, Edward G.; Wang, Huaxiao; Rich, Jonathan J.

1994-01-01

We demonstrate in a simple climate model that there exist nonlinear feedbacks between the atmosphere, ocean, and ice sheets capable of producing century/millennium timescale internal oscillations resembling those seen in the paleoclimate record. Feedbacks involve meridional heat and salt transports in the North Atlantic, surface ocean freshwater fluxes associated with melting and growing continental ice sheets in the northen hemisphere and with Atlantic to Pacific water vapor transport. The positive feedback between the production of North Atlantic Deep Water (NADW) and the meridional salt transport by the Atlantic thermohaline circulation tends to destabilize the climate system, while the negative feedback between the freshwater flux, either to or from the continental ice sheets, and meridional heat flux to the high-latitude North Atlantic, accomplished by the thermohaline circulation, stabilizes the system. The thermohaline circulation plays a central role in both positive and negative feedbacks because of its transport of both heat and salt. Because of asymmetries between the growth and melt phases the oscillations are, in general, accompanied by a growing or decreasing ice volume over each cycle, which in the model is reflected by increasing or decreasing mean salinity.

Cryosphere Science Outreach using the Ice Sheet System Model and a Virtual Ice Sheet Laboratory

NASA Astrophysics Data System (ADS)

Cheng, D. L. C.; Halkides, D. J.; Larour, E. Y.

2015-12-01

Understanding the role of Cryosphere Science within the larger context of Sea Level Rise is both a technical and educational challenge that needs to be addressed if the public at large is to trulyunderstand the implications and consequences of Climate Change. Within this context, we propose a new approach in which scientific tools are used directly inside a mobile/website platform geared towards Education/Outreach. Here, we apply this approach by using the Ice Sheet System Model, a state of the art Cryosphere model developed at NASA, and integrated within a Virtual Ice Sheet Laboratory, with the goal is to outreach Cryospherescience to K-12 and College level students. The approach mixes laboratory experiments, interactive classes/lessons on a website, and a simplified interface to a full-fledged instance of ISSM to validate the classes/lessons. This novel approach leverages new insights from the Outreach/Educational community and the interest of new generations in web based technologies and simulation tools, all of it delivered in a seamlessly integrated web platform. This work was performed at the California Institute of Technology's Jet Propulsion Laboratory undera contract with the National Aeronautics and Space Administration's Cryosphere Science Program.

Uncertainty quantification of Antarctic contribution to sea-level rise using the fast Elementary Thermomechanical Ice Sheet (f.ETISh) model

NASA Astrophysics Data System (ADS)

Bulthuis, Kevin; Arnst, Maarten; Pattyn, Frank; Favier, Lionel

2017-04-01

Uncertainties in sea-level rise projections are mostly due to uncertainties in Antarctic ice-sheet predictions (IPCC AR5 report, 2013), because key parameters related to the current state of the Antarctic ice sheet (e.g. sub-ice-shelf melting) and future climate forcing are poorly constrained. Here, we propose to improve the predictions of Antarctic ice-sheet behaviour using new uncertainty quantification methods. As opposed to ensemble modelling (Bindschadler et al., 2013) which provides a rather limited view on input and output dispersion, new stochastic methods (Le Maître and Knio, 2010) can provide deeper insight into the impact of uncertainties on complex system behaviour. Such stochastic methods usually begin with deducing a probabilistic description of input parameter uncertainties from the available data. Then, the impact of these input parameter uncertainties on output quantities is assessed by estimating the probability distribution of the outputs by means of uncertainty propagation methods such as Monte Carlo methods or stochastic expansion methods. The use of such uncertainty propagation methods in glaciology may be computationally costly because of the high computational complexity of ice-sheet models. This challenge emphasises the importance of developing reliable and computationally efficient ice-sheet models such as the f.ETISh ice-sheet model (Pattyn, 2015), a new fast thermomechanical coupled ice sheet/ice shelf model capable of handling complex and critical processes such as the marine ice-sheet instability mechanism. Here, we apply these methods to investigate the role of uncertainties in sub-ice-shelf melting, calving rates and climate projections in assessing Antarctic contribution to sea-level rise for the next centuries using the f.ETISh model. We detail the methods and show results that provide nominal values and uncertainty bounds for future sea-level rise as a reflection of the impact of the input parameter uncertainties under consideration, as well as a ranking of the input parameter uncertainties in the order of the significance of their contribution to uncertainty in future sea-level rise. In addition, we discuss how limitations posed by the available information (poorly constrained data) pose challenges that motivate our current research.

Criticality and turbulence in a resistive magnetohydrodynamic current sheet

NASA Astrophysics Data System (ADS)

Klimas, Alexander J.; Uritsky, Vadim M.

2017-02-01

Scaling properties of a two-dimensional (2d) plasma physical current-sheet simulation model involving a full set of magnetohydrodynamic (MHD) equations with current-dependent resistivity are investigated. The current sheet supports a spatial magnetic field reversal that is forced through loading of magnetic flux containing plasma at boundaries of the simulation domain. A balance is reached between loading and annihilation of the magnetic flux through reconnection at the current sheet; the transport of magnetic flux from boundaries to current sheet is realized in the form of spatiotemporal avalanches exhibiting power-law statistics of lifetimes and sizes. We identify this dynamics as self-organized criticality (SOC) by verifying an extended set of scaling laws related to both global and local properties of the current sheet (critical susceptibility, finite-size scaling of probability distributions, geometric exponents). The critical exponents obtained from this analysis suggest that the model operates in a slowly driven SOC state similar to the mean-field state of the directed stochastic sandpile model. We also investigate multiscale correlations in the velocity field and find them numerically indistinguishable from certain intermittent turbulence (IT) theories. The results provide clues on physical conditions for SOC behavior in a broad class of plasma systems with propagating instabilities, and suggest that SOC and IT may coexist in driven current sheets which occur ubiquitously in astrophysical and space plasmas.

Criticality and turbulence in a resistive magnetohydrodynamic current sheet.

PubMed

Klimas, Alexander J; Uritsky, Vadim M

2017-02-01

Scaling properties of a two-dimensional (2d) plasma physical current-sheet simulation model involving a full set of magnetohydrodynamic (MHD) equations with current-dependent resistivity are investigated. The current sheet supports a spatial magnetic field reversal that is forced through loading of magnetic flux containing plasma at boundaries of the simulation domain. A balance is reached between loading and annihilation of the magnetic flux through reconnection at the current sheet; the transport of magnetic flux from boundaries to current sheet is realized in the form of spatiotemporal avalanches exhibiting power-law statistics of lifetimes and sizes. We identify this dynamics as self-organized criticality (SOC) by verifying an extended set of scaling laws related to both global and local properties of the current sheet (critical susceptibility, finite-size scaling of probability distributions, geometric exponents). The critical exponents obtained from this analysis suggest that the model operates in a slowly driven SOC state similar to the mean-field state of the directed stochastic sandpile model. We also investigate multiscale correlations in the velocity field and find them numerically indistinguishable from certain intermittent turbulence (IT) theories. The results provide clues on physical conditions for SOC behavior in a broad class of plasma systems with propagating instabilities, and suggest that SOC and IT may coexist in driven current sheets which occur ubiquitously in astrophysical and space plasmas.

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

PubMed

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

2017-02-01

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

Rational design of an on-site volume reduction system for source-separated urine.

PubMed

Pahore, Muhammad Masoom; Ito, Ryusei; Funamizu, Naoyuki

2010-04-01

Human urine contains nitrogen, phosphorus and potassium, which can be applied as fertilizer in agriculture, replacing commercial fertilizer. However, owing to the low nutrient content of the urine, huge quantities must be transported to farmland to meet the nutrient demand of crops. This highly increases the transportation cost for the farmers. To address the transportation issue, a new on-site volume reduction system was tested at the laboratory scale based on water evaporation from vertical gauze sheets. A mathematical water transport model was proposed to evaluate the performance of the system. The mass transfer coefficient and the resistance of water flow through the sheet in the water transport model were obtained from the experiments. The results agreed with the simulated data, thereby confirming the proposed model. The model was then applied to the dry climate of southern Pakistan, having an air temperature of 30-40 degrees C and air humidity of 20-40%, for an 80% volume reduction of 10 L urine per day, which corresponds to a family of 10 members (average for a household in Pakistan). The findings revealed that the estimated size of the vertical sheet is 440-2060 cm2, which is only a small area for setting up the system at a household level.

Successes and Challenges in Linking Observations and Modeling of Marine and Terrestrial Cryospheric Processes

NASA Astrophysics Data System (ADS)

Herzfeld, U. C.; Hunke, E. C.; Trantow, T.; Greve, R.; McDonald, B.; Wallin, B.

2014-12-01

Understanding of the state of the cryosphere and its relationship to other components of the Earth system requires both models of geophysical processes and observations of geophysical properties and processes, however linking observations and models is far from trivial. This paper looks at examples from sea ice and land ice model-observation linkages to examine some approaches, challenges and solutions. In a sea-ice example, ice deformation is analyzed as a key process that indicates fundamental changes in the Arctic sea ice cover. Simulation results from the Los Alamos Sea-Ice Model CICE, which is also the sea-ice component of the Community Earth System Model (CESM), are compared to parameters indicative of deformation as derived from mathematical analysis of remote sensing data. Data include altimeter, micro-ASAR and image data from manned and unmanned aircraft campaigns (NASA OIB and Characterization of Arctic Sea Ice Experiment, CASIE). The key problem to linking data and model results is the derivation of matching parameters on both the model and observation side.For terrestrial glaciology, we include an example of a surge process in a glacier system and and example of a dynamic ice sheet model for Greenland. To investigate the surge of the Bering Bagley Glacier System, we use numerical forward modeling experiments and, on the data analysis side, a connectionist approach to analyze crevasse provinces. In the Greenland ice sheet example, we look at the influence of ice surface and bed topography, as derived from remote sensing data, on on results from a dynamic ice sheet model.

Models for the Representation of Four-Component Systems.

ERIC Educational Resources Information Center

Kartzmark, Elinor M.

1980-01-01

Describes construction of two inexpensive three-dimensional models (tetrahedrons) using glass tubing and colored plastic sheeting. Diagrams show how these models are used in explaining how a point is plotted in a four-component system and how the composition of a point is deduced from its position in the model. (CS)

A synchronous strobed laser light sheet for helicopter model rotor flow visualization

NASA Technical Reports Server (NTRS)

Leighty, Bradley D.; Rhodes, David B.; Jones, Stephen B.; Franke, John M.

1990-01-01

A synchronous, strobed laser light sheet has been developed for use in flow visualization of a helicopter rotor model. The light sheet strobe circuit included selectable blade position, strobe duration, and multiple pulses per revolution for rotors having 2 to 9 blades. The flow was seeded with propylene glycol. Between runs, a calibration grid board was placed in the plane of the laser sheet and recorded with the video camera at the position used to record the flow field. A slip-sync mode permitted slow motion visualization of the flow field over complete rotations of the rotor. The system was used to make two-dimensional flow field cuts of a four-bladed rotor operating at advance ratio of 0.37 at wind tunnel speeds up to 79.25 meters per second (260 feet per second).

Analytical and molecular dynamics studies on the impact loading of single-layered graphene sheet by fullerene

NASA Astrophysics Data System (ADS)

Hosseini-Hashemi, Shahrokh; Sepahi-Boroujeni, Amin; Sepahi-Boroujeni, Saeid

2018-04-01

Normal impact performance of a system including a fullerene molecule and a single-layered graphene sheet is studied in the present paper. Firstly, through a mathematical approach, a new contact law is derived to describe the overall non-bonding interaction forces of the "hollow indenter-target" system. Preliminary verifications show that the derived contact law gives a reliable picture of force field of the system which is in good agreements with the results of molecular dynamics (MD) simulations. Afterwards, equation of the transversal motion of graphene sheet is utilized on the basis of both the nonlocal theory of elasticity and the assumptions of classical plate theory. Then, to derive dynamic behavior of the system, a set including the proposed contact law and the equations of motion of both graphene sheet and fullerene molecule is solved numerically. In order to evaluate outcomes of this method, the problem is modeled by MD simulation. Despite intrinsic differences between analytical and MD methods as well as various errors arise due to transient nature of the problem, acceptable agreements are established between analytical and MD outcomes. As a result, the proposed analytical method can be reliably used to address similar impact problems. Furthermore, it is found that a single-layered graphene sheet is capable of trapping fullerenes approaching with low velocities. Otherwise, in case of rebound, the sheet effectively absorbs predominant portion of fullerene energy.

Potential subglacial lake locations and meltwater drainage pathways beneath the Antarctic and Greenland ice sheets

NASA Astrophysics Data System (ADS)

Livingstone, S. J.; Clark, C. D.; Woodward, J.; Kingslake, J.

2013-11-01

We use the Shreve hydraulic potential equation as a simplified approach to investigate potential subglacial lake locations and meltwater drainage pathways beneath the Antarctic and Greenland ice sheets. We validate the method by demonstrating its ability to recall the locations of >60% of the known subglacial lakes beneath the Antarctic Ice Sheet. This is despite uncertainty in the ice-sheet bed elevation and our simplified modelling approach. However, we predict many more lakes than are observed. Hence we suggest that thousands of subglacial lakes remain to be found. Applying our technique to the Greenland Ice Sheet, where very few subglacial lakes have so far been observed, recalls 1607 potential lake locations, covering 1.2% of the bed. Our results will therefore provide suitable targets for geophysical surveys aimed at identifying lakes beneath Greenland. We also apply the technique to modelled past ice-sheet configurations and find that during deglaciation both ice sheets likely had more subglacial lakes at their beds. These lakes, inherited from past ice-sheet configurations, would not form under current surface conditions, but are able to persist, suggesting a retreating ice-sheet will have many more subglacial lakes than advancing ones. We also investigate subglacial drainage pathways of the present-day and former Greenland and Antarctic ice sheets. Key sectors of the ice sheets, such as the Siple Coast (Antarctica) and NE Greenland Ice Stream system, are suggested to have been susceptible to subglacial drainage switching. We discuss how our results impact our understanding of meltwater drainage, basal lubrication and ice-stream formation.

A statistical study on the shape and position of the magnetotail neutral sheet

NASA Astrophysics Data System (ADS)

Xiao, Sudong; Zhang, Tielong; Ge, Yasong; Wang, Guoqiang; Baumjohann, Wolfgang; Nakamura, Rumi

2016-02-01

We study the average shape and position of the magnetotail neutral sheet based on magnetic field data obtained by Cluster, Geotail, TC-1, and THEMIS from the years 1995 to 2013. All data in the aberrated GSM (geocentric solar magnetospheric) coordinate system are normalized to the same solar wind pressure 2 nPa and downtail distance X ˜ -20RE. Our results show characteristics of the neutral sheet, as follows. (1) The neutral sheet assumes a greater degree of curve in the YZ cross section when the dipole tilt increases, the Earth dipole tilt angle affects the neutral sheet configuration not only in the YZ cross section but also in the XY cross section, and the neutral sheet assumes a more significant degree of tilt in the XY cross section when the dipole tilt increases. (2) Counterclockwise twisting of the neutral sheet with 3.10° is observed, looking along the downtail direction, for the positive interplanetary magnetic field (IMF) BY with a value of 3 to 8 nT, and clockwise twisting of the neutral sheet with 3.37° for the negative IMF BY with a value of -8 to -3 nT, and a northward IMF can result in a greater twisting of the near-tail neutral sheet than southward. The above results can be a reference to the neutral sheet model. Our large database also shows that the displaced ellipse model is effective to study the average shape of the neutral sheet with proper parameters when the dipole tilt angle is larger (less) than 10° (-10° ).

Development of a check sheet for collecting information necessary for occupational safety and health activities and building relevant systems in overseas business places.

PubMed

Kajiki, Shigeyuki; Kobayashi, Yuichi; Uehara, Masamichi; Nakanishi, Shigemoto; Mori, Koji

2016-06-07

This study aimed to develop an information gathering check sheet to efficiently collect information necessary for Japanese companies to build global occupational safety and health management systems in overseas business places. The study group consisted of 2 researchers with occupational physician careers in a foreign-affiliated company in Japan and 3 supervising occupational physicians who were engaged in occupational safety and health activities in overseas business places. After investigating information and sources of information necessary for implementing occupational safety and health activities and building relevant systems, we conducted information acquisition using an information gathering check sheet in the field, by visiting 10 regions in 5 countries (first phase). The accuracy of the information acquired and the appropriateness of the information sources were then verified in study group meetings to improve the information gathering check sheet. Next, the improved information gathering check sheet was used in another setting (3 regions in 1 country) to confirm its efficacy (second phase), and the information gathering check sheet was thereby completed. The information gathering check sheet was composed of 9 major items (basic information on the local business place, safety and health overview, safety and health systems, safety and health staff, planning/implementation/evaluation/improvement, safety and health activities, laws and administrative organs, local medical care systems and public health, and medical support for resident personnel) and 61 medium items. We relied on the following eight information sources: the internet, company (local business place and head office in Japan), embassy/consulate, ISO certification body, university or other educational institutions, and medical institutions (aimed at Japanese people or at local workers). Through multiple study group meetings and a two-phased field survey (13 regions in 6 countries), an information gathering check sheet was completed. We confirmed the possibility that this check sheet would enable the user to obtain necessary information when expanding safety and health activities in a country or region that is new to the user. It is necessary in the future to evaluate safety and health systems and activities using this information gathering check sheet in a local business place in any country in which a Japanese business will be established, and to verify the efficacy of the check sheet by conducting model programs to test specific approaches.

The Potsdam Parallel Ice Sheet Model (PISM-PIK) - Part 1: Model description

NASA Astrophysics Data System (ADS)

Winkelmann, R.; Martin, M. A.; Haseloff, M.; Albrecht, T.; Bueler, E.; Khroulev, C.; Levermann, A.

2010-08-01

We present the Potsdam Parallel Ice Sheet Model (PISM-PIK), developed at the Potsdam Institute for Climate Impact Research to be used for simulations of large-scale ice sheet-shelf systems. It is derived from the Parallel Ice Sheet Model (Bueler and Brown, 2009). Velocities are calculated by superposition of two shallow stress balance approximations within the entire ice covered region: the shallow ice approximation (SIA) is dominant in grounded regions and accounts for shear deformation parallel to the geoid. The plug-flow type shallow shelf approximation (SSA) dominates the velocity field in ice shelf regions and serves as a basal sliding velocity in grounded regions. Ice streams naturally emerge through this approach and can be identified diagnostically as regions with a significant contribution of membrane stresses to the local momentum balance. All lateral boundaries in PISM-PIK are free to evolve, including the grounding line and ice fronts. Ice shelf margins in particular are modeled using Neumann boundary conditions for the SSA equations, reflecting a hydrostatic stress imbalance along the vertical calving face. The ice front position is modeled using a subgrid scale representation of calving front motion (Albrecht et al., 2010) and a physically motivated dynamic calving law based on horizontal spreading rates. The model is validated within the Marine Ice Sheet Model Intercomparison Project (MISMIP) and is used for a dynamic equilibrium simulation of Antarctica under present-day conditions in the second part of this paper (Martin et al., 2010).

Estimating erosion in a riverine watershed: Bayou Liberty-Tchefuncta River in Louisiana.

PubMed

Martin, August; Gunter, James T; Regens, James L

2003-01-01

GOAL, SCOPE, BACKGROUND: Sheet erosion from agricultural, forest and urban lands may increase stream sediment loads as well as transport other pollutants that adversely affect water quality, reduce agricultural and forest production, and increase infrastructure maintenance costs. This study uses spatial analysis techniques and a numerical modeling approach to predict areas with the greatest sheet erosion potential given different soils disturbance scenarios. A Geographic Information System (GIS) and the Universal Soil Loss Equation (USLE) were used to estimate sheet erosion from 0.64 ha parcels of land within the watershed. The Soil Survey of St. Tammany Parish, Louisiana was digitized, required soil attributes entered into the GIS database, and slope factors determined for each 80 x 80 meter parcel in the watershed. The GIS/USLE model used series-specific erosion K factors, a rainfall factor of 89, and a GIS database of scenario-driven cropping and erosion control practice factors to estimate potential soil loss due to sheet erosion. A general trend of increased potential sheet erosion occurred for all land use categories (urban, agriculture/grasslands, forests) as soil disturbance increases from cropping, logging and construction activities. Modeling indicated that rapidly growing urban areas have the greatest potential for sheet erosion. Evergreen and mixed forests (production forest) had lower sheet erosion potentials; with deciduous forests (mostly riparian) having the least sheet erosion potential. Erosion estimates from construction activities may be overestimated because of the value chosen for the erosion control practice factor. This study illustrates the ease with which GIS can be integrated with the Universal Soil Loss Equation to identify areas with high sheet erosion potential for large scale management and policy decision making. The GIS/USLE modeling approach used in this study offers a quick and inexpensive tool for estimating sheet erosion within watersheds using publicly available information. This method can quickly identify discrete locations with relatively precise spatial boundaries (approximately 80 meter resolution) that have a high sheet erosion potential as well as areas where management interventions might be appropriate to prevent or ameliorate erosion.

Complex structures from patterned cell sheets

PubMed Central

Misra, M.; Audoly, B.; Shvartsman, S. Y.

2017-01-01

The formation of three-dimensional structures from patterned epithelial sheets plays a key role in tissue morphogenesis. An important class of morphogenetic mechanisms relies on the spatio-temporal control of apical cell contractility, which can result in the localized bending of cell sheets and in-plane cell rearrangements. We have recently proposed a modified vertex model that can be used to systematically explore the connection between the two-dimensional patterns of cell properties and the emerging three-dimensional structures. Here we review the proposed modelling framework and illustrate it through the computational analysis of the vertex model that captures the salient features of the formation of the dorsal appendages during Drosophila oogenesis. This article is part of the themed issue ‘Systems morphodynamics: understanding the development of tissue hardware’. PMID:28348251

Mutual Inductance Problem for a System Consisting of a Current Sheet and a Thin Metal Plate

NASA Technical Reports Server (NTRS)

Fulton, J. P.; Wincheski, B.; Nath, S.; Namkung, M.

1993-01-01

Rapid inspection of aircraft structures for flaws is of vital importance to the commercial and defense aircraft industry. In particular, inspecting thin aluminum structures for flaws is the focus of a large scale R&D effort in the nondestructive evaluation (NDE) community. Traditional eddy current methods used today are effective, but require long inspection times. New electromagnetic techniques which monitor the normal component of the magnetic field above a sample due to a sheet of current as the excitation, seem to be promising. This paper is an attempt to understand and analyze the magnetic field distribution due to a current sheet above an aluminum test sample. A simple theoretical model, coupled with a two dimensional finite element model (FEM) and experimental data will be presented in the next few sections. A current sheet above a conducting sample generates eddy currents in the material, while a sensor above the current sheet or in between the two plates monitors the normal component of the magnetic field. A rivet or a surface flaw near a rivet in an aircraft aluminum skin will disturb the magnetic field, which is imaged by the sensor. Initial results showed a strong dependence of the flaw induced normal magnetic field strength on the thickness and conductivity of the current-sheet that could not be accounted for by skin depth attenuation alone. It was believed that the eddy current imaging method explained the dependence of the thickness and conductivity of the flaw induced normal magnetic field. Further investigation, suggested the complexity associated with the mutual inductance of the system needed to be studied. The next section gives an analytical model to better understand the phenomenon.

Capabilities and performance of Elmer/Ice, a new-generation ice sheet model

NASA Astrophysics Data System (ADS)

Gagliardini, O.; Zwinger, T.; Gillet-Chaulet, F.; Durand, G.; Favier, L.; de Fleurian, B.; Greve, R.; Malinen, M.; Martín, C.; Råback, P.; Ruokolainen, J.; Sacchettini, M.; Schäfer, M.; Seddik, H.; Thies, J.

2013-08-01

The Fourth IPCC Assessment Report concluded that ice sheet flow models, in their current state, were unable to provide accurate forecast for the increase of polar ice sheet discharge and the associated contribution to sea level rise. Since then, the glaciological community has undertaken a huge effort to develop and improve a new generation of ice flow models, and as a result a significant number of new ice sheet models have emerged. Among them is the parallel finite-element model Elmer/Ice, based on the open-source multi-physics code Elmer. It was one of the first full-Stokes models used to make projections for the evolution of the whole Greenland ice sheet for the coming two centuries. Originally developed to solve local ice flow problems of high mechanical and physical complexity, Elmer/Ice has today reached the maturity to solve larger-scale problems, earning the status of an ice sheet model. Here, we summarise almost 10 yr of development performed by different groups. Elmer/Ice solves the full-Stokes equations, for isotropic but also anisotropic ice rheology, resolves the grounding line dynamics as a contact problem, and contains various basal friction laws. Derived fields, like the age of the ice, the strain rate or stress, can also be computed. Elmer/Ice includes two recently proposed inverse methods to infer badly known parameters. Elmer is a highly parallelised code thanks to recent developments and the implementation of a block preconditioned solver for the Stokes system. In this paper, all these components are presented in detail, as well as the numerical performance of the Stokes solver and developments planned for the future.

46 CFR 160.055-1 - Incorporation by reference.

Code of Federal Regulations, 2010 CFR

2010-10-01

.... 160.055-IA: Sheet 1—Construction and Arrangement, Vinyl Dip Coated, Model 62, Adult. Sheet 2—Construction and Arrangement, Vinyl Dip Coated, Model 66, Child. Dwg. No. 160.055-IB: Sheet 1—Construction and Arrangement, Cloth Covered, Model 63, Adult. Sheet 2—Buoyant Inserts, Model 63. Sheet 3—Construction and...

Ice Sheet Model Intercomparison Project (ISMIP6) contribution to CMIP6

PubMed Central

Nowicki, Sophie M.J.; Payne, Tony; Larour, Eric; Seroussi, Helene; Goelzer, Heiko; Lipscomb, William; Gregory, Jonathan; Abe-Ouchi, Ayako; Shepherd, Andrew

2018-01-01

Reducing the uncertainty in the past, present and future contribution of ice sheets to sea-level change requires a coordinated effort between the climate and glaciology communities. The Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6) is the primary activity within the Coupled Model Intercomparison Project – phase 6 (CMIP6) focusing on the Greenland and Antarctic Ice Sheets. In this paper, we describe the framework for ISMIP6 and its relationship to other activities within CMIP6. The ISMIP6 experimental design relies on CMIP6 climate models and includes, for the first time within CMIP, coupled ice sheet – climate models as well as standalone ice sheet models. To facilitate analysis of the multi-model ensemble and to generate a set of standard climate inputs for standalone ice sheet models, ISMIP6 defines a protocol for all variables related to ice sheets. ISMIP6 will provide a basis for investigating the feedbacks, impacts, and sea-level changes associated with dynamic ice sheets and for quantifying the uncertainty in ice-sheet-sourced global sea-level change. PMID:29697697

Last Interglacial climate and sea-level evolution from a coupled ice sheet-climate model

NASA Astrophysics Data System (ADS)

Goelzer, Heiko; Huybrechts, Philippe; Loutre, Marie-France; Fichefet, Thierry

2016-12-01

As the most recent warm period in Earth's history with a sea-level stand higher than present, the Last Interglacial (LIG, ˜ 130 to 115 kyr BP) is often considered a prime example to study the impact of a warmer climate on the two polar ice sheets remaining today. Here we simulate the Last Interglacial climate, ice sheet, and sea-level evolution with the Earth system model of intermediate complexity LOVECLIM v.1.3, which includes dynamic and fully coupled components representing the atmosphere, the ocean and sea ice, the terrestrial biosphere, and the Greenland and Antarctic ice sheets. In this setup, sea-level evolution and climate-ice sheet interactions are modelled in a consistent framework.Surface mass balance change governed by changes in surface meltwater runoff is the dominant forcing for the Greenland ice sheet, which shows a peak sea-level contribution of 1.4 m at 123 kyr BP in the reference experiment. Our results indicate that ice sheet-climate feedbacks play an important role to amplify climate and sea-level changes in the Northern Hemisphere. The sensitivity of the Greenland ice sheet to surface temperature changes considerably increases when interactive albedo changes are considered. Southern Hemisphere polar and sub-polar ocean warming is limited throughout the Last Interglacial, and surface and sub-shelf melting exerts only a minor control on the Antarctic sea-level contribution with a peak of 4.4 m at 125 kyr BP. Retreat of the Antarctic ice sheet at the onset of the LIG is mainly forced by rising sea level and to a lesser extent by reduced ice shelf viscosity as the surface temperature increases. Global sea level shows a peak of 5.3 m at 124.5 kyr BP, which includes a minor contribution of 0.35 m from oceanic thermal expansion. Neither the individual contributions nor the total modelled sea-level stand show fast multi-millennial timescale variations as indicated by some reconstructions.

Full particle-in-cell simulations of kinetic equilibria and the role of the initial current sheet on steady asymmetric magnetic reconnection

NASA Astrophysics Data System (ADS)

Dargent, J.; Aunai, N.; Belmont, G.; Dorville, N.; Lavraud, B.; Hesse, M.

2016-06-01

> Tangential current sheets are ubiquitous in space plasmas and yet hard to describe with a kinetic equilibrium. In this paper, we use a semi-analytical model, the BAS model, which provides a steady ion distribution function for a tangential asymmetric current sheet and we prove that an ion kinetic equilibrium produced by this model remains steady in a fully kinetic particle-in-cell simulation even if the electron distribution function does not satisfy the time independent Vlasov equation. We then apply this equilibrium to look at the dependence of magnetic reconnection simulations on their initial conditions. We show that, as the current sheet evolves from a symmetric to an asymmetric upstream plasma, the reconnection rate is impacted and the X line and the electron flow stagnation point separate from one another and start to drift. For the simulated systems, we investigate the overall evolution of the reconnection process via the classical signatures discussed in the literature and searched in the Magnetospheric MultiScale data. We show that they seem robust and do not depend on the specific details of the internal structure of the initial current sheet.

Validation of Modelled Ice Dynamics of the Greenland Ice Sheet using Historical Forcing

NASA Astrophysics Data System (ADS)

Hoffman, M. J.; Price, S. F.; Howat, I. M.; Bonin, J. A.; Chambers, D. P.; Tezaur, I.; Kennedy, J. H.; Lenaerts, J.; Lipscomb, W. H.; Neumann, T.; Nowicki, S.; Perego, M.; Saba, J. L.; Salinger, A.; Guerber, J. R.

2015-12-01

Although ice sheet models are used for sea level rise projections, the degree to which these models have been validated by observations is fairly limited, due in part to the limited duration of the satellite observation era and the long adjustment time scales of ice sheets. Here we describe a validation framework for the Greenland Ice Sheet applied to the Community Ice Sheet Model by forcing the model annually with flux anomalies at the major outlet glaciers (Enderlin et al., 2014, observed from Landsat/ASTER/Operation IceBridge) and surface mass balance (van Angelen et al., 2013, calculated from RACMO2) for the period 1991-2012. The ice sheet model output is compared to ice surface elevation observations from ICESat and ice sheet mass change observations from GRACE. Early results show promise for assessing the performance of different model configurations. Additionally, we explore the effect of ice sheet model resolution on validation skill.

Modeling the fracture of ice sheets on parallel computers.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Waisman, Haim; Bell, Robin; Keyes, David

2010-03-01

The objective of this project is to investigate the complex fracture of ice and understand its role within larger ice sheet simulations and global climate change. At the present time, ice fracture is not explicitly considered within ice sheet models due in part to large computational costs associated with the accurate modeling of this complex phenomena. However, fracture not only plays an extremely important role in regional behavior but also influences ice dynamics over much larger zones in ways that are currently not well understood. Dramatic illustrations of fracture-induced phenomena most notably include the recent collapse of ice shelves inmore » Antarctica (e.g. partial collapse of the Wilkins shelf in March of 2008 and the diminishing extent of the Larsen B shelf from 1998 to 2002). Other fracture examples include ice calving (fracture of icebergs) which is presently approximated in simplistic ways within ice sheet models, and the draining of supraglacial lakes through a complex network of cracks, a so called ice sheet plumbing system, that is believed to cause accelerated ice sheet flows due essentially to lubrication of the contact surface with the ground. These dramatic changes are emblematic of the ongoing change in the Earth's polar regions and highlight the important role of fracturing ice. To model ice fracture, a simulation capability will be designed centered around extended finite elements and solved by specialized multigrid methods on parallel computers. In addition, appropriate dynamic load balancing techniques will be employed to ensure an approximate equal amount of work for each processor.« less

Coupled Long-Term Evolution of Climate and the Greenland Ice Sheet During the Last Interglacial and Implications for the Future

NASA Astrophysics Data System (ADS)

Otto-Bliesner, B. L.; Lofverstrom, M.; Lipscomb, W.; Fyke, J. G.; Marshall, S.; Sacks, B.

2017-12-01

The Greenland Ice Sheet (GrIS) is expected to contribute increasingly to global sea level rise by the end of this century, and potentially several meters in this millennium, but still with considerable uncertainty. The rate of Greenland melt will impact on regional sea levels. The Last Interglacial (LIG, 129 ka to 116 ka) is recognized as an important period for testing our knowledge of climate-ice sheet interactions in warm climate states. Although the LIG was discussed in the First Assessment Report of the IPCC, it gained more prominence in the IPCC Fourth and Fifth Assessment (AR4 and AR5) with reconstructions highlighting that global mean sea level was at least 5 m higher (but probably no more than 10 m higher) than present for several thousand years during the LIG. Model results assessed for the AR5 suggest a sea level contribution of 1.4 to 4.3 m from the GrIS. These model simulations, though, did not include all the feedbacks of the climate system and the GrIS. Here, we examine the response of the Arctic climate system and the GrIS in simulations with the Community Earth System Model (CESM) fully coupled to the Community Ice Sheet Model (CISM), using a surface energy balance scheme and without bias corrections. The analysis focuses on how the GrIS responds to the imposed high boreal summer insolation of the LIG and in addition, to the long-term feedbacks of high-latitude vegetation changes. Results will highlight the evolution of the ice sheet and the surface mass balance (patterns of ablation and accumulation) as compared to data-based reconstructions for the LIG. We conclude with a discussion on how the LIG may be informative as a potential process analogue for the GrIS response for future centuries to come.

Current sheet in plasma as a system with a controlling parameter

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fridman, Yu. A., E-mail: yulya-fridman@yandex.ru; Chukbar, K. V., E-mail: Chukbar-KV@nrcki.ru

2015-08-15

A simple kinetic model describing stationary solutions with bifurcated and single-peaked current density profiles of a plane electron beam or current sheet in plasma is presented. A connection is established between the two-dimensional constructions arising in terms of the model and the one-dimensional considerations by Bernstein−Greene−Kruskal facilitating the reconstruction of the distribution function of trapped particles when both the profile of the electric potential and the free particles distribution function are known.

Ice Sheet System Model as Educational Entertainment

NASA Astrophysics Data System (ADS)

Perez, G.

2013-12-01

Understanding the importance of polar ice sheets and their role in the evolution of Sea Level Rise (SLR), as well as Climate Change, is of paramount importance for policy makers as well as the public and schools at large. For example, polar ice sheets and glaciers currently account for 1/3 of the SLR signal, a ratio that will increase in the near to long-term future, which has tremendous societal ramifications. Consequently, it is important to increase awareness about our changing planet. In our increasingly digital society, mobile and web applications are burgeoning venues for such outreach. The Ice Sheet System Model (ISSM) is a software that was developed at the Jet Propulsion Laboratory/CalTech/NASA, in collaboration with University of California Irvine (UCI), with the goal of better understanding the evolution of polar ice sheets. It is a state-of-the-art framework, which relies on higher-end cluster-computing to address some of the aforementioned challenges. In addition, it is a flexible framework that can be deployed on any hardware; in particular, on mobile platforms such as Android or iOS smart phones. Here, we look at how the ISSM development team managed to port their model to these platforms, what the implications are for improving how scientists disseminate their results, and how a broader audience may familiarize themselves with running complex climate models in simplified scenarios which are highly educational and entertaining in content. We also look at the future plans toward a web portal fully integrated with mobile technologies to deliver the best content to the public, and to provide educational plans/lessons that can be used in grades K-12 as well as collegiate under-graduate and graduate programs.

A climate model with cryodynamics and geodynamics

NASA Technical Reports Server (NTRS)

Ghil, M.; Le Treut, H.

1981-01-01

A simplified, zero-dimensional model of the climatic system is presented which attempts to incorporate mechanisms important on the time scale of glaciation cycles: 10,000 to 100,000 years. The ocean-atmosphere radiation balance, continental ice sheet plastic flow, and upper mantle viscous flow are taken into account, with stress on the interaction between the ice sheets and the upper mantle. The model exhibits free, self-sustained oscillations of an amplitude and period comparable to those found in the paleoclimatic record of glaciations, offering mild support for the idea that unforced oscillations can actually exist in the real climatic system itself. The careful study of the interplay between internal mechanisms and external forcing is held to represent an interesting challenge to the theory of ice ages.

Modeling keratinocyte wound healing dynamics: Cell-cell adhesion promotes sustained collective migration.

PubMed

Nardini, John T; Chapnick, Douglas A; Liu, Xuedong; Bortz, David M

2016-07-07

The in vitro migration of keratinocyte cell sheets displays behavioral and biochemical similarities to the in vivo wound healing response of keratinocytes in animal model systems. In both cases, ligand-dependent Epidermal Growth Factor Receptor (EGFR) activation is sufficient to elicit collective cell migration into the wound. Previous mathematical modeling studies of in vitro wound healing assays assume that physical connections between cells have a hindering effect on cell migration, but biological literature suggests a more complicated story. By combining mathematical modeling and experimental observations of collectively migrating sheets of keratinocytes, we investigate the role of cell-cell adhesion during in vitro keratinocyte wound healing assays. We develop and compare two nonlinear diffusion models of the wound healing process in which cell-cell adhesion either hinders or promotes migration. Both models can accurately fit the leading edge propagation of cell sheets during wound healing when using a time-dependent rate of cell-cell adhesion strength. The model that assumes a positive role of cell-cell adhesion on migration, however, is robust to changes in the leading edge definition and yields a qualitatively accurate density profile. Using RNAi for the critical adherens junction protein, α-catenin, we demonstrate that cell sheets with wild type cell-cell adhesion expression maintain migration into the wound longer than cell sheets with decreased cell-cell adhesion expression, which fails to exhibit collective migration. Our modeling and experimental data thus suggest that cell-cell adhesion promotes sustained migration as cells pull neighboring cells into the wound during wound healing. Copyright © 2016 Elsevier Ltd. All rights reserved.

Ice Sheet Model Intercomparison Project (ISMIP6) Contribution to CMIP6

NASA Technical Reports Server (NTRS)

Nowicki, Sophie M. J.; Payne, Tony; Larour, Eric; Seroussi, Helene; Goelzer, Heiko; Lipscomb, William; Gregory, Jonathan; Abe-Ouchi, Ayako; Shepherd, Andrew

2016-01-01

Reducing the uncertainty in the past, present, and future contribution of ice sheets to sea-level change requires a coordinated effort between the climate and glaciology communities. The Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6) is the primary activity within the Coupled Model Intercomparison Project phase 6 (CMIP6) focusing on the Greenland and Antarctic ice sheets. In this paper, we describe the framework for ISMIP6 and its relationship with other activities within CMIP6. The ISMIP6 experimental design relies on CMIP6 climate models and includes, for the first time within CMIP, coupled ice-sheetclimate models as well as standalone ice-sheet models. To facilitate analysis of the multi-model ensemble and to generate a set of standard climate inputs for standalone ice-sheet models, ISMIP6 defines a protocol for all variables related to ice sheets. ISMIP6 will provide a basis for investigating the feedbacks, impacts, and sea-level changes associated with dynamic ice sheets and for quantifying the uncertainty in ice-sheet-sourced global sea-level change.

Ice Sheet Roughness Estimation Based on Impulse Responses Acquired in the Global Ice Sheet Mapping Orbiter Mission

NASA Astrophysics Data System (ADS)

Niamsuwan, N.; Johnson, J. T.; Jezek, K. C.; Gogineni, P.

2008-12-01

The Global Ice Sheet Mapping Orbiter (GISMO) mission was developed to address scientific needs to understand the polar ice subsurface structure. This NASA Instrument Incubator Program project is a collaboration between Ohio State University, the University of Kansas, Vexcel Corporation and NASA. The GISMO design utilizes an interferometric SAR (InSAR) strategy in which ice sheet reflected signals received by a dual-antenna system are used to produce an interference pattern. The resulting interferogram can be used to filter out surface clutter so as to reveal the signals scattered from the base of the ice sheet. These signals are further processed to produce 3D-images representing basal topography of the ice sheet. In the past three years, the GISMO airborne field campaigns that have been conducted provide a set of useful data for studying geophysical properties of the Greenland ice sheet. While topography information can be obtained using interferometric SAR processing techniques, ice sheet roughness statistics can also be derived by a relatively simple procedure that involves analyzing power levels and the shape of the radar impulse response waveforms. An electromagnetic scattering model describing GISMO impulse responses has previously been proposed and validated. This model suggested that rms-heights and correlation lengths of the upper surface profile can be determined from the peak power and the decay rate of the pulse return waveform, respectively. This presentation will demonstrate a procedure for estimating the roughness of ice surfaces by fitting the GISMO impulse response model to retrieved waveforms from selected GISMO flights. Furthermore, an extension of this procedure to estimate the scattering coefficient of the glacier bed will be addressed as well. Planned future applications involving the classification of glacier bed conditions based on the derived scattering coefficients will also be described.

The generic world-sheet action of irrational conformal field theory

DOE Office of Scientific and Technical Information (OSTI.GOV)

Clubok, K.; Halpern, M.B.

1995-05-01

We review developments in the world-sheet action formulation of the generic irrational conformal field theory, including the non-linear and the linearized forms of the action. These systems form a large class of spin-two gauged WZW actions which exhibit exotic gravitational couplings. Integrating out the gravitational field, we also speculate on a connection with sigma models.

Global ice-sheet system interlocked by sea level

NASA Astrophysics Data System (ADS)

Denton, George H.; Hughes, Terence J.; Karlén, Wibjörn

1986-07-01

Denton and Hughes (1983, Quaternary Research20, 125-144) postulated that sea level linked a global ice-sheet system with both terrestrial and grounded marine components during late Quaternary ice ages. Summer temperature changes near Northern Hemisphere melting margins initiated sea-level fluctuations that controlled marine components in both polar hemispheres. It was further proposed that variations of this ice-sheet system amplified and transmitted Milankovitch summer half-year insolation changes between 45 and 75°N into global climatic changes. New tests of this hypothesis implicate sea level as a major control of the areal extent of grounded portions of the Antarctic Ice Sheet, thus fitting the concept of a globally interlocked ice-sheet system. But recent atmospheric modeling results ( Manabe and Broccoli, 1985, Journal of Geophysical Research90, 2167-2190) suggest that factors other than areal changes of the grounded Antarctic Ice Sheet strongly influenced Southern Hemisphere climate and terminated the last ice age simultaneously in both polar hemispheres. Atmospheric carbon dioxide linked to high-latitude oceans is the most likely candidate ( Shackleton and Pisias, 1985, Atmospheric carbon dioxide, orbital forcing, and climate. In "The Carbon Cycle and Atmospheric CO 2: Natural Variations Archean to Present" (E. T. Sundquest and W. S. Broecker, Eds.), pp. 303-318. Geophysical Monograph 32, American Geophysical Union, Washington, D.C.), but another potential influence was high-frequency climatic oscillations (2500 yr). It is postulated that variations in atmospheric carbon dioxide acted through an Antarctic ice shelf linked to the grounded ice sheet to produce and terminate Southern Hemisphere ice-age climate. It is further postulated that Milankovitch summer insolation combined with a warm high-frequency oscillation caused marked recession of Northern Hemisphere ice-sheet melting margins and the North Atlantic polar front about 14,000 14C yr B.P. This permitted renewed formation of North Atlantic Deep Water, which could well have controlled atmospheric carbon dioxide ( W. S. Broecker, D. M. Peteet, and D. Rind, 1985, Nature ( London) 315, 21-26). Combined melting and consequent sea-level rise from the three warming factors initiated irreversible collapse of the interlocked global ice-sheet system, which was at its largest but most vulnerable configuration.

Present-day and future Antarctic ice sheet climate and surface mass balance in the Community Earth System Model

DOE PAGES

Lenaerts, Jan T. M.; Vizcaino, Miren; Fyke, Jeremy Garmeson; ...

2016-02-01

Here, we present climate and surface mass balance (SMB) of the Antarctic ice sheet (AIS) as simulated by the global, coupled ocean–atmosphere–land Community Earth System Model (CESM) with a horizontal resolution of ~1° in the past, present and future (1850–2100). CESM correctly simulates present-day Antarctic sea ice extent, large-scale atmospheric circulation and near-surface climate, but fails to simulate the recent expansion of Antarctic sea ice. The present-day Antarctic ice sheet SMB equals 2280 ± 131Gtyear –1, which concurs with existing independent estimates of AIS SMB. When forced by two CMIP5 climate change scenarios (high mitigation scenario RCP2.6 and high-emission scenariomore » RCP8.5), CESM projects an increase of Antarctic ice sheet SMB of about 70 Gtyear –1 per degree warming. This increase is driven by enhanced snowfall, which is partially counteracted by more surface melt and runoff along the ice sheet’s edges. This intensifying hydrological cycle is predominantly driven by atmospheric warming, which increases (1) the moisture-carrying capacity of the atmosphere, (2) oceanic source region evaporation, and (3) summer AIS cloud liquid water content.« less

a Study of the Impact of Doubling Carbon Dioxide and Solar Radiation Variations on the Climate System.

NASA Astrophysics Data System (ADS)

Chu, Shaoping

The exchange of moisture and heat between the atmosphere and the Earth's surface fundamentally affect the dynamics and thermodynamics of the climate system. In order to trace moisture flow through the climate system and examine its impact on climate, a hydrologic cycle and a land energy balance have been developed and incorporated into a coupled climate-thermodynamic sea ice (CCSI) model. The expanded CCSI model has been tested by comparing computed climate parameters with available observations and GCM modeling results. In general, the expanded model does a good job in simulating the large scale features of the atmospheric circulation and precipitation in both space and time. The expanded model has been used to examine the possibility that increased levels of CO_2 in the atmosphere may induce the growth of Northern Hemisphere ice sheets. Results of the study indicate that if summer ice albedo is high enough, and there is some mechanism for initially maintaining ice through the summer season, then it may be possible to have ice sheet growth under the conditions CO_2 induced warming, mainly the result of decreased summer ice melt in response to the higher land ice albedo, and not an increase in precipitation. The expanded model has also been used to examine the impact of Milankovitch solar radiation variations on the climate system, to study the mechanisms that produce glacial-interglacial cycles, especially with respect to the initiation of ice sheets. The results show the Milankovitch solar radiation variations affect the climate system most in the polar regions with the mean annual surface air temperature varying directly in response to changes in the annually averaged incoming solar radiation. However, the seasonal variations in the surface air temperatures are much more complex with large magnitude variations for brief times during the year. The study indicates that ice sheets may start to grow under the conditions of low insolation that occurred at 25, 70, and 115 kyr BP and a land ice minimum albedo of 0.53, with the largest growth rate at 115 kyr BP, approximately when the current 100 kyr cycle began as observed in the geological record.

Current state and future perspectives on coupled ice-sheet - sea-level modelling

NASA Astrophysics Data System (ADS)

de Boer, Bas; Stocchi, Paolo; Whitehouse, Pippa L.; van de Wal, Roderik S. W.

2017-08-01

The interaction between ice-sheet growth and retreat and sea-level change has been an established field of research for many years. However, recent advances in numerical modelling have shed new light on the precise interaction of marine ice sheets with the change in near-field sea level, and the related stability of the grounding line position. Studies using fully coupled ice-sheet - sea-level models have shown that accounting for gravitationally self-consistent sea-level change will act to slow down the retreat and advance of marine ice-sheet grounding lines. Moreover, by simultaneously solving the 'sea-level equation' and modelling ice-sheet flow, coupled models provide a global field of relative sea-level change that is consistent with dynamic changes in ice-sheet extent. In this paper we present an overview of recent advances, possible caveats, methodologies and challenges involved in coupled ice-sheet - sea-level modelling. We conclude by presenting a first-order comparison between a suite of relative sea-level data and output from a coupled ice-sheet - sea-level model.

Two-dimensional streamflow simulations of the Jordan River, Midvale and West Jordan, Utah

USGS Publications Warehouse

Kenney, Terry A.; Freeman, Michael L.

2011-01-01

The Jordan River in Midvale and West Jordan, Utah, flows adjacent to two U.S. Environmental Protection Agency Superfund sites: Midvale Slag and Sharon Steel. At both sites, geotechnical caps extend to the east bank of the river. The final remediation tasks for these sites included the replacement of a historic sheet-pile dam and the stabilization of the river banks adjacent to the Superfund sites. To assist with these tasks, two hydraulic modeling codes contained in the U.S. Geological Survey (USGS) Multi-Dimensional Surface-Water Modeling System (MD_SWMS), System for Transport and River Modeling (SToRM) and Flow and Sediment Transport and Morphological Evolution of Channels (FaSTMECH), were used to provide predicted water-surface elevations, velocities, and boundary shear-stress values throughout the study reach of the Jordan River. A SToRM model of a 0.7 mile subreach containing the sheet-pile dam was used to compare water-surface elevations and velocities associated with the sheet-pile dam and a proposed replacement structure. Maps showing water-surface elevation and velocity differences computed from simulations of the historic sheet-pile dam and the proposed replacement structure topographies for streamflows of 500 and 1,000 cubic feet per second (ft3/s) were created. These difference maps indicated that the velocities associated with the proposed replacement structure topographies were less than or equal to those associated with the historic sheet-pile dam. Similarly, water-surface elevations associated with the proposed replacement structure topographies were all either greater than or equal to water-surface elevations associated with the sheet-pile dam. A FaSTMECH model was developed for the 2.5-mile study reach to aid engineers in bank stabilization designs. Predicted water-surface elevations, velocities and shear-stress values were mapped on an aerial photograph of the study reach to place these parameters in a spatial context. Profile plots of predicted cross-stream average water-surface elevations and cross-stream maximum and average velocities showed how these parameters change along the study reach for two simulated discharges of 1,040 ft3/s and 2,790 ft3/s. The profile plots for the simulated streamflow of 1,040 ft3/s show that the highest velocities are associated with the constructed sheet-pile replacement structure. Results for the simulated streamflow of 2,790 ft3/s indicate that the geometry of the 7800 South Bridge causes more backwater and higher velocities than the constructed sheet-pile replacement structure.

Conceptual models of the evolution of transgressive dune field systems

NASA Astrophysics Data System (ADS)

A. Hesp, Patrick

2013-10-01

This paper examines the evolutionary paths of some transgressive dune fields that have formed on different coasts of the world, and presents some initial conceptual models of system dynamics for transgressive dune sheets and dune fields. Various evolutionary pathways are conceptualized based on a visual examination of dune fields from around the world. On coasts with high sediment supply, dune sheets and dune fields tend to accumulate as large scale barrier systems with little colonization of vegetation in arid-hyper to arid climate regimes, and as multiple, active discrete phases of dune field and deflation plain couplets in temperate to tropical environments. Active dune fields tend to be singular entities on coasts with low to moderate sediment supply. Landscape complexity and vegetation richness and diversity increases as dune fields evolve from simple active sheets and dunes to single and multiple deflation plains and basins, precipitation ridges, nebkha fields and a host of other dune types associated with vegetation (e.g. trailing ridges, slacks, remnant knobs, gegenwalle ridges and dune track ridges, ‘tree islands' and ‘bush pockets'). Three principal scenarios of transgressive dune sheet and dune field development are discussed, including dune sheets or dune fields evolving directly from the backshore, development following foredune and/or dune field erosion, and development from the breakdown or merging of parabolic dunes. Various stages of evolution are outlined for each scenario. Knowledge of evolutionary patterns and stages in coastal dune fields is very limited and caution is urged in attempts to reverse, change and/or modify dune fields to ‘restore' some perceived loss of ecosystem or dune functioning.

Conceptual models of the evolution of transgressive dune field systems

NASA Astrophysics Data System (ADS)

Hesp, Patrick A.

2013-10-01

This paper examines the evolutionary paths of some transgressive dune fields that have formed on different coasts of the world, and presents some initial conceptual models of system dynamics for transgressive dune sheets and dune fields. Various evolutionary pathways are conceptualized based on a visual examination of dune fields from around the world. On coasts with high sediment supply, dune sheets and dune fields tend to accumulate as large scale barrier systems with little colonization of vegetation in arid-hyper to arid climate regimes, and as multiple, active discrete phases of dune field and deflation plain couplets in temperate to tropical environments. Active dune fields tend to be singular entities on coasts with low to moderate sediment supply. Landscape complexity and vegetation richness and diversity increases as dune fields evolve from simple active sheets and dunes to single and multiple deflation plains and basins, precipitation ridges, nebkha fields and a host of other dune types associated with vegetation (e.g. trailing ridges, slacks, remnant knobs, gegenwalle ridges and dune track ridges, 'tree islands' and 'bush pockets'). Three principal scenarios of transgressive dune sheet and dune field development are discussed, including dune sheets or dune fields evolving directly from the backshore, development following foredune and/or dune field erosion, and development from the breakdown or merging of parabolic dunes. Various stages of evolution are outlined for each scenario. Knowledge of evolutionary patterns and stages in coastal dune fields is very limited and caution is urged in attempts to reverse, change and/or modify dune fields to 'restore' some perceived loss of ecosystem or dune functioning.

Greenland Ice Sheet seasonal and spatial mass variability from model simulations and GRACE (2003-2012)

NASA Astrophysics Data System (ADS)

Alexander, Patrick M.; Tedesco, Marco; Schlegel, Nicole-Jeanne; Luthcke, Scott B.; Fettweis, Xavier; Larour, Eric

2016-06-01

Improving the ability of regional climate models (RCMs) and ice sheet models (ISMs) to simulate spatiotemporal variations in the mass of the Greenland Ice Sheet (GrIS) is crucial for prediction of future sea level rise. While several studies have examined recent trends in GrIS mass loss, studies focusing on mass variations at sub-annual and sub-basin-wide scales are still lacking. At these scales, processes responsible for mass change are less well understood and modeled, and could potentially play an important role in future GrIS mass change. Here, we examine spatiotemporal variations in mass over the GrIS derived from the Gravity Recovery and Climate Experiment (GRACE) satellites for the January 2003-December 2012 period using a "mascon" approach, with a nominal spatial resolution of 100 km, and a temporal resolution of 10 days. We compare GRACE-estimated mass variations against those simulated by the Modèle Atmosphérique Régionale (MAR) RCM and the Ice Sheet System Model (ISSM). In order to properly compare spatial and temporal variations in GrIS mass from GRACE with model outputs, we find it necessary to spatially and temporally filter model results to reproduce leakage of mass inherent in the GRACE solution. Both modeled and satellite-derived results point to a decline (of -178.9 ± 4.4 and -239.4 ± 7.7 Gt yr-1 respectively) in GrIS mass over the period examined, but the models appear to underestimate the rate of mass loss, especially in areas below 2000 m in elevation, where the majority of recent GrIS mass loss is occurring. On an ice-sheet-wide scale, the timing of the modeled seasonal cycle of cumulative mass (driven by summer mass loss) agrees with the GRACE-derived seasonal cycle, within limits of uncertainty from the GRACE solution. However, on sub-ice-sheet-wide scales, some areas exhibit significant differences in the timing of peaks in the annual cycle of mass change. At these scales, model biases, or processes not accounted for by models related to ice dynamics or hydrology, may lead to the observed differences. This highlights the need for further evaluation of modeled processes at regional and seasonal scales, and further study of ice sheet processes not accounted for, such as the role of subglacial hydrology in variations in glacial flow.

Periodontal healing by periodontal ligament cell sheets in a teeth replantation model.

PubMed

Zhou, Yefang; Li, Yusheng; Mao, Ling; Peng, Hao

2012-02-01

Successful transplantation of avulsed teeth is to restore the attachment and regenerate the periodontal support. Different strategies have been applied in treatment from modification of teeth storage, antibiotic usage to peridontium tissue replacement. We developed a novel periodontal ligament cell-sheet delivery system to apply on delayed replanted teeth in promoting periodontal healing in a canine model. Autologous periodontal ligament (PDL) fibroblasts were isolated from extracted premolars of beagle dog. The cell-sheets were fabricated using normal culture dish after stimulation of extracellular matrix formation. Teeth were surgically extracted and attached soft tissues were removed. After root canal treatment, the root of teeth were wrapped by the PDL cell-sheets and replanted back to prior socket accordingly whilst teeth without cell sheets as a control. Eight weeks after surgery, the animals were sacrificed and decalcified specimens were prepared. Regeneration of periodontal tissue was evaluated through histology assay. Multi-layered PDL cell-sheet could be attached on tooth root and most cells on sheet-tooth constructs were viable before replantation. Minimum clinical signs of inflammation were observed in experiment. PDL cell-sheets group show significant higher occurrence of favourable healing (88.4%) than control group with low healing (5.3%). Periodontal ligament and cememtum tissue regeneration was observed in the experimental group, and the regenerated tissues showed high collagen type III, type I and fibronectin expression. The periodontal ligament cell-sheets fabricated through normal cell culture dish has a potential for regeneration of periodontal ligament and may become a novel therapy for avulsed teeth replantation. Copyright © 2011 Elsevier Ltd. All rights reserved.

Rapid Ice-Sheet Changes and Mechanical Coupling to Solid-Earth/Sea-Level and Space Geodetic Observation

NASA Astrophysics Data System (ADS)

Adhikari, S.; Ivins, E. R.; Larour, E. Y.

2015-12-01

Perturbations in gravitational and rotational potentials caused by climate driven mass redistribution on the earth's surface, such as ice sheet melting and terrestrial water storage, affect the spatiotemporal variability in global and regional sea level. Here we present a numerically accurate, computationally efficient, high-resolution model for sea level. Unlike contemporary models that are based on spherical-harmonic formulation, the model can operate efficiently in a flexible embedded finite-element mesh system, thus capturing the physics operating at km-scale yet capable of simulating geophysical quantities that are inherently of global scale with minimal computational cost. One obvious application is to compute evolution of sea level fingerprints and associated geodetic and astronomical observables (e.g., geoid height, gravity anomaly, solid-earth deformation, polar motion, and geocentric motion) as a companion to a numerical 3-D thermo-mechanical ice sheet simulation, thus capturing global signatures of climate driven mass redistribution. We evaluate some important time-varying signatures of GRACE inferred ice sheet mass balance and continental hydrological budget; for example, we identify dominant sources of ongoing sea-level change at the selected tide gauge stations, and explain the relative contribution of different sources to the observed polar drift. We also report our progress on ice-sheet/solid-earth/sea-level model coupling efforts toward realistic simulation of Pine Island Glacier over the past several hundred years.

Evaluation of a 12-km Satellite-Era Reanalysis of Surface Mass Balance for the Greenland Ice Sheet

NASA Astrophysics Data System (ADS)

Cullather, R. I.; Nowicki, S.; Zhao, B.; Max, S.

2016-12-01

The recent contribution to sea level change from the Greenland Ice Sheet is thought to be strongly driven by surface processes including melt and runoff. Global reanalyses are potential means of reconstructing the historical time series of ice sheet surface mass balance (SMB), but lack spatial resolution needed to resolve ablation areas along the periphery of the ice sheet. In this work, the Modern-Era Retrospective analysis for Research and Applications, version 2 (MERRA-2) is used to examine the spatial and temporal variability of surface melt over the Greenland Ice Sheet. MERRA-2 is produced for the period 1980 to the present at a grid spacing of ½° latitude by ⅝° longitude, and includes snow hydrology processes including compaction, meltwater percolation and refreezing, runoff, and a prognostic surface albedo. The configuration of the MERRA-2 system allows for the background model - the Goddard Earth Observing System model, version 5 (GEOS-5) - to be carried in phase space through analyzed states via the computation of analysis increments, a capability referred to as "replay". Here, a MERRA-2 replay integration is conducted in which atmospheric forcing fields are interpolated and adjusted to sub- atmospheric grid-scale resolution. These adjustments include lapse-rate effects on temperature, humidity, precipitation, and other atmospheric variables that are known to have a strong elevation dependency over ice sheets. The surface coupling is performed such that mass and energy are conserved. The atmospheric forcing influences the surface representation, which operates on land surface tiles with an approximate 12-km spacing. This produces a high-resolution, downscaled SMB which is interactively coupled to the reanalysis model. We compare the downscaled SMB product with other reanalyses, regional climate model values, and a second MERRA-2 replay in which the background model has been replaced with a 12-km, non-hydrostatic version of GEOS-5. The assessment focuses on regional changes in SMB and SMB components, the identification of changes and temporal variability in the SMB equilibrium line, and the relation between SMB and other climate variables related to general circulation.

Design and results of the ice sheet model initialisation experiments initMIP-Greenland: an ISMIP6 intercomparison

NASA Astrophysics Data System (ADS)

Goelzer, Heiko; Nowicki, Sophie; Edwards, Tamsin; Beckley, Matthew; Abe-Ouchi, Ayako; Aschwanden, Andy; Calov, Reinhard; Gagliardini, Olivier; Gillet-Chaulet, Fabien; Golledge, Nicholas R.; Gregory, Jonathan; Greve, Ralf; Humbert, Angelika; Huybrechts, Philippe; Kennedy, Joseph H.; Larour, Eric; Lipscomb, William H.; Le clec'h, Sébastien; Lee, Victoria; Morlighem, Mathieu; Pattyn, Frank; Payne, Antony J.; Rodehacke, Christian; Rückamp, Martin; Saito, Fuyuki; Schlegel, Nicole; Seroussi, Helene; Shepherd, Andrew; Sun, Sainan; van de Wal, Roderik; Ziemen, Florian A.

2018-04-01

Earlier large-scale Greenland ice sheet sea-level projections (e.g. those run during the ice2sea and SeaRISE initiatives) have shown that ice sheet initial conditions have a large effect on the projections and give rise to important uncertainties. The goal of this initMIP-Greenland intercomparison exercise is to compare, evaluate, and improve the initialisation techniques used in the ice sheet modelling community and to estimate the associated uncertainties in modelled mass changes. initMIP-Greenland is the first in a series of ice sheet model intercomparison activities within ISMIP6 (the Ice Sheet Model Intercomparison Project for CMIP6), which is the primary activity within the Coupled Model Intercomparison Project Phase 6 (CMIP6) focusing on the ice sheets. Two experiments for the large-scale Greenland ice sheet have been designed to allow intercomparison between participating models of (1) the initial present-day state of the ice sheet and (2) the response in two idealised forward experiments. The forward experiments serve to evaluate the initialisation in terms of model drift (forward run without additional forcing) and in response to a large perturbation (prescribed surface mass balance anomaly); they should not be interpreted as sea-level projections. We present and discuss results that highlight the diversity of data sets, boundary conditions, and initialisation techniques used in the community to generate initial states of the Greenland ice sheet. We find good agreement across the ensemble for the dynamic response to surface mass balance changes in areas where the simulated ice sheets overlap but differences arising from the initial size of the ice sheet. The model drift in the control experiment is reduced for models that participated in earlier intercomparison exercises.

Design and results of the ice sheet model initialisation experiments initMIP-Greenland: an ISMIP6 intercomparison

DOE PAGES

Goelzer, Heiko; Nowicki, Sophie; Edwards, Tamsin; ...

2018-04-19

Earlier large-scale Greenland ice sheet sea-level projections (e.g. those run during the ice2sea and SeaRISE initiatives) have shown that ice sheet initial conditions have a large effect on the projections and give rise to important uncertainties. Here, the goal of this initMIP-Greenland intercomparison exercise is to compare, evaluate, and improve the initialisation techniques used in the ice sheet modelling community and to estimate the associated uncertainties in modelled mass changes. initMIP-Greenland is the first in a series of ice sheet model intercomparison activities within ISMIP6 (the Ice Sheet Model Intercomparison Project for CMIP6), which is the primary activity within themore » Coupled Model Intercomparison Project Phase 6 (CMIP6) focusing on the ice sheets. Two experiments for the large-scale Greenland ice sheet have been designed to allow intercomparison between participating models of (1) the initial present-day state of the ice sheet and (2) the response in two idealised forward experiments. The forward experiments serve to evaluate the initialisation in terms of model drift (forward run without additional forcing) and in response to a large perturbation (prescribed surface mass balance anomaly); they should not be interpreted as sea-level projections. We present and discuss results that highlight the diversity of data sets, boundary conditions, and initialisation techniques used in the community to generate initial states of the Greenland ice sheet. We find good agreement across the ensemble for the dynamic response to surface mass balance changes in areas where the simulated ice sheets overlap but differences arising from the initial size of the ice sheet. The model drift in the control experiment is reduced for models that participated in earlier intercomparison exercises.« less

Design and results of the ice sheet model initialisation experiments initMIP-Greenland: an ISMIP6 intercomparison

DOE Office of Scientific and Technical Information (OSTI.GOV)

Goelzer, Heiko; Nowicki, Sophie; Edwards, Tamsin

Earlier large-scale Greenland ice sheet sea-level projections (e.g. those run during the ice2sea and SeaRISE initiatives) have shown that ice sheet initial conditions have a large effect on the projections and give rise to important uncertainties. Here, the goal of this initMIP-Greenland intercomparison exercise is to compare, evaluate, and improve the initialisation techniques used in the ice sheet modelling community and to estimate the associated uncertainties in modelled mass changes. initMIP-Greenland is the first in a series of ice sheet model intercomparison activities within ISMIP6 (the Ice Sheet Model Intercomparison Project for CMIP6), which is the primary activity within themore » Coupled Model Intercomparison Project Phase 6 (CMIP6) focusing on the ice sheets. Two experiments for the large-scale Greenland ice sheet have been designed to allow intercomparison between participating models of (1) the initial present-day state of the ice sheet and (2) the response in two idealised forward experiments. The forward experiments serve to evaluate the initialisation in terms of model drift (forward run without additional forcing) and in response to a large perturbation (prescribed surface mass balance anomaly); they should not be interpreted as sea-level projections. We present and discuss results that highlight the diversity of data sets, boundary conditions, and initialisation techniques used in the community to generate initial states of the Greenland ice sheet. We find good agreement across the ensemble for the dynamic response to surface mass balance changes in areas where the simulated ice sheets overlap but differences arising from the initial size of the ice sheet. The model drift in the control experiment is reduced for models that participated in earlier intercomparison exercises.« less

The Pliocene-Pleistocene transition and the onset of the Northern Hemisphere glacial inception

NASA Astrophysics Data System (ADS)

Robinson, A.; Calov, R.; Ganopolski, A.

2011-12-01

The Pliocene-Pleistocene transition (PPT, ca. 3.3-2.4 Ma BP) marks a shift in the Earth's climate and is believed to coincide with the inception of the Northern Hemisphere (NH) ice sheets. This transition is not only characterized by a gradual reduction in atmospheric CO2 concentration, paleo records also show a strengthening in the amplitude of δ18O data and intensified ice rafted debris deposition in the North Atlantic. Previous modeling studies have demonstrated that the drop in atmospheric CO2 plays an important role in the glaciation of the NH ice sheets, and more specifically, it is considered to be the primary cause of the glaciation of Greenland. Here we apply a novel approach to produce transient simulations of the entire PPT, in order to study the glaciation of Greenland and the NH ice sheets and additionally, to investigate which conditions are necessary for full-scale glaciation. The fully-coupled Earth system model of intermediate complexity CLIMBER-2 is used to explore the effects of a suite of orbital and CO2 forcing scenarios on total NH glaciation. CLIMBER-2 includes low-resolution sub-models of the atmosphere, vegetation, ocean and ice sheets - the latter is designed to simulate the big NH ice sheets with a rather low resolution (and high computational efficiency). As a refinement, the results of the global simulations are then used to force regional simulations of the Greenland Ice Sheet (GIS) using the higher resolution (20 km) regional climate-ice sheet model, REMBO-SICOPOLIS. We present results of transient simulations driven by orbital forcing and several CO2 reduction scenarios that are consistent with best estimates from data for this time period. We discuss the growth and persistence of the NH ice sheets in terms of the forcing and feedbacks involved. Additionally, we present a set of simulations with the growth of the NH ice sheets disabled, in order to quantify the effect the large ice sheets have on global and regional temperature anomalies. By simulating the Greenland Ice Sheet (GIS) in our high resolution coupled global-regional approach, we identify with greater precision, the conditions neccesary for inception of the GIS and link these to global climatic changes.

Free oscillations in a climate model with ice-sheet dynamics

NASA Technical Reports Server (NTRS)

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

1979-01-01

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

Clouds enhance Greenland ice sheet mass loss

NASA Astrophysics Data System (ADS)

Van Tricht, Kristof; Gorodetskaya, Irina V.; L'Ecuyer, Tristan; Lenaerts, Jan T. M.; Lhermitte, Stef; Noel, Brice; Turner, David D.; van den Broeke, Michiel R.; van Lipzig, Nicole P. M.

2015-04-01

Clouds have a profound influence on both the Arctic and global climate, while they still represent one of the key uncertainties in climate models, limiting the fidelity of future climate projections. The potentially important role of thin liquid-containing clouds over Greenland in enhancing ice sheet melt has recently gained interest, yet current research is spatially and temporally limited, focusing on particular events, and their large scale impact on the surface mass balance remains unknown. We used a combination of satellite remote sensing (CloudSat - CALIPSO), ground-based observations and climate model (RACMO) data to show that liquid-containing clouds warm the Greenland ice sheet 94% of the time. High surface reflectivity (albedo) for shortwave radiation reduces the cloud shortwave cooling effect on the absorbed fluxes, while not influencing the absorption of longwave radiation. Cloud warming over the ice sheet therefore dominates year-round. Only when albedo values drop below ~0.6 in the coastal areas during summer, the cooling effect starts to overcome the warming effect. The year-round excess of energy due to the presence of liquid-containing clouds has an extensive influence on the mass balance of the ice sheet. Simulations using the SNOWPACK snow model showed not only a strong influence of these liquid-containing clouds on melt increase, but also on the increased sublimation mass loss. Simulations with the Community Earth System Climate Model for the end of the 21st century (2080-2099) show that Greenland clouds contain more liquid water path and less ice water path. This implies that cloud radiative forcing will be further enhanced in the future. Our results therefore urge the need for improving cloud microphysics in climate models, to improve future projections of ice sheet mass balance and global sea level rise.

Coupled Northern Hemisphere permafrost-ice-sheet evolution over the last glacial cycle

NASA Astrophysics Data System (ADS)

Willeit, M.; Ganopolski, A.

2015-09-01

Permafrost influences a number of processes which are relevant for local and global climate. For example, it is well known that permafrost plays an important role in global carbon and methane cycles. Less is known about the interaction between permafrost and ice sheets. In this study a permafrost module is included in the Earth system model CLIMBER-2, and the coupled Northern Hemisphere (NH) permafrost-ice-sheet evolution over the last glacial cycle is explored. The model performs generally well at reproducing present-day permafrost extent and thickness. Modeled permafrost thickness is sensitive to the values of ground porosity, thermal conductivity and geothermal heat flux. Permafrost extent at the Last Glacial Maximum (LGM) agrees well with reconstructions and previous modeling estimates. Present-day permafrost thickness is far from equilibrium over deep permafrost regions. Over central Siberia and the Arctic Archipelago permafrost is presently up to 200-500 m thicker than it would be at equilibrium. In these areas, present-day permafrost depth strongly depends on the past climate history and simulations indicate that deep permafrost has a memory of surface temperature variations going back to at least 800 ka. Over the last glacial cycle permafrost has a relatively modest impact on simulated NH ice sheet volume except at LGM, when including permafrost increases ice volume by about 15 m sea level equivalent in our model. This is explained by a delayed melting of the ice base from below by the geothermal heat flux when the ice sheet sits on a porous sediment layer and permafrost has to be melted first. Permafrost affects ice sheet dynamics only when ice extends over areas covered by thick sediments, which is the case at LGM.

Observationally constrained projections of Antarctic ice sheet instability

NASA Astrophysics Data System (ADS)

Edwards, Tamsin; Ritz, Catherine; Durand, Gael; Payne, Anthony; Peyaud, Vincent; Hindmarsh, Richard

2015-04-01

Large parts of the Antarctic ice sheet lie on bedrock below sea level and may be vulnerable to a positive feedback known as Marine Ice Sheet Instability (MISI), a self-sustaining retreat of the grounding line triggered by oceanic or atmospheric changes. There is growing evidence MISI may be underway throughout the Amundsen Sea Embayment (ASE) of West Antarctica, induced by circulation of warm Circumpolar Deep Water. If this retreat is sustained the region could contribute up to 1-2 m to global mean sea level, and if triggered in other areas the potential contribution to sea level on centennial to millennial timescales could be two to three times greater. However, physically plausible projections of Antarctic MISI are challenging: numerical ice sheet models are too low in spatial resolution to resolve grounding line processes or else too computationally expensive to assess modelling uncertainties, and no dynamical models exist of the ocean-atmosphere-ice sheet system. Furthermore, previous numerical ice sheet model projections for Antarctica have not been calibrated with observations, which can reduce uncertainties. Here we estimate the probability of dynamic mass loss in the event of MISI under a medium climate scenario, assessing 16 modelling uncertainties and calibrating the projections with observed mass losses in the ASE from 1992-2011. We project losses of up to 30 cm sea level equivalent (SLE) by 2100 and 72 cm SLE by 2200 (95% credibility interval: CI). Our results are substantially lower than previous estimates. The ASE sustains substantial losses, 83% of the continental total by 2100 and 67% by 2200 (95% CI), but in other regions losses are limited by ice dynamical theory, observations, or a lack of projected triggers.

Systems, Apparatuses, and Methods for Using Durable Adhesively Bonded Joints for Sandwich Structures

NASA Technical Reports Server (NTRS)

Smeltzer, III, Stanley S. (Inventor); Lundgren, Eric C. (Inventor)

2014-01-01

Systems, methods, and apparatus for increasing durability of adhesively bonded joints in a sandwich structure. Such systems, methods, and apparatus includes an first face sheet and an second face sheet as well as an insert structure, the insert structure having a first insert face sheet, a second insert face sheet, and an insert core material. In addition, sandwich core material is arranged between the first face sheet and the second face sheet. A primary bondline may be coupled to the face sheet(s) and the splice. Further, systems, methods, and apparatus of the present disclosure advantageously reduce the load, provide a redundant path, reduce structural fatigue, and/or increase fatigue life.

ISMIP6 - initMIP: Greenland ice sheet model initialisation experiments

NASA Astrophysics Data System (ADS)

Goelzer, Heiko; Nowicki, Sophie; Payne, Tony; Larour, Eric; Abe Ouchi, Ayako; Gregory, Jonathan; Lipscomb, William; Seroussi, Helene; Shepherd, Andrew; Edwards, Tamsin

2016-04-01

Earlier large-scale Greenland ice sheet sea-level projections e.g. those run during ice2sea and SeaRISE initiatives have shown that ice sheet initialisation can have a large effect on the projections and gives rise to important uncertainties. This intercomparison exercise (initMIP) aims at comparing, evaluating and improving the initialization techniques used in the ice sheet modeling community and to estimate the associated uncertainties. It is the first in a series of ice sheet model intercomparison activities within ISMIP6 (Ice Sheet Model Intercomparison Project for CMIP6). The experiments are conceived for the large-scale Greenland ice sheet and are designed to allow intercomparison between participating models of 1) the initial present-day state of the ice sheet and 2) the response in two schematic forward experiments. The latter experiments serve to evaluate the initialisation in terms of model drift (forward run without any forcing) and response to a large perturbation (prescribed surface mass balance anomaly). We present and discuss first results of the intercomparison and highlight important uncertainties with respect to projections of the Greenland ice sheet sea-level contribution.

Stress studies in EFG

NASA Technical Reports Server (NTRS)

1982-01-01

A program to study stress generation mechanisms in silicon sheet growth was started. The purpose of the research is to define post-growth temperature profiles for the sheet that can minimize its stress during growth at high speeds, e.g., greater than 3 cm/min. The initial tasks described concern work in progress toward the development of computing capabilities to (1) model stress-temperature relationships in steady-state ribbon growth, and (2) provide a means to calculate realistic temperature fields in ribbon, given growth system component temperatures as boundary conditions. If it is determined that low stress configurations can be achieved, the modeling is to be tested experimentally by constructing low-stress growth systems for EFG silicon ribbon.

Implications for the crustal Architecture in West Antarctica revealed by the means of depth-to-the-bottom of the magnetic source (DBMS) mapping and 3D FEM geothermal heat flux models

NASA Astrophysics Data System (ADS)

Dziadek, Ricarda; Gohl, Karsten; Kaul, Norbert

2017-04-01

The West Antarctic Rift System (WARS) is one of the largest rift systems in the world, which displays unique coupled relationships between tectonic processes and ice sheet dynamics. Palaeo-ice streams have eroded troughs across the Amundsen Sea Embayment (ASE) that today route warm ocean deep water to the West Antarctic Ice Sheet (WAIS) grounding zone and reinforce dynamic ice sheet thinning. Rift basins, which cut across West Antarctica's landward-sloping shelves, promote ice sheet instability. Young, continental rift systems are regions with significantly elevated geothermal heat flux (GHF), because the transient thermal perturbation to the lithosphere caused by rifting requires 100 m.y. to reach long-term thermal equilibrium. The GHF in this region is, especially on small scales, poorly constrained and suspected to be heterogeneous as a reflection of the distribution of tectonic and volcanic activity along the complex branching geometry of the WARS, which reflects its multi-stage history and structural inheritance. We investigate the crustal architecture and the possible effects of rifting history from the WARS on the ASE ice sheet dynamics, by the use of depth-to-the-bottom of the magnetic source (DBMS) estimates. These are based on airborne-magnetic anomaly data and provide an additional insight into the deeper crustal properties. With the DBMS estimates we reveal spatial changes at the bottom of the igneous crust and the thickness of the magnetic layer, which can be further incorporated into tectonic interpretations. The DBMS also marks an important temperature transition zone of approximately 580°C and therefore serves as a boundary condition for our numerical FEM models in 2D and 3D. On balance, and by comparison to global values, we find average GHF of 90 mWm-2 with spatial variations due to crustal heterogeneities and volcanic activities. This estimate is 30% more than commonly used in ice sheet models in the ASE region.

Interlayer interaction and mechanical properties in multi-layer graphene, Boron-Nitride, Aluminum-Nitride and Gallium-Nitride graphene-like structure: A quantum-mechanical DFT study

NASA Astrophysics Data System (ADS)

Ghorbanzadeh Ahangari, Morteza; Fereidoon, A.; Hamed Mashhadzadeh, Amin

2017-12-01

In present study, we investigated mechanical, electronic and interlayer properties of mono, bi and 3layer of Boron-Nitride (B-N), Aluminum-Nitride (Al-N) and Gallium-Nitride (Ga-N) graphene sheets and compared these results with results obtained from carbonic graphenes (C-graphenes). For reaching this purpose, first we optimized the geometrical parameters of these graphenes by using density functional theory (DFT) method. Then we calculated Young's modulus of graphene sheet by compressing and then elongating these sheets in small increment. Our results indicates that Young's modulus of graphenes didn't changed obviously by increasing the number of layer sheet. We also found that carbonic graphene has greatest Young's modulus among another mentioned sheets because of smallest equilibrium distance between its elements. Next we modeled the van der Waals interfacial interaction exist between two sheets with classical spring model by using general form of Lennard-Jones (L-J) potential for all of mentioned graphenes. For calculating L-J parameters (ε and σ), the potential energy between layers of mentioned graphene as a function of the separation distance was plotted. Moreover, the density of states (DOS) are calculated to understand the electronic properties of these systems better.

FDTD modeling of thin impedance sheets

NASA Technical Reports Server (NTRS)

Luebbers, Raymond J.; Kunz, Karl S.

1991-01-01

Thin sheets of resistive or dielectric material are commonly encountered in radar cross section calculations. Analysis of such sheets is simplified by using sheet impedances. In this paper it is shown that sheet impedances can be modeled easily and accurately using Finite Difference Time Domain (FDTD) methods.

On the Application of Science Systems Engineering and Uncertainty Quantification for Ice Sheet Science and Sea Level Projections

NASA Astrophysics Data System (ADS)

Schlegel, Nicole-Jeanne; Boening, Carmen; Larour, Eric; Limonadi, Daniel; Schodlok, Michael; Seroussi, Helene; Watkins, Michael

2017-04-01

Research and development activities at the Jet Propulsion Laboratory (JPL) currently support the creation of a framework to formally evaluate the observational needs within earth system science. One of the pilot projects of this effort aims to quantify uncertainties in global mean sea level rise projections, due to contributions from the continental ice sheets. Here, we take advantage of established uncertainty quantification tools embedded within the JPL-University of California at Irvine Ice Sheet System Model (ISSM). We conduct sensitivity and Monte-Carlo style sampling experiments on forward simulations of the Greenland and Antarctic ice sheets. By varying internal parameters and boundary conditions of the system over both extreme and credible worst-case ranges, we assess the impact of the different parameter ranges on century-scale sea level rise projections. The results inform efforts to a) isolate the processes and inputs that are most responsible for determining ice sheet contribution to sea level; b) redefine uncertainty brackets for century-scale projections; and c) provide a prioritized list of measurements, along with quantitative information on spatial and temporal resolution, required for reducing uncertainty in future sea level rise projections. Results indicate that ice sheet mass loss is dependent on the spatial resolution of key boundary conditions - such as bedrock topography and melt rates at the ice-ocean interface. This work is performed at and supported by the California Institute of Technology's Jet Propulsion Laboratory. Supercomputing time is also supported through a contract with the National Aeronautics and Space Administration's Cryosphere program.

Virtual Earth System Laboratory (VESL): Effective Visualization of Earth System Data and Process Simulations

NASA Astrophysics Data System (ADS)

Quinn, J. D.; Larour, E. Y.; Cheng, D. L. C.; Halkides, D. J.

2016-12-01

The Virtual Earth System Laboratory (VESL) is a Web-based tool, under development at the Jet Propulsion Laboratory and UC Irvine, for the visualization of Earth System data and process simulations. It contains features geared toward a range of applications, spanning research and outreach. It offers an intuitive user interface, in which model inputs are changed using sliders and other interactive components. Current capabilities include simulation of polar ice sheet responses to climate forcing, based on NASA's Ice Sheet System Model (ISSM). We believe that the visualization of data is most effective when tailored to the target audience, and that many of the best practices for modern Web design/development can be applied directly to the visualization of data: use of negative space, color schemes, typography, accessibility standards, tooltips, etc cetera. We present our prototype website, and invite input from potential users, including researchers, educators, and students.

Uncertainties in the Antarctic Ice Sheet Contribution to Sea Level Rise: Exploration of Model Response to Errors in Climate Forcing, Boundary Conditions, and Internal Parameters

NASA Astrophysics Data System (ADS)

Schlegel, N.; Seroussi, H. L.; Boening, C.; Larour, E. Y.; Limonadi, D.; Schodlok, M.; Watkins, M. M.

2017-12-01

The Jet Propulsion Laboratory-University of California at Irvine Ice Sheet System Model (ISSM) is a thermo-mechanical 2D/3D parallelized finite element software used to physically model the continental-scale flow of ice at high resolutions. Embedded into ISSM are uncertainty quantification (UQ) tools, based on the Design Analysis Kit for Optimization and Terascale Applications (DAKOTA) software. ISSM-DAKOTA offers various UQ methods for the investigation of how errors in model input impact uncertainty in simulation results. We utilize these tools to regionally sample model input and key parameters, based on specified bounds of uncertainty, and run a suite of continental-scale 100-year ISSM forward simulations of the Antarctic Ice Sheet. Resulting diagnostics (e.g., spread in local mass flux and regional mass balance) inform our conclusion about which parameters and/or forcing has the greatest impact on century-scale model simulations of ice sheet evolution. The results allow us to prioritize the key datasets and measurements that are critical for the minimization of ice sheet model uncertainty. Overall, we find that Antartica's total sea level contribution is strongly affected by grounding line retreat, which is driven by the magnitude of ice shelf basal melt rates and by errors in bedrock topography. In addition, results suggest that after 100 years of simulation, Thwaites glacier is the most significant source of model uncertainty, and its drainage basin has the largest potential for future sea level contribution. This work is performed at and supported by the California Institute of Technology's Jet Propulsion Laboratory. Supercomputing time is also supported through a contract with the National Aeronautics and Space Administration's Cryosphere program.

Present-day Circum-Antarctic Simulations using the POPSICLES Coupled Ice Sheet-Ocean Model

NASA Astrophysics Data System (ADS)

Asay-Davis, X.; Martin, D. F.; Price, S. F.; Maltrud, M. E.; Collins, W.

2014-12-01

We present POPSICLES simulation results covering the full Antarctic Ice Sheet and the Southern Ocean spanning the period 1990 to 2010. Simulations are performed at 0.1o (~5 km) ocean resolution and with adaptive ice-sheet model resolution as fine as 500 m. We compare time-averaged melt rates below a number of major ice shelves with those reported by Rignot et al. (2013) as well as other recent studies. We also present seasonal variability and decadal trends in submarine melting from several Antarctic regions. Finally, we explore the influence on basal melting and system dynamics resulting from two different choices of climate forcing: a "normal-year" climatology and the CORE v. 2 forcing data (Large and Yeager 2008).POPSICLES couples the POP2x ocean model, a modified version of the Parallel Ocean Program (Smith and Gent, 2002), and the BISICLES ice-sheet model (Cornford et al., 2012). POP2x includes sub-ice-shelf circulation using partial top cells (Losch, 2008) and boundary layer physics following Holland and Jenkins (1999), Jenkins (2001), and Jenkins et al. (2010). Standalone POP2x output compares well with standard ice-ocean test cases (e.g., ISOMIP; Losch, 2008) and other continental-scale simulations and melt-rate observations (Kimura et al., 2013; Rignot et al., 2013). BISICLES makes use of adaptive mesh refinement and a 1st-order accurate momentum balance similar to the L1L2 model of Schoof and Hindmarsh (2009) to accurately model regions of dynamic complexity, such as ice streams, outlet glaciers, and grounding lines. Results of BISICLES simulations have compared favorably to comparable simulations with a Stokes momentum balance in both idealized tests (MISMIP-3D; Pattyn et al., 2013) and realistic configurations (Favier et al. 2014).A companion presentation, "Response of the Antarctic Ice Sheet to ocean forcing using the POPSICLES coupled ice sheet-ocean model" in session C024 covers the ice-sheet response to these melt rates in the coupled simulation. The figure shows eddy activity in the vertically integrated (barotropic) velocity nearly six years into a POPSICLES simulation of the Antarctic region.

From cyclic ice streaming to Heinrich-like events: the grow-and-surge instability in the Parallel Ice Sheet Model

NASA Astrophysics Data System (ADS)

Feldmann, Johannes; Levermann, Anders

2017-08-01

Here we report on a cyclic, physical ice-discharge instability in the Parallel Ice Sheet Model, simulating the flow of a three-dimensional, inherently buttressed ice-sheet-shelf system which periodically surges on a millennial timescale. The thermomechanically coupled model on 1 km horizontal resolution includes an enthalpy-based formulation of the thermodynamics, a nonlinear stress-balance-based sliding law and a very simple subglacial hydrology. The simulated unforced surging is characterized by rapid ice streaming through a bed trough, resulting in abrupt discharge of ice across the grounding line which is eventually calved into the ocean. We visualize the central feedbacks that dominate the subsequent phases of ice buildup, surge and stabilization which emerge from the interaction between ice dynamics, thermodynamics and the subglacial till layer. Results from the variation of surface mass balance and basal roughness suggest that ice sheets of medium thickness may be more susceptible to surging than relatively thin or thick ones for which the surge feedback loop is damped. We also investigate the influence of different basal sliding laws (ranging from purely plastic to nonlinear to linear) on possible surging. The presented mechanisms underlying our simulations of self-maintained, periodic ice growth and destabilization may play a role in large-scale ice-sheet surging, such as the surging of the Laurentide Ice Sheet, which is associated with Heinrich events, and ice-stream shutdown and reactivation, such as observed in the Siple Coast region of West Antarctica.

Key technologies for manufacturing and processing sheet materials: A global perspective

NASA Astrophysics Data System (ADS)

Demeri, Mahmoud Y.

2001-02-01

Modern industrial technologies continue to seek new materials and processes to produce products that meet design and functional requirements. Sheet materials made from ferrous and non-ferrous metals, laminates, composites, and reinforced plastics constitute a large percentage of today’s products, components, and systems. Major manufacturers of sheet products include automotive, aerospace, appliance, and food-packaging industries. The Second Global Symposium on Innovations in Materials Processing & Manufacturing: Sheet Materials is organized to provide a forum for presenting advances in sheet processing and manufacturing by worldwide researchers and engineers from industrial, research, and academic centers. The symposium, sponsored by the TMS Materials Processing & Manufacturing Division (MPMD), was planned for the 2001 TMS Annual Meeting, New Orleans, Louisiana, February 11 15, 2001. This article is a review of key papers submitted for publication in the concurrent volume. The selected papers present significant developments in the rapidly expanding areas of advanced sheet materials, innovative forming methods, industrial applications, primary and secondary processing, composite processing, and numerical modeling of manufacturing processes.

Two-dimensional models for the optical response of thin films

NASA Astrophysics Data System (ADS)

Li, Yilei; Heinz, Tony F.

2018-04-01

In this work, we present a systematic study of 2D optical models for the response of thin layers of material under excitation by normally incident light. The treatment, within the framework of classical optics, analyzes a thin film supported by a semi-infinite substrate, with both the thin layer and the substrate assumed to exhibit local, isotropic linear response. Starting from the conventional three-dimensional (3D) slab model of the system, we derive a two-dimensional (2D) sheet model for the thin film in which the optical response is described by a sheet optical conductivity. We develop criteria for the applicability of this 2D sheet model for a layer with an optical thickness far smaller than the wavelength of the light. We examine in detail atomically thin semi-metallic and semiconductor van-der-Waals layers and ultrathin metal films as representative examples. Excellent agreement of the 2D sheet model with the 3D slab model is demonstrated over a broad spectral range from the radio frequency limit to the near ultraviolet. A linearized version of system response for the 2D model is also presented for the case where the influence of the optically thin layer is sufficiently weak. Analytical expressions for the applicability and accuracy of the different optical models are derived, and the appropriateness of the linearized treatment for the materials is considered. We discuss the advantages, as well as limitations, of these models for the purpose of deducing the optical response function of the thin layer from experiment. We generalize the theory to take into account in-plane anisotropy, layered thin film structures, and more general substrates. Implications of the 2D model for the transmission of light by the thin film and for the implementation of half- and totally absorbing layers are discussed.

Modeling the Wake as a Continuous Vortex Sheet in a Potential-Flow Solution Using Vortex Panels

DTIC Science & Technology

1989-12-01

Continuous Vortex Sheet ........ 30 0 Redistributing the Vorticity Over anlIncreasing Area ............... 31 System of Linear Equations inG-Primes...i)* 9 ~=- r(x) L~~3 (29) 4v ji -i13 where dl is a differential length along the filament dl = dx 1 ( 30 ) when expressed in the local coordinate frame...which 30 models the wing serves as a pattern for this effort, but modifications must be made since the wake is continually growing and distorting. In

Antarctic contribution to meltwater pulse 1A from reduced Southern Ocean overturning.

PubMed

Golledge, N R; Menviel, L; Carter, L; Fogwill, C J; England, M H; Cortese, G; Levy, R H

2014-09-29

During the last glacial termination, the upwelling strength of the southern polar limb of the Atlantic Meridional Overturning Circulation varied, changing the ventilation and stratification of the high-latitude Southern Ocean. During the same period, at least two phases of abrupt global sea-level rise--meltwater pulses--took place. Although the timing and magnitude of these events have become better constrained, a causal link between ocean stratification, the meltwater pulses and accelerated ice loss from Antarctica has not been proven. Here we simulate Antarctic ice sheet evolution over the last 25 kyr using a data-constrained ice-sheet model forced by changes in Southern Ocean temperature from an Earth system model. Results reveal several episodes of accelerated ice-sheet recession, the largest being coincident with meltwater pulse 1A. This resulted from reduced Southern Ocean overturning following Heinrich Event 1, when warmer subsurface water thermally eroded grounded marine-based ice and instigated a positive feedback that further accelerated ice-sheet retreat.

Triple Value Simulation Model Fact Sheet

EPA Pesticide Factsheets

The Triple Value Simulation (3VS) is a high-level model that accounts for the complex relationships among economic, social and environmental systems in order to explore scenarios and solutions to improve the health of the Bay.

Results of the Greenland ice sheet model initialisation experiments: ISMIP6 - initMIP-Greenland

NASA Astrophysics Data System (ADS)

Goelzer, Heiko; Nowicki, Sophie; Edwards, Tamsin; Beckley, Matthew

2017-04-01

Ice sheet model initialisation has a large effect on projected future sea-level contributions and gives rise to important uncertainties. The goal of this intercomparison exercise for the continental-scale Greenland ice sheet is therefore to compare, evaluate and improve the initialisation techniques used in the ice sheet modelling community. The initMIP-Greenland project is the first in a series of ice sheet model intercomparison activities within ISMIP6 (Ice Sheet Model Intercomparison Project for CMIP6). The experimental set-up has been designed to allow comparison of the initial present-day state of the Greenland ice sheet between participating models and against observations. Furthermore, the initial states are tested with two schematic forward experiments to evaluate the initialisation in terms of model drift (forward run without any forcing) and response to a large perturbation (prescribed surface mass balance anomaly). We present and discuss results that highlight the wide diversity of data sets, boundary conditions and initialisation techniques used in the community to generate initial states of the Greenland ice sheet.

Evaluation of three methods of different levels of complexity to represent the interactions between the Greenland ice sheet and the atmosphere at the century time scale.

NASA Astrophysics Data System (ADS)

Le clec'h, Sébastien; Fettweis, Xavier; Quiquet, Aurelien; Dumas, Christophe; Kageyama, Masa; Charbit, Sylvie; Ritz, Catherine

2017-04-01

Based on numerous studies showing implications of polar ice sheets on the climate system, the climate community recommended the development of methods to account for feedbacks between polar ice sheets and the other climate components. In this study we used three methods of different levels of complexity to represent the interactions between a Greenland ice sheet model (GRISLI) and a regional atmospheric model (MAR) under the RCP8.5 scenario. The simplest method, i.e. uncoupled, does not account for interactions between both models. In this method MAR computes varying atmospheric conditions using the same present-day observed Greenland ice sheet topography and extent. The outputs are then used to force GRISLI. The second method is a one-way coupling method in which the MAR outputs are corrected to account for topography changes before their transfer to GRISLI. The third method is a fully coupled method allowing the full representation of interactions between MAR and GRISLI. In this case, the ice sheet topography and its extent as seen by the atmospheric model is updated for each ice sheet model time step. The three methods are evaluated regarding the Greenland ice sheet response from 2000 to 2150. As expected, the uncoupled method shows a coastal thinning of the ice sheet due to a decreasing surface mass balance for coastal regions related to increased mean surface temperature. The one-way coupling and the full coupling methods tend to amplify the surface mass balance due to surface elevation feedback. The uncoupled method tends to underestimate the Greenland ice sheet volume reduction compared to both coupling methods over 150 years. This underestimation is of the same order of magnitude of the ice loss from the Greenland peripheral glaciers at the end of the 21st century. As for the uncoupled method, the thinning of the ice sheet occurs in coastal regions for both coupling methods. However compared to the one-way coupling method, the fully coupled method tends to increase the spatial variability of the surface mass balance changes through time. Our results also indicate that differences between the two coupling methods increase with time, which suggests that the choice of the method should depend on the timescale considered. Beyond century scale projections the fully coupled method is necessary in order to avoid underestimation of the ice sheet volume reduction, whilst the one-way method seems to be sufficient to represent the interactions between the atmosphere and the GrIS for projections by the end of the century.

Cell Sheet Stiffness Sensing without taking out from culture liquid.

PubMed

Uchida, Ryohei; Tanaka, Nobuyuki; Higashimori, Mitsuru; Tadakuma, Kenjiro; Kaneko, Makoto; Kondo, Makoto; Yamato, Masayuki

2010-01-01

Stiffness could be an important index for evaluating the vitality of cell sheet. This paper challenges the measurement of stiffness of transparent cell sheet in culture liquid without taking it out from petri dish. The system is composed of a micro air nozzle for supplying an air jet and a regular reflective type laser sensor for measuring the the deformation of transparent cell sheet. This system is called as Cell Sheet Stiffness Sensing system (CS(3) system). When an air jet is given to a cell sheet in culture liquid, it pushes away the liquid toward the outer direction at initial phase and reaches the surface of cell sheet. Without any switching motion, the air jet continuously imparts a force to the surface of cell sheet so that the sensor can measure the stiffness of the cell sheet.

Sensitivities of Greenland ice sheet volume inferred from an ice sheet adjoint model

NASA Astrophysics Data System (ADS)

Heimbach, P.; Bugnion, V.

2009-04-01

We present a new and original approach to understanding the sensitivity of the Greenland ice sheet to key model parameters and environmental conditions. At the heart of this approach is the use of an adjoint ice sheet model. Since its introduction by MacAyeal (1992), the adjoint method has become widespread to fit ice stream models to the increasing number and diversity of satellite observations, and to estimate uncertain model parameters such as basal conditions. However, no attempt has been made to extend this method to comprehensive ice sheet models. As a first step toward the use of adjoints of comprehensive three-dimensional ice sheet models we have generated an adjoint of the ice sheet model SICOPOLIS of Greve (1997). The adjoint was generated by means of the automatic differentiation (AD) tool TAF. The AD tool generates exact source code representing the tangent linear and adjoint model of the nonlinear parent model provided. Model sensitivities are given by the partial derivatives of a scalar-valued model diagnostic with respect to the controls, and can be efficiently calculated via the adjoint. By way of example, we determine the sensitivity of the total Greenland ice volume to various control variables, such as spatial fields of basal flow parameters, surface and basal forcings, and initial conditions. Reliability of the adjoint was tested through finite-difference perturbation calculations for various control variables and perturbation regions. Besides confirming qualitative aspects of ice sheet sensitivities, such as expected regional variations, we detect regions where model sensitivities are seemingly unexpected or counter-intuitive, albeit ``real'' in the sense of actual model behavior. An example is inferred regions where sensitivities of ice sheet volume to basal sliding coefficient are positive, i.e. where a local increase in basal sliding parameter increases the ice sheet volume. Similarly, positive ice temperature sensitivities in certain parts of the ice sheet are found (in most regions it is negativ, i.e. an increase in temperature decreases ice sheet volume), the detection of which seems highly unlikely if only conventional perturbation experiments had been used. An effort to generate an efficient adjoint with the newly developed open-source AD tool OpenAD is also under way. Available adjoint code generation tools now open up a variety of novel model applications, notably with regard to sensitivity and uncertainty analyses and ice sheet state estimation or data assimilation.

Effect of Inductive Coil Geometry and Current Sheet Trajectory of a Conical Theta Pinch Pulsed Inductive Plasma Accelerator

NASA Technical Reports Server (NTRS)

Hallock, Ashley K.; Polzin, Kurt A.; Bonds, Kevin W.; Emsellem, Gregory D.

2011-01-01

Results are presented demonstrating the e ect of inductive coil geometry and current sheet trajectory on the exhaust velocity of propellant in conical theta pinch pulsed induc- tive plasma accelerators. The electromagnetic coupling between the inductive coil of the accelerator and a plasma current sheet is simulated, substituting a conical copper frustum for the plasma. The variation of system inductance as a function of plasma position is obtained by displacing the simulated current sheet from the coil while measuring the total inductance of the coil. Four coils of differing geometries were employed, and the total inductance of each coil was measured as a function of the axial displacement of two sep- arate copper frusta both having the same cone angle and length as the coil but with one compressed to a smaller size relative to the coil. The measured relationship between total coil inductance and current sheet position closes a dynamical circuit model that is used to calculate the resulting current sheet velocity for various coil and current sheet con gura- tions. The results of this model, which neglects the pinching contribution to thrust, radial propellant con nement, and plume divergence, indicate that in a conical theta pinch ge- ometry current sheet pinching is detrimental to thruster performance, reducing the kinetic energy of the exhausting propellant by up to 50% (at the upper bound for the parameter range of the study). The decrease in exhaust velocity was larger for coils and simulated current sheets of smaller half cone angles. An upper bound for the pinching contribution to thrust is estimated for typical operating parameters. Measurements of coil inductance for three di erent current sheet pinching conditions are used to estimate the magnetic pressure as a function of current sheet radial compression. The gas-dynamic contribution to axial acceleration is also estimated and shown to not compensate for the decrease in axial electromagnetic acceleration that accompanies the radial compression of the plasma in conical theta pinches.

Results of the Greenland Ice Sheet Model Initialisation Experiments ISMIP6 - initMIP-Greenland

NASA Astrophysics Data System (ADS)

Goelzer, H.; Nowicki, S.; Edwards, T.; Beckley, M.; Abe-Ouchi, A.; Aschwanden, A.; Calov, R.; Gagliardini, O.; Gillet-chaulet, F.; Golledge, N. R.; Gregory, J. M.; Greve, R.; Humbert, A.; Huybrechts, P.; Larour, E. Y.; Lipscomb, W. H.; Le ´h, S.; Lee, V.; Kennedy, J. H.; Pattyn, F.; Payne, A. J.; Rodehacke, C. B.; Rückamp, M.; Saito, F.; Schlegel, N.; Seroussi, H. L.; Shepherd, A.; Sun, S.; Vandewal, R.; Ziemen, F. A.

2016-12-01

Earlier large-scale Greenland ice sheet sea-level projections e.g. those run during ice2sea and SeaRISE initiatives have shown that ice sheet initialisation can have a large effect on the projections and gives rise to important uncertainties. The goal of this intercomparison exercise (initMIP-Greenland) is to compare, evaluate and improve the initialization techniques used in the ice sheet modeling community and to estimate the associated uncertainties. It is the first in a series of ice sheet model intercomparison activities within ISMIP6 (Ice Sheet Model Intercomparison Project for CMIP6). Two experiments for the large-scale Greenland ice sheet have been designed to allow intercomparison between participating models of 1) the initial present-day state of the ice sheet and 2) the response in two schematic forward experiments. The forward experiments serve to evaluate the initialisation in terms of model drift (forward run without any forcing) and response to a large perturbation (prescribed surface mass balance anomaly). We present and discuss final results of the intercomparison and highlight important uncertainties with respect to projections of the Greenland ice sheet sea-level contribution.

FDTD modeling of thin impedance sheets

NASA Technical Reports Server (NTRS)

Luebbers, Raymond; Kunz, Karl

1991-01-01

Thin sheets of resistive or dielectric material are commonly encountered in radar cross section calculations. Analysis of such sheets is simplified by using sheet impedances. It is shown that sheet impedances can be modeled easily and accurately using Finite Difference Time Domain (FDTD) methods. These sheets are characterized by a discontinuity in the tangential magnetic field on either side of the sheet but no discontinuity in tangential electric field. This continuity, or single valued behavior of the electric field, allows the sheet current to be expressed in terms of an impedance multiplying this electric field.

Widespread surface meltwater drainage in Antarctica

NASA Astrophysics Data System (ADS)

Kingslake, J.; Ely, J.; Das, I.; Bell, R. E.

2016-12-01

Surface meltwater is thought to cause ice-shelf disintegration, which accelerates the contribution of ice sheets to sea-level rise. Antarctic surface melting is predicted to increase and trigger further ice-shelf disintegration during this century. These climate-change impacts could be modulated by an active hydrological network analogous to the one in operation in Greenland. Despite some observations of Antarctic surface and sub-surface hydrological systems, large-scale active surface drainage in Antarctica has rarely been studied. We use satellite imagery and aerial photography to reveal widespread active hydrology on the surface of the Antarctic Ice Sheet as far south as 85o and as high as 1800 m a.s.l., often near mountain peaks that protrude through the ice (nunataks) and relatively low-albedo `blue-ice areas'. Despite predominantly sub-zero regional air temperatures, as simulated by a regional climate model, Antarctic active drainage has persisted for decades, transporting water through surface streams and feeding vast melt ponds up to 80 km long. Drainage networks (the largest are over 100 km in length) form on flat ice shelves, steep outlet glaciers and ice-sheet flanks across the West and East Antarctica Ice Sheets. Motivated by the proximity of many drainage systems to low-albedo rock and blue-ice areas, we hypothesize a positive feedback between exposed-rock extent, BIA formation, melting and ice-sheet thinning. This feedback relies on drainage moving water long distances from areas near exposed rock, across the grounding line onto and across ice shelves - a process we observe, but had previously thought to be unlikely in Antarctica. This work highlights previously-overlooked processes, not captured by current regional-scale models, which may accelerate the retreat of the Antarctic Ice Sheet.

Uncertainty Quantification for Ice Sheet Science and Sea Level Projections

NASA Astrophysics Data System (ADS)

Boening, C.; Schlegel, N.; Limonadi, D.; Schodlok, M.; Seroussi, H. L.; Larour, E. Y.; Watkins, M. M.

2017-12-01

In order to better quantify uncertainties in global mean sea level rise projections and in particular upper bounds, we aim at systematically evaluating the contributions from ice sheets and potential for extreme sea level rise due to sudden ice mass loss. Here, we take advantage of established uncertainty quantification tools embedded within the Ice Sheet System Model (ISSM) as well as sensitivities to ice/ocean interactions using melt rates and melt potential derived from MITgcm/ECCO2. With the use of these tools, we conduct Monte-Carlo style sampling experiments on forward simulations of the Antarctic ice sheet, by varying internal parameters and boundary conditions of the system over both extreme and credible worst-case ranges. Uncertainty bounds for climate forcing are informed by CMIP5 ensemble precipitation and ice melt estimates for year 2100, and uncertainty bounds for ocean melt rates are derived from a suite of regional sensitivity experiments using MITgcm. Resulting statistics allow us to assess how regional uncertainty in various parameters affect model estimates of century-scale sea level rise projections. The results inform efforts to a) isolate the processes and inputs that are most responsible for determining ice sheet contribution to sea level; b) redefine uncertainty brackets for century-scale projections; and c) provide a prioritized list of measurements, along with quantitative information on spatial and temporal resolution, required for reducing uncertainty in future sea level rise projections. Results indicate that ice sheet mass loss is dependent on the spatial resolution of key boundary conditions - such as bedrock topography and melt rates at the ice-ocean interface. This work is performed at and supported by the California Institute of Technology's Jet Propulsion Laboratory. Supercomputing time is also supported through a contract with the National Aeronautics and Space Administration's Cryosphere program.

Data assimilation and prognostic whole ice sheet modelling with the variationally derived, higher order, open source, and fully parallel ice sheet model VarGlaS

NASA Astrophysics Data System (ADS)

Brinkerhoff, D. J.; Johnson, J. V.

2013-07-01

We introduce a novel, higher order, finite element ice sheet model called VarGlaS (Variational Glacier Simulator), which is built on the finite element framework FEniCS. Contrary to standard procedure in ice sheet modelling, VarGlaS formulates ice sheet motion as the minimization of an energy functional, conferring advantages such as a consistent platform for making numerical approximations, a coherent relationship between motion and heat generation, and implicit boundary treatment. VarGlaS also solves the equations of enthalpy rather than temperature, avoiding the solution of a contact problem. Rather than include a lengthy model spin-up procedure, VarGlaS possesses an automated framework for model inversion. These capabilities are brought to bear on several benchmark problems in ice sheet modelling, as well as a 500 yr simulation of the Greenland ice sheet at high resolution. VarGlaS performs well in benchmarking experiments and, given a constant climate and a 100 yr relaxation period, predicts a mass evolution of the Greenland ice sheet that matches present-day observations of mass loss. VarGlaS predicts a thinning in the interior and thickening of the margins of the ice sheet.

The Milankovitch theory and climate sensitivity. I - Equilibrium climate model solutions for the present surface conditions. II - Interaction between the Northern Hemisphere ice sheets and the climate system

NASA Technical Reports Server (NTRS)

Neeman, Binyamin U.; Ohring, George; Joseph, Joachim H.

1988-01-01

A seasonal climate model was developed to test the climate sensitivity and, in particular, the Milankovitch (1941) theory. Four climate model versions were implemented to investigate the range of uncertainty in the parameterizations of three basic feedback mechanisms: the ice albedo-temperature, the outgoing long-wave radiation-temperature, and the eddy transport-meridional temperature gradient. It was found that the differences between the simulation of the present climate by the four versions were generally small, especially for annually averaged results. The climate model was also used to study the effect of growing/shrinking of a continental ice sheet, bedrock sinking/uplifting, and sea level changes on the climate system, taking also into account the feedback effects on the climate of the building of the ice caps.

Building clinical data groups for electronic medical record in China.

PubMed

Tu, Haibo; Yu, Yingtao; Yang, Peng; Tang, Xuejun; Hu, Jianping; Rao, Keqin; Pan, Feng; Xu, Yongyong; Liu, Danhong

2012-04-01

This article aims at building clinical data groups for Electronic Medical Records (EMR) in China. These data groups can be reused as basic information units in building the medical sheets of Electronic Medical Record Systems (EMRS) and serve as part of its implementation guideline. The results were based on medical sheets, the forms that are used in hospitals, which were collected from hospitals. To categorize the information in these sheets into data groups, we adopted the Health Level 7 Clinical Document Architecture Release 2 Model (HL7 CDA R2 Model). The regulations and legal documents concerning health informatics and related standards in China were implemented. A set of 75 data groups with 452 data elements was created. These data elements were atomic items that comprised the data groups. Medical sheet items contained clinical records information and could be described by standard data elements that exist in current health document protocols. These data groups match different units of the CDA model. Twelve data groups with 87 standardized data elements described EMR headers, and 63 data groups with 405 standardized data elements constituted the body. The later 63 data groups in fact formed the sections of the model. The data groups had two levels. Those at the first level contained both the second level data groups and the standardized data elements. The data groups were basically reusable information units that served as guidelines for building EMRS and that were used to rebuild a medical sheet and serve as templates for the clinical records. As a pilot study of health information standards in China, the development of EMR data groups combined international standards with Chinese national regulations and standards, and this was the most critical part of the research. The original medical sheets from hospitals contain first hand medical information, and some of their items reveal the data types characteristic of the Chinese socialist national health system. It is possible and critical to localize and stabilize the adopted international health standards through abstracting and categorizing those items for future sharing and for the implementation of EMRS in China.

Computational and Experimental Studies on β-Sheet Breakers Targeting Aβ1–40 Fibrils

PubMed Central

Minicozzi, Velia; Chiaraluce, Roberta; Consalvi, Valerio; Giordano, Cesare; Narcisi, Claudia; Punzi, Pasqualina; Rossi, Giancarlo C.; Morante, Silvia

2014-01-01

In this work we present and compare the results of extensive molecular dynamics simulations of model systems comprising an Aβ1–40 peptide in water in interaction with short peptides (β-sheet breakers) mimicking the 17–21 region of the Aβ1–40 sequence. Various systems differing in the customized β-sheet breaker structure have been studied. Specifically we have considered three kinds of β-sheet breakers, namely Ac-LPFFD-NH2 and two variants thereof, one obtained by substituting the acetyl group with the sulfonic amino acid taurine (Tau-LPFFD-NH2) and a second novel one in which the aspartic acid is substituted by an asparagine (Ac-LPFFN-NH2). Thioflavin T fluorescence, circular dichroism, and mass spectrometry experiments have been performed indicating that β-sheet breakers are able to inhibit in vitro fibril formation and prevent the β sheet folding of portions of the Aβ1–40 peptide. We show that molecular dynamics simulations and far UV circular dichroism provide consistent evidence that the new Ac-LPFFN-NH2 β-sheet breaker is more effective than the other two in stabilizing the native α-helix structure of Aβ1–40. In agreement with these results thioflavin T fluorescence experiments confirm the higher efficiency in inhibiting Aβ1–40 aggregation. Furthermore, mass spectrometry data and molecular dynamics simulations consistently identified the 17–21 Aβ1–40 portion as the location of the interaction region between peptide and the Ac-LPFFN-NH2 β-sheet breaker. PMID:24584938

Decadal-Scale Response of the Antarctic Ice sheet to a Warming Ocean using the POPSICLES Coupled Ice Sheet-Ocean model

NASA Astrophysics Data System (ADS)

Martin, D. F.; Asay-Davis, X.; Cornford, S. L.; Price, S. F.; Ng, E. G.; Collins, W.

2015-12-01

We present POPSICLES simulation results covering the full Antarctic Ice Sheet and the Southern Ocean spanning the period from 1990 to 2010. We use the CORE v. 2 interannual forcing data to force the ocean model. Simulations are performed at 0.1o(~5 km) ocean resolution with adaptive ice sheet resolution as fine as 500 m to adequately resolve the grounding line dynamics. We discuss the effect of improved ocean mixing and subshelf bathymetry (vs. the standard Bedmap2 bathymetry) on the behavior of the coupled system, comparing time-averaged melt rates below a number of major ice shelves with those reported in the literature. We also present seasonal variability and decadal melting trends from several Antarctic regions, along with the response of the ice shelves and the consequent dynamic response of the grounded ice sheet.POPSICLES couples the POP2x ocean model, a modified version of the Parallel Ocean Program, and the BISICLES ice-sheet model. POP2x includes sub-ice-shelf circulation using partial top cells and the commonly used three-equation boundary layer physics. Standalone POP2x output compares well with standard ice-ocean test cases (e.g., ISOMIP) and other continental-scale simulations and melt-rate observations. BISICLES makes use of adaptive mesh refinement and a 1st-order accurate momentum balance similar to the L1L2 model of Schoof and Hindmarsh to accurately model regions of dynamic complexity, such as ice streams, outlet glaciers, and grounding lines. Results of BISICLES simulations have compared favorably to comparable simulations with a Stokes momentum balance in both idealized tests (MISMIP-3d) and realistic configurations.The figure shows the BISICLES-computed vertically-integrated grounded ice velocity field 5 years into a 20-year coupled full-continent Antarctic-Southern-Ocean simulation. Submarine melt rates are painted onto the surface of the floating ice shelves. Grounding lines are shown in green.

Money-center structures in dynamic banking systems

NASA Astrophysics Data System (ADS)

Li, Shouwei; Zhang, Minghui

2016-10-01

In this paper, we propose a dynamic model for banking systems based on the description of balance sheets. It generates some features identified through empirical analysis. Through simulation analysis of the model, we find that banking systems have the feature of money-center structures, that bank asset distributions are power-law distributions, and that contract size distributions are log-normal distributions.

Modeling the effect of doping on the catalyst-assisted growth and field emission properties of plasma-grown graphene sheet

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gupta, Neha; Sharma, Suresh C.; Sharma, Rinku

A theoretical model describing the effect of doping on the plasma-assisted catalytic growth of graphene sheet has been developed. The model accounts the charging rate of the graphene sheet, kinetics of all the plasma species, including the doping species, and the growth rate of graphene nuclei and graphene sheet due to surface diffusion, and accretion of ions on the catalyst nanoparticle. Using the model, it is observed that nitrogen and boron doping can strongly influence the growth and field emission properties of the graphene sheet. The results of the present investigation indicate that nitrogen doping results in reduced thickness andmore » shortened height of the graphene sheet; however, boron doping increases the thickness and height of the graphene sheet. The time evolutions of the charge on the graphene sheet and hydrocarbon number density for nitrogen and boron doped graphene sheet have also been examined. The field emission properties of the graphene sheet have been proposed on the basis of the results obtained. It is concluded that nitrogen doped graphene sheet exhibits better field emission characteristics as compared to undoped and boron doped graphene sheet. The results of the present investigation are consistent with the existing experimental observations.« less

Geoscience laser altimeter system-stellar reference system

NASA Astrophysics Data System (ADS)

Millar, Pamela S.; Sirota, J. Marcos

1998-01-01

GLAS is an EOS space-based laser altimeter being developed to profile the height of the Earth's ice sheets with ~15 cm single shot accuracy from space under NASA's Mission to Planet Earth (MTPE). The primary science goal of GLAS is to determine if the ice sheets are increasing or diminishing for climate change modeling. This is achieved by measuring the ice sheet heights over Greenland and Antarctica to 1.5 cm/yr over 100 km×100 km areas by crossover analysis (Zwally 1994). This measurement performance requires the instrument to determine the pointing of the laser beam to ~5 urad (1 arcsecond), 1-sigma, with respect to the inertial reference frame. The GLAS design incorporates a stellar reference system (SRS) to relate the laser beam pointing angle to the star field with this accuracy. This is the first time a spaceborne laser altimeter is measuring pointing to such high accuracy. The design for the stellar reference system combines an attitude determination system (ADS) with a laser reference system (LRS) to meet this requirement. The SRS approach and expected performance are described in this paper.

Surface-Plasmon-Mediated Gradient Force Enhancement and Mechanical State Transitions of Graphene Sheets

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Peng; Shen, Nian-Hai; Koschny, Thomas

Graphene, a two-dimensional material possessing extraordinary properties in electronics as well as mechanics, provides a great platform for various optoelectronic and opto-mechanical devices. Here in this article, we theoretically study the optical gradient force arising from the coupling of surface plasmon modes on parallel graphene sheets, which can be several orders stronger than that between regular dielectric waveguides. Furthermore, with an energy functional optimization model, possible force-induced deformation of graphene sheets is calculated. We show that the significantly enhanced optical gradient force may lead to mechanical state transitions of graphene sheets, which are accompanied by abrupt changes in reflection andmore » transmission spectra of the system. Our demonstrations illustrate the potential for a broader graphene-related applications such as force sensors and actuators.« less

Surface-Plasmon-Mediated Gradient Force Enhancement and Mechanical State Transitions of Graphene Sheets

DOE PAGES

Zhang, Peng; Shen, Nian-Hai; Koschny, Thomas; ...

2016-12-16

Graphene, a two-dimensional material possessing extraordinary properties in electronics as well as mechanics, provides a great platform for various optoelectronic and opto-mechanical devices. Here in this article, we theoretically study the optical gradient force arising from the coupling of surface plasmon modes on parallel graphene sheets, which can be several orders stronger than that between regular dielectric waveguides. Furthermore, with an energy functional optimization model, possible force-induced deformation of graphene sheets is calculated. We show that the significantly enhanced optical gradient force may lead to mechanical state transitions of graphene sheets, which are accompanied by abrupt changes in reflection andmore » transmission spectra of the system. Our demonstrations illustrate the potential for a broader graphene-related applications such as force sensors and actuators.« less

Surface Energy and Mass Balance Model for Greenland Ice Sheet and Future Projections

NASA Astrophysics Data System (ADS)

Liu, Xiaojian

The Greenland Ice Sheet contains nearly 3 million cubic kilometers of glacial ice. If the entire ice sheet completely melted, sea level would raise by nearly 7 meters. There is thus considerable interest in monitoring the mass balance of the Greenland Ice Sheet. Each year, the ice sheet gains ice from snowfall and loses ice through iceberg calving and surface melting. In this thesis, we develop, validate and apply a physics based numerical model to estimate current and future surface mass balance of the Greenland Ice Sheet. The numerical model consists of a coupled surface energy balance and englacial model that is simple enough that it can be used for long time scale model runs, but unlike previous empirical parameterizations, has a physical basis. The surface energy balance model predicts ice sheet surface temperature and melt production. The englacial model predicts the evolution of temperature and meltwater within the ice sheet. These two models can be combined with estimates of precipitation (snowfall) to estimate the mass balance over the Greenland Ice Sheet. We first compare model performance with in-situ observations to demonstrate that the model works well. We next evaluate how predictions are degraded when we statistically downscale global climate data. We find that a simple, nearest neighbor interpolation scheme with a lapse rate correction is able to adequately reproduce melt patterns on the Greenland Ice Sheet. These results are comparable to those obtained using empirical Positive Degree Day (PDD) methods. Having validated the model, we next drove the ice sheet model using the suite of atmospheric model runs available through the CMIP5 atmospheric model inter-comparison, which in turn built upon the RCP 8.5 (business as usual) scenarios. From this exercise we predict how much surface melt production will increase in the coming century. This results in 4-10 cm sea level equivalent, depending on the CMIP5 models. Finally, we try to bound melt water production from CMIP5 data with the model by assuming that the Greenland Ice Sheet is covered in black carbon (lowering the albedo) and perpetually covered by optically thick clouds (increasing long wave radiation). This upper bound roughly triples surface meltwater production, resulting in 30 cm of sea level rise by 2100. These model estimates, combined with prior research suggesting an additional 40-100 cm of sea level rise associated with dynamical discharge, suggest that the Greenland Ice Sheet is poised to contribute significantly to sea level rise in the coming century.

Spin fluctuations and superconductivity in a 3D tight-binding model for BaFe2As2

DOE Office of Scientific and Technical Information (OSTI.GOV)

Graser, Siegfried; Kemper, Alexander F; Maier, Thomas A

2010-01-01

Despite the wealth of experimental data on the Fe-pnictide compounds of the KFe2As2 type, K=Ba, Ca, or Sr, the main theoretical work based on multiorbital tight-binding models has been restricted so far to the study of the related 1111 compounds. This can be ascribed to the more three-dimensional electronic structure found by ab initio calculations for the 122 materials, making this system less amenable to model development. In addition, the more complicated Brillouin zone BZ of the body-centered tetragonal symmetry does not allow a straightforward unfolding of the electronic band structure into an effective 1Fe/unit cell BZ. Here we presentmore » an effective five-orbital tight-binding fit of the full density functional theory band structure for BaFe2As2 including the kz dispersions. We compare the five-orbital spin fluctuation model to one previously studied for LaOFeAs and calculate the random-phase approximation enhanced susceptibility. Using the fluctuation ex- change approximation to determine the leading pairing instability, we then examine the differences between a strictly two-dimensional model calculation over a single kz cut of the BZ and a completely three-dimensional approach. We find pairing states quite similar to the 1111 materials, with generic quasi-isotropic pairing on the hole sheets and nodal states on the electron sheets at kz=0, which however are gapped as the system is hole doped. On the other hand, a substantial kz dependence of the order parameter remains, with most of the pairing strength deriving from processes near kz=?. These states exhibit a tendency for an enhanced anisotropy on the hole sheets and a reduced anisotropy on the electron sheets near the top of the BZ.« less

Application of GRACE to the assessment of model-based estimates of monthly Greenland Ice Sheet mass balance (2003-2012)

NASA Astrophysics Data System (ADS)

Schlegel, Nicole-Jeanne; Wiese, David N.; Larour, Eric Y.; Watkins, Michael M.; Box, Jason E.; Fettweis, Xavier; van den Broeke, Michiel R.

2016-09-01

Quantifying the Greenland Ice Sheet's future contribution to sea level rise is a challenging task that requires accurate estimates of ice sheet sensitivity to climate change. Forward ice sheet models are promising tools for estimating future ice sheet behavior, yet confidence is low because evaluation of historical simulations is challenging due to the scarcity of continental-wide data for model evaluation. Recent advancements in processing of Gravity Recovery and Climate Experiment (GRACE) data using Bayesian-constrained mass concentration ("mascon") functions have led to improvements in spatial resolution and noise reduction of monthly global gravity fields. Specifically, the Jet Propulsion Laboratory's JPL RL05M GRACE mascon solution (GRACE_JPL) offers an opportunity for the assessment of model-based estimates of ice sheet mass balance (MB) at ˜ 300 km spatial scales. Here, we quantify the differences between Greenland monthly observed MB (GRACE_JPL) and that estimated by state-of-the-art, high-resolution models, with respect to GRACE_JPL and model uncertainties. To simulate the years 2003-2012, we force the Ice Sheet System Model (ISSM) with anomalies from three different surface mass balance (SMB) products derived from regional climate models. Resulting MB is compared against GRACE_JPL within individual mascons. Overall, we find agreement in the northeast and southwest where MB is assumed to be primarily controlled by SMB. In the interior, we find a discrepancy in trend, which we presume to be related to millennial-scale dynamic thickening not considered by our model. In the northwest, seasonal amplitudes agree, but modeled mass trends are muted relative to GRACE_JPL. Here, discrepancies are likely controlled by temporal variability in ice discharge and other related processes not represented by our model simulations, i.e., hydrological processes and ice-ocean interaction. In the southeast, GRACE_JPL exhibits larger seasonal amplitude than predicted by the models while simultaneously having more pronounced trends; thus, discrepancies are likely controlled by a combination of missing processes and errors in both the SMB products and ISSM. At the margins, we find evidence of consistent intra-annual variations in regional MB that deviate distinctively from the SMB annual cycle. Ultimately, these monthly-scale variations, likely associated with hydrology or ice-ocean interaction, contribute to steeper negative mass trends observed by GRACE_JPL. Thus, models should consider such processes at relatively high (monthly-to-seasonal) temporal resolutions to achieve accurate estimates of Greenland MB.

Methods for Using Durable Adhesively Bonded Joints for Sandwich Structures

NASA Technical Reports Server (NTRS)

Smeltzer, Stanley S., III (Inventor); Lundgren, Eric C. (Inventor)

2016-01-01

Systems, methods, and apparatus for increasing durability of adhesively bonded joints in a sandwich structure. Such systems, methods, and apparatus includes an first face sheet and an second face sheet as well as an insert structure, the insert structure having a first insert face sheet, a second insert face sheet, and an insert core material. In addition, sandwich core material is arranged between the first face sheet and the second face sheet. A primary bondline may be coupled to the face sheet(s) and the splice. Further, systems, methods, and apparatus of the present disclosure advantageously reduce the load, provide a redundant path, reduce structural fatigue, and/or increase fatigue life.

An ice sheet model validation framework for the Greenland ice sheet.

PubMed

Price, Stephen F; Hoffman, Matthew J; Bonin, Jennifer A; Howat, Ian M; Neumann, Thomas; Saba, Jack; Tezaur, Irina; Guerber, Jeffrey; Chambers, Don P; Evans, Katherine J; Kennedy, Joseph H; Lenaerts, Jan; Lipscomb, William H; Perego, Mauro; Salinger, Andrew G; Tuminaro, Raymond S; van den Broeke, Michiel R; Nowicki, Sophie M J

2017-01-01

We propose a new ice sheet model validation framework - the Cryospheric Model Comparison Tool (CmCt) - that takes advantage of ice sheet altimetry and gravimetry observations collected over the past several decades and is applied here to modeling of the Greenland ice sheet. We use realistic simulations performed with the Community Ice Sheet Model (CISM) along with two idealized, non-dynamic models to demonstrate the framework and its use. Dynamic simulations with CISM are forced from 1991 to 2013 using combinations of reanalysis-based surface mass balance and observations of outlet glacier flux change. We propose and demonstrate qualitative and quantitative metrics for use in evaluating the different model simulations against the observations. We find that the altimetry observations used here are largely ambiguous in terms of their ability to distinguish one simulation from another. Based on basin- and whole-ice-sheet scale metrics, we find that simulations using both idealized conceptual models and dynamic, numerical models provide an equally reasonable representation of the ice sheet surface (mean elevation differences of <1 m). This is likely due to their short period of record, biases inherent to digital elevation models used for model initial conditions, and biases resulting from firn dynamics, which are not explicitly accounted for in the models or observations. On the other hand, we find that the gravimetry observations used here are able to unambiguously distinguish between simulations of varying complexity, and along with the CmCt, can provide a quantitative score for assessing a particular model and/or simulation. The new framework demonstrates that our proposed metrics can distinguish relatively better from relatively worse simulations and that dynamic ice sheet models, when appropriately initialized and forced with the right boundary conditions, demonstrate predictive skill with respect to observed dynamic changes occurring on Greenland over the past few decades. An extensible design will allow for continued use of the CmCt as future altimetry, gravimetry, and other remotely sensed data become available for use in ice sheet model validation.

Watershed modeling applications in south Texas

USGS Publications Warehouse

Pedraza, Diana E.; Ockerman, Darwin J.

2012-01-01

This fact sheet presents an overview of six selected watershed modeling studies by the USGS and partners that address a variety of water-resource issues in south Texas. These studies provide examples of modeling applications and demonstrate the usefulness and versatility of watershed models in aiding the understanding of hydrologic systems.

Sea-level response to melting of Antarctic ice shelves on multi-centennial timescales with the fast Elementary Thermomechanical Ice Sheet model (f.ETISh v1.0)

NASA Astrophysics Data System (ADS)

Pattyn, Frank

2017-08-01

The magnitude of the Antarctic ice sheet's contribution to global sea-level rise is dominated by the potential of its marine sectors to become unstable and collapse as a response to ocean (and atmospheric) forcing. This paper presents Antarctic sea-level response to sudden atmospheric and oceanic forcings on multi-centennial timescales with the newly developed fast Elementary Thermomechanical Ice Sheet (f.ETISh) model. The f.ETISh model is a vertically integrated hybrid ice sheet-ice shelf model with vertically integrated thermomechanical coupling, making the model two-dimensional. Its marine boundary is represented by two different flux conditions, coherent with power-law basal sliding and Coulomb basal friction. The model has been compared to existing benchmarks. Modelled Antarctic ice sheet response to forcing is dominated by sub-ice shelf melt and the sensitivity is highly dependent on basal conditions at the grounding line. Coulomb friction in the grounding-line transition zone leads to significantly higher mass loss in both West and East Antarctica on centennial timescales, leading to 1.5 m sea-level rise after 500 years for a limited melt scenario of 10 m a-1 under freely floating ice shelves, up to 6 m for a 50 m a-1 scenario. The higher sensitivity is attributed to higher ice fluxes at the grounding line due to vanishing effective pressure. Removing the ice shelves altogether results in a disintegration of the West Antarctic ice sheet and (partially) marine basins in East Antarctica. After 500 years, this leads to a 5 m and a 16 m sea-level rise for the power-law basal sliding and Coulomb friction conditions at the grounding line, respectively. The latter value agrees with simulations by DeConto and Pollard (2016) over a similar period (but with different forcing and including processes of hydrofracturing and cliff failure). The chosen parametrizations make model results largely independent of spatial resolution so that f.ETISh can potentially be integrated in large-scale Earth system models.

Assessing the Impact of Laurentide Ice-sheet Topography on Glacial Climate

NASA Technical Reports Server (NTRS)

Ullman, D. J.; LeGrande, A. N.; Carlson, A. E.; Anslow, F. S.; Licciardi, J. M.

2014-01-01

Simulations of past climates require altered boundary conditions to account for known shifts in the Earth system. For the Last Glacial Maximum (LGM) and subsequent deglaciation, the existence of large Northern Hemisphere ice sheets caused profound changes in surface topography and albedo. While ice-sheet extent is fairly well known, numerous conflicting reconstructions of ice-sheet topography suggest that precision in this boundary condition is lacking. Here we use a high-resolution and oxygen-isotopeenabled fully coupled global circulation model (GCM) (GISS ModelE2-R), along with two different reconstructions of the Laurentide Ice Sheet (LIS) that provide maximum and minimum estimates of LIS elevation, to assess the range of climate variability in response to uncertainty in this boundary condition.We present this comparison at two equilibrium time slices: the LGM, when differences in ice-sheet topography are maximized, and 14 ka, when differences in maximum ice-sheet height are smaller but still exist. Overall, we find significant differences in the climate response to LIS topography, with the larger LIS resulting in enhanced Atlantic Meridional Overturning Circulation and warmer surface air temperatures, particularly over northeastern Asia and the North Pacific. These up- and downstream effects are associated with differences in the development of planetary waves in the upper atmosphere, with the larger LIS resulting in a weaker trough over northeastern Asia that leads to the warmer temperatures and decreased albedo from snow and sea-ice cover. Differences between the 14 ka simulations are similar in spatial extent but smaller in magnitude, suggesting that climate is responding primarily to the larger difference in maximum LIS elevation in the LGM simulations. These results suggest that such uncertainty in ice-sheet boundary conditions alone may significantly impact the results of paleoclimate simulations and their ability to successfully simulate past climates, with implications for estimating climate sensitivity to greenhouse gas forcing utilizing past climate states.

Assessing the role of internal climate variability in Antarctica's contribution to future sea-level rise

NASA Astrophysics Data System (ADS)

Tsai, C. Y.; Forest, C. E.; Pollard, D.

2017-12-01

The Antarctic ice sheet (AIS) has the potential to be a major contributor to future sea-level rise (SLR). Current projections of SLR due to AIS mass loss remain highly uncertain. Better understanding of how ice sheets respond to future climate forcing and variability is essential for assessing the long-term risk of SLR. However, the predictability of future climate is limited by uncertainties from emission scenarios, model structural differences, and the internal variability that is inherently generated within the fully coupled climate system. Among those uncertainties, the impact of internal variability on the AIS changes has not been explicitly assessed. In this study, we quantify the effect of internal variability on the AIS evolutions by using climate fields from two large-ensemble experiments using the Community Earth System Model to force a three-dimensional ice sheet model. We find that internal variability of climate fields, particularly atmospheric fields, among ensemble members leads to significantly different AIS responses. Our results show that the internal variability can cause about 80 mm differences of AIS contribution to SLR by 2100 compared to the ensemble-mean contribution of 380-450 mm. Moreover, using ensemble-mean climate fields as the forcing in the ice sheet model does not produce realistic simulations of the ice loss. Instead, it significantly delays the onset of retreat of the West Antarctic Ice Sheet for up to 20 years and significantly underestimates the AIS contribution to SLR by 0.07-0.11 m in 2100 and up to 0.34 m in the 2250's. Therefore, because the uncertainty caused by internal variability is irreducible, we seek to highlight a critical need to assess the role of internal variability in projecting the AIS loss over the next few centuries. By quantifying the impact of internal variability on AIS contribution to SLR, policy makers can obtain more robust estimates of SLR and implement suitable adaptation strategies.

Implications for Crustal Structures and Heat Fluxes from Depth-to-the-Bottom of the Magnetic Source Estimates in West Antarctica, Amundsen Sea Sector

NASA Astrophysics Data System (ADS)

Dziadek, R.; Ferraccioli, F.; Gohl, K.; Spiegel, C.; Kaul, N. E.

2017-12-01

The West Antarctic Rift System is one of the least understood rift systems on earth, but displays a unique coupled relationship between tectonic processes and ice sheet dynamics. Geothermal heat flux (GHF) is a poorly constrained parameter in Antarctica and suspected to affect basal conditions of ice sheets, i.e., basal melting and subglacial hydrology. Thermomechanical models demonstrate the influential boundary condition of geothermal heat flux for (paleo) ice sheet stability. Young, continental rift systems are regions with significantly elevated geothermal heat flux (GHF), because the transient thermal perturbation to the lithosphere caused by rifting requires 100 Ma to reach long-term thermal equilibrium. We discuss airborne, high-resolution magnetic anomaly data from the Amundsen Sea Sector, to provide additional insight into deeper crustal structures related to the West Antarctic Rift System in the Amundsen/Bellingshausen sector. With the depth-to-the-bottom of the magnetic source (DBMS) estimates we reveal spatial changes at the bottom of the igneous crust and the thickness of the magnetic layer, which can be further incorporated into tectonic interpretations. The DBMS also marks an important temperature transition zone of approximately 580°C and therefore serves as a boundary condition for our numerical FEM thermal models in 2D and 3D.

The role of guide field on magnetic reconnection during island coalescence

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stanier, Adam John; Daughton, William Scott; Simakov, Andrei Nikolaevich

A number of studies have considered how the rate of magnetic reconnection scales in large and weakly collisional systems by the modelling of long reconnecting current sheets. However, this set-up neglects both the formation of the current sheet and the coupling between the diffusion region and a larger system that supplies the magnetic flux. Recent studies of magnetic island merging, which naturally include these features, have found that ion kinetic physics is crucial to describe the reconnection rate and global evolution of such systems. In this paper, the effect of a guide field on reconnection during island merging is considered.more » In contrast to the earlier current sheet studies, we identify a limited range of guide fields for which the reconnection rate, outflow velocity, and pile-up magnetic field increase in magnitude as the guide field increases. The Hall-MHD fluid model is found to reproduce kinetic reconnection rates only for a sufficiently strong guide field, for which ion inertia breaks the frozen-in condition and the outflow becomes Alfvénic in the kinetic system. The merging of large islands occurs on a longer timescale in the zero guide field limit, which may in part be due to a mirror-like instability that occurs upstream of the reconnection region.« less

The role of guide field on magnetic reconnection during island coalescence

DOE PAGES

Stanier, Adam John; Daughton, William Scott; Simakov, Andrei Nikolaevich; ...

2017-02-01

A number of studies have considered how the rate of magnetic reconnection scales in large and weakly collisional systems by the modelling of long reconnecting current sheets. However, this set-up neglects both the formation of the current sheet and the coupling between the diffusion region and a larger system that supplies the magnetic flux. Recent studies of magnetic island merging, which naturally include these features, have found that ion kinetic physics is crucial to describe the reconnection rate and global evolution of such systems. In this paper, the effect of a guide field on reconnection during island merging is considered.more » In contrast to the earlier current sheet studies, we identify a limited range of guide fields for which the reconnection rate, outflow velocity, and pile-up magnetic field increase in magnitude as the guide field increases. The Hall-MHD fluid model is found to reproduce kinetic reconnection rates only for a sufficiently strong guide field, for which ion inertia breaks the frozen-in condition and the outflow becomes Alfvénic in the kinetic system. The merging of large islands occurs on a longer timescale in the zero guide field limit, which may in part be due to a mirror-like instability that occurs upstream of the reconnection region.« less

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data Vehicle analysis Vehicle energy Vehicle modeling Vehicle simulation Wireless power transfer The NREL Systems Analysis and Integration Publications Systems Analysis and Integration Publications NREL publishes technical reports, fact sheets, and other documents about its systems analysis and

Calculations of axisymmetric vortex sheet roll-up using a panel and a filament model

NASA Technical Reports Server (NTRS)

Kantelis, J. P.; Widnall, S. E.

1986-01-01

A method for calculating the self-induced motion of a vortex sheet using discrete vortex elements is presented. Vortex panels and vortex filaments are used to simulate two-dimensional and axisymmetric vortex sheet roll-up. A straight forward application using vortex elements to simulate the motion of a disk of vorticity with an elliptic circulation distribution yields unsatisfactroy results where the vortex elements move in a chaotic manner. The difficulty is assumed to be due to the inability of a finite number of discrete vortex elements to model the singularity at the sheet edge and due to large velocity calculation errors which result from uneven sheet stretching. A model of the inner portion of the spiral is introduced to eliminate the difficulty with the sheet edge singularity. The model replaces the outermost portion of the sheet with a single vortex of equivalent circulation and a number of higher order terms which account for the asymmetry of the spiral. The resulting discrete vortex model is applied to both two-dimensional and axisymmetric sheets. The two-dimensional roll-up is compared to the solution for a semi-infinite sheet with good results.

Styles of Deformation on Either Side of a Ridge-Transform Intersection, Troodos Ophiolite, Cyprus

NASA Astrophysics Data System (ADS)

Titus, S.; Wagner, C.; Alexander, S. O.; Scott, C. P.; Davis, J. R.

2015-12-01

The Troodos ophiolite in Cyprus includes two orthogonal structures - the NS-striking Solea graben and the EW-striking Arakapas fault - that form a ridge-transform intersection. Sheeted dikes and gabbros are preserved on both the inside and outside corners providing a view of mid-crustal deformation in the system. We examine and model these patterns of deformation using existing map and paleomagnetic data combined with new rock magnetic data. The inside corner of the system has been well studied. The most notable feature is the changing orientation of sheeted dikes, which shift from NW- to NE- to E-striking with increasing proximity to the Arakapas fault. Paleomagnetic data from many studies, including our own, show declination anomalies that vary with distance from the ridge and the transform. The three principal axes from anisotropy of magnetic susceptibility (AMS) ellipsoids in the gabbros seem to be correlated with local sheeted dike orientations. The outside corner of the system has been less well studied. Sheeted dike orientations change more subtly; many are NS-striking and dip towards the Solea Graben, but near the inferred ridge-transform intersection, they are NNE-striking. Our new paleomagnetic data from 26 sites record declination and inclination anomalies that vary spatially within the outside corner. AMS data from the gabbros and sheeted dikes again seem loosely linked to sheeted dike orientations. To summarize, the structural and rock magnetic results on either side of the Solea Graben are distinct, confirming the idea that these rocks formed on different sides of a ridge-transform system. The paleomagnetic data yield insights about the styles of deformation following crystallization. The AMS data may yield insights about magmatic plumbing systems when combined systematically with paleomagnetic results. Our results from the outside corner show that patterns of deformation can be complex even on the non-plate boundary side of a ridge-transform system.

A panel method study of vortex sheets with special emphasis on sheets of axisymmetric geometry. M.S. Thesis

NASA Technical Reports Server (NTRS)

Sugioka, I.; Widnall, S. E.

1985-01-01

The self induced evolution of a vortex sheet was simulated by modeling the sheet using an integration of discrete elements of vorticity. Replacing small sections of a vortex sheet by flat panels of constant vorticity is found to reproduce more accurately the initial conditions for the Lagrangian simulation technique than replacement by point vortices. The flat panel method for the vortex sheet was then extended to model axisymmetric vortex sheets. The local and far field velocities induced by the axisymmetric panels were obtained using matched asymptotic analysis, and some of the uncertainties involved in other models of the axisymmetric vortex sheet have been eliminated. One important result of this analysis is the determination of the proper choice of core size for a circular vortex filament which may replace a section of an axisymmetric vortex sheet. Roll-up of both two dimensional and axisymmetric vortex sheets was computed using the panel methods developed in the report.

Power Systems and Energy Storage Modeling for Directed Energy Weapons

DTIC Science & Technology

2014-06-01

neodymium or ytterbium doped yttrium aluminum garnet (YAG) crystal.6 The Maritime Laser Demonstration (MLD) features several 15 kW slab lasers combined...The laser substrate is similar to a fiber optic cable that is doped with a rare earth element (typically neodymium or ytterbium); many fibers can be...but with different elements. A typical construction consists of a sheet of Lithium- cobalt -oxide and a sheet of carbon separated by an insulator

Insolation-driven 100,000-year glacial cycles and hysteresis of ice-sheet volume.

PubMed

Abe-Ouchi, Ayako; Saito, Fuyuki; Kawamura, Kenji; Raymo, Maureen E; Okuno, Jun'ichi; Takahashi, Kunio; Blatter, Heinz

2013-08-08

The growth and reduction of Northern Hemisphere ice sheets over the past million years is dominated by an approximately 100,000-year periodicity and a sawtooth pattern (gradual growth and fast termination). Milankovitch theory proposes that summer insolation at high northern latitudes drives the glacial cycles, and statistical tests have demonstrated that the glacial cycles are indeed linked to eccentricity, obliquity and precession cycles. Yet insolation alone cannot explain the strong 100,000-year cycle, suggesting that internal climatic feedbacks may also be at work. Earlier conceptual models, for example, showed that glacial terminations are associated with the build-up of Northern Hemisphere 'excess ice', but the physical mechanisms underpinning the 100,000-year cycle remain unclear. Here we show, using comprehensive climate and ice-sheet models, that insolation and internal feedbacks between the climate, the ice sheets and the lithosphere-asthenosphere system explain the 100,000-year periodicity. The responses of equilibrium states of ice sheets to summer insolation show hysteresis, with the shape and position of the hysteresis loop playing a key part in determining the periodicities of glacial cycles. The hysteresis loop of the North American ice sheet is such that after inception of the ice sheet, its mass balance remains mostly positive through several precession cycles, whose amplitudes decrease towards an eccentricity minimum. The larger the ice sheet grows and extends towards lower latitudes, the smaller is the insolation required to make the mass balance negative. Therefore, once a large ice sheet is established, a moderate increase in insolation is sufficient to trigger a negative mass balance, leading to an almost complete retreat of the ice sheet within several thousand years. This fast retreat is governed mainly by rapid ablation due to the lowered surface elevation resulting from delayed isostatic rebound, which is the lithosphere-asthenosphere response. Carbon dioxide is involved, but is not determinative, in the evolution of the 100,000-year glacial cycles.

The Plasma Sheet as Natural Symmetry Plane for Dipolarization Fronts in the Earth's Magnetotail

NASA Astrophysics Data System (ADS)

Frühauff, D.; Glassmeier, K.-H.

2017-11-01

In this work, observations of multispacecraft mission Time History of Events and Macroscale Interactions during Substorms are used for statistical investigation of dipolarization fronts in the near-Earth plasma sheet of the magnetotail. Using very stringent criteria, 460 events are detected in almost 10 years of mission data. Minimum variance analysis is used to determine the normal directions of the phase fronts, providing evidence for the existence of a natural symmetry of these phenomena, given by the neutral sheet of the magnetotail. This finding enables the definition of a local coordinate system based on the Tsyganenko model, reflecting the intrinsic orientation of the neutral sheet and, therefore, the dipolarization fronts. In this way, the comparison of events with very different background conditions is improved. Through this study, the statistical results of Liu, Angelopoulos, Runov, et al. (2013) are both confirmed and extended. In a case study, the knowledge of this plane of symmetry helps to explain the concave curvature of dipolarization fronts in the XZ plane through phase propagation speeds of magnetoacoustic waves. A second case study is presented to determine the central current system of a passing dipolarization front through a constellation of three spacecraft. With this information, a statistical analysis of spacecraft observations above and below the neutral sheet is used to provide further evidence for the neutral sheet as the symmetry plane and the central current system. Furthermore, it is shown that the signatures of dipolarization fronts are under certain conditions closely related to that of flux ropes, indicating a possible relationship between these two transient phenomena.

Coupled ice sheet - climate simulations of the last glacial inception and last glacial maximum with a model of intermediate complexity that includes a dynamical downscaling of heat and moisture

NASA Astrophysics Data System (ADS)

Quiquet, Aurélien; Roche, Didier M.

2017-04-01

Comprehensive fully coupled ice sheet - climate models allowing for multi-millenia transient simulations are becoming available. They represent powerful tools to investigate ice sheet - climate interactions during the repeated retreats and advances of continental ice sheets of the Pleistocene. However, in such models, most of the time, the spatial resolution of the ice sheet model is one order of magnitude lower than the one of the atmospheric model. As such, orography-induced precipitation is only poorly represented. In this work, we briefly present the most recent improvements of the ice sheet - climate coupling within the model of intermediate complexity iLOVECLIM. On the one hand, from the native atmospheric resolution (T21), we have included a dynamical downscaling of heat and moisture at the ice sheet model resolution (40 km x 40 km). This downscaling accounts for feedbacks of sub-grid precipitation on large scale energy and water budgets. From the sub-grid atmospheric variables, we compute an ice sheet surface mass balance required by the ice sheet model. On the other hand, we also explicitly use oceanic temperatures to compute sub-shelf melting at a given depth. Based on palaeo evidences for rate of change of eustatic sea level, we discuss the capability of our new model to correctly simulate the last glacial inception ( 116 kaBP) and the ice volume of the last glacial maximum ( 21 kaBP). We show that the model performs well in certain areas (e.g. Canadian archipelago) but some model biases are consistent over time periods (e.g. Kara-Barents sector). We explore various model sensitivities (e.g. initial state, vegetation, albedo) and we discuss the importance of the downscaling of precipitation for ice nucleation over elevated area and for the surface mass balance of larger ice sheets.

Interaction of ice sheets and climate during the past 800 000 years

NASA Astrophysics Data System (ADS)

Stap, L. B.; van de Wal, R. S. W.; de Boer, B.; Bintanja, R.; Lourens, L. J.

2014-12-01

During the Cenozoic, land ice and climate interacted on many different timescales. On long timescales, the effect of land ice on global climate and sea level is mainly set by large ice sheets in North America, Eurasia, Greenland and Antarctica. The climatic forcing of these ice sheets is largely determined by the meridional temperature profile resulting from radiation and greenhouse gas (GHG) forcing. As a response, the ice sheets cause an increase in albedo and surface elevation, which operates as a feedback in the climate system. To quantify the importance of these climate-land ice processes, a zonally averaged energy balance climate model is coupled to five one-dimensional ice sheet models, representing the major ice sheets. In this study, we focus on the transient simulation of the past 800 000 years, where a high-confidence CO2 record from ice core samples is used as input in combination with Milankovitch radiation changes. We obtain simulations of atmospheric temperature, ice volume and sea level that are in good agreement with recent proxy-data reconstructions. We examine long-term climate-ice-sheet interactions by a comparison of simulations with uncoupled and coupled ice sheets. We show that these interactions amplify global temperature anomalies by up to a factor of 2.6, and that they increase polar amplification by 94%. We demonstrate that, on these long timescales, the ice-albedo feedback has a larger and more global influence on the meridional atmospheric temperature profile than the surface-height-temperature feedback. Furthermore, we assess the influence of CO2 and insolation by performing runs with one or both of these variables held constant. We find that atmospheric temperature is controlled by a complex interaction of CO2 and insolation, and both variables serve as thresholds for northern hemispheric glaciation.

A Description of Local Time Asymmetries in the Kronian Current Sheet

NASA Astrophysics Data System (ADS)

Nickerson, J. S.; Hansen, K. C.; Gombosi, T. I.

2012-12-01

Cassini observations imply that Saturn's magnetospheric current sheet is displaced northward above the rotational equator [C.S. Arridge et al., Warping of Saturn's magnetospheric and magnetotail current sheets, Journal of Geophysical Research, Vol. 113, August 2008]. Arridge et al. show that this hinging of the current sheet above the equator occurs over the noon, midnight, and dawn local time sectors. They present an azimuthally independent model to describe this paraboloid-like geometry. We have used our global MHD model, BATS-R-US/SWMF, to study Saturn's magnetospheric current sheet under various solar wind dynamic pressure and solar zenith angle conditions. We show that under reasonable conditions the current sheet does take on the basic shape of the Arridge model in the noon, midnight, and dawn sectors. However, the hinging distance parameter used in the Arridge model is not a constant and does in fact vary in Saturn local time. We recommend that the Arridge model should be adjusted to account for this azimuthal dependence. Arridge et al. does not discuss the shape of the current sheet in the dusk sector due to an absence of data but does presume that the current sheet will assume the same geometry in this region. On the contrary, our model shows that this is not the case. On the dusk side the current sheet hinges (aggressively) southward and cannot be accounted for by the Arridge model. We will present results from our simulations showing the deviation from axisymmetry and the general behavior of the current sheet under different conditions.

Modeling the transition between upper plane bed regime and sheet flow without an active layer formulation. Preliminary results.

NASA Astrophysics Data System (ADS)

Viparelli, E.; Hernandez Moreira, R. R.; Blom, A.

2015-12-01

A perusal of the literature on bedload transport revealed that, notwithstanding the large number of studies on bedform morphology performed in the past decades, the upper plane bed regime has not been thoroughly investigated and the distinction between the upper plane bed and sheet flow transport regimes is still poorly defined. Previous experimental work demonstrated that the upper plane bed regime is characterized by long wavelength and small amplitude bedforms that migrate downstream. These bedforms, however, were not observed in experiments on sheet flow transport suggesting that the upper plane bed and the sheet flow are two different regimes. We thus designed and performed experiments in a sediment feed flume in the hydraulic laboratory of the Department of Civil and Environmental Engineering at the University of South Carolina at Columbia to study the transition from upper plane bed to sheet flow regime. Periodic measurements of water surface and bed elevation, bedform geometry and thicknesses of the bedload layer were performed by eyes, and with cameras, movies and a system of six ultrasonic probes that record the variations of bed elevation at a point over time. We used the time series of bed elevations to determine the probability functions of bed elevation. These probability functions are implemented in a continuous model of river morphodynamics, i.e. a model that does not use the active layer approximation to describe the sediment fluxes between the bedload and the deposit and that should thus be able to capture the details of the vertical and streamwise variation of the deposit grain size distribution. This model is validated against the experimental results for the case of uniform material. We then use the validated model in the attempt to study if and how the spatial distribution of grain sizes in the deposit changes from upper plane bed regime to sheet flow and if these results are influenced by the imposed rates of base level rise.

Experimental design for three interrelated marine ice sheet and ocean model intercomparison projects: MISMIP v. 3 (MISMIP +), ISOMIP v. 2 (ISOMIP +) and MISOMIP v. 1 (MISOMIP1)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Asay-Davis, Xylar S.; Cornford, Stephen L.; Durand, Gaël

Coupled ice sheet-ocean models capable of simulating moving grounding lines are just becoming available. Such models have a broad range of potential applications in studying the dynamics of marine ice sheets and tidewater glaciers, from process studies to future projections of ice mass loss and sea level rise. The Marine Ice Sheet-Ocean Model Intercomparison Project (MISOMIP) is a community effort aimed at designing and coordinating a series of model intercomparison projects (MIPs) for model evaluation in idealized setups, model verification based on observations, and future projections for key regions of the West Antarctic Ice Sheet (WAIS). Here we describe computationalmore » experiments constituting three interrelated MIPs for marine ice sheet models and regional ocean circulation models incorporating ice shelf cavities. These consist of ice sheet experiments under the Marine Ice Sheet MIP third phase (MISMIP+), ocean experiments under the Ice Shelf-Ocean MIP second phase (ISOMIP+) and coupled ice sheet-ocean experiments under the MISOMIP first phase (MISOMIP1). All three MIPs use a shared domain with idealized bedrock topography and forcing, allowing the coupled simulations (MISOMIP1) to be compared directly to the individual component simulations (MISMIP+ and ISOMIP+). The experiments, which have qualitative similarities to Pine Island Glacier Ice Shelf and the adjacent region of the Amundsen Sea, are designed to explore the effects of changes in ocean conditions, specifically the temperature at depth, on basal melting and ice dynamics. In future work, differences between model results will form the basis for the evaluation of the participating models.« less

Investigation on the individual contributions of N-H...O=C and C-H...O=C interactions to the binding energies of beta-sheet models.

PubMed

Wang, Chang-Sheng; Sun, Chang-Liang

2010-04-15

In this article, the binding energies of 16 antiparallel and parallel beta-sheet models are estimated using the analytic potential energy function we proposed recently and the results are compared with those obtained from MP2, AMBER99, OPLSAA/L, and CHARMM27 calculations. The comparisons indicate that the analytic potential energy function can produce reasonable binding energies for beta-sheet models. Further comparisons suggest that the binding energy of the beta-sheet models might come mainly from dipole-dipole attractive and repulsive interactions and VDW interactions between the two strands. The dipole-dipole attractive and repulsive interactions are further obtained in this article. The total of N-H...H-N and C=O...O=C dipole-dipole repulsive interaction (the secondary electrostatic repulsive interaction) in the small ring of the antiparallel beta-sheet models is estimated to be about 6.0 kcal/mol. The individual N-H...O=C dipole-dipole attractive interaction is predicted to be -6.2 +/- 0.2 kcal/mol in the antiparallel beta-sheet models and -5.2 +/- 0.6 kcal/mol in the parallel beta-sheet models. The individual C(alpha)-H...O=C attractive interaction is -1.2 +/- 0.2 kcal/mol in the antiparallel beta-sheet models and -1.5 +/- 0.2 kcal/mol in the parallel beta-sheet models. These values are important in understanding the interactions at protein-protein interfaces and developing a more accurate force field for peptides and proteins. 2009 Wiley Periodicals, Inc.

Global sea-level change during the next 10,000 years: the end of an icehouse?

NASA Astrophysics Data System (ADS)

Van Breedam, Jonas; Huybrechts, Philippe; Goelzer, Heiko; Loutre, Marie-France; Fichefet, Thierry

2015-04-01

Because of the long life-time of atmospheric CO2, any realized future warming is likely to persist for many centuries to millennia. As a consequence, sea-level rise will continue on a multi-millennial timescale, especially from the slower components such as oceanic thermal expansion and above all, from melting of the Greenland and Antarctic ice sheets. The two polar ice sheets have the potential to produce a global eustatic sea-level rise of about 65 m, at least an order of magnitude larger than thermal expansion under extreme forcing scenarios. Other components contributing to sea-level change are the melting of glaciers and ice caps and haline contraction of the ocean from fresh water delivery from land ice, but are less important. We have made projections of future sea-level rise over the next 10,000 years with the Earth System Model of Intermediate Complexity LOVECLIM, which includes high resolution models of the Greenland and Antarctic ice sheets. Four different model parameter sets are considered to explore the model uncertainty. The climate forcing is based on prolonged Radiative Concentration Pathway (RCP) scenarios with an assumed exponential falloff for carbon dioxide concentrations according to global carbon cycle simulations. Six different forcing scenarios are constructed where the highest scenario includes a positive feedback due to the destabilization of methane hydrates and the subsequent emission of methane. By far the largest contribution in the global sea-level projections arises from the polar ice sheets. For the Greenland ice sheet, the ablation is larger than the accumulation for all forcing scenarios shortly after the start of the experiments. The ice sheet continuously melts and nearly disappears in all cases. The Antarctic ice sheet grows during the first decades under low to intermediate forcing scenarios due to increased accumulation. However, the spread between the different scenarios is very large. Under the highest prolonged RCP scenario (and in case methane hydrate starts to destabilize), the model uncertainty does not exclude melting of the entire Antarctic ice sheet after 10,000 years. This would mark the end of the present icehouse, which has existed for about 34 Myr, and would raise global sea-level by up to 70 m from all contributions combined.

Marine Isotope Stage 11 : The Role of Co2, Insolation and Antarctica Ice Sheet On This Interglacial

NASA Astrophysics Data System (ADS)

Raynaud, D.; Loutre, M. F.; Ritz, C.; Barnola, J.-M.; Berger, A.; Chappellaz, J.; Jouzel, J.; Lipenkov, V.; Petit, J.-R.; Vimeux, F.

The Marine Isotopic Stage 11 (MIS 11), around 400kyr BP ago, has been suggested as an analogue for a future climate under natural forcing because of the similar condi- tions of orbitally driven insolation during this interglacial period and the one covering the Holocene and the near future. There are many open questions about unusual MIS 11 climatic conditions (length of the interglacial, temperature, sea level, marine car- bonate system), as recorded in different marine and continental records. The Antarctic Vostok ice core provides the only atmospheric record extending back to MIS 11 and we use it to discuss the Antarctic temperature, the atmospheric CO2 concentration and the ice sheet stability in the central part of East Antarctica during this interglacial. The unique nature of the Vostok atmospheric record leads us to use the available Vos- tok data to drive climate and ice sheet models for MIS 11. A model of intermediate complexity (LLN-2D model) is used to investigate the sensitivity of the simulated MIS 11 deglaciation to the interplay between insolation and CO2. It is shown that the length of the simulated interglacial depends strongly on the phasing between these two climate forcings. We also investigate the response of the Antarctic Ice Sheet to changing climate through simulations performed with the LGGE 3-D ice sheet model. The results indicate that sea level stands during MIS 11 as high as 20 m. above present level, as suggested by different elevated marine terraces, cannot be explained, except by assuming that MIS 11 was very dry over Antarctica.

Amyloid β-sheet mimics that antagonize protein aggregation and reduce amyloid toxicity

NASA Astrophysics Data System (ADS)

Cheng, Pin-Nan; Liu, Cong; Zhao, Minglei; Eisenberg, David; Nowick, James S.

2012-11-01

The amyloid protein aggregation associated with diseases such as Alzheimer's, Parkinson's and type II diabetes (among many others) features a bewildering variety of β-sheet-rich structures in transition from native proteins to ordered oligomers and fibres. The variation in the amino-acid sequences of the β-structures presents a challenge to developing a model system of β-sheets for the study of various amyloid aggregates. Here, we introduce a family of robust β-sheet macrocycles that can serve as a platform to display a variety of heptapeptide sequences from different amyloid proteins. We have tailored these amyloid β-sheet mimics (ABSMs) to antagonize the aggregation of various amyloid proteins, thereby reducing the toxicity of amyloid aggregates. We describe the structures and inhibitory properties of ABSMs containing amyloidogenic peptides from the amyloid-β peptide associated with Alzheimer's disease, β2-microglobulin associated with dialysis-related amyloidosis, α-synuclein associated with Parkinson's disease, islet amyloid polypeptide associated with type II diabetes, human and yeast prion proteins, and Tau, which forms neurofibrillary tangles.

Evidence for Two Separate Heliospheric Current Sheets of Cylindrical Shape During Mid-2012

NASA Astrophysics Data System (ADS)

Wang, Y.-M.; Young, P. R.; Muglach, K.

2014-01-01

During the reversal of the Sun's polar fields at sunspot maximum, outward extrapolations of magnetograph measurements often predict the presence of two or more current sheets extending into the interplanetary medium, instead of the single heliospheric current sheet (HCS) that forms the basis of the standard "ballerina skirt" picture. By comparing potential-field source-surface models of the coronal streamer belt with white-light coronagraph observations, we deduce that the HCS was split into two distinct structures with circular cross sections during mid-2012. These cylindrical current sheets were centered near the heliographic equator and separated in longitude by roughly 180° a corresponding four-sector polarity pattern was observed at Earth. Each cylinder enclosed a negative-polarity coronal hole that was identifiable in extreme ultraviolet images and gave rise to a high-speed stream. The two current sheet systems are shown to be a result of the dominance of the Sun's nonaxisymmetric quadrupole component, as the axial dipole field was undergoing its reversal during solar cycle 24.

Stabilization of Inviscid Vortex Sheets

NASA Astrophysics Data System (ADS)

Protas, Bartosz; Sakajo, Takashi

2017-11-01

In this study we investigate the problem of stabilizing inviscid vortex sheets via feedback control. Such models, expressed in terms of the Birkhoff-Rott equation, are often used to describe the Kevin-Helmholtz instability of shear layers and are known to be strongly unstable to small-scale perturbations. First, we consider the linear stability of a straight vortex sheet in the periodic setting with actuation in the form of an array of point vortices or sources located a certain distance away from the sheet. We establish conditions under which this system is controllable and observable. Next, using methods of the linear control theory, we synthesize a feedback control strategy which stabilizes a straight vortex sheet in the linear regime. Given the poor conditioning of the discretized problem, reliable solution of the resulting algebraic Riccati equation requires the use of high-precision arithmetic. Finally, we demonstrate that this control approach also succeeds in the nonlinear regime, provided the magnitude of the initial perturbation is sufficiently small.

Evidence for Two Separate Heliospheric Current Sheets of Cylindrical Shape During Mid-2012

NASA Technical Reports Server (NTRS)

Wang, Y.-M.; Young, P. R.; Muglach, K.

2013-01-01

During the reversal of the Sun's polar fields at sunspot maximum, outward extrapolations of magnetograph measurements often predict the presence of two or more current sheets extending into the interplanetary medium, instead of the single heliospheric current sheet (HCS) that forms the basis of the standard 'ballerina skirt' picture. By comparing potential-field source-surface models of the coronal streamer belt with white-light coronagraph observations, we deduce that the HCS was split into two distinct structures with circular cross sections during mid-2012. These cylindrical current sheets were centered near the heliographic equator and separated in longitude by roughly 180 deg; a corresponding four-sector polarity pattern was observed at Earth. Each cylinder enclosed a negative-polarity coronal hole that was identifiable in extreme ultraviolet images and gave rise to a high-speed stream. The two current sheet systems are shown to be a result of the dominance of the Sun's nonaxisymmetric quadrupole component, as the axial dipole field was undergoing its reversal during solar cycle 24.

An ice sheet model validation framework for the Greenland ice sheet

NASA Astrophysics Data System (ADS)

Price, Stephen F.; Hoffman, Matthew J.; Bonin, Jennifer A.; Howat, Ian M.; Neumann, Thomas; Saba, Jack; Tezaur, Irina; Guerber, Jeffrey; Chambers, Don P.; Evans, Katherine J.; Kennedy, Joseph H.; Lenaerts, Jan; Lipscomb, William H.; Perego, Mauro; Salinger, Andrew G.; Tuminaro, Raymond S.; van den Broeke, Michiel R.; Nowicki, Sophie M. J.

2017-01-01

We propose a new ice sheet model validation framework - the Cryospheric Model Comparison Tool (CmCt) - that takes advantage of ice sheet altimetry and gravimetry observations collected over the past several decades and is applied here to modeling of the Greenland ice sheet. We use realistic simulations performed with the Community Ice Sheet Model (CISM) along with two idealized, non-dynamic models to demonstrate the framework and its use. Dynamic simulations with CISM are forced from 1991 to 2013, using combinations of reanalysis-based surface mass balance and observations of outlet glacier flux change. We propose and demonstrate qualitative and quantitative metrics for use in evaluating the different model simulations against the observations. We find that the altimetry observations used here are largely ambiguous in terms of their ability to distinguish one simulation from another. Based on basin-scale and whole-ice-sheet-scale metrics, we find that simulations using both idealized conceptual models and dynamic, numerical models provide an equally reasonable representation of the ice sheet surface (mean elevation differences of < 1 m). This is likely due to their short period of record, biases inherent to digital elevation models used for model initial conditions, and biases resulting from firn dynamics, which are not explicitly accounted for in the models or observations. On the other hand, we find that the gravimetry observations used here are able to unambiguously distinguish between simulations of varying complexity, and along with the CmCt, can provide a quantitative score for assessing a particular model and/or simulation. The new framework demonstrates that our proposed metrics can distinguish relatively better from relatively worse simulations and that dynamic ice sheet models, when appropriately initialized and forced with the right boundary conditions, demonstrate a predictive skill with respect to observed dynamic changes that have occurred on Greenland over the past few decades. An extensible design will allow for continued use of the CmCt as future altimetry, gravimetry, and other remotely sensed data become available for use in ice sheet model validation.

An ice sheet model validation framework for the Greenland ice sheet

DOE Office of Scientific and Technical Information (OSTI.GOV)

Price, Stephen F.; Hoffman, Matthew J.; Bonin, Jennifer A.

We propose a new ice sheet model validation framework the Cryospheric Model Comparison Tool (CMCT) that takes advantage of ice sheet altimetry and gravimetry observations collected over the past several decades and is applied here to modeling of the Greenland ice sheet. We use realistic simulations performed with the Community Ice Sheet Model (CISM) along with two idealized, non-dynamic models to demonstrate the framework and its use. Dynamic simulations with CISM are forced from 1991 to 2013 using combinations of reanalysis-based surface mass balance and observations of outlet glacier flux change. We propose and demonstrate qualitative and quanti- tative metricsmore » for use in evaluating the different model simulations against the observations. We find 10 that the altimetry observations used here are largely ambiguous in terms of their ability to distinguish one simulation from another. Based on basin- and whole-ice-sheet scale metrics, the model initial condition as well as output from idealized and dynamic models all provide an equally reasonable representation of the ice sheet surface (mean elevation differences of <1 m). This is likely due to their short period of record, biases inherent to digital elevation models used for model initial conditions, and biases resulting from firn dynamics, which are not explicitly accounted for in the models or observations. On the other hand, we find that the gravimetry observations used here are able to unambiguously distinguish between simulations of varying complexity, and along with the CMCT, can provide a quantitative score for assessing a particular model and/or simulation. The new framework demonstrates that our proposed metrics can distinguish relatively better from relatively worse simulations and that dynamic ice sheet models, when appropriately initialized and forced with the right boundary conditions, demonstrate predictive skill with respect to observed dynamic changes occurring on Greenland over the past few decades. An extensible design will allow for continued use of the CMCT as future altimetry, gravimetry, and other remotely sensed data become available for use in ice sheet model validation.« less

An ice sheet model validation framework for the Greenland ice sheet

DOE PAGES

Price, Stephen F.; Hoffman, Matthew J.; Bonin, Jennifer A.; ...

2017-01-17

We propose a new ice sheet model validation framework the Cryospheric Model Comparison Tool (CMCT) that takes advantage of ice sheet altimetry and gravimetry observations collected over the past several decades and is applied here to modeling of the Greenland ice sheet. We use realistic simulations performed with the Community Ice Sheet Model (CISM) along with two idealized, non-dynamic models to demonstrate the framework and its use. Dynamic simulations with CISM are forced from 1991 to 2013 using combinations of reanalysis-based surface mass balance and observations of outlet glacier flux change. We propose and demonstrate qualitative and quanti- tative metricsmore » for use in evaluating the different model simulations against the observations. We find 10 that the altimetry observations used here are largely ambiguous in terms of their ability to distinguish one simulation from another. Based on basin- and whole-ice-sheet scale metrics, the model initial condition as well as output from idealized and dynamic models all provide an equally reasonable representation of the ice sheet surface (mean elevation differences of <1 m). This is likely due to their short period of record, biases inherent to digital elevation models used for model initial conditions, and biases resulting from firn dynamics, which are not explicitly accounted for in the models or observations. On the other hand, we find that the gravimetry observations used here are able to unambiguously distinguish between simulations of varying complexity, and along with the CMCT, can provide a quantitative score for assessing a particular model and/or simulation. The new framework demonstrates that our proposed metrics can distinguish relatively better from relatively worse simulations and that dynamic ice sheet models, when appropriately initialized and forced with the right boundary conditions, demonstrate predictive skill with respect to observed dynamic changes occurring on Greenland over the past few decades. An extensible design will allow for continued use of the CMCT as future altimetry, gravimetry, and other remotely sensed data become available for use in ice sheet model validation.« less

An ice sheet model validation framework for the Greenland ice sheet

PubMed Central

Price, Stephen F.; Hoffman, Matthew J.; Bonin, Jennifer A.; Howat, Ian M.; Neumann, Thomas; Saba, Jack; Tezaur, Irina; Guerber, Jeffrey; Chambers, Don P.; Evans, Katherine J.; Kennedy, Joseph H.; Lenaerts, Jan; Lipscomb, William H.; Perego, Mauro; Salinger, Andrew G.; Tuminaro, Raymond S.; van den Broeke, Michiel R.; Nowicki, Sophie M. J.

2018-01-01

We propose a new ice sheet model validation framework – the Cryospheric Model Comparison Tool (CmCt) – that takes advantage of ice sheet altimetry and gravimetry observations collected over the past several decades and is applied here to modeling of the Greenland ice sheet. We use realistic simulations performed with the Community Ice Sheet Model (CISM) along with two idealized, non-dynamic models to demonstrate the framework and its use. Dynamic simulations with CISM are forced from 1991 to 2013 using combinations of reanalysis-based surface mass balance and observations of outlet glacier flux change. We propose and demonstrate qualitative and quantitative metrics for use in evaluating the different model simulations against the observations. We find that the altimetry observations used here are largely ambiguous in terms of their ability to distinguish one simulation from another. Based on basin- and whole-ice-sheet scale metrics, we find that simulations using both idealized conceptual models and dynamic, numerical models provide an equally reasonable representation of the ice sheet surface (mean elevation differences of <1 m). This is likely due to their short period of record, biases inherent to digital elevation models used for model initial conditions, and biases resulting from firn dynamics, which are not explicitly accounted for in the models or observations. On the other hand, we find that the gravimetry observations used here are able to unambiguously distinguish between simulations of varying complexity, and along with the CmCt, can provide a quantitative score for assessing a particular model and/or simulation. The new framework demonstrates that our proposed metrics can distinguish relatively better from relatively worse simulations and that dynamic ice sheet models, when appropriately initialized and forced with the right boundary conditions, demonstrate predictive skill with respect to observed dynamic changes occurring on Greenland over the past few decades. An extensible design will allow for continued use of the CmCt as future altimetry, gravimetry, and other remotely sensed data become available for use in ice sheet model validation. PMID:29697704

An Ice Sheet Model Validation Framework for the Greenland Ice Sheet

NASA Technical Reports Server (NTRS)

Price, Stephen F.; Hoffman, Matthew J.; Bonin, Jennifer A.; Howat, Ian M.; Neumann, Thomas A.; Saba, Jack; Tezaur, Irina; Guerber, Jeffrey R.; Chambers, Don P.; Evans, Katherine J.;

Prediction of stress- and strain-based forming limits of automotive thin sheets by numerical, theoretical and experimental methods

NASA Astrophysics Data System (ADS)

Béres, Gábor; Weltsch, Zoltán; Lukács, Zsolt; Tisza, Miklós

2018-05-01

Forming limit is a complex concept of limit values related to the onset of local necking in the sheet metal. In cold sheet metal forming, major and minor limit strains are influenced by the sheet thickness, strain path (deformation history) as well as material parameters and microstructure. Forming Limit Curves are plotted in ɛ1 - ɛ2 coordinate system providing the classic strain-based Forming Limit Diagram (FLD). Using the appropriate constitutive model, the limit strains can be changed into the stress-based Forming Limit Diagram (SFLD), irrespective of the strain path. This study is about the effect of the hardening model parameters on defining of limit stress values during Nakazima tests for automotive dual phase (DP) steels. Five limit strain pairs were specified experimentally with the loading of five different sheet geometries, which performed different strain-paths from pure shear (-2ɛ2=ɛ1) up to biaxial stretching (ɛ2=ɛ1). The former works of Hill, Levy-Tyne and Keeler-Brazier made possible some kind of theoretical strain determination, too. This was followed by the stress calculation based on the experimental and theoretical strain data. Since the n exponent in the Nádai expression is varying with the strain at some DP steels, we applied the least-squares method to fit other hardening model parameters (Ludwik, Voce, Hockett-Sherby) to calculate the stress fields belonging to each limit strains. The results showed that each model parameters could produce some discrepancies between the limit stress states in the range of higher equivalent strains than uniaxial stretching. The calculated hardening models were imported to FE code to extend and validate the results by numerical simulations.

Preparation of high bioactivity multilayered bone-marrow mesenchymal stem cell sheets for myocardial infarction using a 3D-dynamic system.

PubMed

Wang, Yingwei; Zhang, Jianhua; Qin, Zixi; Fan, Zepei; Lu, Cheng; Chen, Baoxin; Zhao, Jupeng; Li, Xiaojuan; Xiao, Fei; Lin, Xi; Wu, Zheng

2018-05-01

Cell sheet techniques offer a promising future for myocardial infarction (MI) therapy; however, insufficient nutrition supply remains the major limitation in maintaining stem cell bioactivity in vitro. In order to enhance cell sheet mechanical strength and bioactivity, a decellularized porcine pericardium (DPP) scaffold was prepared by the phospholipase A2 method, and aspartic acid was used as a spacer arm to improve the vascular endothelial growth factor crosslink efficiency on the DPP scaffold. Based on this scaffold, multilayered bone marrow mesenchymal stem cell sheets were rapidly constructed, using RAD16-I peptide hydrogel as a temporary 3D scaffold, and cell sheets were cultured in either the 3D-dynamic system (DCcs) or the traditional static condition (SCcs). The multilayered structure, stem cell bioactivity, and ultrastructure of DCcs and SCcs were assessed. The DCcs exhibited lower apoptosis, lower differentiation, and an improved paracrine effect after a 48 h culture in vitro compared to the SCcs. Four groups were set to evaluate the cell sheet effect in rat MI model: sham group, MI control group, DCcs group, and SCcs group. The DCcs group improved cardiac function and decreased the infarcted area compared to the MI control group, while no significant improvements were observed in the SCcs group. Improved cell survival, angiogenesis, and Sca-1 + cell and c-kit + cell amounts were observed in the DCcs group. In conclusion, the DCcs maintained higher stem cell bioactivity by using the 3D-dynamic system to provide sufficient nutrition, and transplanting DCcs significantly improved the cardiac function and angiogenesis. This study provides an efficient method to prepare vascular endothelial growth factor covalent decellularized pericardium scaffold with aspartic acid, and a multilayered bone marrow mesenchymal stem cell (BMSC) sheet is constructed on it using a 3D-dynamic system. The dynamic nutrition supply showed a significant benefit on BMSC bioactivity in vitro, including decreasing cell apoptosis, reducing stem cell differentiation, and improving growth factor secretion. These favorable bioactivity improved BMSC survival, angiogenesis, and cardiac function of the infarcted myocardium. The study highlights the importance of dynamic nutrition supply on maintaining stem cell bioactivity within cell sheet, and it stresses the necessity and significance of setting a standard for assessing cell sheet products before transplantation in the future application. Copyright © 2018 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Machine Vision Within The Framework Of Collective Neural Assemblies

NASA Astrophysics Data System (ADS)

Gupta, Madan M.; Knopf, George K.

1990-03-01

The proposed mechanism for designing a robust machine vision system is based on the dynamic activity generated by the various neural populations embedded in nervous tissue. It is postulated that a hierarchy of anatomically distinct tissue regions are involved in visual sensory information processing. Each region may be represented as a planar sheet of densely interconnected neural circuits. Spatially localized aggregates of these circuits represent collective neural assemblies. Four dynamically coupled neural populations are assumed to exist within each assembly. In this paper we present a state-variable model for a tissue sheet derived from empirical studies of population dynamics. Each population is modelled as a nonlinear second-order system. It is possible to emulate certain observed physiological and psychophysiological phenomena of biological vision by properly programming the interconnective gains . Important early visual phenomena such as temporal and spatial noise insensitivity, contrast sensitivity and edge enhancement will be discussed for a one-dimensional tissue model.

Multifunctional cell-culture platform for aligned cell sheet monitoring, transfer printing, and therapy.

PubMed

Kim, Seok Joo; Cho, Hye Rim; Cho, Kyoung Won; Qiao, Shutao; Rhim, Jung Soo; Soh, Min; Kim, Taeho; Choi, Moon Kee; Choi, Changsoon; Park, Inhyuk; Hwang, Nathaniel S; Hyeon, Taeghwan; Choi, Seung Hong; Lu, Nanshu; Kim, Dae-Hyeong

2015-03-24

While several functional platforms for cell culturing have been proposed for cell sheet engineering, a soft integrated system enabling in vitro physiological monitoring of aligned cells prior to their in vivo applications in tissue regeneration has not been reported. Here, we present a multifunctional, soft cell-culture platform equipped with ultrathin stretchable nanomembrane sensors and graphene-nanoribbon cell aligners, whose system modulus is matched with target tissues. This multifunctional platform is capable of aligning plated cells and in situ monitoring of cellular physiological characteristics during proliferation and differentiation. In addition, it is successfully applied as an in vitro muscle-on-a-chip testing platform. Finally, a simple but high-yield transfer printing mechanism is proposed to deliver cell sheets for scaffold-free, localized cell therapy in vivo. The muscle-mimicking stiffness of the platform allows the high-yield transfer printing of multiple cell sheets and results in successful therapies in diseased animal models. Expansion of current results to stem cells will provide unique opportunities for emerging classes of tissue engineering and cell therapy technologies.

Greenland Ice Sheet flow response to runoff variability

NASA Astrophysics Data System (ADS)

Stevens, Laura A.; Behn, Mark D.; Das, Sarah B.; Joughin, Ian; Noël, Brice P. Y.; Broeke, Michiel R.; Herring, Thomas

2016-11-01

We use observations of ice sheet surface motion from a Global Positioning System network operating from 2006 to 2014 around North Lake in west Greenland to investigate the dynamical response of the Greenland Ice Sheet's ablation area to interannual variability in surface melting. We find no statistically significant relationship between runoff season characteristics and ice flow velocities within a given year or season. Over the 7 year time series, annual velocities at North Lake decrease at an average rate of -0.9 ± 1.1 m yr-2, consistent with the negative trend in annual velocities observed in neighboring regions over recent decades. We find that net runoff integrated over several preceding years has a negative correlation with annual velocities, similar to findings from the two other available decadal records of ice velocity in western Greenland. However, we argue that this correlation is not necessarily evidence for a direct hydrologic mechanism acting on the timescale of multiple years but could be a statistical construct. Finally, we stress that neither the decadal slowdown trend nor the negative correlation between velocity and integrated runoff is predicted by current ice-sheet models, underscoring that these models do not yet capture all the relevant feedbacks between runoff and ice dynamics needed to predict long-term trends in ice sheet flow.

Scene-based Shack-Hartmann wavefront sensor for light-sheet microscopy

NASA Astrophysics Data System (ADS)

Lawrence, Keelan; Liu, Yang; Dale, Savannah; Ball, Rebecca; VanLeuven, Ariel J.; Sornborger, Andrew; Lauderdale, James D.; Kner, Peter

2018-02-01

Light-sheet microscopy is an ideal imaging modality for long-term live imaging in model organisms. However, significant optical aberrations can be present when imaging into an organism that is hundreds of microns or greater in size. To measure and correct optical aberrations, an adaptive optics system must be incorporated into the microscope. Many biological samples lack point sources that can be used as guide stars with conventional Shack-Hartmann wavefront sensors. We have developed a scene-based Shack-Hartmann wavefront sensor for measuring the optical aberrations in a light-sheet microscopy system that does not require a point-source and can measure the aberrations for different parts of the image. The sensor has 280 lenslets inside the pupil, creates an image from each lenslet with a 500 micron field of view and a resolution of 8 microns, and has a resolution for the wavefront gradient of 75 milliradians per lenslet. We demonstrate the system on both fluorescent bead samples and zebrafish embryos.

Methods for Tier 1 Modeling within the Training Range Environmental Evaluation and Characterization System

DTIC Science & Technology

2009-08-01

properties, part b. USLE K-Factor by Organic Matter Content Soil -Texture Classification Dry Bulk Density, g/cm3 Field Capacity, % Available...Universal Soil Loss Equation ( USLE ) can be used to estimate annual average sheet and rill erosion, A (tons/acre-yr), from the equation A R K L S...erodibility factors, K, for various soil classifications and percent organic matter content ( USLE Fact Sheet 2008). Textural Class Average Less than 2

Antarctic glaciations under Pliocene climate conditions from numerical modeling and compilation of local field-based reconstructions

NASA Astrophysics Data System (ADS)

Bernales, Jorge; Rogozhina, Irina; Greve, Ralf

2014-05-01

The mid-Pliocene (3.15 to 2.85 million years before present) is the most recent period in Earth's history when temperatures and CO2 concentrations were likely sustainedly higher than pre-industrial values. Furthermore, the positions of the continents and their sea-land distributions had already reached their present configuration, sharing some similarities with today's patterns of ocean circulation and vegetation distributions. Although significant differences exist -such as a peak sea level that could have been 22 ± 10 m higher than it is today and sea surface temperatures particularly warmer at higher latitudes, mid-Pliocene has been identified as an ideal interval for studying the climate system under conditions similar to those projected for the end of this century. Among the sources of uncertainty in the projections, the response of the Antarctic ice sheet (AIS) to warmer-than-today conditions seems to play a central role. Therefore, a better understanding of AIS's behavior during periods like the mid-Pliocene will provide valuable information that could help improve future predictions. For this purpose, we have compiled a wide range of local field-based reconstructions of the ice-sheet margin from Pliocene sediments (with the inclusions of organic matters such as, for instance, diatoms or palynoflora, or ice rafted debris), geochemical records, volcanic ashes and rocks, and geomorphology, and designed numerical experiments of the AIS dynamics during the mid-Pliocene warm period using the large-scale polythermal ice sheet-shelf model SICOPOLIS (Greve, 1997 [1]; Sato and Greve, 2012 [2]). The model is run with a horizontal resolution of 40 × 40 km by the climatology obtained from the PlioMIP Atmosphere Ocean Global Circulation Model experiments (Dolan et al., 2012 [3]). Parameters of the AIS model (e.g. ice calving, sub-ice shelf and surface ice melt, basal sliding, etc.) have initially been estimated using ice-sheet simulations driven by the present-day climate and ocean conditions and calibrated against available remote-sensed and in-situ observations. In our Pliocene experiments, we employ alternative parameterizations of sub-ice shelf and ice surface melting processes to test the likelihood of numerous controversial theories and reconstructions arguing for or against significant retreat of the East Antarctic ice sheet from the coasts (locally up to 450 km) in the mid-Pliocene. Finally, we assess the sensitivity of the modeled West Antarctic/Antarctic Peninsula ice geometry to the above parameters and emphasize a crucial role of surface mass balance model parameters in modeling the Pliocene ice sheet configuration in agreement with existing reconstructions on a regional scale. References [1] Greve, R. (1997). Application of a polythermal three-dimensional ice sheet model to the Greenland ice sheet: response to steady-state and transient climate scenarios. Journal of Climate, 10(5), 901-918. [2] Sato, T., and Greve, R. (2012). Sensitivity experiments for the Antarctic ice sheet with varied sub-ice-shelf melting rates. Annals of Glaciology, 53(60), 221-228. [3] Dolan, A. M., Koenig, S. J., Hill, D. J., Haywood, A. M., and DeConto, R. M. (2012). Pliocene Ice Sheet Modelling Intercomparison Project (PLISMIP)-experimental design. Geoscientific Model Development, 5(4), 963-974.

The magnetosphere of Neptune - Its response to daily rotation

NASA Technical Reports Server (NTRS)

Voigt, Gerd-Hannes; Ness, Norman F.

1990-01-01

The Neptunian magnetosphere periodically changes every eight hours between a pole-on magnetosphere with only one polar cusp and an earth-type magnetosphere with two polar cusps. In the pole-on configuration, the tail current sheet has an almost circular shape with plasma currents closing entirely within the magnetosphere. Eight hours later the tail current sheet assumes an almost flat shape with plasma currents touching the magnetotail boundary and closing over the tail magnetopause. Magnetic field and tail current sheet configurations have been calculated in a three-dimensional model, but the plasma- and thermodynamic conditions were investigated in a simplified two-dimensional MHD equilibrium magnetosphere. It was found that the free energy in the tail region of the two-dimensional model becomes independent of the dipole tilt angle. It is conjectured that the Neptunian magnetotail might assume quasi-static equilibrium states that make the free energy of the system independent of its daily rotation.

Collective behavior in two-dimensional biological systems: Receptor clustering and beta-sheet aggregation

NASA Astrophysics Data System (ADS)

Guo, Chinlin

We studied two particular biomedical systems which exhibit collective molecular behavior. One is clustering of tumor necrosis factor receptor I (TNFR1), and another is β-sheet folding and aggregation. Receptor clustering has been shown to be a crucial step in many signaling events but its biological meaning has not been adequately addressed. Here, via a simple lattice model, we show how cells use this clustering machinery to enhance sensitivity as well as robustness. On the other hand, intracellular deposition of aggregated protein rich in β-sheet is a prominent cytopathological feature of most neurodegenerative diseases. How this aggregation occurs and how it responds to therapy is not completely understood. Here, we started from a reconstruction of the H-bond potential and carry out a full investigation of β-sheet thermodynamics as well as kinetics. We show that β-sheet aggregation is most likely due to molecular stacking and found that the minimal length of an aggregate mutant polymer corresponds well with the number observed in adult Huntington's disease. We have also shown that molecular agents such as dendrimers might fail at high-dose therapy; instead, a potential therapy strategy is to block β-turn formation. Our predictions can be used for future experimental tests and clinical trials.

Greenland Regional and Ice Sheet-wide Geometry Sensitivity to Boundary and Initial conditions

NASA Astrophysics Data System (ADS)

Logan, L. C.; Narayanan, S. H. K.; Greve, R.; Heimbach, P.

2017-12-01

Ice sheet and glacier model outputs require inputs from uncertainly known initial and boundary conditions, and other parameters. Conservation and constitutive equations formalize the relationship between model inputs and outputs, and the sensitivity of model-derived quantities of interest (e.g., ice sheet volume above floatation) to model variables can be obtained via the adjoint model of an ice sheet. We show how one particular ice sheet model, SICOPOLIS (SImulation COde for POLythermal Ice Sheets), depends on these inputs through comprehensive adjoint-based sensitivity analyses. SICOPOLIS discretizes the shallow-ice and shallow-shelf approximations for ice flow, and is well-suited for paleo-studies of Greenland and Antarctica, among other computational domains. The adjoint model of SICOPOLIS was developed via algorithmic differentiation, facilitated by the source transformation tool OpenAD (developed at Argonne National Lab). While model sensitivity to various inputs can be computed by costly methods involving input perturbation simulations, the time-dependent adjoint model of SICOPOLIS delivers model sensitivities to initial and boundary conditions throughout time at lower cost. Here, we explore both the sensitivities of the Greenland Ice Sheet's entire and regional volumes to: initial ice thickness, precipitation, basal sliding, and geothermal flux over the Holocene epoch. Sensitivity studies such as described here are now accessible to the modeling community, based on the latest version of SICOPOLIS that has been adapted for OpenAD to generate correct and efficient adjoint code.

Nonlinear Dynamics of Non-uniform Current-Vortex Sheets in Magnetohydrodynamic Flows

NASA Astrophysics Data System (ADS)

Matsuoka, C.; Nishihara, K.; Sano, T.

2017-04-01

A theoretical model is proposed to describe fully nonlinear dynamics of interfaces in two-dimensional MHD flows based on an idea of non-uniform current-vortex sheet. Application of vortex sheet model to MHD flows has a crucial difficulty because of non-conservative nature of magnetic tension. However, it is shown that when a magnetic field is initially parallel to an interface, the concept of vortex sheet can be extended to MHD flows (current-vortex sheet). Two-dimensional MHD flows are then described only by a one-dimensional Lagrange parameter on the sheet. It is also shown that bulk magnetic field and velocity can be calculated from their values on the sheet. The model is tested by MHD Richtmyer-Meshkov instability with sinusoidal vortex sheet strength. Two-dimensional ideal MHD simulations show that the nonlinear dynamics of a shocked interface with density stratification agrees fairly well with that for its corresponding potential flow. Numerical solutions of the model reproduce properly the results of the ideal MHD simulations, such as the roll-up of spike, exponential growth of magnetic field, and its saturation and oscillation. Nonlinear evolution of the interface is found to be determined by the Alfvén and Atwood numbers. Some of their dependence on the sheet dynamics and magnetic field amplification are discussed. It is shown by the model that the magnetic field amplification occurs locally associated with the nonlinear dynamics of the current-vortex sheet. We expect that our model can be applicable to a wide variety of MHD shear flows.

Implementing an empirical scalar constitutive relation for ice with flow-induced polycrystalline anisotropy in large-scale ice sheet models

NASA Astrophysics Data System (ADS)

Graham, Felicity S.; Morlighem, Mathieu; Warner, Roland C.; Treverrow, Adam

2018-03-01

The microstructure of polycrystalline ice evolves under prolonged deformation, leading to anisotropic patterns of crystal orientations. The response of this material to applied stresses is not adequately described by the ice flow relation most commonly used in large-scale ice sheet models - the Glen flow relation. We present a preliminary assessment of the implementation in the Ice Sheet System Model (ISSM) of a computationally efficient, empirical, scalar, constitutive relation which addresses the influence of the dynamically steady-state flow-compatible induced anisotropic crystal orientation patterns that develop when ice is subjected to the same stress regime for a prolonged period - sometimes termed tertiary flow. We call this the ESTAR flow relation. The effect on ice flow dynamics is investigated by comparing idealised simulations using ESTAR and Glen flow relations, where we include in the latter an overall flow enhancement factor. For an idealised embayed ice shelf, the Glen flow relation overestimates velocities by up to 17 % when using an enhancement factor equivalent to the maximum value prescribed in the ESTAR relation. Importantly, no single Glen enhancement factor can accurately capture the spatial variations in flow across the ice shelf generated by the ESTAR flow relation. For flow line studies of idealised grounded flow over varying topography or variable basal friction - both scenarios dominated at depth by bed-parallel shear - the differences between simulated velocities using ESTAR and Glen flow relations depend on the value of the enhancement factor used to calibrate the Glen flow relation. These results demonstrate the importance of describing the deformation of anisotropic ice in a physically realistic manner, and have implications for simulations of ice sheet evolution used to reconstruct paleo-ice sheet extent and predict future ice sheet contributions to sea level.

The balance sheet technique. Volume I. The balance sheet analysis technique for preconstruction review of airports and highways

DOE Office of Scientific and Technical Information (OSTI.GOV)

LaBelle, S.J.; Smith, A.E.; Seymour, D.A.

1977-02-01

The technique applies equally well to new or existing airports. The importance of accurate accounting of emissions, cannot be overstated. The regional oxidant modelling technique used in conjunction with a balance sheet review must be a proportional reduction technique. This type of emission balancing presumes equality of all sources in the analysis region. The technique can be applied successfully in the highway context, either in planning at the system level or looking only at projects individually. The project-by-project reviews could be used to examine each project in the same way as the airport projects are examined for their impact onmore » regional desired emission levels. The primary limitation of this technique is that it should not be used when simulation models have been used for regional oxidant air quality. In the case of highway projects, the balance sheet technique might appear to be limited; the real limitations are in the transportation planning process. That planning process is not well-suited to the needs of air quality forecasting. If the transportation forecasting techniques are insensitive to change in the variables that affect HC emissions, then no internal emission trade-offs can be identified, and the initial highway emission forecasts are themselves suspect. In general, the balance sheet technique is limited by the quality of the data used in the review. Additionally, the technique does not point out effective trade-off strategies, nor does it indicate when it might be worthwhile to ignore small amounts of excess emissions. Used in the context of regional air quality plans based on proportional reduction models, the balance sheet analysis technique shows promise as a useful method by state or regional reviewing agencies.« less

Modelling the effects of ice-sheet activity on CO2 outgassing by Icelandic volcanoes

NASA Astrophysics Data System (ADS)

Armitage, J. J.; Ferguson, D.; Petersen, K. D.; Creyts, T. T.

2017-12-01

Glacial cycles may play a significant role in mediating the flux of magmatic CO2 between the Earth's mantle and atmosphere. In Iceland, it is thought that late-Pleistocene deglaciation led to a significant volcanic pulse, evidenced by increased post-glacial lava volumes and changes in melt chemistry consistent with depressurization. Investigating the extent to which glacial activity may have affected volcanic CO2 emissions from Iceland, and crucially over what timescale, requires detailed knowledge of how the magma system responded to the growth and collapse of the ice-sheet before and after the LGM. To investigate this, we coupled a model of magma generation and transport with a history of ice-sheet activity. Our results show that the emplacement and removal of the LGM ice-sheet likely led to two significant pulses of magmatic CO2. The first, and most significant of these, is associated with ice-sheet growth and occurs as the magma system recovers from glacial loading. This recovery happens from the base of the melting region upwards, producing a pulse of CO2 rich magma that is predicted to reach the surface around 20 ka after the loading event, close in time to the LGM. The second peak in CO2 output occurs abruptly following deglaciation as a consequence of increased rates of melt generation and transport in the shallow mantle. Although these post-glacial melts are relatively depleted in CO2, the increase in magma flux leads to a short-lived period of elevated CO2 emissions. Our results therefore suggest a negative feedback, whereby ice-sheet growth produces a delayed pulse of magmatic CO2, which, in addition to increased geothermal heat flux, may contribute towards driving deglaciation, which itself then causes further magmatism and CO2 outgassing. This model is consistent with the seismic structure of the asthenosphere below Iceland, and the established compositional and volumetric trends for sub- and post-glacial volcanism in Iceland. These trends show that the earliest subglacial events involved small volumes of enriched melts, while eruptions that were synchronous with or immediately followed deglaciation involved larger volumes of more depleted melts.

Quantifying Uncertainty in the Greenland Surface Mass Balance Elevation Feedback

NASA Astrophysics Data System (ADS)

Edwards, T.

2015-12-01

As the shape of the Greenland ice sheet responds to changes in surface mass balance (SMB) and dynamics, it affects the surface mass balance through the atmospheric lapse rate and by altering atmospheric circulation patterns. Positive degree day models include simplified representations of this feedback, but it is difficult to simulate with state-of-the-art models because it requires coupling of regional climate models with dynamical ice sheet models, which is technically challenging. This difficulty, along with the high computational expense of regional climate models, also drastically limits opportunities for exploring the impact of modelling uncertainties on sea level projections. We present a parameterisation of the SMB-elevation feedback in the MAR regional climate model that provides a far easier and quicker estimate than atmosphere-ice sheet model coupling, which can be used with any ice sheet model. This allows us to use ensembles of different parameter values and ice sheet models to assess the effect of uncertainty in the feedback and ice sheet model structure on future sea level projections. We take a Bayesian approach to uncertainty in the feedback parameterisation, scoring the results from multiple possible "SMB lapse rates" according to how well they reproduce a MAR simulation with altered ice sheet topography. We test the impact of the resulting parameterisation on sea level projections using five ice sheet models forced by MAR (in turned forced by two different global climate models) under the emissions scenario A1B. The estimated additional sea level contribution due to the SMB-elevation feedback is 4.3% at 2100 (95% credibility interval 1.8-6.9%), and 9.6% at 2200 (3.6-16.0%).

On the Utilization of Ice Flow Models and Uncertainty Quantification to Interpret the Impact of Surface Radiation Budget Errors on Estimates of Greenland Ice Sheet Surface Mass Balance and Regional Estimates of Mass Balance

NASA Astrophysics Data System (ADS)

Schlegel, N.; Larour, E. Y.; Gardner, A. S.; Lang, C.; Miller, C. E.; van den Broeke, M. R.

2016-12-01

How Greenland ice flow may respond to future increases in surface runoff and to increases in the frequency of extreme melt events is unclear, as it requires detailed comprehension of Greenland surface climate and the ice sheet's sensitivity to associated uncertainties. With established uncertainty quantification tools run within the framework of Ice Sheet System Model (ISSM), we conduct decadal-scale forward modeling experiments to 1) quantify the spatial resolution needed to effectively force distinct components of the surface radiation budget, and subsequently surface mass balance (SMB), in various regions of the ice sheet and 2) determine the dynamic response of Greenland ice flow to variations in components of the net radiation budget. The Glacier Energy and Mass Balance (GEMB) software is a column surface model (1-D) that has recently been embedded as a module within ISSM. Using the ISSM-GEMB framework, we perform sensitivity analyses to determine how perturbations in various components of the surface radiation budget affect model output; these model experiments allow us predict where and on what spatial scale the ice sheet is likely to dynamically respond to changes in these parameters. Preliminary results suggest that SMB should be forced at at least a resolution of 23 km to properly capture dynamic ice response. In addition, Monte-Carlo style sampling analyses reveals that the areas with the largest uncertainty in mass flux are located near the equilibrium line altitude (ELA), upstream of major outlet glaciers in the North and West of the ice sheet. Sensitivity analysis indicates that these areas are also the most vulnerable on the ice sheet to persistent, far-field shifts in SMB, suggesting that continued warming, and upstream shift in the ELA, are likely to result in increased velocities, and consequentially SMB-induced thinning upstream of major outlet glaciers. Here, we extend our investigation to consider various components of the surface radiation budget separately, in order to determine how and where errors in these fields may independently impact ice flow. This work was performed at the California Institute of Technology's Jet Propulsion Laboratory under a contract with the National Aeronautics and Space Administration's Cryosphere and Interdisciplinary Research in Earth Science Programs.

Reconstruction of North American drainage basins and river discharge since the Last Glacial Maximum

NASA Astrophysics Data System (ADS)

Wickert, Andrew D.

2016-11-01

Over the last glacial cycle, ice sheets and the resultant glacial isostatic adjustment (GIA) rearranged river systems. As these riverine threads that tied the ice sheets to the sea were stretched, severed, and restructured, they also shrank and swelled with the pulse of meltwater inputs and time-varying drainage basin areas, and sometimes delivered enough meltwater to the oceans in the right places to influence global climate. Here I present a general method to compute past river flow paths, drainage basin geometries, and river discharges, by combining models of past ice sheets, glacial isostatic adjustment, and climate. The result is a time series of synthetic paleohydrographs and drainage basin maps from the Last Glacial Maximum to present for nine major drainage basins - the Mississippi, Rio Grande, Colorado, Columbia, Mackenzie, Hudson Bay, Saint Lawrence, Hudson, and Susquehanna/Chesapeake Bay. These are based on five published reconstructions of the North American ice sheets. I compare these maps with drainage reconstructions and discharge histories based on a review of observational evidence, including river deposits and terraces, isotopic records, mineral provenance markers, glacial moraine histories, and evidence of ice stream and tunnel valley flow directions. The sharp boundaries of the reconstructed past drainage basins complement the flexurally smoothed GIA signal that is more often used to validate ice-sheet reconstructions, and provide a complementary framework to reduce nonuniqueness in model reconstructions of the North American ice-sheet complex.

Variation simulation for compliant sheet metal assemblies with applications

NASA Astrophysics Data System (ADS)

Long, Yufeng

Sheet metals are widely used in discrete products, such as automobiles, aircraft, furniture and electronics appliances, due to their good manufacturability and low cost. A typical automotive body assembly consists of more than 300 parts welded together in more than 200 assembly fixture stations. Such an assembly system is usually quite complex, and takes a long time to develop. As the automotive customer demands products of increasing quality in a shorter time, engineers in automotive industry turn to computer-aided engineering (CAE) tools for help. Computers are an invaluable resource for engineers, not only to simplify and automate the design process, but also to share design specifications with manufacturing groups so that production systems can be tooled up quickly and efficiently. Therefore, it is beneficial to develop computerized simulation and evaluation tools for development of automotive body assembly systems. It is a well-known fact that assembly architectures (joints, fixtures, and assembly lines) have a profound impact on dimensional quality of compliant sheet metal assemblies. To evaluate sheet metal assembly architectures, a special dimensional analysis tool need be developed for predicting dimensional variation of the assembly. Then, the corresponding systematic tools can be established to help engineers select the assembly architectures. In this dissertation, a unified variation model is developed to predict variation in compliant sheet metal assemblies by considering fixture-induced rigid-body motion, deformation and springback. Based on the unified variation model, variation propagation models in multiple assembly stations with various configurations are established. To evaluate the dimensional capability of assembly architectures, quantitative indices are proposed based on the sensitivity matrix, which are independent of the variation level of the process. Examples are given to demonstrate their applications in selecting robust assembly architectures, and some useful guidelines for selection of assembly architectures are summarized. In addition, to enhance the fault diagnosis, a systematic methodology is proposed for selection of measurement configurations. Specifically, principles involved in selecting measurements are generalized first; then, the corresponding quantitative indices are developed to evaluate the measurement configurations, and finally, examples are present.

Inferring unknow boundary conditions of the Greenland Ice Sheet by assimilating ICESat-1 and IceBridge altimetry intothe Ice Sheet System Model.

NASA Astrophysics Data System (ADS)

Larour, E. Y.; Khazendar, A.; Seroussi, H. L.; Schlegel, N.; Csatho, B. M.; Schenk, A. F.; Rignot, E. J.; Morlighem, M.

2014-12-01

Altimetry signals from missions such as ICESat-1, CryoSat, EnviSat, as well as altimeters onboard Operation IceBridge provide vital insights into processes such as surface mass balance, mass transport and ice-flow dynamics. Historically however, ice-flow models have been focused on assimilating surface velocities from satellite-based radar observations, to infer properties such as basal friction or the position of the bedrock. Here, we leverage a new methodology based on automatic differentation of the Ice Sheet System Model to assimilate surface altimetry data into a reconstruction of the past decade of ice flow on the North Greenland area. We infer corrections to boundary conditions such as basal friction and surface mass balance, as well as corrections to the ice hardness, to best-match the observed altimetry record. We compare these corrections between glaciers such as Petermann Glacier, 79 North and Zacchariae Isstrom. The altimetry signals exhibit very different patterns between East and West, which translate into very different signatures for the inverted boundary conditions. This study gives us greater insights into what differentiates different basins, both in terms of mass transport and ice-flow dynamics, and what could bethe controlling mechanisms behind the very different evolutions of these basins.

Numerical simulation of the paleohydrology of glacial Lake Oshkosh, eastern Wisconsin, USA

USGS Publications Warehouse

Clark, J.A.; Befus, K.M.; Hooyer, T.S.; Stewart, P.W.; Shipman, T.D.; Gregory, C.T.; Zylstra, D.J.

2008-01-01

Proglacial lakes, formed during retreat of the Laurentide ice sheet, evolved quickly as outlets became ice-free and the earth deformed through glacial isostatic adjustment. With high-resolution digital elevation models (DEMs) and GIS methods, it is possible to reconstruct the evolution of surface hydrology. When a DEM deforms through time as predicted by our model of viscoelastic earth relaxation, the entire surface hydrologic system with its lakes, outlets, shorelines and rivers also evolves without requiring assumptions of outlet position. The method is applied to proglacial Lake Oshkosh in Wisconsin (13,600 to 12,900??cal yr BP). Comparison of predicted to observed shoreline tilt indicates the ice sheet was about 400??m thick over the Great Lakes region. During ice sheet recession, each of the five outlets are predicted to uplift more than 100??m and then subside approximately 30??m. At its maximum extent, Lake Oshkosh covered 6600??km2 with a volume of 111??km3. Using the Hydrologic Engineering Center-River Analysis System model, flow velocities during glacial outburst floods up to 9??m/s and peak discharge of 140,000??m3/s are predicted, which could drain 33.5??km3 of lake water in 10??days and transport boulders up to 3??m in diameter. ?? 2007 University of Washington.

A synthesis of the basal thermal state of the Greenland Ice Sheet

PubMed Central

MacGregor, Joseph A.; Fahnestock, Mark A.; Catania, Ginny A.; Aschwanden, Andy; Clow, Gary D.; Colgan, William T.; Gogineni, S. Prasad; Morlighem, Mathieu; Nowicki, Sophie M. J.; Paden, John D.; Price, Stephen F.; Seroussi, Hélène

2017-01-01

The basal thermal state of an ice sheet (frozen or thawed) is an important control upon its evolution, dynamics and response to external forcings. However, this state can only be observed directly within sparse boreholes or inferred conclusively from the presence of subglacial lakes. Here we synthesize spatially extensive inferences of the basal thermal state of the Greenland Ice Sheet to better constrain this state. Existing inferences include outputs from the eight thermomechanical ice-flow models included in the SeaRISE effort. New remote-sensing inferences of the basal thermal state are derived from Holocene radiostratigraphy, modern surface velocity and MODIS imagery. Both thermomechanical modeling and remote inferences generally agree that the Northeast Greenland Ice Stream and large portions of the southwestern ice-drainage systems are thawed at the bed, whereas the bed beneath the central ice divides, particularly their west-facing slopes, is frozen. Elsewhere, there is poor agreement regarding the basal thermal state. Both models and remote inferences rarely represent the borehole-observed basal thermal state accurately near NorthGRIP and DYE-3. This synthesis identifies a large portion of the Greenland Ice Sheet (about one third by area) where additional observations would most improve knowledge of its overall basal thermal state. PMID:28163988

A synthesis of the basal thermal state of the Greenland Ice Sheet.

PubMed

MacGregor, Joseph A; Fahnestock, Mark A; Catania, Ginny A; Aschwanden, Andy; Clow, Gary D; Colgan, William T; Gogineni, S Prasad; Morlighem, Mathieu; Nowicki, Sophie M J; Paden, John D; Price, Stephen F; Seroussi, Hélène

2016-08-10

The basal thermal state of an ice sheet (frozen or thawed) is an important control upon its evolution, dynamics and response to external forcings. However, this state can only be observed directly within sparse boreholes or inferred conclusively from the presence of subglacial lakes. Here we synthesize spatially extensive inferences of the basal thermal state of the Greenland Ice Sheet to better constrain this state. Existing inferences include outputs from the eight thermomechanical ice-flow models included in the SeaRISE effort. New remote-sensing inferences of the basal thermal state are derived from Holocene radiostratigraphy, modern surface velocity and MODIS imagery. Both thermomechanical modeling and remote inferences generally agree that the Northeast Greenland Ice Stream and large portions of the southwestern ice-drainage systems are thawed at the bed, whereas the bed beneath the central ice divides, particularly their west-facing slopes, is frozen. Elsewhere, there is poor agreement regarding the basal thermal state. Both models and remote inferences rarely represent the borehole-observed basal thermal state accurately near NorthGRIP and DYE-3. This synthesis identifies a large portion of the Greenland Ice Sheet (about one third by area) where additional observations would most improve knowledge of its overall basal thermal state.

A synthesis of the basal thermal state of the Greenland Ice Sheet

USGS Publications Warehouse

MacGregor, Joseph A; Fahnestock, Mark A; Catania, Ginny A; Aschwanden, Andy; Clow, Gary D.; Colgan, William T.; Gogineni, Prasad S.; Morlighem, Mathieu; Nowicki, Sophie M .J.; Paden, John D; Price, Stephen F.; Seroussi, Helene

2016-01-01

The basal thermal state of an ice sheet (frozen or thawed) is an important control upon its evolution, dynamics and response to external forcings. However, this state can only be observed directly within sparse boreholes or inferred conclusively from the presence of subglacial lakes. Here we synthesize spatially extensive inferences of the basal thermal state of the Greenland Ice Sheet to better constrain this state. Existing inferences include outputs from the eight thermomechanical ice-flow models included in the SeaRISE effort. New remote-sensing inferences of the basal thermal state are derived from Holocene radiostratigraphy, modern surface velocity and MODIS imagery. Both thermomechanical modeling and remote inferences generally agree that the Northeast Greenland Ice Stream and large portions of the southwestern ice-drainage systems are thawed at the bed, whereas the bed beneath the central ice divides, particularly their west-facing slopes, is frozen. Elsewhere, there is poor agreement regarding the basal thermal state. Both models and remote inferences rarely represent the borehole-observed basal thermal state accurately near NorthGRIP and DYE-3. This synthesis identifies a large portion of the Greenland Ice Sheet (about one third by area) where additional observations would most improve knowledge of its overall basal thermal state.

Geological and geomorphological insights into Antarctic ice sheet evolution.

PubMed

Sugden, David E; Bentley, Michael J; O Cofaigh, Colm

2006-07-15

Technical advances in the study of ice-free parts of Antarctica can provide quantitative records that are useful for constraining and refining models of ice sheet evolution and behaviour. Such records improve our understanding of system trajectory, influence the questions we ask about system stability and help to define the ice-sheet processes that are relevant on different time-scales. Here, we illustrate the contribution of cosmogenic isotope analysis of exposed bedrock surfaces and marine geophysical surveying to the understanding of Antarctic ice sheet evolution on a range of time-scales. In the Dry Valleys of East Antarctica, 3He dating of subglacial flood deposits that are now exposed on mountain summits provide evidence of an expanded and thicker Mid-Miocene ice sheet. The survival of surface boulders for approximately 14Myr, the oldest yet measured, demonstrates exceptionally low rates of subsequent erosion and points to the persistence and stability of the dry polar desert climate since that time. Increasingly, there are constraints on West Antarctic ice sheet fluctuations during Quaternary glacial cycles. In the Sarnoff Mountains of Marie Byrd Land in West Antarctica, 10Be and 26Al cosmogenic isotope analysis of glacial erratics and bedrock reveal steady thinning of the ice sheet from 10400 years ago to the present, probably as a result of grounding line retreat. In the Antarctic Peninsula, offshore analysis reveals an extensive ice sheet at the last glacial maximum. Based on radiocarbon dating, deglaciation began by 17000cal yr BP and was complete by 9500cal yr BP. Deglaciation of the west and east sides of the Antarctic Peninsula ice sheet occurred at different times and rates, but was largely complete by the Early Holocene. At that time ice shelves were less extensive on the west side of the Antarctic Peninsula than they are today. The message from the past is that individual glacier drainage basins in Antarctica respond in different and distinctive ways to global climate change, depending on the link between regional topography and climate setting.

The feasibility of imaging subglacial hydrology beneath ice streams with ground-based electromagnetics

NASA Astrophysics Data System (ADS)

Siegfried, M. R.; Key, K.

2017-12-01

Subglacial hydrologic systems in Antarctica and Greenland play a fundamental role in ice-sheet dynamics, yet critical aspects of these systems remain poorly understood due to a lack of observations. Ground-based electromagnetic (EM) geophysical methods are established for mapping groundwater in many environments, but have never been applied to imaging lakes beneath ice sheets. Here we study the feasibility of passive and active source EM imaging for quantifying the nature of subglacial water systems beneath ice streams, with an emphasis on the interfaces between ice and basal meltwater, as well as deeper groundwater in the underlying sediments. Specifically, we look at the passive magnetotelluric method and active-source EM methods that use a large loop transmitter and receivers that measure either frequency-domain or transient soundings. We describe a suite of model studies that exam the data sensitivity as a function of ice thickness, water conductivity and hydrologic system geometry for models representative of a subglacial lake and a grounding zone estuary. We show that EM data are directly sensitive to groundwater and can image its lateral and depth extent. By combining the conductivity obtained from EM data with ice thickness and geological structure from conventional geophysical techniques such as ground-penetrating radar and active seismic techniques, EM data have the potential to provide new insights on the interaction between ice, rock, and water at critical ice-sheet boundaries.

Triangular-shaped landforms reveal subglacial drainage routes in SW Finland

NASA Astrophysics Data System (ADS)

Mäkinen, J.; Kajuutti, K.; Palmu, J.-P.; Ojala, A.; Ahokangas, E.

2017-05-01

The aim of this study is to present the first evidence of triangular-shaped till landforms and related erosional features indicative of subglacial drainage within the ice stream bed of the Scandinavian ice sheet in Finland. Previously unidentified grouped patterns of Quaternary deposits with triangular landforms can be recognized from LiDAR-based DEMs. The triangular landforms occur as segments within geomorphologically distinguishable routes that are associated with eskers. The morphological and sedimentological characteristics as well as the distribution of the triangular landforms are interpreted to involve the creep of saturated deforming till, flow and pressure fluctuations of subglacial meltwater associated with meltwater erosion. There are no existing models for the formation of this kind of large-scale drainage systems, but we claim that they represent an efficient drainage system for subglacial meltwater transfer under high pressure conditions. Our hypothesis is that the routed, large-scale subglacial drainage systems described herein form a continuum between channelized (eskers) and more widely spread small-scale distributed subglacial drainage. Moreover, the transition from the conduit dominated drainage to triangular-shaped subglacial landforms takes place about 50-60 km from the ice margin. We provide an important contribution towards a more realistic representation of ice sheet hydrological drainage systems that could be used to improve paleoglaciological models and to simulate likely responses of ice sheets to increased meltwater production.

Centennial-scale Holocene climate variations amplified by Antarctic Ice Sheet discharge

NASA Astrophysics Data System (ADS)

Bakker, Pepijn; Clark, Peter U.; Golledge, Nicholas R.; Schmittner, Andreas; Weber, Michael E.

2017-01-01

Proxy-based indicators of past climate change show that current global climate models systematically underestimate Holocene-epoch climate variability on centennial to multi-millennial timescales, with the mismatch increasing for longer periods. Proposed explanations for the discrepancy include ocean-atmosphere coupling that is too weak in models, insufficient energy cascades from smaller to larger spatial and temporal scales, or that global climate models do not consider slow climate feedbacks related to the carbon cycle or interactions between ice sheets and climate. Such interactions, however, are known to have strongly affected centennial- to orbital-scale climate variability during past glaciations, and are likely to be important in future climate change. Here we show that fluctuations in Antarctic Ice Sheet discharge caused by relatively small changes in subsurface ocean temperature can amplify multi-centennial climate variability regionally and globally, suggesting that a dynamic Antarctic Ice Sheet may have driven climate fluctuations during the Holocene. We analysed high-temporal-resolution records of iceberg-rafted debris derived from the Antarctic Ice Sheet, and performed both high-spatial-resolution ice-sheet modelling of the Antarctic Ice Sheet and multi-millennial global climate model simulations. Ice-sheet responses to decadal-scale ocean forcing appear to be less important, possibly indicating that the future response of the Antarctic Ice Sheet will be governed more by long-term anthropogenic warming combined with multi-centennial natural variability than by annual or decadal climate oscillations.

New developments in tribomechanical modeling of automotive sheet steel forming

NASA Astrophysics Data System (ADS)

Khandeparkar, Tushar; Chezan, Toni; van Beeck, Jeroen

2018-05-01

Forming of automotive sheet metal body panels is a complex process influenced by both the material properties and contact conditions in the forming tooling. Material properties are described by the material constitutive behavior and the material flow into the forming die can be described by the tribological system. This paper investigates the prediction accuracy of the forming process using the Tata Steel state of the art description of the material constitutive behavior in combination with different friction models. A cross-die experiment is used to investigate the accuracy of local deformation modes typically seen in automotive sheet metal forming operations. Results of advanced friction models as well as the classical Coulomb friction description are compared to the experimentally measured strain distribution and material draw-in. Two hot-dip galvanized coated steel forming grades were used for the investigations. The results show that the accuracy of the simulation is not guaranteed by the advanced friction models for the entire investigated blank holder force range, both globally and locally. A measurable difference between the calculated and measured local strains is seen for both studied models even in the case where the global indicator, i.e. the draw-in, is well predicted.

Fact sheets and slides summarizing Soil and Water Assessment Tool (SWAT) and Integrated Farm Systems Model (IFSM)

USDA-ARS?s Scientific Manuscript database

Water quality models address nonpoint source pollution from agricultural land at a range of scales and complexities and involve a variety of input parameters. It is often difficult for conservationists and stakeholders to understand and reconcile water quality results from different models. However,...

Efficient meltwater drainage through supraglacial streams and rivers on the southwest Greenland ice sheet.

PubMed

Smith, Laurence C; Chu, Vena W; Yang, Kang; Gleason, Colin J; Pitcher, Lincoln H; Rennermalm, Asa K; Legleiter, Carl J; Behar, Alberto E; Overstreet, Brandon T; Moustafa, Samiah E; Tedesco, Marco; Forster, Richard R; LeWinter, Adam L; Finnegan, David C; Sheng, Yongwei; Balog, James

2015-01-27

Thermally incised meltwater channels that flow each summer across melt-prone surfaces of the Greenland ice sheet have received little direct study. We use high-resolution WorldView-1/2 satellite mapping and in situ measurements to characterize supraglacial water storage, drainage pattern, and discharge across 6,812 km(2) of southwest Greenland in July 2012, after a record melt event. Efficient surface drainage was routed through 523 high-order stream/river channel networks, all of which terminated in moulins before reaching the ice edge. Low surface water storage (3.6 ± 0.9 cm), negligible impoundment by supraglacial lakes or topographic depressions, and high discharge to moulins (2.54-2.81 cm⋅d(-1)) indicate that the surface drainage system conveyed its own storage volume every <2 d to the bed. Moulin discharges mapped inside ∼52% of the source ice watershed for Isortoq, a major proglacial river, totaled ∼41-98% of observed proglacial discharge, highlighting the importance of supraglacial river drainage to true outflow from the ice edge. However, Isortoq discharges tended lower than runoff simulations from the Modèle Atmosphérique Régional (MAR) regional climate model (0.056-0.112 km(3)⋅d(-1) vs. ∼0.103 km(3)⋅d(-1)), and when integrated over the melt season, totaled just 37-75% of MAR, suggesting nontrivial subglacial water storage even in this melt-prone region of the ice sheet. We conclude that (i) the interior surface of the ice sheet can be efficiently drained under optimal conditions, (ii) that digital elevation models alone cannot fully describe supraglacial drainage and its connection to subglacial systems, and (iii) that predicting outflow from climate models alone, without recognition of subglacial processes, may overestimate true meltwater export from the ice sheet to the ocean.

Efficient meltwater drainage through supraglacial streams and rivers on the southwest Greenland ice sheet

PubMed Central

Smith, Laurence C.; Chu, Vena W.; Yang, Kang; Gleason, Colin J.; Pitcher, Lincoln H.; Rennermalm, Asa K.; Legleiter, Carl J.; Behar, Alberto E.; Overstreet, Brandon T.; Moustafa, Samiah E.; Tedesco, Marco; Forster, Richard R.; LeWinter, Adam L.; Finnegan, David C.; Sheng, Yongwei; Balog, James

2015-01-01

Thermally incised meltwater channels that flow each summer across melt-prone surfaces of the Greenland ice sheet have received little direct study. We use high-resolution WorldView-1/2 satellite mapping and in situ measurements to characterize supraglacial water storage, drainage pattern, and discharge across 6,812 km2 of southwest Greenland in July 2012, after a record melt event. Efficient surface drainage was routed through 523 high-order stream/river channel networks, all of which terminated in moulins before reaching the ice edge. Low surface water storage (3.6 ± 0.9 cm), negligible impoundment by supraglacial lakes or topographic depressions, and high discharge to moulins (2.54–2.81 cm⋅d−1) indicate that the surface drainage system conveyed its own storage volume every <2 d to the bed. Moulin discharges mapped inside ∼52% of the source ice watershed for Isortoq, a major proglacial river, totaled ∼41–98% of observed proglacial discharge, highlighting the importance of supraglacial river drainage to true outflow from the ice edge. However, Isortoq discharges tended lower than runoff simulations from the Modèle Atmosphérique Régional (MAR) regional climate model (0.056–0.112 km3⋅d−1 vs. ∼0.103 km3⋅d−1), and when integrated over the melt season, totaled just 37–75% of MAR, suggesting nontrivial subglacial water storage even in this melt-prone region of the ice sheet. We conclude that (i) the interior surface of the ice sheet can be efficiently drained under optimal conditions, (ii) that digital elevation models alone cannot fully describe supraglacial drainage and its connection to subglacial systems, and (iii) that predicting outflow from climate models alone, without recognition of subglacial processes, may overestimate true meltwater export from the ice sheet to the ocean. PMID:25583477

Cell sheet-based tissue engineering for fabricating 3-dimensional heart tissues.

PubMed

Shimizu, Tatsuya

2014-01-01

In addition to stem cell biology, tissue engineering is an essential research field for regenerative medicine. In contrast to cell injection, bioengineered tissue transplantation minimizes cell loss and has the potential to repair tissue defects. A popular approach is scaffold-based tissue engineering, which utilizes a biodegradable polymer scaffold for seeding cells; however, new techniques of cell sheet-based tissue engineering have been developed. Cell sheets are harvested from temperature-responsive culture dishes by simply lowering the temperature. Monolayer or stacked cell sheets are transplantable directly onto damaged tissues and cell sheet transplantation has already been clinically applied. Cardiac cell sheet stacking produces pulsatile heart tissue; however, lack of vasculature limits the viable tissue thickness to 3 layers. Multistep transplantation of triple-layer cardiac cell sheets cocultured with endothelial cells has been used to form thick vascularized cardiac tissue in vivo. Furthermore, in vitro functional blood vessel formation within 3-dimensional (3D) tissues has been realized by successfully imitating in vivo conditions. Triple-layer cardiac cell sheets containing endothelial cells were layered on vascular beds and the constructs were media-perfused using novel bioreactor systems. Interestingly, cocultured endothelial cells migrate into the vascular beds and form perfusable blood vessels. An in vitro multistep procedure has also enabled the fabrication of thick, vascularized heart tissues. Cell sheet-based tissue engineering has revealed great potential to fabricate 3D cardiac tissues and should contribute to future treatment of severe heart diseases and human tissue model production.

Modeling of deformation behavior and texture evolution in magnesium alloy using the intermediate $$\\phi$$-model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Dongsheng; Ahzi, Said; M'Guil, S. M.

2014-01-06

The viscoplastic intermediate phi-model was applied in this work to predict the deformation behavior and texture evolution in a magnesium alloy, an HCP material. We simulated the deformation behavior with different intergranular interaction strengths and compared the predicted results with available experimental results. In this approach, elasticity is neglected and the plastic deformation mechanisms are assumed as a combination of crystallographic slip and twinning systems. Tests are performed for rolling (plane strain compression) of random textured Mg polycrystal as well as for tensile and compressive tests on rolled Mg sheets. Simulated texture evolutions agree well with experimental data. Activities of twinning and slip, predicted by the intermediatemore » $$\\phi$$-model, reveal the strong anisotropic behavior during tension and compression of rolled sheets.« less

Capabilities and performance of the new generation ice-sheet model Elmer/Ice

NASA Astrophysics Data System (ADS)

Gagliardini, O.; Zwinger, T.; Durand, G.; Favier, L.; de Fleurian, B.; Gillet-chaulet, F.; Seddik, H.; Greve, R.; Mallinen, M.; Martin, C.; Raback, P.; Ruokolainen, J.; Schäfer, M.; Thies, J.

2012-12-01

Since the Fourth IPCC Assessment Report, and its conclusion about the inability of ice-sheet flow models to forecast the current increase of polar ice sheet discharge and associated contribution to sea-level rise, a huge development effort has been undertaken by the glaciological community. All around the world, models have been improved and, interestingly, a significant number of new ice-sheet models have emerged. Among them, the parallel finite-element model Elmer/Ice (based on the open-source multi-physics code Elmer) was one of the first full-Stokes models used to make projections of the future of the whole Greenland ice sheet for the coming two centuries. Originally developed to solve dedicated local ice flow problems of high mechanical and physical complexity, Elmer/Ice has today reached the maturity to solve larger scale problems, earning the status of an ice-sheet model. In this presentation, we summarise the almost 10 years of development performed by different groups. We present the components already included in Elmer/Ice, its numerical performance, selected applications, as well as developments planed for the future.

Capabilities and performance of Elmer/Ice, a new generation ice-sheet model

NASA Astrophysics Data System (ADS)

Gagliardini, O.; Zwinger, T.; Gillet-Chaulet, F.; Durand, G.; Favier, L.; de Fleurian, B.; Greve, R.; Malinen, M.; Martín, C.; Råback, P.; Ruokolainen, J.; Sacchettini, M.; Schäfer, M.; Seddik, H.; Thies, J.

2013-03-01

The Fourth IPCC Assessment Report concluded that ice-sheet flow models are unable to forecast the current increase of polar ice sheet discharge and the associated contribution to sea-level rise. Since then, the glaciological community has undertaken a huge effort to develop and improve a new generation of ice-flow models, and as a result, a significant number of new ice-sheet models have emerged. Among them is the parallel finite-element model Elmer/Ice, based on the open-source multi-physics code Elmer. It was one of the first full-Stokes models used to make projections for the evolution of the whole Greenland ice sheet for the coming two centuries. Originally developed to solve local ice flow problems of high mechanical and physical complexity, Elmer/Ice has today reached the maturity to solve larger scale problems, earning the status of an ice-sheet model. Here, we summarise almost 10 yr of development performed by different groups. We present the components already included in Elmer/Ice, its numerical performance, selected applications, as well as developments planned for the future.

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

NASA Astrophysics Data System (ADS)

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

2008-12-01

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

A Transient Initialization Routine of the Community Ice Sheet Model for the Greenland Ice Sheet

NASA Astrophysics Data System (ADS)

van der Laan, Larissa; van den Broeke, Michiel; Noël, Brice; van de Wal, Roderik

2017-04-01

The Community Ice Sheet Model (CISM) is to be applied in future simulations of the Greenland Ice Sheet under a range of climate change scenarios, determining the sensitivity of the ice sheet to individual climatic forcings. In order to achieve reliable results regarding ice sheet stability and assess the probability of future occurrence of tipping points, a realistic initial ice sheet geometry is essential. The current work describes and evaluates the development of a transient initialization routine, using NGRIP 18O isotope data to create a temperature anomaly field. Based on the latter, surface mass balance components runoff and precipitation are perturbed for the past 125k years. The precipitation and runoff fields originate from a downscaled 1 km resolution version of the regional climate model RACMO2.3 for the period 1961-1990. The result of the initialization routine is a present-day ice sheet with a transient memory of the last glacial-interglacial cycle, which will serve as the future runs' initial condition.

46 CFR 160.052-1 - Incorporation by reference.

Code of Federal Regulations, 2010 CFR

2010-10-01

..., Model AP. Sheet 2—Cutting Pattern and General Arrangement, Model CPM. Sheet 3—Cutting Pattern and General Arrangement, Model CPS. Sheet 4—Insert Patterns. (c) Copies on file. The manufacturer shall keep a... Specifications and Standards may be purchased from the Business Service Center, General Services Administration...

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

PubMed Central

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

2012-01-01

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

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

PubMed

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

2012-10-02

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

Antarctic glacial history from numerical models and continental margin sediments

USGS Publications Warehouse

Barker, P.F.; Barrett, P.J.; Cooper, A. K.; Huybrechts, P.

1999-01-01

The climate record of glacially transported sediments in prograded wedges around the Antarctic outer continental shelf, and their derivatives in continental rise drifts, may be combined to produce an Antarctic ice sheet history, using numerical models of ice sheet response to temperature and sea-level change. Examination of published models suggests several preliminary conclusions about ice sheet history. The ice sheet's present high sensitivity to sea-level change at short (orbital) periods was developed gradually as its size increased, replacing a declining sensitivity to temperature. Models suggest that the ice sheet grew abruptly to 40% (or possibly more) of its present size at the Eocene-Oligocene boundary, mainly as a result of its own temperature sensitivity. A large but more gradual middle Miocene change was externally driven, probably by development of the Antarctic Circumpolar Current (ACC) and Polar Front, provided that a few million years' delay can be explained. The Oligocene ice sheet varied considerably in size and areal extent, but the late Miocene ice sheet was more stable, though significantly warmer than today's. This difference probably relates to the confining effect of the Antarctic continental margin. Present-day numerical models of ice sheet development are sufficient to guide current sampling plans, but sea-ice formation, polar wander, basal topography and ice streaming can be identified as factors meriting additional modelling effort in the future.

On the azimuthal size of flux ropes near lunar orbit

NASA Astrophysics Data System (ADS)

Kiehas, S. A.; Angelopoulos, V.; Runov, A.; Li, S.-S.

2013-07-01

We present Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon's Interaction with the Sun (ARTEMIS) dual-probe observations of flux ropes in the Earth's magnetotail near lunar orbit. On 15 July 2011 between 0400 and 0500 UT, the ARTEMIS probes (P1 and P2) are separated by ˜ (9/10/3) RE(XGSW/YGSW/ZGSW). GSW denotes the Geocentric Solar Wind coordinate system and differs from the GSM coordinate system in that its X axis is antiparallel to the solar wind. P1 is near midnight and P2 in the postmidnight sector at ˜ -13 RE YGSW. During a ˜ 50 min interval on 15 July 2011, P1 crossed the current sheet and encountered a flux rope thereafter. During the same interval, P2 observed only one flux rope near the time P1 crossed the current sheet but no flux rope or traveling compression region (TCR) for P1's subsequent flux rope observation. A Tsyganenko-Fairfield model and minimum variance analysis during the current sheet crossing are used to infer the current sheet location with respect to the probes. We find the distance between P2 and the plasma sheet boundary to be less than 3 RE. Under these circumstances, P2 would be expected to observe a TCR if the flux rope observed by P1 extended to the postmidnight location of P2. The lack of such observations indicates that, contrary to previous models and simulation results, flux ropes may be spatially confined in the dusk-dawn direction and do not extend across the entire cross section of the tail near lunar orbit.

Unveiling climate and ice-sheet history from drilling in high-latitude margins and future perspectives

NASA Astrophysics Data System (ADS)

Escutia Dotti, Carlota

2010-05-01

Polar ice is an important component of the climate system, affecting global sea level, ocean circulation and heat transport, marine productivity, and albedo. During the last decades drilling in the Arctic (IODP ACEX and Bering Expeditions) and in Antarctica (ODP Legs 178, 188, IODP Expedition 318 and ANDRILL) has revealed regional information about sea ice and ice sheets development and evolution. Integration of this data with numerical modeling provide an understanding of the early development of the ice sheets and their variability through the Cenozoic. Much of this work points to atmospheric CO2 and other greenhouse gases concentrations as important triggering mechanism driving the onset of glaciation and subsequent ice volume variability. With current increasing atmospheric greenhouse gases concentrations resulting in rapidly rising global temperatures, studies of polar climates become increasingly prominent on the research agenda. Despite of the relevance of the high-latitudes in the global climate systems, the short- and long-term history of the ice sheets and sea-ice and its relationships with paleoclimatic, paleoceanographic, and sea level changes is still poorly understood. A multinational, multiplatform scientific drilling strategy is being developed to recover key physical evidence from selected high-latitude areas. This strategy is aimed at addressing key knowledge gaps about the role of polar ice in climate change, targeting questions such as timing of events, rates of change, tipping points, regional variations, and northern vs. southern hemispheres (in phase or out-of-phase) variability. This data is critical to provide constrains to sea-ice and ice sheet models, which are the basis for forecasting the future of the cryosphere in a warming world.

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

NASA Astrophysics Data System (ADS)

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

2015-12-01

We present a new, complete ice thickness change reconstruction of the NE sector of the Greenland Ice Sheet for 1978-2014, partitioned into changes due to surface processes and ice dynamics. Elevation changes are computed from all available stereoscopic DEMs, and laser altimetry data (ICESat, ATM, LVIS). Surface Mass Balance and firn-compaction estimates are from RACMO2.3. Originating nearly at the divide of the Greenland Ice Sheet (GrIS), the dynamically active North East Ice Stream (NEGIS) is capable of rapidly transmitting ice-marginal forcing far inland. Thus, NEGIS provides a possible mechanism for a rapid drawdown of ice from the ice sheet interior as marginal warming, thinning and retreat continues. Our altimetry record shows accelerating dynamic thinning of Zachariæ Isstrom, initially limited to the deepest part of the fjord near the calving front (1978-2000) and then extending at least 75 km inland. At the same time, changes over the Nioghalvfjerdsfjorden (N79) Glacier are negligible. We also detect localized large dynamic changes at higher elevations on the ice sheet. These thickness changes, often occurring at the onset of fast flow, could indicate rapid variations of basal lubrication due to rerouting of subglacial drainage. We investigate the possible causes of the observed spatiotemporal pattern of ice sheet elevation changes using the Ice Sheet System Model (ISSM). This work build on our previous studies examining the sensitivity of ice flow within the Northeast Greenland Ice Stream (NEGIS) to key fields, including ice viscosity, basal drag. We assimilate the new altimetry record into ISSM to improve the reconstruction of basal friction and ice viscosity. Finally, airborne geophysical (gravity, magnetic) and ice-penetrating radar data is examined to identify the potential geologic controls on the ice thickness change pattern. Our study provides the first comprehensive reconstruction of ice thickness changes for the entire NEGIS drainage basin during the last 40 years. Through the use of ISSM, we examine possible mechanism explaining the observed changes. The improved understanding gained through this research will contribute better projections of future ice loss from this most vulnerable region of the GrIS.

Proglacial River Reveals Substantial Greenland Ice Sheet Climate Sensitivity and Meltwater Routing Delays

NASA Astrophysics Data System (ADS)

van As, D.; Mikkelsen, A. B.; Holtegaard Nielsen, M.; Claesson Liljedahl, L.; Lindback, K.; Pitcher, L. H.; Hasholt, B.

2016-12-01

A 12.000 km2 area of the Greenland ice sheet discharges meltwater via the proglacial Watson River in west Greenland. In a ten-year time span of continuous monitoring (2006-2015), the river discharged 3.8 km3 to 11.2 km3 yr-1. The large interannual variability is for an important part explained by hypsometric amplification: the flattening of the ice sheet with elevation adds 70% meltwater discharge sensitivity to atmospheric temperature. Comparing river discharge with ice sheet surface meltwater production from an observation-based surface mass balance model we quantify multiple-day routing delays for meltwater transit through the supra-, en-, sub- and proglacial system. This delay increases with ice sheet surface elevation: on average five days for surface water at the previous-known equilibrium line altitude (ELA) of ca. 1550 m, and seven days at the 2009-2015 ELA of ca. 1800 m above sea level. A flooding of the Kangerlussuaq bridge as in July 2012 thus requires a multi-day high-melt episode and can therefore be anticipated by in-situ monitoring of ice sheet melt. No evidence of significant en- or subglacial meltwater retention is found.

Reconstructing the groundwater flow in the Baltic Basin during the Last glaciation

NASA Astrophysics Data System (ADS)

Saks, T.; Sennikovs, J.; Timuhins, A.; Kalvāns, A.

2012-04-01

In last decades it has been discussed that most large ice sheets tend to reside on warm beds even in harsh clima tic conditions and subglacial melting occurs due to geothermal heat flow and deformation heat of the ice flow. However the subglacial groundwater recharge and flow conditions have been addressed in only few studies. The aim of this study is to establish the groundwater flow pattern in the Baltic Basin below the Scandinavian ice sheet during the Late Weichselian glaciation. The calculation results are compared to the known distribution of the groundwater body of the glacial origin found in Cambrian - Vendian (Cm-V) aquifer in the Northern Estonia which is believed to have originated as a result of subglacial meltwater infiltration during the reoccurring glaciations. Steady state regional groundwater flow model of the Baltic Basin was used to simulate the groundwater flow beneath the ice sheet with its geometry adjusted to reflect the subglacial topography. Ice thickness modelling data (Argus&Peltier, 2010) was used for the setup of the boundary conditions: the meltwater pressure at the ice bed was assumed equal to the overlying ice mass. The modelling results suggest two main recharge areas of the Cm-V aquifer system, and reversed groundwater flow that persisted for at least 14 thousand years. Model results show that the groundwater flow velocities in the Cm-V aquifer in the recharge area in N-Estonia beneath the ice sheet exceeded the present velocities by a factor of 10 on average. The calculated meltwater volume recharged into the Cm-V aquifer system during the Late Weichselian corresponds roughly to the estimated, however, considering the fact, that the study area has been glaciated at least 4 times this is an overestimation. The modeling results attest the hypothesis of light dO18 groundwater glacial origin in the Cm-V aquifer system, however the volumes, timing and processes involved in the meltwater intrusion are yet to be explored. This study was financed by the European Social fund Nr. 2009/0212/1DP/1.1.1.2.0/09/APIA/VIAA/060

Water Accounting Plus (WA+) - a water accounting procedure for complex river basins based on satellite measurements

NASA Astrophysics Data System (ADS)

Karimi, P.; Bastiaanssen, W. G. M.; Molden, D.

2012-11-01

Coping with the issue of water scarcity and growing competition for water among different sectors requires proper water management strategies and decision processes. A pre-requisite is a clear understanding of the basin hydrological processes, manageable and unmanageable water flows, the interaction with land use and opportunities to mitigate the negative effects and increase the benefits of water depletion on society. Currently, water professionals do not have a common framework that links hydrological flows to user groups of water and their benefits. The absence of a standard hydrological and water management summary is causing confusion and wrong decisions. The non-availability of water flow data is one of the underpinning reasons for not having operational water accounting systems for river basins in place. In this paper we introduce Water Accounting Plus (WA+), which is a new framework designed to provide explicit spatial information on water depletion and net withdrawal processes in complex river basins. The influence of land use on the water cycle is described explicitly by defining land use groups with common characteristics. Analogous to financial accounting, WA+ presents four sheets including (i) a resource base sheet, (ii) a consumption sheet, (iii) a productivity sheet, and (iv) a withdrawal sheet. Every sheet encompasses a set of indicators that summarize the overall water resources situation. The impact of external (e.g. climate change) and internal influences (e.g. infrastructure building) can be estimated by studying the changes in these WA+ indicators. Satellite measurements can be used for 3 out of the 4 sheets, but is not a precondition for implementing WA+ framework. Data from hydrological models and water allocation models can also be used as inputs to WA+.

PRISM4: Pliocene Research, Interpretation and Synoptic Mapping mid Piacenzian paleoenvironmental reconstruction

NASA Astrophysics Data System (ADS)

Dowsett, H. J.; Dolan, A. M.; Rowley, D. B.; Moucha, R.; Forte, A. M.; Mitrovica, J. X.; Pound, M. J.; Salzmann, U.; Robinson, M. M.; Chandler, M. A.; Foley, K.; Haywood, A.

2016-12-01

Past Intervals in Earth history provide unique windows into conditions much different than those observed today. We investigated the paleoenvironments of a past warm interval in the mid Piacenzian ( 3 million years ago). The PRISM4 reconstruction contains twelve internally consistent and integrated data sets representing our best synoptic understanding of surface temperature, vegetation, soils, lakes, ice sheets, topography, and bathymetry. Starting points in the generation of our Piacenzian reconstruction are basic geochemical, faunal, floral, soil, cryospheric, topographic, bathymetric, sedimentologic, and stratigraphic data. Marine and terrestral temperature estimates are based upon multiple proxies (including faunal, floral, geochemical, and biomarker analyses). The reconstruction of Piacenzian global vegetation is based on the integration of paleobotanical data and BIOME4 model outputs. Antarctic and Greenland ice sheets are derived from the previous PRISM3 and PLISMIP (Pliocene Ice Sheet Model Intercomparison Project) results, respectively. Paleogeography is based upon an initial ETOPO1 digital elevation model incorporating PRISM4 ice sheets, GIA, and adjustments due to mantle convection. Soils are determined through comparison of sedimentological and stratigraphic data with the BIOME reconstruction. Lakes are determined from stratigraphic and sedimentological data. Sea-level equivalent (+20 m) is estimated from the reduced volume of the PRISM4 ice sheets and is consistent with our PRISM4 paleogeography. While not an analog for future conditions, the PRISM4 conceptual reconstruction provides insights into processes that occurred in the past and can inform us about the future. We will discuss the use of these data as boundary conditions and verification for global climate model simulations of the Pliocene, aimed at improving our understanding of the climate system as we prepare for future changes.

VISL: A Virtual Ice Sheet Laboratory For Outreach and K-12 Education

NASA Astrophysics Data System (ADS)

Halkides, D. J.; Larour, E. Y.; Cheng, D. L.; Perez, G.; Romero, V.; Saks, O.

2014-12-01

We present a prototype Virtual Ice Sheet Laboratory (VISL) geared to K-12 classrooms and the general public, with the goal of improving climate literacy, especially in regards to the crucial role of the polar ice sheets in Earth's climate and sea level. VISL will allow users to perform guided experiments using the Ice Sheet System Model (ISSM), a state-of-the-art ice flow model developed at NASA's Jet Propulsion Laboratory and UC Irvine that simulates the near-term evolution of the ice sheets on Greenland and Antarctica. VISL users will access ISSM via a graphical interface that can be launched from a web browser on a computer, tablet or smart phone. Users select climate conditions and run time by moving graphic sliders then watch how a given region evolves in time under those conditions. Lesson plans will include conceptual background, instructions for table top experiments related to the concepts addressed in a given lesson, and a guide for performing model experiments and interpreting their results. Activities with different degrees of complexity will aim for consistency with NGSS Physical Science criteria for different grade bands (K-2, 3-5, 6-8, and 9-12), although they will not be labeled as such to encourage a broad user base. Activities will emphasize the development of physical intuition and critical thinking skills, understanding conceptual and computational models, as well as observation recording, concept articulation, hypothesis formulation and testing, and mathematical analysis. At our present phase of development, we seek input from the greater science education and outreach communities regarding VISL's planned content, as well as additional features and topic areas that educators and students would find useful.

VISL: A Virtual Ice Sheet Laboratory For Outreach and K-12 Education

NASA Astrophysics Data System (ADS)

Cheng, D. L. C.; Halkides, D. J.; Larour, E. Y.; Moore, J.; Dunn, S.; Perez, G.

2015-12-01

We present an update on our developing Virtual Ice Sheet Laboratory (VISL). Geared to K-12 classrooms and the general public, VISL's main goal is to improve climate literacy, especially in regards to the crucial role of the polar ice sheets in Earth's climate and sea level. VISL will allow users to perform guided experiments using the Ice Sheet System Model (ISSM), a state-of-the-art ice flow model developed at NASA's Jet Propulsion Laboratory and UC Irvine that simulates the near-term evolution of the ice sheets on Greenland and Antarctica. VISL users will access ISSM via a graphical interface that can be launched from a web browser on a computer, tablet or smart phone. Users select climate conditions and run time by moving graphic sliders then watch how a given region evolves in time under those conditions. Lesson plans will include conceptual background, instructions for table top experiments related to the concepts addressed in a given lesson, and a guide for performing model experiments and interpreting their results. Activities with different degrees of complexity will aim for consistency with NGSS Physical Science criteria for different grade bands (K-2, 3-5, 6-8, and 9-12), although they will not be labeled as such to encourage a broad user base. Activities will emphasize the development of physical intuition and critical thinking skills, understanding conceptual and computational models, as well as observation recording, concept articulation, hypothesis formulation and testing, and mathematical analysis. At our present phase of development, we seek input from the greater science education and outreach communities regarding VISL's planned content, as well as additional features and topic areas that educators and students would find useful.

Data assimilation of surface altimetry on the North-Easter Ice Stream using the Ice Sheet System Model (ISSM)

NASA Astrophysics Data System (ADS)

Larour, Eric; Utke, Jean; Morlighem, Mathieu; Seroussi, Helene; Csatho, Beata; Schenk, Anton; Rignot, Eric; Khazendar, Ala

2014-05-01

Extensive surface altimetry data has been collected on polar ice sheets over the past decades, following missions such as Envisat and IceSat. This data record will further increase in size with the new CryoSat mission, the ongoing Operation IceBridge Mission and the soon to launch IceSat-2 mission. In order to make the best use of these dataset, ice flow models need to improve on the way they ingest surface altimetry to infer: 1) parameterizations of poorly known physical processes such as basal friction; 2) boundary conditions such as Surface Mass Balance (SMB). Ad-hoc sensitivity studies and adjoint-based inversions have so far been the way ice sheet models have attempted to resolve the impact of 1) on their results. As for boundary conditions or the lack thereof, most studies assume that they are a fixed quantity, which, though prone to large errors from the measurement itself, is not varied according to the simulated results. Here, we propose a method based on automatic differentiation to improve boundary conditions at the base and surface of the ice sheet during a short-term transient run for which surface altimetry observations are available. The method relies on minimizing a cost-function, the best fit between modeled surface evolution and surface altimetry observations, using gradients that are computed for each time step from automatic differentiation of the ISSM (Ice Sheet System Model) code. The approach relies on overloaded operators using the ADOLC (Automatic Differentiation by OverLoading in C++) package. It is applied to the 79 North Glacier, Greenland, for a short term transient spanning a couple of decades before the start of the retreat of the Zachariae Isstrom outlet glacier. Our results show adjustments required on the basal friction and the SMB of the whole basin to best fit surface altimetry observations, along with sensitivities each one of these parameters has on the overall cost function. Our approach presents a pathway towards assimilating multiple datasets in transient ice flow models of Greenland and Antarctica, which will become increasingly important as the amount of available observations becomes too large to assess on a case by case basis. This work was performed at the California Institute of Technology's Jet Propulsion Laboratory under a contract with the National Aeronautics and Space Administration's Cryosphere Science Program.

The influence of ice sheets on temperature during the past 38 million years inferred from a one-dimensional ice sheet-climate model

NASA Astrophysics Data System (ADS)

Stap, Lennert B.; van de Wal, Roderik S. W.; de Boer, Bas; Bintanja, Richard; Lourens, Lucas J.

2017-09-01

Since the inception of the Antarctic ice sheet at the Eocene-Oligocene transition (˜ 34 Myr ago), land ice has played a crucial role in Earth's climate. Through feedbacks in the climate system, land ice variability modifies atmospheric temperature changes induced by orbital, topographical, and greenhouse gas variations. Quantification of these feedbacks on long timescales has hitherto scarcely been undertaken. In this study, we use a zonally averaged energy balance climate model bidirectionally coupled to a one-dimensional ice sheet model, capturing the ice-albedo and surface-height-temperature feedbacks. Potentially important transient changes in topographic boundary conditions by tectonics and erosion are not taken into account but are briefly discussed. The relative simplicity of the coupled model allows us to perform integrations over the past 38 Myr in a fully transient fashion using a benthic oxygen isotope record as forcing to inversely simulate CO2. Firstly, we find that the results of the simulations over the past 5 Myr are dependent on whether the model run is started at 5 or 38 Myr ago. This is because the relation between CO2 and temperature is subject to hysteresis. When the climate cools from very high CO2 levels, as in the longer transient 38 Myr run, temperatures in the lower CO2 range of the past 5 Myr are higher than when the climate is initialised at low temperatures. Consequently, the modelled CO2 concentrations depend on the initial state. Taking the realistic warm initialisation into account, we come to a best estimate of CO2, temperature, ice-volume-equivalent sea level, and benthic δ18O over the past 38 Myr. Secondly, we study the influence of ice sheets on the evolution of global temperature and polar amplification by comparing runs with ice sheet-climate interaction switched on and off. By passing only albedo or surface height changes to the climate model, we can distinguish the separate effects of the ice-albedo and surface-height-temperature feedbacks. We find that ice volume variability has a strong enhancing effect on atmospheric temperature changes, particularly in the regions where the ice sheets are located. As a result, polar amplification in the Northern Hemisphere decreases towards warmer climates as there is little land ice left to melt. Conversely, decay of the Antarctic ice sheet increases polar amplification in the Southern Hemisphere in the high-CO2 regime. Our results also show that in cooler climates than the pre-industrial, the ice-albedo feedback predominates the surface-height-temperature feedback, while in warmer climates they are more equal in strength.

Insolation-driven 100 kyr glacial cycles and millennial climate change

NASA Astrophysics Data System (ADS)

Abe-Ouchi, A.; Saito, F.; Kawamura, K.; Raymo, M. E.; Okuno, J.; Takahashi, K.; Blatter, H.

2013-12-01

The waxing and waning of Northern Hemisphere ice sheets over the past one million years is dominated by an approximately 100-kyr periodicity and a sawtooth pattern (gradual growth and fast termination). Milankovitch theory proposes that summer insolation at high northern latitudes drives the glacial cycles, and statistical tests demonstrated that the glacial cycles are indeed linked to eccentricity, obliquity and precession cycles. However, insolation alone cannot explain the strong 100 kyr cycle which presumably arises through internal climatic feedbacks. Prior work with conceptual models, for example, showed that glacial terminations are associated with the build-up of Northern Hemisphere 'excess ice', but the physical mechanisms of 100-kyr cycle at work remain unclear. Here, using comprehensive climate and ice sheet models, we show that the ~100-kyr periodicity is explained by insolation and internal feedback amongst the climate, ice sheet and lithosphere/asthenosphere system (reference). We found that equilibrium states of ice sheets exhibit hysteresis responses to summer insolation, and that the shape and position of the hysteresis loop play a key role in determining the periodicities of glacial cycles. The hysteresis loop of the North American ice sheet is such that, after its inception, the ice sheet mass balance remains mostly positive or neutral through several precession cycles whose amplitude decreases towards an eccentricity minimum. The larger the ice sheet grows and extends towards lower latitudes, the smaller is the insolation required to turn the mass balance to negative. Therefore, once the large ice sheet is established, only a moderate increase in insolation can trigger a negative mass balance, leading to a complete retreat within several thousand years, due to the delayed isostatic rebound. The effect of ocean circulation and millennial scale climate change are not playing the dominant role for determing the 100kyr cycle, but are effective for modifying the speed and geographical pattern of the waxing and waning of the Northern Hemisphere ice sheets and their melt water. (reference of the basic results: Abe-Ouchi et al, 2013, Insolation-driven 100,000 year glacial cycles and hysteresis of ice-sheet volume, Nature, 500, 190-193.)

Challenges for understanding Antarctic surface hydrology and ice-shelf stability

NASA Astrophysics Data System (ADS)

Kingslake, J.; Bell, R. E.; Banwell, A. F.; Boghosian, A.; Spergel, J.; Trusel, L. D.

2017-12-01

It is widely hypothesized that surface meltwater can contribute to ice mass loss in Antarctica through its impact on ice-shelf stability. Meltwater potentially expedites ice-shelf calving by flowing into and enlarging existing crevasses, and could even trigger ice-shelf disintegration via stresses generated by melt ponds. When ice shelves collapse, the adjacent grounded ice accelerates and thins, which contributes to sea-level rise. How these mechanisms mediate the interactions between the atmosphere, the ocean and the ice sheet is the subject of long-standing research efforts. The drainage of water across the surface of the Antarctic Ice Sheet and its ice shelves is beginning to be recognized as another important aspect of the system. Recent studies have revealed that surface meltwater drainage is more widespread than previously thought and that surface hydrological systems in Antarctica may expand and proliferate this century. Contrasting hypotheses regarding the impact of the proliferation of drainage systems on ice-shelf stability have emerged. Surface drainage could deliver meltwater to vulnerable area or export meltwater from ice shelves entirely. Which behavior dominates may have a large impact on the future response of the Antarctic Ice Sheet to atmospheric warming. We will discuss these recent discoveries and hypotheses, as well as new detailed studies of specific areas where hydrological systems are well developed, such as Amery and Nimrod Ice Shelves. We will highlight analogies that can be drawn with Greenlandic (near-)surface hydrology and, crucially, where hydrological systems on the two ice sheets are very different, leading to potentially important gaps in our understanding. Finally, we will look ahead to the key questions that we argue will need to be if we are to determine the role Antarctic surface hydrology could play in the future of the ice sheet. These include: Where does meltwater pond today and how will this change this century? What coupled glaciological-hydrological dynamics control how drainage systems will change as melt rates increase this century? How do we incorporate surface hydrology into ice-sheet models? While we may be currently unable to answer these and related questions, we aim to start the discussion on how the community can move towards answering them in the future.

Regional Patterns of Stress Transfer in the Ablation Zone of the Western Greenland Ice Sheet

NASA Astrophysics Data System (ADS)

Andrews, L. C.; Hoffman, M. J.; Neumann, T.; Catania, G. A.; Luethi, M. P.; Hawley, R. L.

2016-12-01

Current understanding of the subglacial system indicates that the seasonal evolution of ice flow is strongly controlled by the gradual upstream progression of an inefficient - efficient transition within the subglacial hydrologic system followed by the reduction of melt and a downstream collapse of the efficient system. Using a spatiotemporally dense network of GPS-derived surface velocities from the Pâkitsoq Region of the western Greenland Ice Sheet, we find that this pattern of subglacial development is complicated by heterogeneous bed topography, resulting in complex patterns of ice flow. Following low elevation melt onset, early melt season strain rate anomalies are dominated by regional extension, which then gives way to spatially expansive compression. However, once daily minimum ice velocities fall below the observed winter background velocities, an alternating spatial pattern of extension and compression prevails. This pattern of strain rate anomalies is correlated with changing basal topography and differences in the magnitude of diurnal surface ice speeds. Along subglacial ridges, diurnal variability in ice speed is large, suggestive of a mature, efficient subglacial system. In regions of subglacial lows, diurnal variability in ice velocity is relatively low, likely associated with a less developed efficient subglacial system. The observed pattern suggests that borehole observations and modeling results demonstrating the importance of longitudinal stress transfer at a single field location are likely widely applicable in our study area and other regions of the Greenland Ice Sheet with highly variable bed topography. Further, the complex pattern of ice flow and evidence of spatially extensive longitudinal stress transfer add to the body of work indicating that the bed character plays an important role in the development of the subglacial system; closely matching diurnal ice velocity patterns with subglacial models may be difficult without coupling these models to high order ice flow models.

On the Reconstruction of Palaeo-Ice Sheets: Recent Advances and Future Challenges

NASA Technical Reports Server (NTRS)

Stokes, Chris R.; Tarasov, Lev; Blomdin, Robin; Cronin, Thomas M.; Fisher, Timothy G.; Gyllencreutz, Richard; Hattestrand, Clas; Heyman, Jacob; Hindmarsh, Richard C. A.; Hughes, Anna L. C.;

On the reconstruction of palaeo-ice sheets: Recent advances and future challenges

USGS Publications Warehouse

Stokes, Chris R.; Tarasov, Lev; Blomdin, Robin; Cronin, Thomas M.; Fisher, Timothy G.; Gyllencreutz, Richard; Hattestrand, Clas; Heyman, Jakob; Hindmarsh, Richard C. A.; Hughes, Anna L. C.; Jakobsson, Martin; Kirchner, Nina; Livingstone, Stephen J.; Margold, Martin; Murton, Julian B.; Noormets, Riko; Peltier, W. Richard; Peteet, Dorothy M.; Piper, David J. W.; Preusser, Frank; Renssen, Hans; Roberts, David H.; Roche, Didier M.; Saint-Ange, Francky; Stroeven, Arjen P.; Teller, James T.

2015-01-01

Reconstructing the growth and decay of palaeo-ice sheets is critical to understanding mechanisms of global climate change and associated sea-level fluctuations in the past, present and future. The significance of palaeo-ice sheets is further underlined by the broad range of disciplines concerned with reconstructing their behaviour, many of which have undergone a rapid expansion since the 1980s. In particular, there has been a major increase in the size and qualitative diversity of empirical data used to reconstruct and date ice sheets, and major improvements in our ability to simulate their dynamics in numerical ice sheet models. These developments have made it increasingly necessary to forge interdisciplinary links between sub-disciplines and to link numerical modelling with observations and dating of proxy records. The aim of this paper is to evaluate recent developments in the methods used to reconstruct ice sheets and outline some key challenges that remain, with an emphasis on how future work might integrate terrestrial and marine evidence together with numerical modelling. Our focus is on pan-ice sheet reconstructions of the last deglaciation, but regional case studies are used to illustrate methodological achievements, challenges and opportunities. Whilst various disciplines have made important progress in our understanding of ice-sheet dynamics, it is clear that data-model integration remains under-used, and that uncertainties remain poorly quantified in both empirically-based and numerical ice-sheet reconstructions. The representation of past climate will continue to be the largest source of uncertainty for numerical modelling. As such, palaeo-observations are critical to constrain and validate modelling. State-of-the-art numerical models will continue to improve both in model resolution and in the breadth of inclusion of relevant processes, thereby enabling more accurate and more direct comparison with the increasing range of palaeo-observations. Thus, the capability is developing to use all relevant palaeo-records to more strongly constrain deglacial (and to a lesser extent pre-LGM) ice sheet evolution. In working towards that goal, the accurate representation of uncertainties is required for both constraint data and model outputs. Close cooperation between modelling and data-gathering communities is essential to ensure this capability is realised and continues to progress.

A coronal magnetic field model with horizontal volume and sheet currents

NASA Technical Reports Server (NTRS)

Zhao, Xuepu; Hoeksema, J. Todd

1994-01-01

When globally mapping the observed photospheric magnetic field into the corona, the interaction of the solar wind and magnetic field has been treated either by imposing source surface boundary conditions that tacitly require volume currents outside the source surface or by limiting the interaction to thin current sheets between oppositely directed field regions. Yet observations and numerical Magnetohydrodynamic (MHD) calculations suggest the presence of non-force-free volume currents throughout the corona as well as thin current sheets in the neighborhoods of the interfaces between closed and open field lines or between oppositely directed open field lines surrounding coronal helmet-streamer structures. This work presents a model including both horizontal volume currents and streamer sheet currents. The present model builds on the magnetostatic equilibria developed by Bogdan and Low and the current-sheet modeling technique developed by Schatten. The calculation uses synoptic charts of the line-of-sight component of the photospheric magnetic field measured at the Wilcox Solar Observatory. Comparison of an MHD model with the calculated model results for the case of a dipole field and comparison of eclipse observations with calculations for CR 1647 (near solar minimum) show that this horizontal current-current-sheet model reproduces polar plumes and axes of corona streamers better than the source-surface model and reproduces polar plumes and axes of corona streamers better than the source-surface model and reproduces coro nal helmet structures better than the current-sheet model.

Modelling the climate and ice sheets of the mid-Pliocene warm period: a test of model dependency

NASA Astrophysics Data System (ADS)

Dolan, Aisling; Haywood, Alan; Lunt, Daniel; Hill, Daniel

2010-05-01

The mid-Pliocene warm period (MPWP; c. 3.0 - 3.3 million years ago) has been the subject of a large number of published studies during the last decade. It is an interval in Earth history, where conditions were similar to those predicted by climate models for the end of the 21st Century. Not only is it important to increase our understanding of the climate dynamics in a warmer world, it is also important to determine exactly how well numerical models can retrodict a climate significantly different from the present day, in order to have confidence in them for predicting the future climate. Previous General Circulation Model (GCM) simulations have indicated that MPWP mean annual surface temperatures were on average 2 to 3˚C warmer than the pre-industrial era. Coastal stratigraphy and benthic oxygen isotope records suggest that terrestrial ice volumes were reduced when compared to modern. Ice sheet modelling studies have supported this decrease in cryospheric extent. Generally speaking, both climate and ice sheet modelling studies have only used results from one numerical model when simulating the climate of the MPWP. However, recent projects such as PMIP (the Palaeoclimate Modelling Intercomparison Project) have emphasised the need to explore the dependency of past climate predictions on the specific climate model which is used. Here we present a comparison of MPWP climatologies produced by three atmosphere only GCMs from the Goddard Institute of Space Studies (GISS), the National Centre for Atmospheric Research (NCAR) and the Hadley Centre for Climate Prediction and Research (GCMAM3, CAM3-CLM and HadAM3 respectively). We focus on the ability of the GCMs to simulate climate fields needed to drive an offline ice sheet model to assess whether there are any significant differences between the climatologies. By taking the different temperature and precipitation predictions simulated by the three models as a forcing, and adopting GCM-specific topography, we have used the British Antarctic Survey thermomechanically coupled ice sheet model (BASISM) to test the extent to which equilibrium state ice sheets in the Northern Hemisphere are GCM dependent. Initial results which do not use GCM-specific topography suggest that employing different GCM climatologies with only small differences in surface air temperature and precipitation has a dramatic effect on the resultant Greenland ice sheet, where the end-member ice sheets vary from near modern to almost zero ice volume. As an extension of this analysis, we will also present results using a second ice sheet model (Glimmer), with a view to testing the degree to which end-member ice sheets are ice sheet model dependent, something which has not previously been addressed. Initially, BASISM and Glimmer will be internally optimised for performance, but we will also present a comparison where BASISM will be configured to the Glimmer model setup in a further test of ice sheet model dependency.

Modeling Primary Breakup: A Three-Dimensional Eulerian Level Set/Vortex Sheet Method for Two-Phase Interface Dynamics

NASA Technical Reports Server (NTRS)

Herrmann, M.

2003-01-01

This paper is divided into four parts. First, the level set/vortex sheet method for three-dimensional two-phase interface dynamics is presented. Second, the LSS model for the primary breakup of turbulent liquid jets and sheets is outlined and all terms requiring subgrid modeling are identified. Then, preliminary three-dimensional results of the level set/vortex sheet method are presented and discussed. Finally, conclusions are drawn and an outlook to future work is given.

ENVIRONMENTAL INFORMATION MANAGEMENT SYSTEM (EIMS) FACT SHEET

EPA Science Inventory

The purpose of the fact sheet is to provide information about the US EPA Office of Research and Developments Environmental Information Management System. The fact sheet indicates the type of records that are in EIMS, systems that are integrated with EIMS as well as some highligh...

The influence of meltwater on the thermal structure and flow of the Greenland Ice Sheet

NASA Astrophysics Data System (ADS)

Poinar, Kristin

As the climate has warmed over the past decades, the amount of melt on the Greenland Ice Sheet has increased, and areas higher on the ice sheet have begun to melt regularly. This increase in melt has been hypothesized to enhance ice flow in myriad ways, including through basal lubrication and englacial refreezing. By developing and interpreting thermal ice-sheet models and analyzing remote sensing data, I evaluate the effect of these processes on ice flow and sea-level rise from the Greenland Ice Sheet. I first develop a thermal ice sheet model that is applicable to western Greenland. Key components of this model are its treatment of multiple phases (solid ice and liquid water) and its viscosity-dependent velocity field. I apply the model to Jakobshavn Isbrae, a fast-flowing outlet glacier. This is an important benchmark for my model, which I next apply to the topics outlined above. I use the thermal model to calculate the effect of englacial latent-heat transfer (meltwater refreezing within englacial features such as firn and crevasses) on ice dynamics in western Greenland. I find that in slow-moving areas, this can significantly warm the ice, but that englacial latent heat transfer has only a minimal effect on ice motion (60%) of the ice flux into the ocean, evidence of deep englacial warming is virtually absent. Thus, the effects of englacial latent heat transfer on ice motion are likely limited to slow-moving regions, which limits its importance to ice-sheet mass balance. Next, I couple a model for ice fracture to a modified version of my thermal model to calculate the depth and shape evolution of water-filled crevasses that form in crevasse fields. At most elevations and for typical water input volumes, crevasses penetrate to the top ~200--300 meters depth, warm the ice there by ~10°C, and may persist englacially, in a liquid state, for multiple decades. The surface hydrological network limits the amount of water that can reach most crevasses. We find that the depth and longevity of such crevasses is relatively robust to realistic increases in melt volumes over the coming century, so that we should not expect large changes in the englacial hydrological system under near-future climate regimes. These inferences put important constraints on the timescales of the Greenland supraglacial-to-subglacial water cycle. Finally, I assess the likelihood that higher-elevation surface melt could deliver water to regions where the bed is currently frozen. This hypothetical process is important because it could potentially greatly accelerate the seaward motion of the ice sheet. By analyzing surface strain rates and comparing them to my modeled basal temperature field, I find that this scenario is unlikely to occur: the conditions necessary to form surface-to-bed conduits are rarely found at higher elevations (~1600 meters) that may overlie frozen beds.

Modeling of subglacial hydrological development following rapid supraglacial lake drainage.

PubMed

Dow, C F; Kulessa, B; Rutt, I C; Tsai, V C; Pimentel, S; Doyle, S H; van As, D; Lindbäck, K; Pettersson, R; Jones, G A; Hubbard, A

2015-06-01

The rapid drainage of supraglacial lakes injects substantial volumes of water to the bed of the Greenland ice sheet over short timescales. The effect of these water pulses on the development of basal hydrological systems is largely unknown. To address this, we develop a lake drainage model incorporating both (1) a subglacial radial flux element driven by elastic hydraulic jacking and (2) downstream drainage through a linked channelized and distributed system. Here we present the model and examine whether substantial, efficient subglacial channels can form during or following lake drainage events and their effect on the water pressure in the surrounding distributed system. We force the model with field data from a lake drainage site, 70 km from the terminus of Russell Glacier in West Greenland. The model outputs suggest that efficient subglacial channels do not readily form in the vicinity of the lake during rapid drainage and instead water is evacuated primarily by a transient turbulent sheet and the distributed system. Following lake drainage, channels grow but are not large enough to reduce the water pressure in the surrounding distributed system, unless preexisting channels are present throughout the domain. Our results have implications for the analysis of subglacial hydrological systems in regions where rapid lake drainage provides the primary mechanism for surface-to-bed connections. Model for subglacial hydrological analysis of rapid lake drainage eventsLimited subglacial channel growth during and following rapid lake drainagePersistence of distributed drainage in inland areas where channel growth is limited.

Modeling of subglacial hydrological development following rapid supraglacial lake drainage

PubMed Central

Dow, C F; Kulessa, B; Rutt, I C; Tsai, V C; Pimentel, S; Doyle, S H; van As, D; Lindbäck, K; Pettersson, R; Jones, G A; Hubbard, A

2015-01-01

The rapid drainage of supraglacial lakes injects substantial volumes of water to the bed of the Greenland ice sheet over short timescales. The effect of these water pulses on the development of basal hydrological systems is largely unknown. To address this, we develop a lake drainage model incorporating both (1) a subglacial radial flux element driven by elastic hydraulic jacking and (2) downstream drainage through a linked channelized and distributed system. Here we present the model and examine whether substantial, efficient subglacial channels can form during or following lake drainage events and their effect on the water pressure in the surrounding distributed system. We force the model with field data from a lake drainage site, 70 km from the terminus of Russell Glacier in West Greenland. The model outputs suggest that efficient subglacial channels do not readily form in the vicinity of the lake during rapid drainage and instead water is evacuated primarily by a transient turbulent sheet and the distributed system. Following lake drainage, channels grow but are not large enough to reduce the water pressure in the surrounding distributed system, unless preexisting channels are present throughout the domain. Our results have implications for the analysis of subglacial hydrological systems in regions where rapid lake drainage provides the primary mechanism for surface-to-bed connections. Key Points Model for subglacial hydrological analysis of rapid lake drainage events Limited subglacial channel growth during and following rapid lake drainage Persistence of distributed drainage in inland areas where channel growth is limited PMID:26640746

The Atlantic Meridional Overturning Circulation Stability Influenced by the Melting of the Greenland Ice Sheet under Various Warming Scenarios

NASA Astrophysics Data System (ADS)

Gierz, P.; Lohmann, G.; Wei, W.; Barbi, D.

2012-12-01

In this study, we aim to model melting processes of the Greenland ice sheet over the next 1000 years using the Earth system model COSMOS with a dynamic ice sheet module. Of primary interest is the resulting impact on the Atlantic meridional overturning circulation (GMOC/AMOC), which is expected to slow in response to a large freshwater (eg melt water) input. Six warming scenarios will be considered, one set corresponding to the IPCC's RPC Scenario 6, and another set corresponding to RPC Scenario 4.5, each time with 0.5, 1, and 2% increase of greenhouse gas concentration per year. It is expected that the freshwater input will slow down the AMOC overturning; each scenario producing a unique braking signal corresponding to how rapidly the Greenland ice sheet is forced to melt. It will be interesting to see if there is a CO2 threshold level at which the slowdown of the AMOC begins and the melting phenomena becomes unstable and positively reinforces itself or instead, as previous studies have demonstrated with a prescribed amount of melting, if the freshwater input always allows for an eventual recovery of the AMOC to a stable state regardless of the rapidity with which the salinity anomalies develop. The primary difference between this set of experiments and those in previous studies shall be the dynamic nature of the ice sheet model, as we will allow the Greenland ice sheet to melt solely based upon atmospheric conditions rather than prescribing a salinity change directly into the ocean model. It is expected that higher levels of greenhouse gases will result in more rapid melting, which in turn will have a stronger braking affect on the AMOC, possibly with longer recovery times to the starting equilibrium point. It will additionally be of interest to see if it is possible to create a shift in this equilibrium, suggesting that the rapidity with which density anomalies are introduced may create a new stable deep water formation rate. PRELIMINARY RESULTS - AMOC downwelling strength with changes in dynamically modeled Ice Sheet volume. AMOC seems to decrease with varying magnitudes depending upon the rate of carbon dioxide release and the amount of meltwater generated.

Hot gas ingestion characteristics and flow visualization of a vectored thrust STOVL concept

NASA Technical Reports Server (NTRS)

Johns, Albert L.; Neiner, George H.; Bencic, Timothy J.; Flood, Joseph D.; Amuedo, Kurt C.; Strock, Thomas W.; Williams, Ben R.

1990-01-01

A 9.2 percent scale short takeoff and vertical landing (STOVL) hot gas ingestion model was designed and built by McDonnell Douglas Corporation (MCAIR) and tested in the NASA Lewis Research Center 9- by 15-Foot Low Speed Wind Tunnel (LSWT). Hot gas ingestion, the entrainment of heated engine exhaust into the inlet flow field, is a key development issue for advanced short takeoff and vertical landing aircraft. The Phase 1 test program, conducted by NASA Lewis and McDonnell Douglas Corporation, evaluated the hot ingestion phenomena and control techniques and Phase 2 test program which was conducted by NASA Lewis are both reported. The Phase 2 program was conducted at exhaust nozzles temperatures up to 1460 R and utilized a sheet laser system for flow visualization of the model flow field in and out of ground effects. Hot gas ingestion levels were measured for the several forward nozzle splay configurations and with flow control/lift improvement devices which reduced the hot gas ingestion. The model support system had four degrees of freedom, heated high pressure air for nozzle flow, and a suction system exhaust for inlet flow. The headwind (freestream) velocity for Phase 1 was varied from 8 to 90 kn, with primary data taken in the 8 to 23 kn headwind velocity range. Phase 2 headwind velocity varied from 10 to 23 kn. Results of both Phase 1 and 2 are presented. A description of the model, facility, a new model support system, and a sheet laser illumination system are also provided. Results are presented over a range of main landing gear height (model height) above the ground plane at a 10 kn headwind velocity. The results contain the compressor face pressure and temperature distortions, total pressure recovery, compressor face temperature rise, and the environmental effects of the hot gas. The environmental effects include the ground plane temperature and pressure distributions, model airframe heating, and the location of the ground flow separation. Results from the sheet laser flow visualization test are also shown.

Energy balance in the core of the Saturn plasma sheet: H2O chemistry

NASA Astrophysics Data System (ADS)

Shemansky, D. E.; Yoshii, J.; Liu, X.

2011-10-01

A model of the weakly ionized plasma at Saturn has been developed to investigate the properties of the system. Energy balance is a critical consideration. The present model is based on two sources of mass, H2O, and HI. H2O is a variable. HI is a significant volume of gas flowing through the plasma imposed by the source at Saturn [1,2,3]. The energy sources are solar radiation and heterogeneous magnetosphere electrons. The model calculations produce energy rates, species partitioning, and relaxation lifetimes. For the first time the state of the ambient plasma sheet electrons is directly connected to the energy forcing functions. Within limits of knowledge, the predicted state of the core region of the plasma sheet in neutral and ionized gas corresponds satisfactorily to observation. The dominant ions in these calculations are H2O+ and H3O+ with lifetimes of several days. The lifetime of H2O is roughly 60 days. In calculations carried out so far the predicted source rate for H2O is lower than the rates quoted from the Enceladus encounters.

Integrated System Health Management (ISHM) for Test Stand and J-2X Engine: Core Implementation

NASA Technical Reports Server (NTRS)

Figueroa, Jorge F.; Schmalzel, John L.; Aguilar, Robert; Shwabacher, Mark; Morris, Jon

2008-01-01

ISHM capability enables a system to detect anomalies, determine causes and effects, predict future anomalies, and provides an integrated awareness of the health of the system to users (operators, customers, management, etc.). NASA Stennis Space Center, NASA Ames Research Center, and Pratt & Whitney Rocketdyne have implemented a core ISHM capability that encompasses the A1 Test Stand and the J-2X Engine. The implementation incorporates all aspects of ISHM; from anomaly detection (e.g. leaks) to root-cause-analysis based on failure mode and effects analysis (FMEA), to a user interface for an integrated visualization of the health of the system (Test Stand and Engine). The implementation provides a low functional capability level (FCL) in that it is populated with few algorithms and approaches for anomaly detection, and root-cause trees from a limited FMEA effort. However, it is a demonstration of a credible ISHM capability, and it is inherently designed for continuous and systematic augmentation of the capability. The ISHM capability is grounded on an integrating software environment used to create an ISHM model of the system. The ISHM model follows an object-oriented approach: includes all elements of the system (from schematics) and provides for compartmentalized storage of information associated with each element. For instance, a sensor object contains a transducer electronic data sheet (TEDS) with information that might be used by algorithms and approaches for anomaly detection, diagnostics, etc. Similarly, a component, such as a tank, contains a Component Electronic Data Sheet (CEDS). Each element also includes a Health Electronic Data Sheet (HEDS) that contains health-related information such as anomalies and health state. Some practical aspects of the implementation include: (1) near real-time data flow from the test stand data acquisition system through the ISHM model, for near real-time detection of anomalies and diagnostics, (2) insertion of the J-2X predictive model providing predicted sensor values for comparison with measured values and use in anomaly detection and diagnostics, and (3) insertion of third-party anomaly detection algorithms into the integrated ISHM model.

The frequency response of a coupled ice sheet-ice shelf-ocean system to climate forcing variability

NASA Astrophysics Data System (ADS)

Goldberg, D.; Snow, K.; Jordan, J. R.; Holland, P.; Arthern, R. J.

2017-12-01

Changes at the West Antarctic ice-ocean boundary in recent decades has triggered significant increases in the regions contribution to global sea-level rise, coincident with large scale, and in some cases potentially unstable, grounding line retreat. Much of the induced change is thought to be driven by fluctuations in the oceanic heat available at the ice-ocean boundary, transported on-shelf via warm Circumpolar Deep Water (CDW). However, the processes in which ocean heat drives ice-sheet loss remains poorly understood, with observational studies routinely hindered by the extreme environment notorious to the Antarctic region. In this study we apply a novel synchronous coupled ice-ocean model, developed within the MITgcm, and are thus able to provide detailed insight into the impacts of short time scale (interannual to decadal) climate variability and feedbacks within the ice-ocean system. Feedbacks and response are assessed in an idealised ice-sheet/ocean-cavity configuration in which the far field ocean condition is adjusted to emulate periodic climate variability patterns. We reveal a non-linear response of the ice-sheet to periodic variations in thermocline depth. These non-linearities illustrate the heightened sensitivity of fast flowing ice-shelves to periodic perturbations in heat fluxes occurring at interannual and decadal time scales. The results thus highlight how small perturbations in variable climate forcing, like that of ENSO, may trigger large changes in ice-sheet response.

Writing with ring currents: selectively hydrogenated polycyclic aromatics as finite models of graphene and graphane

PubMed Central

Fowler, Patrick W.; Gibson, Christopher M.; Bean, David E.

2014-01-01

Alternating partial hydrogenation of the interior region of a polycyclic aromatic hydrocarbon gives a finite model system representing systems on the pathway from graphene to the graphane modification of the graphene sheet. Calculations at the DFT and coupled Hartree–Fock levels confirm that sp2 cycles of bare carbon centres isolated by selective hydrogenation retain the essentially planar geometry and electron delocalization of the annulene that they mimic. Delocalization is diagnosed by the presence of ring currents, as detected by ipsocentric calculation and visualization of the current density induced in the π system by a perpendicular external magnetic field. These induced ‘ring’ currents have essentially the same sense, strength and orbital origin as in the free hydrocarbon. Subjected to the important experimental proviso of the need for atomic-scale control of hydrogenation, this finding predicts the possibility of writing single, multiple and concentric diatropic and/or paratropic ring currents on the graphene/graphane sheet. The implication is that pathways for free flow of ballistic current can be modelled in the same way. PMID:24611026

A multiresolution method for climate system modeling: application of spherical centroidal Voronoi tessellations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ringler, Todd; Ju, Lili; Gunzburger, Max

2008-11-14

During the next decade and beyond, climate system models will be challenged to resolve scales and processes that are far beyond their current scope. Each climate system component has its prototypical example of an unresolved process that may strongly influence the global climate system, ranging from eddy activity within ocean models, to ice streams within ice sheet models, to surface hydrological processes within land system models, to cloud processes within atmosphere models. These new demands will almost certainly result in the develop of multiresolution schemes that are able, at least regionally, to faithfully simulate these fine-scale processes. Spherical centroidal Voronoimore » tessellations (SCVTs) offer one potential path toward the development of a robust, multiresolution climate system model components. SCVTs allow for the generation of high quality Voronoi diagrams and Delaunay triangulations through the use of an intuitive, user-defined density function. In each of the examples provided, this method results in high-quality meshes where the quality measures are guaranteed to improve as the number of nodes is increased. Real-world examples are developed for the Greenland ice sheet and the North Atlantic ocean. Idealized examples are developed for ocean–ice shelf interaction and for regional atmospheric modeling. In addition to defining, developing, and exhibiting SCVTs, we pair this mesh generation technique with a previously developed finite-volume method. Our numerical example is based on the nonlinear, shallow water equations spanning the entire surface of the sphere. This example is used to elucidate both the potential benefits of this multiresolution method and the challenges ahead.« less

Watershed scale response to climate change--Trout Lake Basin, Wisconsin

USGS Publications Warehouse

Walker, John F.; Hunt, Randall J.; Hay, Lauren E.; Markstrom, Steven L.

2012-01-01

Fourteen basins for which the Precipitation Runoff Modeling System has been calibrated and evaluated were selected as study sites. Precipitation Runoff Modeling System is a deterministic, distributed parameter watershed model developed to evaluate the effects of various combinations of precipitation, temperature, and land use on streamflow and general basin hydrology. Output from five General Circulation Model simulations and four emission scenarios were used to develop an ensemble of climate-change scenarios for each basin. These ensembles were simulated with the corresponding Precipitation Runoff Modeling System model. This fact sheet summarizes the hydrologic effect and sensitivity of the Precipitation Runoff Modeling System simulations to climate change for the Trout River Basin at Trout Lake in northern Wisconsin.

Watershed scale response to climate change--Clear Creek Basin, Iowa

USGS Publications Warehouse

Christiansen, Daniel E.; Hay, Lauren E.; Markstrom, Steven L.

2012-01-01

Fourteen basins for which the Precipitation Runoff Modeling System has been calibrated and evaluated were selected as study sites. Precipitation Runoff Modeling System is a deterministic, distributed parameter watershed model developed to evaluate the effects of various combinations of precipitation, temperature, and land use on streamflow and general basin hydrology. Output from five General Circulation Model simulations and four emission scenarios were used to develop an ensemble of climate-change scenarios for each basin. These ensembles were simulated with the corresponding Precipitation Runoff Modeling System model. This fact sheet summarizes the hydrologic effect and sensitivity of the Precipitation Runoff Modeling System simulations to climate change for the Clear Creek Basin, near Coralville, Iowa.

Watershed scale response to climate change--Feather River Basin, California

USGS Publications Warehouse

Koczot, Kathryn M.; Markstrom, Steven L.; Hay, Lauren E.

2012-01-01

Fourteen basins for which the Precipitation Runoff Modeling System has been calibrated and evaluated were selected as study sites. Precipitation Runoff Modeling System is a deterministic, distributed parameter watershed model developed to evaluate the effects of various combinations of precipitation, temperature, and land use on streamflow and general basin hydrology. Output from five General Circulation Model simulations and four emission scenarios were used to develop an ensemble of climate-change scenarios for each basin. These ensembles were simulated with the corresponding Precipitation Runoff Modeling System model. This fact sheet summarizes the hydrologic effect and sensitivity of the Precipitation Runoff Modeling System simulations to climate change for the Feather River Basin, California.

Watershed scale response to climate change--South Fork Flathead River Basin, Montana

USGS Publications Warehouse

Chase, Katherine J.; Hay, Lauren E.; Markstrom, Steven L.

2012-01-01

Fourteen basins for which the Precipitation Runoff Modeling System has been calibrated and evaluated were selected as study sites. Precipitation Runoff Modeling System is a deterministic, distributed parameter watershed model developed to evaluate the effects of various combinations of precipitation, temperature, and land use on streamflow and general basin hydrology. Output from five General Circulation Model simulations and four emission scenarios were used to develop an ensemble of climate-change scenarios for each basin. These ensembles were simulated with the corresponding Precipitation Runoff Modeling System model. This fact sheet summarizes the hydrologic effect and sensitivity of the Precipitation Runoff Modeling System simulations to climate change for the South Fork Flathead River Basin, Montana.

Watershed scale response to climate change--Cathance Stream Basin, Maine

USGS Publications Warehouse

Dudley, Robert W.; Hay, Lauren E.; Markstrom, Steven L.; Hodgkins, Glenn A.

2012-01-01

Fourteen basins for which the Precipitation Runoff Modeling System has been calibrated and evaluated were selected as study sites. Precipitation Runoff Modeling System is a deterministic, distributed parameter watershed model developed to evaluate the effects of various combinations of precipitation, temperature, and land use on streamflow and general basin hydrology. Output from five General Circulation Model simulations and four emission scenarios were used to develop an ensemble of climate-change scenarios for each basin. These ensembles were simulated with the corresponding Precipitation Runoff Modeling System model. This fact sheet summarizes the hydrologic effect and sensitivity of the Precipitation Runoff Modeling System simulations to climate change for the Cathance Stream Basin, Maine.

Watershed scale response to climate change--Pomperaug River Watershed, Connecticut

USGS Publications Warehouse

Bjerklie, David M.; Hay, Lauren E.; Markstrom, Steven L.

2012-01-01

Fourteen basins for which the Precipitation Runoff Modeling System has been calibrated and evaluated were selected as study sites. Precipitation Runoff Modeling System is a deterministic, distributed parameter watershed model developed to evaluate the effects of various combinations of precipitation, temperature, and land use on streamflow and general basin hydrology. Output from five General Circulation Model simulations and four emission scenarios were used to develop an ensemble of climate-change scenarios for each basin. These ensembles were simulated with the corresponding Precipitation Runoff Modeling System model. This fact sheet summarizes the hydrologic effect and sensitivity of the Precipitation Runoff Modeling System simulations to climate change for the Pomperaug River Basin at Southbury, Connecticut.

Watershed scale response to climate change--Starkweather Coulee Basin, North Dakota

USGS Publications Warehouse

Vining, Kevin C.; Hay, Lauren E.; Markstrom, Steven L.

2012-01-01

Fourteen basins for which the Precipitation Runoff Modeling System has been calibrated and evaluated were selected as study sites. Precipitation Runoff Modeling System is a deterministic, distributed parameter watershed model developed to evaluate the effects of various combinations of precipitation, temperature, and land use on streamflow and general basin hydrology. Output from five General Circulation Model simulations and four emission scenarios were used to develop an ensemble of climate-change scenarios for each basin. These ensembles were simulated with the corresponding Precipitation Runoff Modeling System model. This fact sheet summarizes the hydrologic effect and sensitivity of the Precipitation Runoff Modeling System simulations to climate change for the Starkweather Coulee Basin near Webster, North Dakota.

Watershed scale response to climate change--Sagehen Creek Basin, California

USGS Publications Warehouse

Markstrom, Steven L.; Hay, Lauren E.; Regan, R. Steven

2012-01-01

Fourteen basins for which the Precipitation Runoff Modeling System has been calibrated and evaluated were selected as study sites. Precipitation Runoff Modeling System is a deterministic, distributed parameter watershed model developed to evaluate the effects of various combinations of precipitation, temperature, and land use on streamflow and general basin hydrology. Output from five General Circulation Model simulations and four emission scenarios were used to develop an ensemble of climate-change scenarios for each basin. These ensembles were simulated with the corresponding Precipitation Runoff Modeling System model. This fact sheet summarizes the hydrologic effect and sensitivity of the Precipitation Runoff Modeling System simulations to climate change for the Sagehen Creek Basin near Truckee, California.

Watershed scale response to climate change--Sprague River Basin, Oregon

USGS Publications Warehouse

Risley, John; Hay, Lauren E.; Markstrom, Steven L.

2012-01-01

Fourteen basins for which the Precipitation Runoff Modeling System has been calibrated and evaluated were selected as study sites. Precipitation Runoff Modeling System is a deterministic, distributed parameter watershed model developed to evaluate the effects of various combinations of precipitation, temperature, and land use on streamflow and general basin hydrology. Output from five General Circulation Model simulations and four emission scenarios were used to develop an ensemble of climate-change scenarios for each basin. These ensembles were simulated with the corresponding Precipitation Runoff Modeling System model. This fact sheet summarizes the hydrologic effect and sensitivity of the Precipitation Runoff Modeling System simulations to climate change for the Sprague River Basin near Chiloquin, Oregon.

Watershed scale response to climate change--Black Earth Creek Basin, Wisconsin

USGS Publications Warehouse

Hunt, Randall J.; Walker, John F.; Westenbroek, Steven M.; Hay, Lauren E.; Markstrom, Steven L.

2012-01-01

Fourteen basins for which the Precipitation Runoff Modeling System has been calibrated and evaluated were selected as study sites. Precipitation Runoff Modeling System is a deterministic, distributed parameter watershed model developed to evaluate the effects of various combinations of precipitation, temperature, and land use on streamflow and general basin hydrology. Output from five General Circulation Model simulations and four emission scenarios were used to develop an ensemble of climate-change scenarios for each basin. These ensembles were simulated with the corresponding Precipitation Runoff Modeling System model. This fact sheet summarizes the hydrologic effect and sensitivity of the Precipitation Runoff Modeling System simulations to climate change for the Black Earth Creek Basin, Wisconsin.

Watershed scale response to climate change--East River Basin, Colorado

USGS Publications Warehouse

Battaglin, William A.; Hay, Lauren E.; Markstrom, Steven L.

2012-01-01

Fourteen basins for which the Precipitation Runoff Modeling System has been calibrated and evaluated were selected as study sites. Precipitation Runoff Modeling System is a deterministic, distributed parameter watershed model developed to evaluate the effects of various combinations of precipitation, temperature, and land use on streamflow and general basin hydrology. Output from five General Circulation Model simulations and four emission scenarios were used to develop an ensemble of climate-change scenarios for each basin. These ensembles were simulated with the corresponding Precipitation Runoff Modeling System model. This fact sheet summarizes the hydrologic effect and sensitivity of the Precipitation Runoff Modeling System simulations to climate change for the East River Basin, Colorado.

Watershed scale response to climate change--Naches River Basin, Washington

USGS Publications Warehouse

Mastin, Mark C.; Hay, Lauren E.; Markstrom, Steven L.

2012-01-01

Fourteen basins for which the Precipitation Runoff Modeling System has been calibrated and evaluated were selected as study sites. Precipitation Runoff Modeling System is a deterministic, distributed parameter watershed model developed to evaluate the effects of various combinations of precipitation, temperature, and land use on streamflow and general basin hydrology. Output from five General Circulation Model simulations and four emission scenarios were used to develop an ensemble of climate-change scenarios for each basin. These ensembles were simulated with the corresponding Precipitation Runoff Modeling System model. This fact sheet summarizes the hydrologic effect and sensitivity of the Precipitation Runoff Modeling System simulations to climate change for the Naches River Basin below Tieton River in Washington.

Watershed scale response to climate change--Flint River Basin, Georgia

USGS Publications Warehouse

Hay, Lauren E.; Markstrom, Steven L.

2012-01-01

Fourteen basins for which the Precipitation Runoff Modeling System has been calibrated and evaluated were selected as study sites. Precipitation Runoff Modeling System is a deterministic, distributed parameter watershed model developed to evaluate the effects of various combinations of precipitation, temperature, and land use on streamflow and general basin hydrology. Output from five General Circulation Model simulations and four emission scenarios were used to develop an ensemble of climate-change scenarios for each basin. These ensembles were simulated with the corresponding Precipitation Runoff Modeling System model. This fact sheet summarizes the hydrologic effect and sensitivity of the Precipitation Runoff Modeling System simulations to climate change for the Flint River Basin at Montezuma, Georgia.

The Effect of Solar Forcing on the Greenland Ice Sheet during the Holocene - A Model Study

NASA Astrophysics Data System (ADS)

Bügelmayer, Marianne; Roche, Didier; Renssen, Hans

2014-05-01

Abrupt climate changes did not only happen during glacials but also during interglacials such as the Holocene. Marine sediments provide evidence for the periodic occurrence of centennial-scale events with enhanced iceberg discharge during the past 11.000 years (Bond et al., 2001). These events were chronologically linked to reduced solar activity as reconstructed using cosmogenic isotopes (Bond et al., 2001), indicating that even an external forcing that is considered to be small, has a potential impact on climate due to several feedback mechanisms (Renssen et al., 2006). The interactions between climate and solar irradiance have been investigated using numerical models (e.g. Haigh, 1996; Renssen et al, 2006), but so far without dynamically computing the Greenland ice sheet and iceberg calving. Thus, the impact of solar variations on iceberg discharge and the underlying mechanisms have not been analysed so far. To analyse the effect of variations in solar activity on the Greenland ice sheet (GIS) and the iceberg calving, as well as possible feedback mechanisms that enhance the impact of the total solar irradiance, we use the earth system model of intermediate complexity (iLOVECLIM, Roche et al., 2013), coupled to the ice sheet/ice shelf model GRISLI (Ritz et al., 2001) and to a dynamic-thermodynamic iceberg module (Jongma et al., 2009, Bügelmayer et al., 2014) to perform transient experiments of the last 6000 years. The experiments are conducted applying reconstructed atmospheric greenhouse gas concentrations, volcanic aerosol loads, orbital parameters and variations in the total solar irradiance. We present the response of the coupled model to different solar irradiance scenarios to evaluate modeled GIS sensitivity to relatively modest variations in radiative forcing. Moreover, we investigate the dependence of the model results on the chosen model sensitivity. References: Bond, G., Kromer, B., Beer, J., Muscheler, R., Evans, M. N., Showers, W., … Bonani, G. (2001): Persistent solar influence on North Atlantic climate during the Holocene. Science (New York, N.Y.), 294(5549), 2130-6. doi:10.1126/science.1065680 Bügelmayer, M., Roche, D.M., Renssen, H. (2014): How do icebergs affect the Greenland ice sheet under pre-industrial conditions? - A model study with a fully coupled ice sheet-climate model. The Cryosphere Discussions 8, 187-228. Haigh, J. D. (1996): The Impact of Solar Variability on Climate. Science, 272, 981-984. Jongma, J.I., Driesschaert, E., Fichefet, T., Goosse, H., Renssen, H., (2009): The effect of dynamic-thermodynamic icebergs on the Southern Ocean climate in a three-dimensional model. Ocean Modelling 26, 104-113. Renssen, H., Goosse, H., Muscheler, R., & Branch, R. (2006): Coupled climate model simulation of Holocene cooling events: oceanic feedback amplifies solar forcing. Climate of the Past, 2, 79-90. Ritz, C., Rommelaere, V. and Dumas, C.(2001): Modeling the evolution of Antarctic ice sheet over the last 420,000 years: Implications for altitude changes in the Vostok region, Journal of Geophysical Research, 106, 31943-31964, doi:10.1029/2001JD900232. Roche, D.M., Dumas, C., Bügelmayer, M., Charbit, S., Ritz, C. (2013): Adding a dynamical cryosphere into iLOVECLIM (version 1.0) - Part 1: Coupling with the GRISLI ice-sheet model, Geoscientific Model Development Discussion, 6, 5215-5249.

Solar Heating Systems: Student Manual.

ERIC Educational Resources Information Center

Green, Joanne; And Others

This Student Manual for a Solar Heating System curriculum contains 22 units of instructional materials for students to use in a course or courses on solar heating systems (see note). For each unit (task), objectives, assignment sheets, laboratory assignments, information sheets, checkpoints (tests), and job sheets are provided. Materials are set…

46 CFR 160.047-1 - Incorporation by reference.

Code of Federal Regulations, 2010 CFR

2010-10-01

..., Models AK-1, and AF-1. Sheet 2, Rev. 2—Cutting Pattern and General Arrangement, Models CKM-1 and CFM-1. Sheet 3, Rev. 2—Cutting Pattern and General Arrangement, Models CKS-1 and CFS-1. Sheet 4, Rev. 1—Pad... Business Service Center, General Services Administration, Washington, DC 20407; (3) The military...

Multi-dimensional modelling of gas turbine combustion using a flame sheet model in KIVA II

NASA Technical Reports Server (NTRS)

Cheng, W. K.; Lai, M.-C.; Chue, T.-H.

1991-01-01

A flame sheet model for heat release is incorporated into a multi-dimensional fluid mechanical simulation for gas turbine application. The model assumes that the chemical reaction takes place in thin sheets compared to the length scale of mixing, which is valid for the primary combustion zone in a gas turbine combustor. In this paper, the details of the model are described and computational results are discussed.

Modelled Growth and Decay of the Cordilleran Ice Sheet Through the Last Glacial Cycle

NASA Astrophysics Data System (ADS)

Marshall, S. J.; Banwell, A.

2015-12-01

The Cordilleran Ice Sheet in western North America had an enigmatic evolution during the last glacial cycle, developing out of sync with the larger Laurentide and global glaciation. The geological record suggests that the ice sheet emerged late, ca. 45 ka, growing to be a fully-established ice sheet in isotope stages 3 and 2 and deglaciating late in the glacial cycle. This has been a challenge to model, and is a paleoclimatic curiosity, because the western Cordillera of North America is heavily glacierized today, and one would intuitively expect it to act as an inception centre for the Pleistocene ice sheets. The region receives heavy precipitation, and modest cooling should induce large-scale glacier expansion. Indeed, a Cordilleran Ice Sheet quickly nucleates in isotope substage 5d in most ice sheet modeling studies to date, and is a resilient feature throughout the glaciation. The fact that a full-scale Cordilleran Ice Sheet did not develop until relatively late argues for either: (a) ice sheet models that have been inadequate in resolving the process of alpine-style glaciation, i.e., the coalescence of alpine icefields, or (b) a climatic history in western North America that deviated strongly from the hemispheric-scale cooling which drove the growth of the Laurentide and Scandinavian Ice Sheets, as recorded in Greenland. We argue that reasonable reconstructions of Cordilleran Ice Sheet growth and decay implicate a combination of these two considerations. Sufficient model resolution is required to capture the valley-bottom melt that suppresses icefield coalescence, while early-glacial cooling must have been modest in the Pacific sector of North America. We argue for a persistent warm, dry climate relative to that in eastern North America and the Atlantic sector, likely associated with positive feedbacks between atmospheric circulation and the nascent Laurentide Ice Sheet (i.e., peristent circulation patterns similar to those of 2014-2015). This must have been disrupted as the Laurentide thickened and advanced southward, allowing the Cordilleran Ice Sheet to emerge from numerous isolated icefield complexes.

Growth and nonlinear response of driven water bells

NASA Astrophysics Data System (ADS)

Kolinski, John M.; Aharoni, Hillel; Fineberg, Jay; Sharon, Eran

2017-04-01

A water bell forms when a fluid jet impacts upon a target and separates into a two-dimensional sheet. Depending on the angle of separation from the target, the sheet can curve into a variety of different geometries. We show analytically that harmonic perturbations of water bells have linear wave solutions with geometry-dependent growth. We test the predictions of this model experimentally with a custom target system, and observe growth in agreement with the model below a critical forcing amplitude. Once the critical forcing amplitude is exceeded, a nonlinear transcritical bifurcation occurs; the response amplitude increases linearly with increasing forcing amplitude, albeit with a fundamentally different spatial form, and distinct nodes appear in the amplitude envelope.

How and when to terminate the Pleistocene ice ages?

NASA Astrophysics Data System (ADS)

Abe-Ouchi, A.; Saito, F.; Kawamura, K.; Takahashi, K.; Raymo, M. E.; Okuno, J.; Blatter, H.

2015-12-01

Climate change with wax and wane of large Northern Hemisphere ice sheet occurred in the past 800 thousand years characterized by 100 thousand year cycle with a large amplitude of sawtooth pattern, following a transition from a period of 40 thousand years cycle with small amplitude of ice sheet change at about 1 million years ago. Although the importance of insolation as the ultimate driver is now appreciated, the mechanism what determines timing and strength of terminations are far from clearly understood. Here we show, using comprehensive climate and ice-sheet models, that insolation and internal feedbacks between the climate, the ice sheets and the lithosphere-asthenosphere system explain the 100,000-year periodicity. The responses of equilibrium states of ice sheets to summer insolation show hysteresis, with the shape and position of the hysteresis loop playing a key part in determining the periodicities of glacial cycles. The hysteresis loop of the North American ice sheet is such that after inception of the ice sheet, its mass balance remains mostly positive through several precession cycles, whose amplitudes decrease towards an eccentricity minimum. The larger the ice sheet grows and extends towards lower latitudes, the smaller is the insolation required to make the mass balance negative. Therefore, once a large ice sheet is established, a moderate increase in insolation is sufficient to trigger a negative mass balance, leading to an almost complete retreat of the ice sheet within several thousand years. We discuss further the mechanism which determine the timing of ice age terminations by examining the role of astronomical forcing and change of atmospheric carbon dioxide contents through sensitivity experiments and comparison of several ice age cycles with different settings of astronomical forcings.

Antarctic climate and ice-sheet configuration during the early Pliocene interglacial at 4.23 Ma

NASA Astrophysics Data System (ADS)

Golledge, Nicholas R.; Thomas, Zoë A.; Levy, Richard H.; Gasson, Edward G. W.; Naish, Timothy R.; McKay, Robert M.; Kowalewski, Douglas E.; Fogwill, Christopher J.

2017-07-01

The geometry of Antarctic ice sheets during warm periods of the geological past is difficult to determine from geological evidence, but is important to know because such reconstructions enable a more complete understanding of how the ice-sheet system responds to changes in climate. Here we investigate how Antarctica evolved under orbital and greenhouse gas conditions representative of an interglacial in the early Pliocene at 4.23 Ma, when Southern Hemisphere insolation reached a maximum. Using offline-coupled climate and ice-sheet models, together with a new synthesis of high-latitude palaeoenvironmental proxy data to define a likely climate envelope, we simulate a range of ice-sheet geometries and calculate their likely contribution to sea level. In addition, we use these simulations to investigate the processes by which the West and East Antarctic ice sheets respond to environmental forcings and the timescales over which these behaviours manifest. We conclude that the Antarctic ice sheet contributed 8.6 ± 2.8 m to global sea level at this time, under an atmospheric CO2 concentration identical to present (400 ppm). Warmer-than-present ocean temperatures led to the collapse of West Antarctica over centuries, whereas higher air temperatures initiated surface melting in parts of East Antarctica that over one to two millennia led to lowering of the ice-sheet surface, flotation of grounded margins in some areas, and retreat of the ice sheet into the Wilkes Subglacial Basin. The results show that regional variations in climate, ice-sheet geometry, and topography produce long-term sea-level contributions that are non-linear with respect to the applied forcings, and which under certain conditions exhibit threshold behaviour associated with behavioural tipping points.

Response of the Antarctic ice sheet to ocean forcing using the POPSICLES coupled ice sheet-ocean model

NASA Astrophysics Data System (ADS)

Martin, D. F.; Asay-Davis, X.; Price, S. F.; Cornford, S. L.; Maltrud, M. E.; Ng, E. G.; Collins, W.

2014-12-01

We present the response of the continental Antarctic ice sheet to sub-shelf-melt forcing derived from POPSICLES simulation results covering the full Antarctic Ice Sheet and the Southern Ocean spanning the period 1990 to 2010. Simulations are performed at 0.1 degree (~5 km) ocean resolution and ice sheet resolution as fine as 500 m using adaptive mesh refinement. A comparison of fully-coupled and comparable standalone ice-sheet model results demonstrates the importance of two-way coupling between the ice sheet and the ocean. The POPSICLES model couples the POP2x ocean model, a modified version of the Parallel Ocean Program (Smith and Gent, 2002), and the BISICLES ice-sheet model (Cornford et al., 2012). BISICLES makes use of adaptive mesh refinement to fully resolve dynamically-important regions like grounding lines and employs a momentum balance similar to the vertically-integrated formulation of Schoof and Hindmarsh (2009). Results of BISICLES simulations have compared favorably to comparable simulations with a Stokes momentum balance in both idealized tests like MISMIP3D (Pattyn et al., 2013) and realistic configurations (Favier et al. 2014). POP2x includes sub-ice-shelf circulation using partial top cells (Losch, 2008) and boundary layer physics following Holland and Jenkins (1999), Jenkins (2001), and Jenkins et al. (2010). Standalone POP2x output compares well with standard ice-ocean test cases (e.g., ISOMIP; Losch, 2008) and other continental-scale simulations and melt-rate observations (Kimura et al., 2013; Rignot et al., 2013). A companion presentation, "Present-day circum-Antarctic simulations using the POPSICLES coupled land ice-ocean model" in session C027 describes the ocean-model perspective of this work, while we focus on the response of the ice sheet and on details of the model. The figure shows the BISICLES-computed vertically-integrated ice velocity field about 1 month into a 20-year coupled Antarctic run. Groundling lines are shown in green.

Latest status of the clinical and industrial applications of cell sheet engineering and regenerative medicine.

PubMed

Egami, Mime; Haraguchi, Yuji; Shimizu, Tatsuya; Yamato, Masayuki; Okano, Teruo

2014-01-01

Cell sheet engineering, which allows tissue engineering to be realized without the use of biodegradable scaffolds as an original approach, using a temperature-responsive intelligent surface, has been applied in regenerative medicine for various tissues, and a number of clinical studies have been already performed for life-threatening diseases. By using the results and findings obtained from the initial clinical studies, additional investigative clinical studies in several tissues with cell sheet engineering are currently in preparation stage. For treating many patients effectively by cell sheet engineering, an automated system integrating cell culture, cell-sheet fabrication, and layering is essential, and the system should include an advanced three-dimensional suspension cell culture system and an in vitro bioreactor system to scale up the production of cultured cells and fabricate thicker vascularized tissues. In this paper, cell sheet engineering, its clinical application, and further the authors' challenge to develop innovative cell culture systems under newly legislated regulatory platform in Japan are summarized and discussed.

Theoretical modeling of the plasma-assisted catalytic growth and field emission properties of graphene sheet

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sharma, Suresh C.; Gupta, Neha

2015-12-15

A theoretical modeling for the catalyst-assisted growth of graphene sheet in the presence of plasma has been investigated. It is observed that the plasma parameters can strongly affect the growth and field emission properties of graphene sheet. The model developed accounts for the charging rate of the graphene sheet; number density of electrons, ions, and neutral atoms; various elementary processes on the surface of the catalyst nanoparticle; surface diffusion and accretion of ions; and formation of carbon-clusters and large graphene islands. In our investigation, it is found that the thickness of the graphene sheet decreases with the plasma parameters, numbermore » density of hydrogen ions and RF power, and consequently, the field emission of electrons from the graphene sheet surface increases. The time evolution of the height of graphene sheet with ion density and sticking coefficient of carbon species has also been examined. Some of our theoretical results are in compliance with the experimental observations.« less

Stress and efficiency studies in EFG

NASA Technical Reports Server (NTRS)

1986-01-01

The goals of this program were: (1) to define minimum stress configurations for silicon sheet growth at high speeds; (2) to quantify dislocation electrical activity and their limits on minority carrier diffusion length in deformed silicon; and (3) to study reasons for degradation of lifetime with increases in doping level in edge-defined film-fed growth (EFG) materials. A finite element model was developed for calculating residual stress with plastic deformation. A finite element model was verified for EFG control variable relationships to temperature field of the sheet to permit prediction of profiles and stresses encountered in EFG systems. A residual stress measurement technique was developed for finite size EFG material blanks using shadow Moire interferometry. Transient creep response of silicon was investigated in the temperature range between 800 and 1400 C in strain and strain regimes of interest in stress analysis of sheet growth. Quantitative relationships were established between minority carrier diffusion length and dislocation densities using Electron Beam Induced Current (EBIC) measurement in FZ silicon deformed in four point bending tests.

Dynamic Antarctic ice sheet during the early to mid-Miocene

PubMed Central

DeConto, Robert M.; Pollard, David; Levy, Richard H.

2016-01-01

Geological data indicate that there were major variations in Antarctic ice sheet volume and extent during the early to mid-Miocene. Simulating such large-scale changes is problematic because of a strong hysteresis effect, which results in stability once the ice sheets have reached continental size. A relatively narrow range of atmospheric CO2 concentrations indicated by proxy records exacerbates this problem. Here, we are able to simulate large-scale variability of the early to mid-Miocene Antarctic ice sheet because of three developments in our modeling approach. (i) We use a climate–ice sheet coupling method utilizing a high-resolution atmospheric component to account for ice sheet–climate feedbacks. (ii) The ice sheet model includes recently proposed mechanisms for retreat into deep subglacial basins caused by ice-cliff failure and ice-shelf hydrofracture. (iii) We account for changes in the oxygen isotopic composition of the ice sheet by using isotope-enabled climate and ice sheet models. We compare our modeling results with ice-proximal records emerging from a sedimentological drill core from the Ross Sea (Andrill-2A) that is presented in a companion article. The variability in Antarctic ice volume that we simulate is equivalent to a seawater oxygen isotope signal of 0.52–0.66‰, or a sea level equivalent change of 30–36 m, for a range of atmospheric CO2 between 280 and 500 ppm and a changing astronomical configuration. This result represents a substantial advance in resolving the long-standing model data conflict of Miocene Antarctic ice sheet and sea level variability. PMID:26903645

Empirical potential for molecular simulation of graphene nanoplatelets

NASA Astrophysics Data System (ADS)

Bourque, Alexander J.; Rutledge, Gregory C.

2018-04-01

A new empirical potential for layered graphitic materials is reported. Interatomic interactions within a single graphene sheet are modeled using a Stillinger-Weber potential. Interatomic interactions between atoms in different sheets of graphene in the nanoplatelet are modeled using a Lennard-Jones interaction potential. The potential is validated by comparing molecular dynamics simulations of tensile deformation with the reported elastic constants for graphite. The graphite is found to fracture into graphene nanoplatelets when subjected to ˜15% tensile strain normal to the basal surface of the graphene stack, with an ultimate stress of 2.0 GPa and toughness of 0.33 GPa. This force field is useful to model molecular interactions in an important class of composite systems comprising 2D materials like graphene and multi-layer graphene nanoplatelets.

Land Ice Verification and Validation Kit

DOE Office of Scientific and Technical Information (OSTI.GOV)

2015-07-15

To address a pressing need to better understand the behavior and complex interaction of ice sheets within the global Earth system, significant development of continental-scale, dynamical ice-sheet models is underway. The associated verification and validation process of these models is being coordinated through a new, robust, python-based extensible software package, the Land Ice Verification and Validation toolkit (LIVV). This release provides robust and automated verification and a performance evaluation on LCF platforms. The performance V&V involves a comprehensive comparison of model performance relative to expected behavior on a given computing platform. LIVV operates on a set of benchmark and testmore » data, and provides comparisons for a suite of community prioritized tests, including configuration and parameter variations, bit-4-bit evaluation, and plots of tests where differences occur.« less

Repair Mechanism of Osteochondral Defect Promoted by Bioengineered Chondrocyte Sheet

PubMed Central

Kamei, Naosuke; Adachi, Nobuo; Hamanishi, Michio; Kamei, Goki; Mahmoud, Elhussein Elbadry; Nakano, Tomohiro; Iwata, Takanori; Yamato, Masayuki; Okano, Teruo; Ochi, Mitsuo

2015-01-01

Cell sheet engineering has developed as a remarkable method for cell transplantation. In the field of cartilage regeneration, several studies previously reported that cartilage defects could be regenerated by transplantation of a chondrocyte sheet using cell sheet engineering. However, it remains unclear how such a thin cell sheet could repair a deep cartilage defect. We, therefore, focused on the mechanism of cartilage repair using cell sheet engineering in this study. Chondrocyte sheets and synovial cell sheets were fabricated using cell sheet engineering, and these allogenic cell sheets were transplanted to cover an osteochondral defect in a rat model. Macroscopic and histological evaluation was performed at 4 and 12 weeks after transplantation. Analysis of the gene expression of each cell sheet and of the regenerated tissue at 1 week after transplantation was performed. In addition, green fluorescent protein (GFP) transgenic rats were used as donors (transplanted chondrocyte sheets) or recipients (osteochondral defect models) to identify the cell origin of regenerated cartilage. Cartilage repair was significantly better in the group implanted with a chondrocyte sheet than in that with a synovial cell sheet. The results of gene expression analysis suggest that the possible factor contributing to cartilage repair might be TGFβ1. Cell tracking experiments using GFP transgenic rats showed that the regenerated cartilage was largely composed of cells derived from the transplanted chondrocyte sheets. PMID:25396711

NREL's System Advisor Model Simplifies Complex Energy Analysis (Fact Sheet)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Not Available

2015-01-01

NREL has developed a tool -- the System Advisor Model (SAM) -- that can help decision makers analyze cost, performance, and financing of any size grid-connected solar, wind, or geothermal power project. Manufacturers, engineering and consulting firms, research and development firms, utilities, developers, venture capital firms, and international organizations use SAM for end-to-end analysis that helps determine whether and how to make investments in renewable energy projects.

Towards a super-strainable paper using the Layer-by-Layer technique.

PubMed

Marais, Andrew; Utsel, Simon; Gustafsson, Emil; Wågberg, Lars

2014-01-16

The Layer-by-Layer technique was used to build a polyelectrolyte multilayer on the surface of pulp fibres. The treated fibres were then used to prepare paper sheets and the mechanical properties of these sheets were evaluated as a function of the number of bi-layers on the fibres. Two different systems were studied: polyethyleneimine (PEI)/nanofibrillated cellulose (NFC), and polyallylamine hydrochloride (PAH)/hyaluronic acid (HA). Model experiments using dual polarization interferometry and SiO₂ surfaces showed that the two systems gave different thicknesses for a given number of layers. The outer layer was found to be a key parameter in the PEI/NFC system, whereas it was less important in the PAH/HA system. The mechanical properties of the sheets made from the PAH/HA treated fibres were significantly greater than those made from untreated fibres, reaching 70 Nm/g in tensile index and 6.5% in strain at break. Such a modification could be very useful for 3D forming of paper, opening new perspectives in for example the packaging industry, with a renewable and biodegradable product as a potential substitute for some of the traditional oil-based plastics. Copyright © 2013 Elsevier Ltd. All rights reserved.

Asymmetry of the Martian Current Sheet in a Multi-fluid MHD Model

NASA Astrophysics Data System (ADS)

Panoncillo, S. G.; Egan, H. L.; Dong, C.; Connerney, J. E. P.; Brain, D. A.; Jakosky, B. M.

2017-12-01

The solar wind carries interplanetary magnetic field (IMF) lines toward Mars, where they drape around the planet's conducting ionosphere, creating a current sheet behind the planet where the magnetic field has opposite polarity on either side. In its simplest form, the current sheet is often thought of as symmetric, extending behind the planet along the Mars-Sun line. Observations and model simulations, however, demonstrate that this idealized representation is only an approximation, and the actual scenario is much more complex. The current sheet can have 3D structure, move back and forth, and be situated dawnward or duskward of the Mars-Sun line. In this project, we utilized a library of global plasma model results for Mars consisting of a collection of multi-fluid MHD simulations where solar max/min, sub-solar longitude, and the orbital position of Mars are varied individually. The model includes Martian crustal fields, and was run for identical steady solar wind conditions. This library was created for the purpose of comparing model results to MAVEN data; we looked at the results of this model library to investigate current sheet asymmetries. By altering one variable at a time we were able to measure how these variables influence the location of the current sheet. We found that the current sheet is typically shifted toward the dusk side of the planet, and that modeled asymmetries are especially prevalent during solar min. Previous model studies that lack crustal fields have found that, for a Parker spiral IMF, the current sheet will shift dawnward, while our results typically show the opposite. This could expose certain limitations in the models used, or it could reveal an interaction between the solar wind and the plasma environment of Mars that has not yet been explored. MAVEN data may be compared to the model results to confirm the sense of the modeled asymmetry. These results help us to probe the physics controlling the Martian magnetotail and atmospheric escape from Mars.

An investigation of the astronomical theory of the ice ages using a simple climate-ice sheet model

NASA Technical Reports Server (NTRS)

Pollard, D.

1978-01-01

The astronomical theory of the Quaternary ice ages is incorporated into a simple climate model for global weather; important features of the model include the albedo feedback, topography and dynamics of the ice sheets. For various parameterizations of the orbital elements, the model yields realistic assessments of the northern ice sheet. Lack of a land-sea heat capacity contrast represents one of the chief difficulties of the model.

Density Functional Theory (DFT) study of β-Hairpins in Antiparallel β-Sheets, A New Classification Based upon H-bond Topology

PubMed Central

Roy, Dipankar; Pohl, Gabor; Ali-Torres, Jorge; Marianski, Mateusz; Dannenberg, J. J.

2012-01-01

We present a new classification of β-turns specific to antiparallel β-sheets based upon the topology of H-bond formation. This classification results from ONIOM calculations using B3LYP/D95** DFT and AM1 semiempirical calculations as the high and low levels respectively. We chose acetyl(Ala)6NH2 as a model system as it is the simplest all alanine system that can form all the H-bonds required for a β-turn in a sheet. Of the ten different conformation we have found, the most stable structures have C7 cyclic H-bonds in place of the C10 interactions specified in the classic definition. Also, the chiralities specified for the i+1st and i+2nd residues in the classic definition disappear when the structures are optimized using our techniques, as the energetic differences between the four diastereomers of each structure are not substantial for eight of the ten conformations. PMID:22731966

Density functional theory study of β-hairpins in antiparallel β-sheets, a new classification based upon H-bond topology.

PubMed

Roy, Dipankar; Pohl, Gabor; Ali-Torres, Jorge; Marianski, Mateusz; Dannenberg, J J

2012-07-10

We present a new classification of β-turns specific to antiparallel β-sheets based upon the topology of H-bond formation. This classification results from ONIOM calculations using B3LYP/D95** density functional theory and AM1 semiempirical calculations as the high and low levels, respectively. We chose acetyl(Ala)(6)NH(2) as a model system as it is the simplest all-alanine system that can form all the H-bonds required for a β-turn in a sheet. Of the 10 different conformations we have found, the most stable structures have C(7) cyclic H-bonds in place of the C(10) interactions specified in the classic definition. Also, the chiralities specified for residues i + 1 and i + 2 in the classic definition disappear when the structures are optimized using our techniques, as the energetic differences among the four diastereomers of each structure are not substantial for 8 of the 10 conformations.

The Effects of Plastic Anisotropy in Warm and Hot Forming of Magnesium Sheet Materials

NASA Astrophysics Data System (ADS)

Taleff, Eric M.; Antoniswamy, Aravindha R.; Carpenter, Alexander J.; Yavuz, Emre

Mg alloy sheet materials often exhibit plastic anisotropy at room temperature as a result of the limited slip systems available in the HCP lattice combined with a commonly strong basal texture. Less well studied is plastic anisotropy developed at the elevated temperatures associated with warm and hot forming. At these elevated temperatures, particularly above 200°C, the activation of additional slip systems significantly increases ductility. However, plastic anisotropy is also induced at elevated temperatures by a strong crystallographic texture, and it can require an accounting in material constitutive models to achieve accurate forming simulations. The type and degree of anisotropy under these conditions depend on both texture and deformation mechanism. The current understanding of plastic anisotropy in Mg AZ31B and ZEK100 sheet materials at elevated temperatures is reviewed in this article. The recent construction of material forming cases is also reviewed with strategies to account for plastic anisotropy in forming simulations.

Presentations - Lande, Lauren and others, 2015 | Alaska Division of

Science.gov Websites

Details Title: A petrological model for emplacement of the ultramafic Ni-Cu-PGE Alpha complex, eastern , Newberry, R.J., and Twelker, Evan, 2015, A petrological model for emplacement of the ultramafic Ni-Cu-PGE Sheets Maps & Other Oversized Sheets Sheet 1 A petrological model for emplacement of the ultramafic

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

NASA Technical Reports Server (NTRS)

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

2012-01-01

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

The East Antarctic Ice Sheet and the Gamburtsev Subglacial Mountains (Invited)

NASA Astrophysics Data System (ADS)

Bell, R. E.; Studinger, M.; Ferraccioli, F.; Damaske, D.; Finn, C.; Braaten, D. A.; Fahnestock, M. A.; Jordan, T. A.; Corr, H.; Elieff, S.; Frearson, N.; Block, A. E.; Rose, K.

2009-12-01

Models of the onset of glaciation in Antarctica routinely document the early growth of the ice sheet on the summit of the Gamburtsev Subglacial Mountains in the center of the East Antarctic Craton. While ice sheet models replicate the formation of the East Antarctic ice sheet 35 million years ago, the age, evolution and structure of the Gamburtsev Mountains remain completely unresolved. During the International Polar Year scientists from seven nations have launched a major collaborative program (AGAP) to explore the Gamburtsev Subglacial Mountains buried by the East Antarctic ice sheet and bounded by numerous subglacial lakes. The AGAP umbrella is a multi-national, multi-disciplinary effort and includes aerogeophysics, passive seismology, traverse programs and will be complimented by future ice core and bedrock drilling. A major new airborne data set including gravity; magnetics; ice thickness; SAR images of the ice-bed interface; near-surface and deep internal layers; and ice surface elevation is providing insights into a more dynamic East Antarctica. More than 120,000 km of aerogeophysical data have been acquired from two remote field camps during the 2008/09 field season. AGAP effort was designed to address several fundamental questions including: 1) What role does topography play in the nucleation of continental ice sheets? 2) How do tectonic processes control the formation, distribution, and stability of subglacial lakes? The preliminary analysis of this major new data set indicated these 3000m high mountains are deeply dissected by a dendritic system. The northern margin of the mountain range terminates against the inland extent of the Lambert Graben. Evidence of the onset of glaciation is preserved as cirques and U shaped valleys along the axis of the uplifted massifs. The geomorphology reflects the interaction between the ice sheet and the Gamburtsev Mountains. Bright reflectors in the radar data in the deep valleys indicate the presence of water that has the potential to influence ice sheet flow. Crevassing and disrupted internal layers are present in the deep ice found in the inland extent of the Lambert Graben. Preliminary analysis indicates both a more dynamic East Antarctic ice sheet and a more complex tectonic evolution for East Antarctica.

A magnetospheric magnetic field model with flexible current systems driven by independent physical parameters

NASA Technical Reports Server (NTRS)

Hilmer, Robert V.; Voigt, Gerd-Hannes

1995-01-01

A tilt-dependent magnetic field model of the Earth's magnetosphere with variable magnetopause standoff distance is presented. Flexible analytic representations for the ring and cross-tail currents, each composed of the elements derived from the Tsyganenko and Usmanov (1982) model, are combined with the fully shielded vacuum dipole configurations of Voigt (1981). Although the current sheet does not warp in the y-z plane, changes in the shape and position of the neutral sheet with dipole tilt are consistent with both MHD equilibrium theory and observations. In addition, there is good agreement with observed Delta B profiles and the average equatorial contours of magnetic field magnitude. While the dipole field is rigorously shielded within the defined magnetopause, the ring and cross-tails currents are not similarly confined, consequently, the model's region of validity is limited to the inner magnetosphere. The model depends on four independent external parameters. We present a simple but limited method of simulating several substorm related magnetic field changes associated with the disrupion of the near-Earth cross-tail current sheet and collapse of the midnight magnetotail field region. This feature further facilitates the generation of magnetic field configuration time sequences useful in plasma convection simulations of real magnetospheric events.

Investigating the Impact of Aerosol Deposition on Snow Melt over the Greenland Ice Sheet Using a New Kernel

NASA Astrophysics Data System (ADS)

Li, Y.; Flanner, M.

2017-12-01

Accelerating surface melt on the Greenland Ice Sheet (GrIS) has led to a doubling of Greenland's contribution to global sea level rise during recent decades. The darkening effect due to black carbon (BC), dust, and other light absorbing impurities (LAI) enhances snow melt by boosting its absorption of solar energy. It is therefore important for coupled aerosol-climate and ice sheet models to include snow darkening effects from LAI, and yet most do not. In this study, we develop an aerosol deposition—snow melt kernel based on the Community Earth System Model (CESM) to investigate changes in melt flux due to variations in the amount and timing of aerosol deposition on the GrIS. The Community Land Model (CLM) component of CESM is driven with a large range of aerosol deposition fluxes to determine non-linear relationships between melt perturbation and deposition amount occurring in different months and location (thereby capturing variations in base state associated with elevation and latitude). The kernel product will include climatological-mean effects and standard deviations associated with interannual variability. Finally, the kernel will allow aerosol deposition fluxes from any global or regional aerosol model to be translated into surface melt perturbations of the GrIS, thus extending the utility of state-of-the-art aerosol models.

High Resolution Photogrammetric Digital Elevation Models Across Calving Fronts and Meltwater Channels in Greenland

NASA Astrophysics Data System (ADS)

Le Bel, D. A.; Brown, S.; Zappa, C. J.; Bell, R. E.; Frearson, N.; Tinto, K. J.

2014-12-01

Photogrammetric digital elevation models (DEMs) are a powerful approach for understanding elevation change and dynamics along the margins of the large ice sheets. The IcePod system, mounted on a New York Air National Guard LC-130, can measure high-resolution surface elevations with a Riegl VQ580 scanning laser altimeter and Imperx Bobcat IGV-B6620 color visible-wavelength camera (6600x4400 resolution); the surface temperature with a Sofradir IRE-640L infrared camera (spectral response 7.7-9.5 μm, 640x512 resolution); and the structure of snow and ice with two radar systems. We show the use of IcePod imagery to develop DEMs across calving fronts and meltwater channels in Greenland. Multiple over-flights of the Kangerlussaq Airport ramp have provided a test of the technique at a location with accurate, independently-determined elevation. Here the photogrammetric DEM of the airport, constrained by ground control measurements, is compared with the Lidar results. In July 2014 the IcePod ice-ocean imaging system surveyed the calving fronts of five outlet glaciers north of Jakobshavn Isbrae. We used Agisoft PhotoScan to develop a DEM of each calving front using imagery captured by the IcePod systems. Adjacent to the ice sheet, meltwater plumes foster mixing in the fjord, moving warm ocean water into contact with the front of the ice sheet where it can undercut the ice front and trigger calving. The five glaciers provide an opportunity to examine the calving front structure in relation to ocean temperature, fjord circulation, and spatial scale of the meltwater plumes. The combination of the accurate DEM of the calving front and the thermal imagery used to constrain the temperature and dynamics of the adjacent plume provides new insights into the ice-ocean interactions. Ice sheet margins provide insights into the connections between the surface meltwater and the fate of the water at the ice sheet base. Surface meltwater channels are visualized here for the first time using the combination of Lidar, photogrammetry DEMs and infrared imagery. These techniques leverage electromagnetic surface properties that allow us to identify the presence of water, measure the slope and elevation of the channel, as well as the two-dimensional temperature variability of the water/ice/snow in multiple melt channels within a drainage system.

Particulate photocatalyst sheets for Z-scheme water splitting: advantages over powder suspension and photoelectrochemical systems and future challenges.

PubMed

Wang, Qian; Hisatomi, Takashi; Katayama, Masao; Takata, Tsuyoshi; Minegishi, Tsutomu; Kudo, Akihiko; Yamada, Taro; Domen, Kazunari

2017-04-28

Water splitting using semiconductor photocatalysts has been attracting growing interest as a means of solar energy based conversion of water to hydrogen, a clean and renewable fuel. Z-scheme photocatalytic water splitting based on the two-step excitation of an oxygen evolution photocatalyst (OEP) and a hydrogen evolution photocatalyst (HEP) is a promising approach toward the utilisation of visible light. In particular, a photocatalyst sheet system consisting of HEP and OEP particles embedded in a conductive layer has been recently proposed as a new means of obtaining efficient and scalable redox mediator-free Z-scheme solar water splitting. In this paper, we discuss the advantages and disadvantages of the photocatalyst sheet approach compared to conventional photocatalyst powder suspension and photoelectrochemical systems through an examination of the water splitting activity of Z-scheme systems based on SrTiO 3 :La,Rh as the HEP and BiVO 4 :Mo as the OEP. This photocatalyst sheet was found to split pure water much more efficiently than the powder suspension and photoelectrochemical systems, because the underlying metal layer efficiently transfers electrons from the OEP to the HEP. The photocatalyst sheet also outperformed a photoelectrochemical parallel cell during pure water splitting. The effects of H + /OH - concentration overpotentials and of the IR drop are reduced in the case of the photocatalyst sheet compared to photoelectrochemical systems, because the HEP and OEP are situated in close proximity to one another. Therefore, the photocatalyst sheet design is well-suited to efficient large-scale applications. Nevertheless, it is also noted that the photocatalytic activity of these sheets drops markedly with increasing background pressure because of reverse reactions involving molecular oxygen under illumination as well as delays in gas bubble desorption. It is shown that appropriate surface modifications allow the photocatalyst sheet to maintain its water splitting activity at elevated pressure. Accordingly, we conclude that the photocatalyst sheet system is a viable option for the realisation of efficient solar fuel production.

Multiscale modelling of a composite electroactive polymer structure

NASA Astrophysics Data System (ADS)

Wang, P.; Lassen, B.; Jones, R. W.; Thomsen, B.

2010-12-01

Danfoss PolyPower has developed a tubular actuator comprising a dielectric elastomer sheet with specially shaped compliant electrodes rolled into a tube. This paper is concerned with the modelling of this kind of tubular actuator. This is a challenging task due to the system's multiscale nature which is caused by the orders of magnitude difference between the length and thickness of the sheets as well as the thickness of the electrodes and the elastomer in the sheets. A further complication is the presence of passive parts at both ends of the actuator, i.e. areas without electrodes which are needed in order to avoid short circuits between negative and positively charged electrodes on the two sides of the sheet. Due to the complexities in shape and size it is necessary to introduce some simplifying assumptions. This paper presents a set of models where the three-dimensional problem has been reduced to two-dimensional problems, ensuring that the resulting models can be handled numerically within the framework of the finite element method. These models have been derived by expressing Navier's equation in elliptical cylindrical coordinates in order to take full advantage of the special shape of these actuators. Emphasis is placed on studying the passive parts of the actuator, as these degrade the effectiveness of the actuator. Two approaches are used here to model the passive parts: a spring-stiffness analogy model and a longitudinal section model of the actuator. The models have been compared with experimental results for the force-elongation characteristics of the commercially available PolyPower 'InLastor push' actuator. The comparison shows good agreement between model and experiments for the case where the passive parts were taken into account. One of the models developed is subsequently used to study geometric effects—specifically the effect of changing the ellipticity of the tubular actuator on the actuator's performance is investigated.

Incorporation of an Energy Equation into a Pulsed Inductive Thruster Performance Model

NASA Technical Reports Server (NTRS)

Polzin, Kurt A.; Reneau, Jarred P.; Sankaran, Kameshwaran

2011-01-01

A model for pulsed inductive plasma acceleration containing an energy equation to account for the various sources and sinks in such devices is presented. The model consists of a set of circuit equations coupled to an equation of motion and energy equation for the plasma. The latter two equations are obtained for the plasma current sheet by treating it as a one-element finite volume, integrating the equations over that volume, and then matching known terms or quantities already calculated in the model to the resulting current sheet-averaged terms in the equations. Calculations showing the time-evolution of the various sources and sinks in the system are presented to demonstrate the efficacy of the model, with two separate resistivity models employed to show an example of how the plasma transport properties can affect the calculation. While neither resistivity model is fully accurate, the demonstration shows that it is possible within this modeling framework to time-accurately update various plasma parameters.

Using Indigenous Materials for Construction

DTIC Science & Technology

2015-07-01

Theoretical models were devised for prediction of the structural attributes of indigenous ferrocement sheets and sandwich composite panels comprising the...indigenous ferrocement skins and aerated concrete core. Structural designs were developed for these indigenous sandwich composite panels in typical...indigenous materials and building systems developed in the project were evaluated. Numerical modeling capabilities were developed for structural

Sea-level response to abrupt ocean warming of Antarctic ice shelves

NASA Astrophysics Data System (ADS)

Pattyn, Frank

2016-04-01

Antarctica's contribution to global sea-level rise increases steadily. A fundamental question remains whether the ice discharge will lead to marine ice sheet instability (MISI) and collapse of certain sectors of the ice sheet or whether ice loss will increase linearly with the warming trends. Therefore, we employ a newly developed ice sheet model of the Antarctic ice sheet, called f.ETISh (fast Elementary Thermomechanical Ice Sheet model) to simulate ice sheet response to abrupt perturbations in ocean and atmospheric temperature. The f.ETISh model is a vertically integrated hybrid (SSA/SIA) ice sheet model including ice shelves. Although vertically integrated, thermomechanical coupling is ensured through a simplified representation of ice sheet thermodynamics based on an analytical solution of the vertical temperature profile, including strain heating and horizontal advection. The marine boundary is represented by a flux condition either coherent with power-law basal sliding (Pollard & Deconto (2012) based on Schoof (2007)) or according to Coulomb basal friction (Tsai et al., 2015), both taking into account ice-shelf buttressing. Model initialization is based on optimization of the basal friction field. Besides the traditional MISMIP tests, new tests with respect to MISI in plan-view models have been devised. The model is forced with stepwise ocean and atmosphere temperature perturbations. The former is based on a parametrised sub-shelf melt (limited to ice shelves), while the latter is based on present-day mass balance/surface temperature and corrected for elevation changes. Surface melting is introduced using a PDD model. Results show a general linear response in mass loss to ocean warming. Nonlinear response due to MISI occurs under specific conditions and is highly sensitive to the basal conditions near the grounding line, governed by both the initial conditions and the basal sliding/deformation model. The Coulomb friction model leads to significantly higher sensitivity compared to power-law sliding. On longer time scales, West-antarctic inter-basin connections favor nonlinear response.

Spatial distirbution of Antarctic mass flux due to iceberg transport

NASA Astrophysics Data System (ADS)

Comeau, Darin; Hunke, Elizabeth; Turner, Adrian

Under a changing climate that sees amplified warming in the polar regions, the stability of the West Antarctic ice sheet and its impact on sea level rise is of great importance. Icebergs are at the interface of the land-ice, ocean, and sea ice systems, and represent approximately half of the mass flux from the Antarctic ice sheet to the ocean. Calved icebergs transport freshwater away from the coast and exchange heat with the ocean, thereby affecting stratification and circulation, with subsequent indirect thermodynamic effects to the sea ice system. Icebergs also dynamically interact with surrounding sea ice pack, as well as serving as nutrient sources for biogeochemical activity. The spatial pattern of these fluxes transported from the continent to the ocean is generally poorly represented in current global climate models. We are implementing an iceberg model into the new Accelerated Climate Model for Energy (ACME) within the MPAS-Seaice model, which uses a variable resolution, unstructured grid framework. This capability will allow for full coupling with the land ice model to inform calving fluxes, and the ocean model for freshwater and heat exchange, giving a complete representation of the iceberg lifecycle and increasing the fidelity of ACME southern cryosphere simulations.

Equilibrium sensitivities of the Greenland ice sheet inferred from the adjoint of the three- dimensional thermo-mechanical model SICOPOLIS

NASA Astrophysics Data System (ADS)

Heimbach, P.; Bugnion, V.

2008-12-01

We present a new and original approach to understanding the sensitivity of the Greenland ice sheet to key model parameters and environmental conditions. At the heart of this approach is the use of an adjoint ice sheet model. MacAyeal (1992) introduced adjoints in the context of applying control theory to estimate basal sliding parameters (basal shear stress, basal friction) of an ice stream model which minimize a least-squares model vs. observation misfit. Since then, this method has become widespread to fit ice stream models to the increasing number and diversity of satellite observations, and to estimate uncertain model parameters. However, no attempt has been made to extend this method to comprehensive ice sheet models. Here, we present a first step toward moving beyond limiting the use of control theory to ice stream models. We have generated an adjoint of the three-dimensional thermo-mechanical ice sheet model SICOPOLIS of Greve (1997). The adjoint was generated using the automatic differentiation (AD) tool TAF. TAF generates exact source code representing the tangent linear and adjoint model of the parent model provided. Model sensitivities are given by the partial derivatives of a scalar-valued model diagnostic or "cost function" with respect to the controls, and can be efficiently calculated via the adjoint. An effort to generate an efficient adjoint with the newly developed open-source AD tool OpenAD is also under way. To gain insight into the adjoint solutions, we explore various cost functions, such as local and domain-integrated ice temperature, total ice volume or the velocity of ice at the margins of the ice sheet. Elements of our control space include initial cold ice temperatures, surface mass balance, as well as parameters such as appear in Glen's flow law, or in the surface degree-day or basal sliding parameterizations. Sensitivity maps provide a comprehensive view, and allow a quantification of where and to which variables the ice sheet model is most sensitive to. The model used in the present study includes simplifications in the model physics, parameterizations which rely on uncertain empirical constants, and is unable to capture fast ice streams. Nevertheless, as a proof-of-concept, this method can readily be extended to incorporate higher-order physics or parameterizations (or be applied to other models). It also opens the door to ice sheet state estimation: using the model's physics jointly with field and satellite observations to estimate a best estimate of the state of the ice sheets.

Covalent addition of chitosan to graphene sheets: Density functional theory explorations of quadrupole coupling constants

NASA Astrophysics Data System (ADS)

Mokhtari, Ali; Harismah, Kun; Mirzaei, Mahmoud

2015-12-01

Density functional theory (DFT) calculations have been performed to detect the stabilities and properties of chitosan-functionalized graphene and graphene-oxide structures (G-Chit and GO-Chit). The model systems with two different sizes of sheets have been optimized and the molecular and atomic properties have been evaluated for them. The results indicated that investigated G-Chit and GO-Chit structures could be considered as stable structures but with different properties. The properties for GO and GO-Chit structures are almost similar; however, they are different from the original G and G-Chit structures. The results also indicated that the properties could be also size-dependent, in which different molecular and atomic properties have been observed for the investigate G sheets.

75 FR 26294 - Notice of Availability of the Models for Plant-Specific Adoption of Technical Specifications Task...

Federal Register 2010, 2011, 2012, 2013, 2014

2010-05-11

... an errata sheet are available in the Agencywide Documents Access and Management System (ADAMS) under... Agencywide Documents Access and Management System (ADAMS): Publicly available documents created or received... facilitate expedited approval of plant-specific adoption of TSTF-493, Revision 4. Documents: You can access...

Fun at Antarctic grounding lines: Ice-shelf channels and sediment transport

NASA Astrophysics Data System (ADS)

Drews, Reinhard; Mayer, Christoph; Eisen, Olaf; Helm, Veit; Ehlers, Todd A.; Pattyn, Frank; Berger, Sophie; Favier, Lionel; Hewitt, Ian H.; Ng, Felix; Fürst, Johannes J.; Gillet-Chaulet, Fabien; Bergeot, Nicolas; Matsuoka, Kenichi

2017-04-01

Meltwater beneath the polar ice sheets drains, in part, through subglacial conduits. Landforms created by such drainages are abundant in areas formerly covered by ice sheets during the last glacial maximum. However, observations of subglacial conduit dynamics under a contemporary ice sheet are lacking. We present results from ice-penetrating radar to infer the existence of subglacial conduits upstream of the grounding line of Roi Baudouin Ice Shelf, Antarctica. The conduits are aligned with ice-shelf channels, and underlain by esker ridges formed from sediment deposition due to reduced water outflow speed near the grounding line. In turn, the eskers modify local ice flow to initiate the bottom topography of the ice-shelf channels, and create small surface ridges extending onto the shelf. Relict features on the shelf are interpreted to indicate a history of these interactions and variability of past subglacial drainages. Because ice-shelf channels are loci where intense melting occurs to thin an ice shelf, these findings expose a novel link between subglacial drainage, sedimentation, and ice-shelf stability. To investigate the role of sediment transport beneath ice sheets further, we model the sheet-shelf system of the Ekstömisen catchment, Antarctica. A 3D finite element model (Elmer/ICE) is used to solve the transients full Stokes equation for isotropic, isothermal ice with a dynamic grounding line. We initialize the model with surface topography from the TanDEM-X satellites and by inverting simultaneously for ice viscosity and basal drag using present-day surface velocities. Results produce a flow field which is consitent with sattelite and on-site observations. Solving the age-depth relationship allows comparison with radar isochrones from airborne data, and gives information about the atmospheric/dynamic history of this sector. The flow field will eventually be used to identify potential sediment sources and sinks which we compare with more than 400 km of seismic profiles collected over the floating ice shelves and the grounded ice sheet.

Mapping the band structure of a surface phononic crystal

NASA Astrophysics Data System (ADS)

Maznev, A. A.; Wright, O. B.; Matsuda, O.

2011-01-01

We map the band structure of surface acoustic modes of a periodic array of copper lines embedded in a SiO2 film on a silicon substrate by means of the laser-induced transient grating technique. A detailed map of the lowest sheet of the ω(k) surface and partial maps of two higher-order sheets are obtained. We discuss the topology of the ω(k) surface and explain how it arises from the Rayleigh and Sezawa modes of the film/substrate system. In the vicinity of the bandgap formed at the Brillouin zone boundary, the first and second dispersion sheets take the form of a saddle and a bowl, respectively, in agreement with a weak perturbation model. The shape of the third dispersion sheet, however, appears to defy expectations based on the perturbation approach. In particular, it contains minima located off the symmetry directions, which implies the existence of zero group velocity modes with an obliquely directed wavevector.

Magneto-mechanical modeling of electrical steel sheets

NASA Astrophysics Data System (ADS)

Aydin, U.; Rasilo, P.; Martin, F.; Singh, D.; Daniel, L.; Belahcen, A.; Rekik, M.; Hubert, O.; Kouhia, R.; Arkkio, A.

2017-10-01

A simplified multiscale approach and a Helmholtz free energy based approach for modeling the magneto-mechanical behavior of electrical steel sheets are compared. The models are identified from uniaxial magneto-mechanical measurements of two different electrical steel sheets which show different magneto-elastic behavior. Comparison with the available measurement data of the materials shows that both models successfully model the magneto-mechanical behavior of one of the studied materials, whereas for the second material only the Helmholtz free energy based approach is successful.

Meltwater drainage beneath ice sheets: What can we learn from uniting observations of paleo- and contemporary subglacial hydrology?

NASA Astrophysics Data System (ADS)

Simkins, L. M.; Carter, S. P.; Greenwood, S. L.; Schroeder, D. M.

2017-12-01

Understanding meltwater at the base of ice sheets is critical for predicting ice flow and subglacial sediment deformation. Whereas much progress has been made with observing contemporary systems, these efforts have been limited by the short temporal scales of remote sensing data, the restricted spatial coverage of radar sounding data, and the logistical challenges of direct access. Geophysical and sedimentological data from deglaciated continental shelves reveal broad spatial and temporal perspectives of subglacial hydrology, that complement observations of contemporary systems. Massive bedrock channels, such as those on the sediment-scoured inner continental shelf of the Amundsen Sea and the western Antarctic Peninsula, are up to hundreds of meters deep, which indicate either catastrophic drainage events or slower channel incision over numerous glaciations or sub-bank full drainage events. The presence of these deep channels has implications for further ice loss as they may provide conduits today for warm water incursion into sub-ice shelf cavities. Sediment-based subglacial channels, widespread in the northern hemisphere terrestrial domain and increasingly detected on both Arctic and Antarctic marine margins, help characterize more ephemeral drainage systems active during ice sheet retreat. Importantly, some observed sediment-based channels are connected to upstream subglacial lakes and terminate at paleo-grounding lines. From these records of paleo-subglacial hydrology, we extract the relative timing of meltwater drainage, estimate water fluxes, and contemplate the sources and ultimate fate of basal meltwater, refining predictive models for modern systems. These insights provided by geological data fill a gap in knowledge regarding spatial and temporal dynamics of subglacial hydrology and offer hindsight into meltwater drainage influence/association with ice flow and retreat behavior. The union of information gathered from paleo- and contemporary subglacial hydrology strengthens our understanding of the nature of meltwater drainage beneath ice sheets and informs better theory and numerical models.

Dynamics of poroelastocapillary rise

NASA Astrophysics Data System (ADS)

Nasouri, Babak; Elfring, Gwynn

2017-11-01

The surface-tension-driven rise of a liquid between two elastic sheets can result in their deformation or coalescence depending on their flexibility. When the sheets are poroelastic, the flexibility of the immersed parts of the sheets can change considerably thereby altering the dynamical behavior of the system. To better understand this phenomenon, we study the poroelastocapillary rise of a wetting liquid between poroelastic sheets. Using the lubrication theory and linear elasticity, we quantify the effects of the change in material properties of the wet sheets on the capillary rise and the equilibrium state of the system.

47 CFR 32.101 - Structure of the balance sheet accounts.

Code of Federal Regulations, 2011 CFR

2011-10-01

... 47 Telecommunication 2 2011-10-01 2011-10-01 false Structure of the balance sheet accounts. 32.101... UNIFORM SYSTEM OF ACCOUNTS FOR TELECOMMUNICATIONS COMPANIES Instructions for Balance Sheet Accounts § 32.101 Structure of the balance sheet accounts. The Balance Sheet accounts shall be maintained as follows...

47 CFR 32.101 - Structure of the balance sheet accounts.

Code of Federal Regulations, 2010 CFR

2010-10-01

... 47 Telecommunication 2 2010-10-01 2010-10-01 false Structure of the balance sheet accounts. 32.101... UNIFORM SYSTEM OF ACCOUNTS FOR TELECOMMUNICATIONS COMPANIES Instructions for Balance Sheet Accounts § 32.101 Structure of the balance sheet accounts. The Balance Sheet accounts shall be maintained as follows...

Open Energy Info (OpenEI) (Fact Sheet)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Not Available

2010-12-01

The Open Energy Information (OpenEI.org) initiative is a free, open-source, knowledge-sharing platform. OpenEI was created to provide access to data, models, tools, and information that accelerate the transition to clean energy systems through informed decisions.

Preforming of polydioxanone sheets for orbital wall fractures - A technical note.

PubMed

Kruber, Daniel; Hierl, Thomas; Doerfler, Hans-Martin; Huempfner-Hierl, Heike; Krause, Matthias

2018-07-01

Polydioxanone (PDS) sheets are commonly used in the treatment of orbital wall fractures. A potential drawback of PDS is that it may be difficult to adapt to the anatomy of the orbital walls. Therefore a study was conceived to test the feasibility of preforming PDS sheets. PDS sheet material was water-heated and preformed using a template based on a statistical anatomical model. Then the deformed sheet was cooled, stored and compared to the original model to investigate post-deformation changes. PDS sheet material could easily be deformed using a mould. No significant post-cooling shape changes were noticed. PDS sheet material can be preformed into complex geometric shapes. This could be a benefit in the treatment of orbital wall fractures. Copyright © 2018 European Association for Cranio-Maxillo-Facial Surgery. Published by Elsevier Ltd. All rights reserved.

How effective is albedo modification (solar radiation management geoengineering) in preventing sea-level rise from the Greenland Ice Sheet?

NASA Astrophysics Data System (ADS)

Applegate, Patrick J.; Keller, Klaus

2015-08-01

Albedo modification (AM) is sometimes characterized as a potential means of avoiding climate threshold responses, including large-scale ice sheet mass loss. Previous work has investigated the effects of AM on total sea-level rise over the present century, as well as AM’s ability to reduce long-term (≫103 yr) contributions to sea-level rise from the Greenland Ice Sheet (GIS). These studies have broken new ground, but neglect important feedbacks in the GIS system, or are silent on AM’s effectiveness over the short time scales that may be most relevant for decision-making (<103 yr). Here, we assess AM’s ability to reduce GIS sea-level contributions over decades to centuries, using a simplified ice sheet model. We drive this model using a business-as-usual base temperature forcing scenario, as well as scenarios that reflect AM-induced temperature stabilization or temperature drawdown. Our model results suggest that (i) AM produces substantial near-term reductions in the rate of GIS-driven sea-level rise. However, (ii) sea-level rise contributions from the GIS continue after AM begins. These continued sea level rise contributions persist for decades to centuries after temperature stabilization and temperature drawdown begin, unless AM begins in the next few decades. Moreover, (iii) any regrowth of the GIS is delayed by decades or centuries after temperature drawdown begins, and is slow compared to pre-AM rates of mass loss. Combined with recent work that suggests AM would not prevent mass loss from the West Antarctic Ice Sheet, our results provide a nuanced picture of AM’s possible effects on future sea-level rise.

On the plumbing system of volcanic complexes: field constraints from the Isle of Skye (UK) and FEM elasto-plastic modelling including gravity and tectonics.

NASA Astrophysics Data System (ADS)

Bistacchi, A.; Pisterna, R.; Romano, V.; Rust, D.; Tibaldi, A.

2009-04-01

The plumbing system that connects a sub-volcanic magma reservoir to the surface has been the object of field characterization and mechanical modelling efforts since the pioneering work by Anderson (1936), who produced a detailed account of the spectacular Cullin Cone-sheet Complex (Isle of Skye, UK) and a geometrical and mechanical model aimed at defining the depth to the magma chamber. Since this work, the definition of the stress state in the half space comprised between the magma reservoir and the surface (modelled either as a flat surface or a surface comprising a volcanic edifice) was considered the key point in reconstructing dike propagation paths from the magma chamber. In fact, this process is generally seen as the propagation in an elastic media of purely tensional joints (mode I or opening mode propagation), which follow trajectories perpendicular to the least compressive principal stress axis. Later works generally used different continuum mechanics methodologies (analytic, BEM, FEM) to solve the problem of a pressure source (the magma chamber, either a point source or a finite volume) in an elastic (in some cases heterogeneous) half space (bounded by a flat topography or topped by a "volcano"). All these models (with a few limited exceptions) disregard the effect of the regional stress field, which is caused by tectonic boundary forces and gravitational body load, and consider only the pressure source represented by the magma chamber (review in Gudmundsson, 2006). However, this is only a (sometimes subordinate) component of the total stress field. Grosfils (2007) first introduced the gravitational load (but not tectonic stresses) in an elastic model solved with FEM in a 2D axisymmetric half-space, showing that "failure to incorporate gravitational loading correctly" affect the calculated stress pattern and many of the predictions that can be drawn from the models. In this contribution we report on modelling results that include: 2D axisymmetric or true 3D geometry; gravitational body load; anisotropic tectonic stresses; different shapes and depths of the magma chamber; different overpressure levels in the magma chamber; different shapes of the topographic surface (e.g. flat, volcano, caldera); linear-elastic or elasto-plastic Drucker-Prager rheology. The latter point, which in our opinion constitutes a fundamental improvement in the model, has proven necessary because in a purely elastic model the stress state would rise at levels that cannot be sustained by geologic materials. Particularly around and above the magma chamber, yielding is expected, influencing the stress field in the remaining modelling domain. The non-linear problem has been solved with the commercial finite element package Comsol Multiphysics, using a parametric solver. At the same time, a field structural analysis of the classical Cuillin Cone-sheet Complex has been performed. This analysis has shown that four distinct families of cone sheets of different age do exist. Among these, the sheets with the higher dip angle range (80-65°) are confirmed as purely tensional joints, but those with a lower dip angle range (60-40°) are quite often (when suitable markers are available) associated with a measurable shear component. Combining these new field observations with mechanical modelling results, we propose a new interpretation for the Cuillin Cone Sheet Complex. The plumbing system was composed by both purely tensional joints and mesoscopic faults with a shear component, produced in response to the regional stress field perturbed by the magma chamber, and later passively re-used as magma emplacement conduits. Under this assumption, the observed geometry of the Cuillin Cone-sheet Complex is consistent with a relatively shallow magma chamber with a flattened laccolite shape. The shape of the palaeotopography, now completely eroded, has also been considered, but is more weakly constrained by modelling results. References: Anderson E.M., 1936. The dynamics of the formation of cone-sheets, ring-dykes and cauldron subsidences. Proc R Soc Edinburgh, 56, 128-157. Grosfils E.B., 2007. Magma reservoir failure on the terrestrial planets: Assessing the importance of gravitational loading in simple elastic models. Journal of Volcanology and Geothermal Research, 166 (2), 47-75. Gudmundsson A. , 2006. How local stresses control magma-chamber ruptures, dyke injections, and eruptions in composite volcanoes. Earth Science Reviews, 79 (1), 1-31.

Fracture on Curved Surfaces

NASA Astrophysics Data System (ADS)

Mitchell, Noah; Koning, Vinzenz; Vitelli, Vincenzo; Irvine, William T. M.

2014-03-01

When an elastic film conforms to a surface with Gaussian curvature, stresses arise in the film. As a result, cracks--typically studied in flat materials--interact with curvature when propagating through the system. Using silicone elastomer sheets that conform to the surface of a Gaussian bump, we find experimental evidence for the deflection of a crack propagating through the material. We interpret our experiments with reference to analytical modeling and simulations of a simplified model system.

Complex Greenland outlet glacier flow captured

PubMed Central

Aschwanden, Andy; Fahnestock, Mark A.; Truffer, Martin

2016-01-01

The Greenland Ice Sheet is losing mass at an accelerating rate due to increased surface melt and flow acceleration in outlet glaciers. Quantifying future dynamic contributions to sea level requires accurate portrayal of outlet glaciers in ice sheet simulations, but to date poor knowledge of subglacial topography and limited model resolution have prevented reproduction of complex spatial patterns of outlet flow. Here we combine a high-resolution ice-sheet model coupled to uniformly applied models of subglacial hydrology and basal sliding, and a new subglacial topography data set to simulate the flow of the Greenland Ice Sheet. Flow patterns of many outlet glaciers are well captured, illustrating fundamental commonalities in outlet glacier flow and highlighting the importance of efforts to map subglacial topography. Success in reproducing present day flow patterns shows the potential for prognostic modelling of ice sheets without the need for spatially varying parameters with uncertain time evolution. PMID:26830316

Bessel light sheet structured illumination microscopy

NASA Astrophysics Data System (ADS)

Noshirvani Allahabadi, Golchehr

Biomedical study researchers using animals to model disease and treatment need fast, deep, noninvasive, and inexpensive multi-channel imaging methods. Traditional fluorescence microscopy meets those criteria to an extent. Specifically, two-photon and confocal microscopy, the two most commonly used methods, are limited in penetration depth, cost, resolution, and field of view. In addition, two-photon microscopy has limited ability in multi-channel imaging. Light sheet microscopy, a fast developing 3D fluorescence imaging method, offers attractive advantages over traditional two-photon and confocal microscopy. Light sheet microscopy is much more applicable for in vivo 3D time-lapsed imaging, owing to its selective illumination of tissue layer, superior speed, low light exposure, high penetration depth, and low levels of photobleaching. However, standard light sheet microscopy using Gaussian beam excitation has two main disadvantages: 1) the field of view (FOV) of light sheet microscopy is limited by the depth of focus of the Gaussian beam. 2) Light-sheet images can be degraded by scattering, which limits the penetration of the excitation beam and blurs emission images in deep tissue layers. While two-sided sheet illumination, which doubles the field of view by illuminating the sample from opposite sides, offers a potential solution, the technique adds complexity and cost to the imaging system. We investigate a new technique to address these limitations: Bessel light sheet microscopy in combination with incoherent nonlinear Structured Illumination Microscopy (SIM). Results demonstrate that, at visible wavelengths, Bessel excitation penetrates up to 250 microns deep in the scattering media with single-side illumination. Bessel light sheet microscope achieves confocal level resolution at a lateral resolution of 0.3 micron and an axial resolution of 1 micron. Incoherent nonlinear SIM further reduces the diffused background in Bessel light sheet images, resulting in confocal quality images in thick tissue. The technique was applied to live transgenic zebra fish tg(kdrl:GFP), and the sub-cellular structure of fish vasculature genetically labeled with GFP was captured in 3D. The superior speed of the microscope enables us to acquire signal from 200 layers of a thick sample in 4 minutes. The compact microscope uses exclusively off-the-shelf components and offers a low-cost imaging solution for studying small animal models or tissue samples.

Troughs on Martian Ice Sheets: Analysis of Their Closure and Mass Balance

NASA Technical Reports Server (NTRS)

Fountain, A.; Kargel, J.; Lewis, K.; MacAyeal, D.; Pfeffer, T.; Zwally, J.

2000-01-01

At the Copenhagen workshop on Martian polar processes, Ralf Greve commented that the flow regime surrounding scarps and troughs of the Martian polar ice sheets cannot be modeled using traditional "plan view" ice-sheet models. Such models are inadequate because they typically use reduced equations that embody certain simplifications applicable only to terrestrial ice sheets where the upper ice sheet surface is smooth. In response to this suggestion, we have constructed a 2-dimensional, time dependent "side view" (two spatial dimensions: one horizontal, one vertical) model of scarp closure that is designed to overcome the difficulties described by Greve. The purpose of the model is to evaluate the scales of stress variation and styles of flow closure so as to estimate errors that may be encountered by "plan view" models. We show that there may be avenues whereby the complications associated with scarp closure can be overcome in "plan view" models through appropriate parameterizations of 3-dimensional effects. Following this, we apply the flow model to simulate the evolution of a typical scarp on the North Polar Cap of Mars. Our simulations investigate: (a) the role of "radiation trapping" (see our companion abstract) in creating and maintaining "spiral-like" scarps on the ice sheet, (b) the consequences of different flowlaws and ice compositions on scarp evolution and, in particular, scarp age, and (c) the role of dust and debris in scarp evolution.

Abrupt glacial climate shifts controlled by ice sheet changes.

PubMed

Zhang, Xu; Lohmann, Gerrit; Knorr, Gregor; Purcell, Conor

2014-08-21

During glacial periods of the Late Pleistocene, an abundance of proxy data demonstrates the existence of large and repeated millennial-scale warming episodes, known as Dansgaard-Oeschger (DO) events. This ubiquitous feature of rapid glacial climate change can be extended back as far as 800,000 years before present (BP) in the ice core record, and has drawn broad attention within the science and policy-making communities alike. Many studies have been dedicated to investigating the underlying causes of these changes, but no coherent mechanism has yet been identified. Here we show, by using a comprehensive fully coupled model, that gradual changes in the height of the Northern Hemisphere ice sheets (NHISs) can alter the coupled atmosphere-ocean system and cause rapid glacial climate shifts closely resembling DO events. The simulated global climate responses--including abrupt warming in the North Atlantic, a northward shift of the tropical rainbelts, and Southern Hemisphere cooling related to the bipolar seesaw--are generally consistent with empirical evidence. As a result of the coexistence of two glacial ocean circulation states at intermediate heights of the ice sheets, minor changes in the height of the NHISs and the amount of atmospheric CO2 can trigger the rapid climate transitions via a local positive atmosphere-ocean-sea-ice feedback in the North Atlantic. Our results, although based on a single model, thus provide a coherent concept for understanding the recorded millennial-scale variability and abrupt climate changes in the coupled atmosphere-ocean system, as well as their linkages to the volume of the intermediate ice sheets during glacials.

Substorm Electric And Magnetic Fields In The Earth's Magnetotail: Observations Compared To The WINDMI Model

NASA Astrophysics Data System (ADS)

Srinivas, P. G.; Spencer, E. A.; Vadepu, S. K.; Horton, W., Jr.

2017-12-01

We compare satellite observations of substorm electric fields and magnetic fields to the output of a low dimensional nonlinear physics model of the nightside magnetosphere called WINDMI. The electric and magnetic field satellite data are used to calculate the E X B drift, which is one of the intermediate variables of the WINDMI model. The model uses solar wind and IMF measurements from the ACE spacecraft as input into a system of 8 nonlinear ordinary differential equations. The state variables of the differential equations represent the energy stored in the geomagnetic tail, central plasma sheet, ring current and field aligned currents. The output from the model is the ground based geomagnetic westward auroral electrojet (AL) index, and the Dst index.Using ACE solar wind data, IMF data and SuperMAG identification of substorm onset times up to December 2015, we constrain the WINDMI model to trigger substorm events, and compare the model intermediate variables to THEMIS and GEOTAIL satellite data in the magnetotail. By forcing the model to be consistent with satellite electric and magnetic field observations, we are able to track the magnetotail energy dynamics, the field aligned current contributions, energy injections into the ring current, and ensure that they are within allowable limts. In addition we are able to constrain the physical parameters of the model, in particular the lobe inductance, the plasma sheet capacitance, and the resistive and conductive parameters in the plasma sheet and ionosphere.

Lava heating and loading of ice sheets on early Mars: Predictions for meltwater generation, groundwater recharge, and resulting landforms

NASA Astrophysics Data System (ADS)

Cassanelli, James P.; Head, James W.

2016-06-01

Recent modeling studies of the early Mars climate predict a predominantly cold climate, characterized by the formation of regional ice sheets across the highland areas of Mars. Formation of the predicted "icy highlands" ice sheets is coincident with a peak in the volcanic flux of Mars involving the emplacement of the Late Noachian - Early Hesperian ridged plains unit. We explore the relationship between the predicted early Mars "icy highlands" ice sheets, and the extensive early flood volcanism to gain insight into the surface conditions prevalent during the Late Noachian to Early Hesperian transition period. Using Hesperia Planum as a type area, we develop an ice sheet lava heating and loading model. We quantitatively assess the thermal and melting processes involved in the lava heating and loading process following the chronological sequence of lava emplacement. We test a broad range of parameters to thoroughly constrain the lava heating and loading process and outline predictions for the formation of resulting geological features. We apply the theoretical model to a study area within the Hesperia Planum region and assess the observed geology against predictions derived from the ice sheet lava heating and loading model. Due to the highly cratered nature of the Noachian highlands terrain onto which the volcanic plains were emplaced, we predict highly asymmetrical lava loading conditions. Crater interiors are predicted to accumulate greater thicknesses of lava over more rapid timescales, while in the intercrater plains, lava accumulation occurs over longer timescales and does not reach great thicknesses. We find that top-down melting due to conductive heat transfer from supraglacial lava flows is generally limited when the emplaced lava flows are less than ∼10 m thick, but is very significant at lava flow thicknesses of ∼100 m or greater. We find that bottom-up cryosphere and ice sheet melting is most likely to occur within crater interiors where lavas accumulate to a sufficient thickness to raise the ice-melting isotherm to the base of the superposed lavas. In these locations, if lava accumulation occurs rapidly, bottom-up melting of the ice sheet can continue, or begin, after lava accumulation has completed in a process we term "deferred melting". Subsurface mass loss through melting of the buried ice sheets is predicted to cause substantial subsidence in the superposed lavas, leading to the formation of associated collapse features including fracture systems, depressions, surface faulting and folding, wrinkle-ridge formation, and chaos terrain. In addition, if meltwater generated from the lava heating and loading process becomes trapped at the lava flow margins due to the presence of impermeable confining units, large highly pressurized episodic flooding events could occur. Examination of the study area reveals geological features which are generally consistent with those predicted to form as a result of the ice sheet lava heating and loading process, suggesting the presence of surface snow and ice during the Late Noachian to Early Hesperian period.

The mechanism of propulsion of a model microswimmer in a viscoelastic fluid next to a solid boundary

NASA Astrophysics Data System (ADS)

Ives, Thomas R.; Morozov, Alexander

2017-12-01

In this paper, we study the swimming of a model organism, the so-called Taylor's swimming sheet, in a viscoelastic fluid close to a solid boundary. This situation comprises natural habitats of many swimming microorganisms, and while previous investigations have considered the effects of both swimming next to a boundary and swimming in a viscoelastic fluid, seldom have both effects been considered simultaneously. We re-visit the small wave amplitude result obtained by Elfring and Lauga ["Theory of locomotion through complex fluids," in Complex Fluids in Biological Systems, Biological and Medical Physics, Biomedical Engineering, edited by S. E. Spagnolie (Springer New York, New York, NY, 2015), pp. 283-317] and give a mechanistic explanation to the decoupling of the effects of viscoelasticity, which tend to slow the sheet, and the presence of the boundary, which tends to speed up the sheet. We also develop a numerical spectral method capable of finding the swimming speed of a waving sheet with an arbitrary amplitude and waveform. We use it to show that the decoupling mentioned earlier does not hold at finite wave amplitudes and that for some parameters the presence of a boundary can cause the viscoelastic effects to increase the swimming speed of microorganisms.

M theory through the looking glass: Tachyon condensation in the E{sub 8} heterotic string

DOE Office of Scientific and Technical Information (OSTI.GOV)

Horava, Petr; Keeler, Cynthia A.

2008-03-15

We study the spacetime decay to nothing in string theory and M-theory. First we recall a nonsupersymmetric version of heterotic M-theory, in which bubbles of nothing--connecting the two E{sub 8} boundaries by a throat--are expected to be nucleated. We argue that the fate of this system should be addressed at weak string coupling, where the nonperturbative instanton instability is expected to turn into a perturbative tachyonic one. We identify the unique string theory that could describe this process: The heterotic model with one E{sub 8} gauge group and a singlet tachyon. We then use world sheet methods to study themore » tachyon condensation in the Neveu-Schwarz-Ramond formulation of this model, and show that it induces a world sheet super-Higgs effect. The main theme of our analysis is the possibility of making meaningful alternative gauge choices for world sheet supersymmetry, in place of the conventional superconformal gauge. We show in a version of unitary gauge how the world sheet gravitino assimilates the Goldstino and becomes dynamical. This picture clarifies recent results of Hellerman and Swanson. We also present analogs of R{sub {xi}} gauges, and note the importance of logarithmic conformal field theories in the context of tachyon condensation.« less

Monte Carlo Simulation for Polychromatic X-Ray Fluorescence Computed Tomography with Sheet-Beam Geometry

PubMed Central

Jiang, Shanghai

2017-01-01

X-ray fluorescence computed tomography (XFCT) based on sheet beam can save a huge amount of time to obtain a whole set of projections using synchrotron. However, it is clearly unpractical for most biomedical research laboratories. In this paper, polychromatic X-ray fluorescence computed tomography with sheet-beam geometry is tested by Monte Carlo simulation. First, two phantoms (A and B) filled with PMMA are used to simulate imaging process through GEANT 4. Phantom A contains several GNP-loaded regions with the same size (10 mm) in height and diameter but different Au weight concentration ranging from 0.3% to 1.8%. Phantom B contains twelve GNP-loaded regions with the same Au weight concentration (1.6%) but different diameter ranging from 1 mm to 9 mm. Second, discretized presentation of imaging model is established to reconstruct more accurate XFCT images. Third, XFCT images of phantoms A and B are reconstructed by filter back-projection (FBP) and maximum likelihood expectation maximization (MLEM) with and without correction, respectively. Contrast-to-noise ratio (CNR) is calculated to evaluate all the reconstructed images. Our results show that it is feasible for sheet-beam XFCT system based on polychromatic X-ray source and the discretized imaging model can be used to reconstruct more accurate images. PMID:28567054

Translating hydrologically-relevant variables from the ice sheet model SICOPOLIS to the Greenland Analog Project hydrologic modeling domain

NASA Astrophysics Data System (ADS)

Vallot, Dorothée; Applegate, Patrick; Pettersson, Rickard

2013-04-01

Projecting future climate and ice sheet development requires sophisticated models and extensive field observations. Given the present state of our knowledge, it is very difficult to say what will happen with certainty. Despite the ongoing increase in atmospheric greenhouse gas concentrations, the possibility that a new ice sheet might form over Scandinavia in the far distant future cannot be excluded. The growth of a new Scandinavian Ice Sheet would have important consequences for buried nuclear waste repositories. The Greenland Analogue Project, initiated by the Swedish Nuclear Fuel and Waste Management Company (SKB), is working to assess the effects of a possible future ice sheet on groundwater flow by studying a constrained domain in Western Greenland by field measurements (including deep bedrock drilling in front of the ice sheet) combined with numerical modeling. To address the needs of the GAP project, we interpolated results from an ensemble of ice sheet model runs to the smaller and more finely resolved modeling domain used in the GAP project's hydrologic modeling. Three runs have been chosen with three fairly different positive degree-day factors among those that reproduced the modern ice margin at the borehole position. The interpolated results describe changes in hydrologically-relevant variables over two time periods, 115 ka to 80 ka, and 20 ka to 1 ka. In the first of these time periods, the ice margin advances over the model domain; in the second time period, the ice margin retreats over the model domain. The spatially-and temporally dependent variables that we treated include the ice thickness, basal melting rate, surface mass balance, basal temperature, basal thermal regime (frozen or thawed), surface temperature, and basal water pressure. The melt flux is also calculated.

An advanced constitutive model in the sheet metal forming simulation: the Teodosiu microstructural model and the Cazacu Barlat yield criterion

NASA Astrophysics Data System (ADS)

Alves, J. L.; Oliveira, M. C.; Menezes, L. F.

2004-06-01

Two constitutive models used to describe the plastic behavior of sheet metals in the numerical simulation of sheet metal forming process are studied: a recently proposed advanced constitutive model based on the Teodosiu microstructural model and the Cazacu Barlat yield criterion is compared with a more classical one, based on the Swift law and the Hill 1948 yield criterion. These constitutive models are implemented into DD3IMP, a finite element home code specifically developed to simulate sheet metal forming processes, which generically is a 3-D elastoplastic finite element code with an updated Lagrangian formulation, following a fully implicit time integration scheme, large elastoplastic strains and rotations. Solid finite elements and parametric surfaces are used to model the blank sheet and tool surfaces, respectively. Some details of the numerical implementation of the constitutive models are given. Finally, the theory is illustrated with the numerical simulation of the deep drawing of a cylindrical cup. The results show that the proposed advanced constitutive model predicts with more exactness the final shape (medium height and ears profile) of the formed part, as one can conclude from the comparison with the experimental results.

Laurentide Ice-Sheet Meltwater Sources to the Gulf of Mexico During the Last Deglaciation: Assessing Data Reconstructions Using Water Isotope Enabled Simulations

NASA Astrophysics Data System (ADS)

Vetter, L.; LeGrande, A. N.; Ullman, D. J.; Carlson, A. E.

2017-12-01

Sediment cores from the Gulf of Mexico show evidence of meltwater derived from the Laurentide Ice Sheet during the last deglaciation. Recent studies using geochemical measurements of individual foraminifera suggest changes in the oxygen isotopic composition of the meltwater as deglaciation proceeded. Here we use the water isotope enabled climate model simulations (NASA GISS ModelE-R) to investigate potential sources of meltwater within the ice sheet. We find that initial melting of the ice sheet from the southern margin contributed an oxygen isotope value reflecting a low-elevation, local precipitation source. As deglacial melting proceeded, meltwater delivered to the Gulf of Mexico had a more negative oxygen isotopic value, which the climate model simulates as being sourced from the high-elevation, high-latitude interior of the ice sheet. This study demonstrates the utility of combining stable isotope analyses with climate model simulations to investigate past changes in the hydrologic cycle.

Influence of temperature fluctuations on equilibrium
ice sheet volume

NASA Astrophysics Data System (ADS)

Bøgeholm Mikkelsen, Troels; Grinsted, Aslak; Ditlevsen, Peter

2018-01-01

Forecasting the future sea level relies on accurate modeling of the response of the Greenland and Antarctic ice sheets to changing temperatures. The surface mass balance (SMB) of the Greenland Ice Sheet (GrIS) has a nonlinear response to warming. Cold and warm anomalies of equal size do not cancel out and it is therefore important to consider the effect of interannual fluctuations in temperature. We find that the steady-state volume of an ice sheet is biased toward larger size if interannual temperature fluctuations are not taken into account in numerical modeling of the ice sheet. We illustrate this in a simple ice sheet model and find that the equilibrium ice volume is approximately 1 m SLE (meters sea level equivalent) smaller when the simple model is forced with fluctuating temperatures as opposed to a stable climate. It is therefore important to consider the effect of interannual temperature fluctuations when designing long experiments such as paleo-spin-ups. We show how the magnitude of the potential bias can be quantified statistically. For recent simulations of the Greenland Ice Sheet, we estimate the bias to be 30 Gt yr-1 (24-59 Gt yr-1, 95 % credibility) for a warming of 3 °C above preindustrial values, or 13 % (10-25, 95 % credibility) of the present-day rate of ice loss. Models of the Greenland Ice Sheet show a collapse threshold beyond which the ice sheet becomes unsustainable. The proximity of the threshold will be underestimated if temperature fluctuations are not taken into account. We estimate the bias to be 0.12 °C (0.10-0.18 °C, 95 % credibility) for a recent estimate of the threshold. In light of our findings it is important to gauge the extent to which this increased variability will influence the mass balance of the ice sheets.

Development of a Prediction Model Based on RBF Neural Network for Sheet Metal Fixture Locating Layout Design and Optimization.

PubMed

Wang, Zhongqi; Yang, Bo; Kang, Yonggang; Yang, Yuan

2016-01-01

Fixture plays an important part in constraining excessive sheet metal part deformation at machining, assembly, and measuring stages during the whole manufacturing process. However, it is still a difficult and nontrivial task to design and optimize sheet metal fixture locating layout at present because there is always no direct and explicit expression describing sheet metal fixture locating layout and responding deformation. To that end, an RBF neural network prediction model is proposed in this paper to assist design and optimization of sheet metal fixture locating layout. The RBF neural network model is constructed by training data set selected by uniform sampling and finite element simulation analysis. Finally, a case study is conducted to verify the proposed method.

Development of a Prediction Model Based on RBF Neural Network for Sheet Metal Fixture Locating Layout Design and Optimization

PubMed Central

Wang, Zhongqi; Yang, Bo; Kang, Yonggang; Yang, Yuan

2016-01-01

Fixture plays an important part in constraining excessive sheet metal part deformation at machining, assembly, and measuring stages during the whole manufacturing process. However, it is still a difficult and nontrivial task to design and optimize sheet metal fixture locating layout at present because there is always no direct and explicit expression describing sheet metal fixture locating layout and responding deformation. To that end, an RBF neural network prediction model is proposed in this paper to assist design and optimization of sheet metal fixture locating layout. The RBF neural network model is constructed by training data set selected by uniform sampling and finite element simulation analysis. Finally, a case study is conducted to verify the proposed method. PMID:27127499

Rebreathing expired gases from bedding: a cause of cot death?

PubMed Central

Bolton, D P; Taylor, B J; Campbell, A J; Galland, B C; Cresswell, C

1993-01-01

The reported association of cot death and sleeping prone could be due to rebreathing of expired gases. A mechanical model simulating the respiratory system of an infant, exhaling warm humidified air with an end tidal carbon dioxide of 5%, has been used to investigate this. Some commonly used bedding materials caused an accumulation of carbon dioxide of 7% to over 10% with the model lying face down. This phenomenon persisted even with the head inclined at 45 degrees, but only on very soft materials, and could be a cause of cot death in a baby unresponsive to asphyxial blood gas changes. A coir fibre mattress allowed complete dispersal of exhalate as did a rubber sheet between any mattress and the covering sheet. PMID:8215518

Formation and Reconnection of Three-Dimensional Current Sheets in the Solar Corona

NASA Technical Reports Server (NTRS)

Edmondson, J. K.; Antiochos, S. K.; DeVore, C. R.; Zurbuchen, T. H.

2010-01-01

Current-sheet formation and magnetic reconnection are believed to be the basic physical processes responsible for much of the activity observed in astrophysical plasmas, such as the Sun s corona. We investigate these processes for a magnetic configuration consisting of a uniform background field and an embedded line dipole, a topology that is expected to be ubiquitous in the corona. This magnetic system is driven by a uniform horizontal flow applied at the line-tied photosphere. Although both the initial field and the driver are translationally symmetric, the resulting evolution is calculated using a fully three-dimensional magnetohydrodynamic (3D MHD) simulation with adaptive mesh refinement that resolves the current sheet and reconnection dynamics in detail. The advantage of our approach is that it allows us to apply directly the vast body of knowledge gained from the many studies of 2D reconnection to the fully 3D case. We find that a current sheet forms in close analogy to the classic Syrovatskii 2D mechanism, but the resulting evolution is different than expected. The current sheet is globally stable, showing no evidence for a disruption or a secondary instability even for aspect ratios as high as 80:1. The global evolution generally follows the standard Sweet- Parker 2D reconnection model except for an accelerated reconnection rate at a very thin current sheet, due to the tearing instability and the formation of magnetic islands. An interesting conclusion is that despite the formation of fully 3D structures at small scales, the system remains close to 2D at global scales. We discuss the implications of our results for observations of the solar corona. Subject Headings: Sun: corona Sun: magnetic fields Sun: reconnection

Exploring reconnection, current sheets, and dissipation in a laboratory MHD turbulence experiment

NASA Astrophysics Data System (ADS)

Schaffner, D. A.

2015-12-01

The Swarthmore Spheromak Experiment (SSX) can serve as a testbed for studying MHD turbulence in a controllable laboratory setting, and in particular, explore the phenomena of reconnection, current sheets and dissipation in MHD turbulence. Plasma with turbulently fluctuating magnetic and velocity fields can be generated using a plasma gun source and launched into a flux-conserving cylindrical tunnel. No background magnetic field is applied so internal fields are allowed to evolve dynamically. Point measurements of magnetic and velocity fluctuations yield broadband power-law spectra with a steepening breakpoint indicative of the onset of a dissipation scale. The frequency range at which this steepening occurs can be correlated to the ion inertial scale of the plasma, a length which is characteristic of the size of current sheets in MHD plasmas and suggests a connection to dissipation. Observation of non-Gaussian intermittent jumps in magnetic field magnitude and angle along with measurements of ion temperature bursts suggests the presence of current sheets embedded within the turbulent plasma, and possibly even active reconnection sites. Additionally, structure function analysis coupled with appeals to fractal scaling models support the hypothesis that current sheets are associated with dissipation in this system.

The Periodic Flapping and Breathing of Saturn's Magnetodisk During Equinox

NASA Astrophysics Data System (ADS)

Sorba, A. M.; Achilleos, N.; Guio, P.; Arridge, C. S.; Dougherty, M. K.; Sergis, N.

2017-12-01

Periodic variations have been observed in many field and particle properties in Saturn's magnetosphere, modulated at a period close to the planetary rotation rate. Magnetic field observations by Cassini's magnetometer instrument suggest that in the outer magnetosphere (beyond 12 Saturn radii) Saturn's current sheet is periodically displaced with respect to the rotational equator, to a first approximation acting as a rotating, tilted disk. This manifests as a `flapping' mode when observed by the spacecraft. Recent studies suggest the magnetosphere also has a `breathing' mode, expanding and contracting with a period close to the planetary rotation rate. We model these two modes in tandem by combining a global, geometrical model of a tilted and rippled current sheet with a local, force-balance model of Saturn's magnetodisk, accounting for the magnetospheric size and hot plasma content. We simulate the breathing behavior by introducing an azimuthal dependence of the system size. We fit Cassini magnetometer data acquired on equatorial orbits from 23 Oct - 17 Dec 2009 (Revs 120-122), close to Saturn equinox, in order that seasonal effects on the current sheet are minimised. We find that our model characterises well the amplitude and phase of the oscillations in the data, for those passes that show clear periodic signatures in the field. In particular, the Bθ (meridional) component can only be characterised when the breathing mode is included. This study introduces calculations for an oscillating boundary under conditions of constant solar wind dynamic pressure, which provide a good basis for understanding the complex relationship between current sheet dynamics and the periodic field perturbations.

Atmospheric and oceanic impacts of Antarctic glaciation across the Eocene-Oligocene transition.

PubMed

Kennedy, A T; Farnsworth, A; Lunt, D J; Lear, C H; Markwick, P J

2015-11-13

The glaciation of Antarctica at the Eocene-Oligocene transition (approx. 34 million years ago) was a major shift in the Earth's climate system, but the mechanisms that caused the glaciation, and its effects, remain highly debated. A number of recent studies have used coupled atmosphere-ocean climate models to assess the climatic effects of Antarctic glacial inception, with often contrasting results. Here, using the HadCM3L model, we show that the global atmosphere and ocean response to growth of the Antarctic ice sheet is sensitive to subtle variations in palaeogeography, using two reconstructions representing Eocene and Oligocene geological stages. The earlier stage (Eocene; Priabonian), which has a relatively constricted Tasman Seaway, shows a major increase in sea surface temperature over the Pacific sector of the Southern Ocean in response to the ice sheet. This response does not occur for the later stage (Oligocene; Rupelian), which has a more open Tasman Seaway. This difference in temperature response is attributed to reorganization of ocean currents between the stages. Following ice sheet expansion in the earlier stage, the large Ross Sea gyre circulation decreases in size. Stronger zonal flow through the Tasman Seaway allows salinities to increase in the Ross Sea, deep-water formation initiates and multiple feedbacks then occur amplifying the temperature response. This is potentially a model-dependent result, but it highlights the sensitive nature of model simulations to subtle variations in palaeogeography, and highlights the need for coupled ice sheet-climate simulations to properly represent and investigate feedback processes acting on these time scales. © 2015 The Author(s).

Assembly of Triblock Amphiphilic Peptides into One-Dimensional Aggregates and Network Formation.

PubMed

Ozgur, Beytullah; Sayar, Mehmet

2016-10-06

Peptide assembly plays a key role in both neurological diseases and development of novel biomaterials with well-defined nanostructures. Synthetic model peptides provide a unique platform to explore the role of intermolecular interactions in the assembly process. A triblock peptide architecture designed by the Hartgerink group is a versatile system which relies on Coulomb interactions, hydrogen bonding, and hydrophobicity to guide these peptides' assembly at three different length scales: β-sheets, double-wall ribbon-like aggregates, and finally a highly porous network structure which can support gels with ≤1% by weight peptide concentration. In this study, by using molecular dynamics simulations of a structure based implicit solvent coarse grained model, we analyzed this hierarchical assembly process. Parametrization of our CG model is based on multiple-state points from atomistic simulations, which enables this model to represent the conformational adaptability of the triblock peptide molecule based on the surrounding medium. Our results indicate that emergence of the double-wall β-sheet packing mechanism, proposed in light of the experimental evidence, strongly depends on the subtle balance of the intermolecular forces. We demonstrate that, even though backbone hydrogen bonding dominates the early nucleation stages, depending on the strength of the hydrophobic and Coulomb forces, alternative structures such as zero-dimensional aggregates with two β-sheets oriented orthogonally (which we refer to as a cross-packed structure) and β-sheets with misoriented hydrophobic side chains are also feasible. We discuss the implications of these competing structures for the three different length scales of assembly by systematically investigating the influence of density, counterion valency, and hydrophobicity.

Research on Al-alloy sheet forming formability during warm/hot sheet hydroforming based on elliptical warm bulging test

NASA Astrophysics Data System (ADS)

Cai, Gaoshen; Wu, Chuanyu; Gao, Zepu; Lang, Lihui; Alexandrov, Sergei

2018-05-01

An elliptical warm/hot sheet bulging test under different temperatures and pressure rates was carried out to predict Al-alloy sheet forming limit during warm/hot sheet hydroforming. Using relevant formulas of ultimate strain to calculate and dispose experimental data, forming limit curves (FLCS) in tension-tension state of strain (TTSS) area are obtained. Combining with the basic experimental data obtained by uniaxial tensile test under the equivalent condition with bulging test, complete forming limit diagrams (FLDS) of Al-alloy are established. Using a quadratic polynomial curve fitting method, material constants of fitting function are calculated and a prediction model equation for sheet metal forming limit is established, by which the corresponding forming limit curves in TTSS area can be obtained. The bulging test and fitting results indicated that the sheet metal FLCS obtained were very accurate. Also, the model equation can be used to instruct warm/hot sheet bulging test.

A Simple Class Exercise on Plate Tectonic Motion.

ERIC Educational Resources Information Center

Bates, Denis E. B.

1990-01-01

Presented is an activity in which students construct a model of plate divergence with two sheets of paper to show the separation of two continental plates in a system of spreading ridges and faults. Diagrams and procedures are described. (CW)

Rate and style of ice stream retreat constrained by new surface-exposure ages: The Minch, NW Scotland

NASA Astrophysics Data System (ADS)

Bradwell, Tom; Small, David; Fabel, Derek; Dove, Dayton; Cofaigh, Colm O.; Clark, Chris; Consortium, Britice-Chrono

2016-04-01

Chronologically constrained studies of former ice-sheet extents and dynamics are important for understanding past cryospheric responses and modelling future ice-sheet and sea-level change. As part of the BRITICE-CHRONO project, we present new geomorphological and chronological data from a marine-terminating ice stream system in NW Europe that operated during the Late Weichselian Glaciation. A suite of 51 cosmogenic-nuclide exposure ages from ice sheet moraines and glacially transported boulders constrain the maximum extent of the ice sheet on the continental shelf (~28 ka BP) and its subsequent retreat, between ~27 and 16 ka BP, into a large marine embayment (ca. 7000 km2; the Minch, NW Scotland). Recently acquired swath bathymetry and acoustic sub-bottom profiler data reveal several large transverse grounding-zone wedges up to 40 m thick and 5 km wide with diagnostic acoustic-facies architecture. These seabed sediment wedges mark former quasi-stable positions of grounded marine-terminating ice-stream fronts; their size and thickness suggest long-lived stillstands of the order of centuries. Statistically significant clusters of exposure ages from glacial deposits on islands and intervening headlands shed important new light on the age of these marine grounding-zone wedges and, by inference, the rate and timing of Minch palaeo-ice stream retreat. We find strong evidence for episodic ice stream retreat on the continental shelf between ~28-24 ka BP, in the outer Minch between ~24-22 ka BP, and in the central Minch between 22-18.5 ka BP. In contrast, final ice stream deglaciation (<18 ka) across the deepest parts of the inner Minch embayment, was probably rapid and uninterrupted - with the ice sheet margin at or close to the present-day coastline in NW Scotland by 16.1 ka BP. It is hoped that these results will form the empirical basis for future ice-sheet modelling of this dynamically sensitive sector of the British-Irish Ice Sheet.

Ocean Tide Influences on the Antarctic and Greenland Ice Sheets

NASA Astrophysics Data System (ADS)

Padman, Laurie; Siegfried, Matthew R.; Fricker, Helen A.

2018-03-01

Ocean tides are the main source of high-frequency variability in the vertical and horizontal motion of ice sheets near their marine margins. Floating ice shelves, which occupy about three quarters of the perimeter of Antarctica and the termini of four outlet glaciers in northern Greenland, rise and fall in synchrony with the ocean tide. Lateral motion of floating and grounded portions of ice sheets near their marine margins can also include a tidal component. These tide-induced signals provide insight into the processes by which the oceans can affect ice sheet mass balance and dynamics. In this review, we summarize in situ and satellite-based measurements of the tidal response of ice shelves and grounded ice, and spatial variability of ocean tide heights and currents around the ice sheets. We review sensitivity of tide heights and currents as ocean geometry responds to variations in sea level, ice shelf thickness, and ice sheet mass and extent. We then describe coupled ice-ocean models and analytical glacier models that quantify the effect of ocean tides on lower-frequency ice sheet mass loss and motion. We suggest new observations and model developments to improve the representation of tides in coupled models that are used to predict future ice sheet mass loss and the associated contribution to sea level change. The most critical need is for new data to improve maps of bathymetry, ice shelf draft, spatial variability of the drag coefficient at the ice-ocean interface, and higher-resolution models with improved representation of tidal energy sinks.

Tissue-engineered thyroid cell sheet rescued hypothyroidism in rat models after receiving total thyroidectomy comparing with nontransplantation models.

PubMed

Arauchi, Ayumi; Shimizu, Tatsuya; Yamato, Masayuki; Obara, Takao; Okano, Teruo

2009-12-01

For hormonal deficiency caused by endocrine organ diseases, continuous oral hormone administration is indispensable to supplement the shortage of hormones. In this study, as a more effective therapy, we have tried to reconstruct the three-dimensional thyroid tissue by the cell sheet technology, a novel tissue engineering approach. The cell suspension obtained from rat thyroid gland was cultured on temperature-responsive culture dishes, from which confluent cells detach as a cell sheet simply by reducing temperature without any enzymatic treatment. The 8-week-old Lewis rats were exposed to total thyroidectomy as hypothyroidism models and received thyroid cell sheet transplantation 1 week after total thyroidectomy. Serum levels of free triiodothyronine (fT(3)) and free thyroxine (fT(4)) significantly decreased 1 week after total thyroidectomy. On the other hand, transplantation of the thyroid cell sheets was able to restore the thyroid function 1 week after the cell sheet transplantation, and improvement was maintained for 4 weeks. Moreover, morphological analyses showed typical thyroid follicle organization, and anti-thyroid-transcription-factor-1 antibody staining demonstrated the presence of follicle epithelial cells. The presence of functional microvessels was also detected within the engineered thyroid tissues. In conclusion, our results indicate that thyroid cell sheets transplanted in a model of total thyroidectomy can reorganize histologically to resemble a typical thyroid gland and restore thyroid function in vivo. In this study, we are the first to confirm that engineered thyroid tissue can repair hypothyroidism models in rats and, therefore, cell sheet transplantation of endocrine organs may be suitable for the therapy of hormonal deficiency.

Physical basis for a thick ice shelf in the Arctic Basin during the penultimate glacial maximum

NASA Astrophysics Data System (ADS)

Gasson, E.; DeConto, R.; Pollard, D.; Clark, C.

2017-12-01

A thick ice shelf covering the Arctic Ocean during glacial stages was discussed in a number of publications in the 1970s. Although this hypothesis has received intermittent attention, the emergence of new geophysical evidence for ice grounding in water depths of up to 1 km in the central Arctic Basin has renewed interest into the physical plausibility and significance of an Arctic ice shelf. Various ice shelf configurations have been proposed, from an ice shelf restricted to the Amerasian Basin (the `minimum model') to a complete ice shelf cover in the Arctic. Attempts to simulate an Arctic ice shelf have been limited. Here we use a hybrid ice sheet / shelf model that has been widely applied to the Antarctic ice sheet to explore the potential for thick ice shelves forming in the Arctic Basin. We use a climate forcing appropriate for MIS6, the penultimate glacial maximum. We perform a number of experiments testing different ice sheet / shelf configurations and compare the model results with ice grounding locations and inferred flow directions. Finally, we comment on the potential significance of an Arctic ice shelf to the global glacial climate system.

An Imminent Revolution in Modeling Interactions of Ice Sheets With Climate

NASA Astrophysics Data System (ADS)

Hughes, T.

2008-12-01

Modeling continental ice sheets was inaugurated by meteorologists William Budd and Uwe Radok, with mathematician Richard Jenssen, in 1971. Their model calculated the thermal and mechanical regime using measured surface accumulation rates, temperatures, and elevations, and bed topography. This top-down approach delivered a basal thermal regime of temperatures or melting rates for an assumed basal geothermal heat flux. When Philippe Huybrechts and others incorporated time, largely unknownpast surface conditions had a major effect on present basal thermal conditions. This approach produced ice-sheet models with only a slow response to external forcing, whereas the glacial geological record and climate records from ice and ocean cores show that ice sheets can have rapid changes in size and shape independent of external forcing. These top-down models were wholly inadequate for reconstructing former ice sheets at the LGM for CLIMAP in 1981. Ice-sheet areas,elevations, and volumes provided the albedo, surface topography, and sea-surface area as input to climate models. A bottom-up model based on dated glacial geology was developed to provide the areal extent and basal thermal regime of ice sheets at the LGM. Basal thermal conditions determined ice-bed coupling and therefore the elevation of ice sheets. High convex ice surfaces for slow sheet flow lower about 20 percent when a frozen bed becomes thawed. As further basal melting drowns bedrock bumps that "pin" basal ice, the ice surface becomes concave in fast stream flow that ends as low floating ice shelves at marine ice margins. A revolution in modeling interactions between glaciation, climate, and sea level is driven by new Greenland and Antarctic data from Earth-orbiting satellites, airborne and surface traverses, and deep drilling. We anticipate continuous data acquisition of surface albedo, accumulation/ablation rates, elevations, velocities, and temperatures over a whole ice sheet, mapping basal thermal conditions by radar, seismic, and magnetic profiling, and direct measurement of basal conditions by deep drilling and coring into the ice and the bed. These data allow calculating the geothermal heat flux and mapping flow of basal meltwater from geothermal sources to sinks at the termini of ice streams, which discharge up to 90 percent of the ice. James Fastook has a preliminary solution of the full momentum equation needed to model ice streams. Douglas MacAyeal has pioneered modeling catastrophic ice-shelf disintegration that releases "armadas" of icebergs into the world ocean, to extract heat from ocean surface water and thereby reduce the critical ocean-to-atmosphere heat exchange that drives global climate. Ice sheets are the only component of Earth's climate machine that can destroy itself-- swiftly--and thereby radically and rapidly alter global climate and sea level.

A JavaScript API for the Ice Sheet System Model (ISSM) 4.11: towards an online interactive model for the cryosphere community

NASA Astrophysics Data System (ADS)

Larour, Eric; Cheng, Daniel; Perez, Gilberto; Quinn, Justin; Morlighem, Mathieu; Duong, Bao; Nguyen, Lan; Petrie, Kit; Harounian, Silva; Halkides, Daria; Hayes, Wayne

2017-12-01

Earth system models (ESMs) are becoming increasingly complex, requiring extensive knowledge and experience to deploy and use in an efficient manner. They run on high-performance architectures that are significantly different from the everyday environments that scientists use to pre- and post-process results (i.e., MATLAB, Python). This results in models that are hard to use for non-specialists and are increasingly specific in their application. It also makes them relatively inaccessible to the wider science community, not to mention to the general public. Here, we present a new software/model paradigm that attempts to bridge the gap between the science community and the complexity of ESMs by developing a new JavaScript application program interface (API) for the Ice Sheet System Model (ISSM). The aforementioned API allows cryosphere scientists to run ISSM on the client side of a web page within the JavaScript environment. When combined with a web server running ISSM (using a Python API), it enables the serving of ISSM computations in an easy and straightforward way. The deep integration and similarities between all the APIs in ISSM (MATLAB, Python, and now JavaScript) significantly shortens and simplifies the turnaround of state-of-the-art science runs and their use by the larger community. We demonstrate our approach via a new Virtual Earth System Laboratory (VESL) website (http://vesl.jpl.nasa.gov, VESL(2017)).

Predicting pulsar scintillation from refractive plasma sheets

NASA Astrophysics Data System (ADS)

Simard, Dana; Pen, Ue-Li

2018-07-01

The dynamic and secondary spectra of many pulsars show evidence for long-lived, aligned images of the pulsar that are stationary on a thin scattering sheet. One explanation for this phenomenon considers the effects of wave crests along sheets in the ionized interstellar medium, such as those due to Alfvén waves propagating along current sheets. If these sheets are closely aligned to our line of sight to the pulsar, high bending angles arise at the wave crests and a selection effect causes alignment of images produced at different crests, similar to grazing reflection off of a lake. Using geometric optics, we develop a simple parametrized model of these corrugated sheets that can be constrained with a single observation and that makes observable predictions for variations in the scintillation of the pulsar over time and frequency. This model reveals qualitative differences between lensing from overdense and underdense corrugated sheets: only if the sheet is overdense compared to the surrounding interstellar medium can the lensed images be brighter than the line-of-sight image to the pulsar, and the faint lensed images are closer to the pulsar at higher frequencies if the sheet is underdense, but at lower frequencies if the sheet is overdense.

Predicting Pulsar Scintillation from Refractive Plasma Sheets

NASA Astrophysics Data System (ADS)

Simard, Dana; Pen, Ue-Li

2018-05-01

The dynamic and secondary spectra of many pulsars show evidence for long-lived, aligned images of the pulsar that are stationary on a thin scattering sheet. One explanation for this phenomenon considers the effects of wave crests along sheets in the ionized interstellar medium, such as those due to Alfvén waves propagating along current sheets. If these sheets are closely aligned to our line-of-sight to the pulsar, high bending angles arise at the wave crests and a selection effect causes alignment of images produced at different crests, similar to grazing reflection off of a lake. Using geometric optics, we develop a simple parameterized model of these corrugated sheets that can be constrained with a single observation and that makes observable predictions for variations in the scintillation of the pulsar over time and frequency. This model reveals qualitative differences between lensing from overdense and underdense corrugated sheets: Only if the sheet is overdense compared to the surrounding interstellar medium can the lensed images be brighter than the line-of-sight image to the pulsar, and the faint lensed images are closer to the pulsar at higher frequencies if the sheet is underdense, but at lower frequencies if the sheet is overdense.

Atmospherically-driven collapse of a marine-based ice stream

NASA Astrophysics Data System (ADS)

Greenwood, S. L.; Clason, C. C.

2016-12-01

Marine-terminating glaciers and the sectors of ice sheets that are grounded below sea level are widely considered to be vulnerable to unstable retreat. The southern sector of the retreating Fennoscandian Ice Sheet comprised a large, aqueous-terminating ice sheet catchment grounded well below sea level throughout its deglaciation. However, the behaviour, timing of and controls upon ice sheet retreat through the Baltic and Bothnian basins have thus far been inferred only indirectly from peripheral, terrestrial-based geological archives. Recent acquisition of high-resolution multibeam bathymetry opens these basins up, for the first time, to direct investigation of their glacial footprint and palaeo-ice sheet behaviour. Multibeam data reveal a rich glacial landform legacy of the Bothnian Sea deglaciation. A late-stage palaeo-ice stream formed a narrow corridor of fast flow. Its pathway is overprinted by a vast field of basal crevasse squeeze ridges, while abundant traces of high subglacial meltwater volumes call for considerable input of surface meltwater to the subglacial system. We interpret a short-lived ice stream event under high extension, precipitating large-scale hydrofracture-driven collapse of the ice sheet sector under conditions of high surface melting. Experiments with a physically-based numerical flowline model indicate that the rate and pattern of Bothnian Sea ice stream retreat are most sensitive to surface mass balance change and crevasse propagation, while remarkably insensitive to submarine melting and sea level change. We interpret strongly atmospherically-driven retreat of this marine-based ice sheet sector.

Subglacial hydrology and the formation of ice streams

PubMed Central

Kyrke-Smith, T. M; Katz, R. F; Fowler, A. C

2014-01-01

Antarctic ice streams are associated with pressurized subglacial meltwater but the role this water plays in the dynamics of the streams is not known. To address this, we present a model of subglacial water flow below ice sheets, and particularly below ice streams. The base-level flow is fed by subglacial melting and is presumed to take the form of a rough-bedded film, in which the ice is supported by larger clasts, but there is a millimetric water film which submerges the smaller particles. A model for the film is given by two coupled partial differential equations, representing mass conservation of water and ice closure. We assume that there is no sediment transport and solve for water film depth and effective pressure. This is coupled to a vertically integrated, higher order model for ice-sheet dynamics. If there is a sufficiently small amount of meltwater produced (e.g. if ice flux is low), the distributed film and ice sheet are stable, whereas for larger amounts of melt the ice–water system can become unstable, and ice streams form spontaneously as a consequence. We show that this can be explained in terms of a multi-valued sliding law, which arises from a simplified, one-dimensional analysis of the coupled model. PMID:24399921

Exploring the free energy landscape of a model β-hairpin peptide and its isoform.

PubMed

Narayanan, Chitra; Dias, Cristiano L

2014-10-01

Secondary structural transitions from α-helix to β-sheet conformations are observed in several misfolding diseases including Alzheimer's and Parkinson's. Determining factors contributing favorably to the formation of each of these secondary structures is therefore essential to better understand these disease states. β-hairpin peptides form basic components of anti-parallel β-sheets and are suitable model systems for characterizing the fundamental forces stabilizing β-sheets in fibrillar structures. In this study, we explore the free energy landscape of the model β-hairpin peptide GB1 and its E2 isoform that preferentially adopts α-helical conformations at ambient conditions. Umbrella sampling simulations using all-atom models and explicit solvent are performed over a large range of end-to-end distances. Our results show the strong preference of GB1 and the E2 isoform for β-hairpin and α-helical conformations, respectively, consistent with previous studies. We show that the unfolded states of GB1 are largely populated by misfolded β-hairpin structures which differ from each other in the position of the β-turn. We discuss the energetic factors contributing favorably to the formation of α-helix and β-hairpin conformations in these peptides and highlight the energetic role of hydrogen bonds and non-bonded interactions. © 2014 Wiley Periodicals, Inc.

The use of platelet-rich fibrin combined with periodontal ligament and jaw bone mesenchymal stem cell sheets for periodontal tissue engineering.

PubMed

Wang, Zhong-Shan; Feng, Zhi-Hong; Wu, Guo-Feng; Bai, Shi-Zhu; Dong, Yan; Chen, Fa-Ming; Zhao, Yi-Min

2016-06-21

Periodontal regeneration involves the restoration of at least three unique tissues: cementum, periodontal ligament tissue (PDL) and alveolar bone tissue. Here, we first isolated human PDL stem cells (PDLSCs) and jaw bone mesenchymal stem cells (JBMSCs). These cells were then induced to form cell sheets using an ascorbic acid-rich approach, and the cell sheet properties, including morphology, thickness and gene expression profile, were compared. Platelet-rich fibrin (PRF) derived from human venous blood was then fabricated into bioabsorbable fibrin scaffolds containing various growth factors. Finally, the in vivo potential of a cell-material construct based on PDLSC sheets, PRF scaffolds and JBMSC sheets to form periodontal tissue was assessed in a nude mouse model. In this model, PDLSC sheet/PRF/JBMSC sheet composites were placed in a simulated periodontal space comprising human treated dentin matrix (TDM) and hydroxyapatite (HA)/tricalcium phosphate (TCP) frameworks. Eight weeks after implantation, the PDLSC sheets tended to develop into PDL-like tissues, while the JBMSC sheets tended to produce predominantly bone-like tissues. In addition, the PDLSC sheet/PRF/JBMSC sheet composites generated periodontal tissue-like structures containing PDL- and bone-like tissues. Further improvements in this cell transplantation design may have the potential to provide an effective approach for future periodontal tissue regeneration.

14 CFR Sec. 1-4 - System of accounts coding.

Code of Federal Regulations, 2010 CFR

2010-01-01

... General Accounting Provisions Sec. 1-4 System of accounts coding. (a) A four digit control number is assigned for each balance sheet and profit and loss account. Each balance sheet account is numbered sequentially, within blocks, designating basic balance sheet classifications. The first two digits of the four...

Can Steady Magnetospheric Convection Events Inject Plasma into the Ring Current?

NASA Astrophysics Data System (ADS)

Lemon, C.; Chen, M. W.; Guild, T. B.

2009-12-01

Steady Magnetospheric Convection (SMC) events are characterized by several-hour periods of enhanced convection that are devoid of substorm signatures. There has long been a debate about whether substorms are necessary to inject plasma into the ring current, or whether enhanced convection is sufficient. If ring current injections occur during SMC intervals, this would suggest that substorms are unnecessary. We use a combination of simulations and data observations to examine this topic. Our simulation model computes the energy-dependent plasma drift in a self-consistent electric and magnetic field, which allows us to accurately model the transport of plasma from the plasma sheet (where the plasma pressure is much larger than the magnetic pressure) into the inner magnetosphere (where plasma pressure is much less than the magnetic pressure). In regions where the two pressures are comparable (i.e. the inner plasma sheet), feedback between the plasma and magnetic field is critical for accurately modeling the physical evolution of the system. Our previous work has suggested that entropy losses in the plasma sheet (such as caused by substorms) may be necessary to inject a ring current. However, it is not yet clear whether other small-scale processes (e.g. bursty bulk flows) can provide sufficient entropy loss in the plasma sheet to allow for the penetration of plasma into the ring current. We combine our simulation results with data observations in order to better understand the physical processes required to inject a ring current.

Marine ice sheet model performance depends on basal sliding physics and sub-shelf melting

NASA Astrophysics Data System (ADS)

Gladstone, Rupert Michael; Warner, Roland Charles; Galton-Fenzi, Benjamin Keith; Gagliardini, Olivier; Zwinger, Thomas; Greve, Ralf

2017-01-01

Computer models are necessary for understanding and predicting marine ice sheet behaviour. However, there is uncertainty over implementation of physical processes at the ice base, both for grounded and floating glacial ice. Here we implement several sliding relations in a marine ice sheet flow-line model accounting for all stress components and demonstrate that model resolution requirements are strongly dependent on both the choice of basal sliding relation and the spatial distribution of ice shelf basal melting.Sliding relations that reduce the magnitude of the step change in basal drag from grounded ice to floating ice (where basal drag is set to zero) show reduced dependence on resolution compared to a commonly used relation, in which basal drag is purely a power law function of basal ice velocity. Sliding relations in which basal drag goes smoothly to zero as the grounding line is approached from inland (due to a physically motivated incorporation of effective pressure at the bed) provide further reduction in resolution dependence.A similar issue is found with the imposition of basal melt under the floating part of the ice shelf: melt parameterisations that reduce the abruptness of change in basal melting from grounded ice (where basal melt is set to zero) to floating ice provide improved convergence with resolution compared to parameterisations in which high melt occurs adjacent to the grounding line.Thus physical processes, such as sub-glacial outflow (which could cause high melt near the grounding line), impact on capability to simulate marine ice sheets. If there exists an abrupt change across the grounding line in either basal drag or basal melting, then high resolution will be required to solve the problem. However, the plausible combination of a physical dependency of basal drag on effective pressure, and the possibility of low ice shelf basal melt rates next to the grounding line, may mean that some marine ice sheet systems can be reliably simulated at a coarser resolution than currently thought necessary.

A Historical Forcing Ice Sheet Model Validation Framework for Greenland

NASA Astrophysics Data System (ADS)

Price, S. F.; Hoffman, M. J.; Howat, I. M.; Bonin, J. A.; Chambers, D. P.; Kalashnikova, I.; Neumann, T.; Nowicki, S.; Perego, M.; Salinger, A.

2014-12-01

We propose an ice sheet model testing and validation framework for Greenland for the years 2000 to the present. Following Perego et al. (2014), we start with a realistic ice sheet initial condition that is in quasi-equilibrium with climate forcing from the late 1990's. This initial condition is integrated forward in time while simultaneously applying (1) surface mass balance forcing (van Angelen et al., 2013) and (2) outlet glacier flux anomalies, defined using a new dataset of Greenland outlet glacier flux for the past decade (Enderlin et al., 2014). Modeled rates of mass and elevation change are compared directly to remote sensing observations obtained from GRACE and ICESat. Here, we present a detailed description of the proposed validation framework including the ice sheet model and model forcing approach, the model-to-observation comparison process, and initial results comparing model output and observations for the time period 2000-2013.

Representing grounding line migration in synchronous coupling between a marine ice sheet model and a z-coordinate ocean model

NASA Astrophysics Data System (ADS)

Goldberg, D. N.; Snow, K.; Holland, P.; Jordan, J. R.; Campin, J.-M.; Heimbach, P.; Arthern, R.; Jenkins, A.

2018-05-01

Synchronous coupling is developed between an ice sheet model and a z-coordinate ocean model (the MITgcm). A previously-developed scheme to allow continuous vertical movement of the ice-ocean interface of a floating ice shelf ("vertical coupling") is built upon to allow continuous movement of the grounding line, or point of floatation of the ice sheet ("horizontal coupling"). Horizontal coupling is implemented through the maintenance of a thin layer of ocean ( ∼ 1 m) under grounded ice, which is inflated into the real ocean as the ice ungrounds. This is accomplished through a modification of the ocean model's nonlinear free surface evolution in a manner akin to a hydrological model in the presence of steep bathymetry. The coupled model is applied to a number of idealized geometries and shown to successfully represent ocean-forced marine ice sheet retreat while maintaining a continuous ocean circulation.

Challenges faced by ice sheet projections: lessons from the SeaRISE effort

NASA Astrophysics Data System (ADS)

Nowicki, S.

2013-12-01

Projecting the future evolution of the Greenland and Antarctic ice sheets is a problem of enormous societal importance, as ice sheet influence our future sea levels. This crucial issue is however a non trivial task, as demonstrated by the Sea level Response to Ice Sheet Evolution (SeaRISE) effort: prescribing simple external forcings to a group of ice sheet models results in a spread in responses. Understanding the source of the diversity in the model results is therefore crucial in order to reduce the uncertainty in the projection. Just as in any future climate simulation, the analysis presented here demonstrates that the model spread in the SeaRISE effort is due to a number of factors. First is the problem of obtaining an initial configuration for the projection. The two commonly used methods, interglacial spin-up or data assimilation, have both advantages and drawbacks, and will affect the determination of fields that cannot be measured (such as basal slipperiness). Second is the uncertainty in actual observations, which includes but is not limited to surface mass balance, basal topography, ice thickness, and surface velocities. An additional issue with these observations is that they can be transient quantities which are not measured at the same time, but ice sheet models require them to be simultaneous. Third is the uncertainty in the models' physics and discretization, which is limited by our understanding (or lack of understanding) of crucial processes that often occur at subgrid scale relative to the resolution used by continental ice sheet models, and thus require parameterization. Grounding line migration and sliding laws are such an example. Fourth is the determination of the future forcing scenarios and their implementation as the external forcing. Unfortunately, as demonstrated in this analysis, all ice sheet models face these limitations to some degree, so that it is extremely difficult to identify a set of models and projections that should be trusted in preference to others. One model might be more suitable for assessing the impact of a warmer atmosphere because of its initialization procedure, but its deficiencies in capturing grounding line migration, for example, might make its projections for oceanic forcing unreliable. More work is thus required to evaluate individual ice sheet models' skills in projection, but this crucial and challenging task is left for future studies.

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

PubMed

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

2015-04-24

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

Clouds enhance Greenland ice sheet meltwater runoff.

PubMed

Van Tricht, K; Lhermitte, S; Lenaerts, J T M; Gorodetskaya, I V; L'Ecuyer, T S; Noël, B; van den Broeke, M R; Turner, D D; van Lipzig, N P M

2016-01-12

The Greenland ice sheet has become one of the main contributors to global sea level rise, predominantly through increased meltwater runoff. The main drivers of Greenland ice sheet runoff, however, remain poorly understood. Here we show that clouds enhance meltwater runoff by about one-third relative to clear skies, using a unique combination of active satellite observations, climate model data and snow model simulations. This impact results from a cloud radiative effect of 29.5 (±5.2) W m(-2). Contrary to conventional wisdom, however, the Greenland ice sheet responds to this energy through a new pathway by which clouds reduce meltwater refreezing as opposed to increasing surface melt directly, thereby accelerating bare-ice exposure and enhancing meltwater runoff. The high sensitivity of the Greenland ice sheet to both ice-only and liquid-bearing clouds highlights the need for accurate cloud representations in climate models, to better predict future contributions of the Greenland ice sheet to global sea level rise.

Clouds enhance Greenland ice sheet meltwater runoff

PubMed Central

Van Tricht, K.; Lhermitte, S.; Lenaerts, J. T. M.; Gorodetskaya, I. V.; L'Ecuyer, T. S.; Noël, B.; van den Broeke, M. R.; Turner, D. D.; van Lipzig, N. P. M.

2016-01-01

The Greenland ice sheet has become one of the main contributors to global sea level rise, predominantly through increased meltwater runoff. The main drivers of Greenland ice sheet runoff, however, remain poorly understood. Here we show that clouds enhance meltwater runoff by about one-third relative to clear skies, using a unique combination of active satellite observations, climate model data and snow model simulations. This impact results from a cloud radiative effect of 29.5 (±5.2) W m−2. Contrary to conventional wisdom, however, the Greenland ice sheet responds to this energy through a new pathway by which clouds reduce meltwater refreezing as opposed to increasing surface melt directly, thereby accelerating bare-ice exposure and enhancing meltwater runoff. The high sensitivity of the Greenland ice sheet to both ice-only and liquid-bearing clouds highlights the need for accurate cloud representations in climate models, to better predict future contributions of the Greenland ice sheet to global sea level rise. PMID:26756470

Friction and lubrication modelling in sheet metal forming: Influence of lubrication amount, tool roughness and sheet coating on product quality

NASA Astrophysics Data System (ADS)

Hol, J.; Wiebenga, J. H.; Carleer, B.

2017-09-01

In the stamping of automotive parts, friction and lubrication play a key role in achieving high quality products. In the development process of new automotive parts, it is therefore crucial to accurately account for these effects in sheet metal forming simulations. This paper presents a selection of results considering friction and lubrication modelling in sheet metal forming simulations of a front fender product. For varying lubrication conditions, the front fender can either show wrinkling or fractures. The front fender is modelled using different lubrication amounts, tool roughness’s and sheet coatings to show the strong influence of friction on both part quality and the overall production stability. For this purpose, the TriboForm software is used in combination with the AutoForm software. The results demonstrate that the TriboForm software enables the simulation of friction behaviour for varying lubrication conditions, i.e. resulting in a generally applicable approach for friction characterization under industrial sheet metal forming process conditions.

Myosin II activity is required for functional leading-edge cells and closure of epidermal sheets in fish skin ex vivo.

PubMed

Morita, Toshiyuki; Tsuchiya, Akiko; Sugimoto, Masazumi

2011-09-01

Re-epithelialization in skin wound healing is a process in which epidermal sheets grow and close the wound. Although the actin-myosin system is thought to have a pivotal role in re-epithelialization, its role is not clear. In fish skin, re-epithelialization occurs around 500 μm/h and is 50 times faster than in mammalian skin. We had previously reported that leading-edge cells of the epidermal outgrowth have both polarized large lamellipodia and "purse string"-like actin filament cables in the scale-skin culture system of medaka fish, Oryzias latipes (Cell Tissue Res, 2007). The actin purse-string (APS) is a supracellular contractile machinery in which adherens junctions (AJs) link intracellular myosin II-including actin cables between neighboring cells. In this study, we developed a modified "face-to-face" scale-skin culture system as an ex vivo model to study epidermal wound healing, and examined the role of the actin-myosin system in the rapid re-epithelialization using a myosin II ATPase inhibitor, blebbistatin. A low level of blebbistatin suppressed the formation of APS and induced the dissociation of keratocytes from the leading edge without attenuating the growth of the epidermal sheet or the migration rate of solitary keratocytes. AJs in the superficial layer showed no obvious changes elicited by blebbistatin. However, two epidermal sheets without APSs did not make a closure with each other, which was confirmed by inhibiting the connecting AJs between the superficial layers. These results suggest that myosin II activity is required for functional leading-edge cells and for epidermal closure.

Translation by anisotropic peeling or fracturing in elastic media

NASA Astrophysics Data System (ADS)

Zheng, Zhong; Lister, John; Neufeld, Jerome

2017-11-01

The influence of rock anisotropy on the direction of hydraulic fracturing is an important open question. Two canonical systems have been proposed to investigate the fundamental aspects of such fluid-structure interaction problems: (i) Fluid injection and fracturing into an infinite elastic matrix (e.g., solid gelatin) and (ii) Fluid invasion and peeling beneath a deforming elastic sheet (e.g., bending plate). We investigate the second system and impose a non-uniform prewetting film thickness beneath the elastic sheet. We notice that while the bulk of the elastic sheet retains the static blister shape, a non-uniform prewetting film thickness can cause a horizontal translation of the blister. In particular, for a step jump in prewetting film thickness, asymptotic analysis indicates that, under constant fluid injection, the horizontal translation follows a t 7 / 17 time dependence in cartesian coordinates, and the prefactor of power-law translation depends on the ratio of the distinct prewetting film thicknesses on either side. We also provide numerical and experimental evidence demonstrating anisotropic blister evolution. This can be thought of as a model system for fluid-driven fracturing where the non-uniform prewetting film thickness mimics heterogeneity in material toughness.

Two-dimensional potential double layers and discrete auroras

NASA Technical Reports Server (NTRS)

Kan, J. R.; Lee, L. C.; Akasofu, S.-I.

1979-01-01

This paper is concerned with the formation of the acceleration region for electrons which produce the visible auroral arc and with the formation of the inverted V precipitation region. The former is embedded in the latter, and both are associated with field-aligned current sheets carried by plasma sheet electrons. It is shown that an electron current sheet driven from the plasma sheet into the ionosphere leads to the formation of a two-dimensional potential double layer. For a current sheet of a thickness less than the proton gyrodiameter solutions are obtained in which the field-aligned potential drop is distributed over a length much greater than the Debye length. For a current sheet of a thickness much greater than the proton gyrodiameter solutions are obtained in which the potential drop is confined to a distance on the order of the Debye length. The electric field in the two-dimensional double-layer model is the zeroth-order field inherent to the current sheet configuration, in contrast to those models in which the electric field is attributed to the first-order field due to current instabilities or turbulences. The maximum potential in the two-dimensional double-layer models is on the order of the thermal energy of plasma sheet protons, which ranges from 1 to 10 keV.

Uranium nitride: a cubic antiferromagnet with anisotropic critical behavior

DOE Office of Scientific and Technical Information (OSTI.GOV)

Buyers, W J.L.; Holden, T M; Svensson, E C

1977-11-01

Highly anisotropic critical scattering associated with the transition at T/sub N/ = 49.5 K to the type-I antiferromagnetic structure has been observed in uranium nitride. The transverse susceptibility is found to be unobservably small. The longitudinal susceptibility diverges at T/sub N/ and its anisotropy shows that the spins within the (001) ferromagnetic sheets of the (001) domain are much more highly correlated than they are with the spins lying in adjacent (001) sheets. The correlation range within the sheets is much greater than that expected for a Heisenberg system with the same T/sub N/. The rod-like scattering extended along themore » spin and domain direction is reminiscent of two-dimensional behavior. The results are inconsistent with a simple localized model and may reflect the itinerant nature of the 5f electrons.« less

A System Scale Theory for Fast Magnetic Reconnection

NASA Astrophysics Data System (ADS)

Knoll, D.; Chacon, L.; Lapenta, G.

2005-12-01

Magnetic reconnection is at the root of explosive phenomena such as solar flares, coronal mass ejections, plasmoid ejection from earth's magnetotail and major disruptions in magnetic fusion energy experiments. Plasmas in all the above mentioned cases are known to have negligible electric resistivity. This small resistivity can not explain the reconnection time scales observed in nature, when using the resistive MHD model. Recently much progress has been made considering the Hall MHD model. Hall physics has been shown to facility fast reconnection when the magnetic field shear scale length is in the order of the ion inertial length. However, in many systems of interest the initial scale lengths of the problem can not justify the use of Hall MHD. Thus a successful system scale theory must involve a current sheet thinning mechanism which brings the relevant scales down to the Hall scales. In this presentation we give examples of how naturally occurring hydrodynamic flows can provide such current sheet thinning [1,2,3] and where these occur in solar [4] and magnetosphere application [5]. We also discuss the primary obstacle for such flow to drive current sheet thinning, the build up of magnetic pressure, and how Hall MHD may overcome this obstacle. [1] Knoll and Brackbill, Phys. Plasmas, vol. 9, 2002 [2] Knoll and Chacon, PRL, vol. 88, 2002 [3] Knoll and Chacon, Phys. Plasmas, 2005 (submitted) [4] Lapenta and Knoll, ApJ, vol. 624, 2005 [5] Brackbill and Knoll, PRL, vol. 86, 2001

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 may change the predicted uplift velocities by more than 0.1 mm/yr, while changes more recent than 55 kyr BP may change the predicted uplift 10 kyr ago by more than 5 m. Despite their differences we find that all three reconstructions can equally well fit observations of the present day uplift in Fennoscandia, as well as the observed sea-level curve along the Ångerman river, Sweden, albeit with different optimal earth models. However, only for ANU can a single optimal earth model be determined as a bifurcation in the optimal viscosity arises from the generally faster present day rebound rates in ICE-5G and UMISM, resulting in a range of well-fitting earth models for the latter reconstructions. Studying models with a reasonable fit to observed present day uplift velocities we find general trends of over- and under-prediction, indicating that all three ice-sheet reconstructions need improvement. In general, all three reconstructions tend to over-predict the uplift rates in southwestern Fennoscandia, whereas over Finland ICE-5G generally over-predicts and ANU generally under-predicts the uplift rates. UMISM tend to under-predict the velocities over central to northern Sweden and similar trends can also be seen in ANU and ICE-5G.

Micro-fluidic partitioning between polymeric sheets for chemical amplification and processing

DOEpatents

Anderson, Brian L.

2017-01-24

A system for fluid partitioning for chemical amplification or other chemical processing or separations of a sample, comprising a first dispenser of a first polymeric sheet, wherein the first polymeric sheet contains chambers; a second dispenser of a second polymeric sheet wherein the first dispenser and the second dispenser are positioned so that the first polymeric sheet and the second polymeric sheet become parallel; a dispenser of the fluid positioned to dispense the fluid between the first polymeric sheet and the second polymeric sheet; and a seal unit that seals the first polymeric sheet and the second polymeric sheet together thereby sealing the sample between the first polymeric sheet and the second polymeric sheet and partitioning the fluid for chemical amplification or other chemical processing or separations.

Micro-fluidic partitioning between polymeric sheets for chemical amplification and processing

DOEpatents

Anderson, Brian L.

2015-05-26

A system for fluid partitioning for chemical amplification or other chemical processing or separations of a sample, comprising a first dispenser of a first polymeric sheet, wherein the first polymeric sheet contains chambers; a second dispenser of a second polymeric sheet wherein the first dispenser and the second dispenser are positioned so that the first polymeric sheet and the second polymeric sheet become parallel; a dispenser of the fluid positioned to dispense the fluid between the first polymeric sheet and the second polymeric sheet; and a seal unit that seals the first polymeric sheet and the second polymeric sheet together thereby sealing the sample between the first polymeric sheet and the second polymeric sheet and partitioning the fluid for chemical amplification or other chemical processing or separations.

Synergistic effect of temperature and point defect on the mechanical properties of single layer and bi-layer graphene

NASA Astrophysics Data System (ADS)

Debroy, Sanghamitra; Pavan Kumar, V.; Vijaya Sekhar, K.; Acharyya, Swati Ghosh; Acharyya, Amit

2017-10-01

The present study reports a comprehensive molecular dynamics simulation of the effect of a) temperature (300-1073 K at intervals of every 100 K) and b) point defect on the mechanical behaviour of single (armchair and zigzag direction) and bilayer layer graphene (AA and AB stacking). Adaptive intermolecular reactive bond order (AIREBO) potential function was used to describe the many-body short-range interatomic interactions for the single layer graphene sheet. Moreover, Lennard Jones model was considered for bilayer graphene to incorporate the van der Waals interactions among the interlayers of graphene. The effect of temperature on the strain energy of single layer and bilayer graphene was studied in order to understand the difference in mechanical behaviour of the two systems. The strength of the pristine single layer graphene was found to be higher as compared to bilayer AA stacked graphene at all temperatures. It was observed at 1073 K and in the presence of vacancy defect the strength for single layer armchair sheet falls by 30% and for bilayer armchair sheet by 33% as compared to the pristine sheets at 300 K. The AB stacked graphene sheet was found to have a two-step rupture process. The strength of pristine AB sheet was found to decrease by 22% on increase of temperature from 300 K to 1073 K.

Cyber Security for Lighting Systems

DOE Office of Scientific and Technical Information (OSTI.GOV)

None

Fact sheet discusses cyber threats unique to lighting control systems in buildings and helps facility managers identify the types of lighting control systems that could introduce cybersecurity risks. Download the fact sheet.

Decadal-scale sensitivity of Northeast Greenland ice flow to errors in surface mass balance using ISSM

NASA Astrophysics Data System (ADS)

Schlegel, N.-J.; Larour, E.; Seroussi, H.; Morlighem, M.; Box, J. E.

2013-06-01

The behavior of the Greenland Ice Sheet, which is considered a major contributor to sea level changes, is best understood on century and longer time scales. However, on decadal time scales, its response is less predictable due to the difficulty of modeling surface climate, as well as incomplete understanding of the dynamic processes responsible for ice flow. Therefore, it is imperative to understand how modeling advancements, such as increased spatial resolution or more comprehensive ice flow equations, might improve projections of ice sheet response to climatic trends. Here we examine how a finely resolved climate forcing influences a high-resolution ice stream model that considers longitudinal stresses. We simulate ice flow using a two-dimensional Shelfy-Stream Approximation implemented within the Ice Sheet System Model (ISSM) and use uncertainty quantification tools embedded within the model to calculate the sensitivity of ice flow within the Northeast Greenland Ice Stream to errors in surface mass balance (SMB) forcing. Our results suggest that the model tends to smooth ice velocities even when forced with extreme errors in SMB. Indeed, errors propagate linearly through the model, resulting in discharge uncertainty of 16% or 1.9 Gt/yr. We find that mass flux is most sensitive to local errors but is also affected by errors hundreds of kilometers away; thus, an accurate SMB map of the entire basin is critical for realistic simulation. Furthermore, sensitivity analyses indicate that SMB forcing needs to be provided at a resolution of at least 40 km.

Channelized subglacial drainage over a deformable bed

USGS Publications Warehouse

Walder, J.S.; Fowler, A.

1994-01-01

We develop theoretically a description of a possible subglacial drainage mechanism for glaciers and ice sheets moving over saturated, deformable till. The model is based on the plausible assumption that flow of water in a thin film at the ice-till interface is unstable to the formation of a channelized drainage system, and is restricted to the case in which meltwater cannot escape through the till to an underlying aquifer. In describing the physics of such channelized drainage, we have generalized and extended Rothlisberger's model of channels cut into basal ice to include "canals' cut into the till, paying particular attention to the role of sediment properties and the mechanics of sediment transport. We show that sediment-floored Rothlisberger (R) channels can exist for high effective pressures, and wide, shallow, ice-roofed canals cut into the till for low effective pressures. Canals should form a distributed, non-arborescent system, unlike R channels. Geologic evidence derived from land forms and deposits left by the Pleistocene ice sheets in North America and Europe is consistent with predictions of the model. -from Authors

Design and development of LED-based irregular leather area measuring machine

NASA Astrophysics Data System (ADS)

Adil, Rehan; Khan, Sarah Jamal

2012-01-01

Using optical sensor array, a precision motion control system in a conveyer follows the irregular shaped leather sheet to measure its surface area. In operation, irregular shaped leather sheet passes on conveyer belt and optical sensor array detects the leather sheet edge. In this way outside curvature of the leather sheet is detected and is then feed to the controller to measure its approximate area. Such system can measure irregular shapes, by neglecting rounded corners, ellipses etc. To minimize the error in calculating surface area of irregular curve to the above mentioned system, the motion control system only requires the footprint of the optical sensor to be small and the distance between the sensors is to be minimized. In the proposed technique surface area measurement of irregular shaped leather sheet is done by defining velocity and detecting position of the move. The motion controller takes the information and creates the necessary edge profile on point-to-point bases. As a result irregular shape of leather sheet is mapped and is then feed to the controller to calculate surface area.

System for harvesting water wave energy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Zhong Lin; Su, Yanjie; Zhu, Guang

A generator for harvesting energy from water in motion includes a sheet of a hydrophobic material, having a first side and an opposite second side, that is triboelectrically more negative than water. A first electrode sheet is disposed on the second side of the sheet of a hydrophobic material. A second electrode sheet is disposed on the second side of the sheet of a hydrophobic material and is spaced apart from the first electrode sheet. Movement of the water across the first side induces an electrical potential imbalance between the first electrode sheet and the second electrode sheet.

Ice shelf fracture parameterization in an ice sheet model

NASA Astrophysics Data System (ADS)

Sun, Sainan; Cornford, Stephen L.; Moore, John C.; Gladstone, Rupert; Zhao, Liyun

2017-11-01

Floating ice shelves exert a stabilizing force onto the inland ice sheet. However, this buttressing effect is diminished by the fracture process, which on large scales effectively softens the ice, accelerating its flow, increasing calving, and potentially leading to ice shelf breakup. We add a continuum damage model (CDM) to the BISICLES ice sheet model, which is intended to model the localized opening of crevasses under stress, the transport of those crevasses through the ice sheet, and the coupling between crevasse depth and the ice flow field and to carry out idealized numerical experiments examining the broad impact on large-scale ice sheet and shelf dynamics. In each case we see a complex pattern of damage evolve over time, with an eventual loss of buttressing approximately equivalent to halving the thickness of the ice shelf. We find that it is possible to achieve a similar ice flow pattern using a simple rule of thumb: introducing an enhancement factor ˜ 10 everywhere in the model domain. However, spatially varying damage (or equivalently, enhancement factor) fields set at the start of prognostic calculations to match velocity observations, as is widely done in ice sheet simulations, ought to evolve in time, or grounding line retreat can be slowed by an order of magnitude.

Chemsheet as a Simulation Platform for Pyrometallurgical Processes

NASA Astrophysics Data System (ADS)

Penttilä, Karri; Salminen, Justin; Tripathi, Nagendra; Koukkari, Pertti

ChemSheet is a thermodynamic multi-phase multi-component simulation software, which is used as an Add-in in Microsoft Excel. In ChemSheet, the unique Constrained Gibbs free energy method can be used to include dynamic constraints and reaction rates of kinetically slow reactions, yet retaining full consistency of the multiphase thermodynamic model. With appropriate data, ChemSheet models can be used to simulate reactors and processes in all fields of thermochemistry. The presentation will cover off-line modeling of Cu-flash smelters and advanced thermochemical simulation coupled with on-line process control of Cu-Ni smelting. The presentation will describe an off-line model of Cu-smelter based on critically assessed properties of the Al-Ca-Cu-Fe-O-S-Si -system (slag, matte and liquid metal) by using the quasichemical model. A four-stage reactor model (shaft, settler, uptake and bath) is used for optimizing process parameters and feed particle distribution. As a second example, an advanced thermochemical model of a Ni-Cu sulphide smelting plant will be given. The on-line model covers the operation of treating Ni-Cu-S concentrate via roasters, electric furnace and converters, producing a high grade Bessemer matte product for further refining. The model integrates the thermochemistry of the roasters and electric furnace, and predicts important process parameters such as degree of sulphur elimination in the fluid-bed roasters, matte grade, iron metallization, slag losses and the iron to silica ratio in the electric furnace slag. Both models can be used to assist process engineers and operators in calculating the addition rates of coke, flux and air for different feed scenarios.

Ice-sheet contributions to future sea-level change.

PubMed

Gregory, J M; Huybrechts, P

2006-07-15

Accurate simulation of ice-sheet surface mass balance requires higher spatial resolution than is afforded by typical atmosphere-ocean general circulation models (AOGCMs), owing, in particular, to the need to resolve the narrow and steep margins where the majority of precipitation and ablation occurs. We have developed a method for calculating mass-balance changes by combining ice-sheet average time-series from AOGCM projections for future centuries, both with information from high-resolution climate models run for short periods and with a 20km ice-sheet mass-balance model. Antarctica contributes negatively to sea level on account of increased accumulation, while Greenland contributes positively because ablation increases more rapidly. The uncertainty in the results is about 20% for Antarctica and 35% for Greenland. Changes in ice-sheet topography and dynamics are not included, but we discuss their possible effects. For an annual- and area-average warming exceeding 4.5+/-0.9K in Greenland and 3.1+/-0.8K in the global average, the net surface mass balance of the Greenland ice sheet becomes negative, in which case it is likely that the ice sheet would eventually be eliminated, raising global-average sea level by 7m.

Final NPDES Electronic Reporting Rule Fact Sheet

EPA Pesticide Factsheets

Fact sheet explaining the National Pollution Discharge Elimination System (NPDES) Electronic Reporting Rule. The fact sheet provides information on the purpose of the rule, benefits and implementation.

The impact of dynamic topography on the bedrock elevation and volume of the Pliocene Antarctic Ice Sheet

NASA Astrophysics Data System (ADS)

Austermann, Jacqueline; Pollard, David; Mitrovica, Jerry X.; Moucha, Robert; Forte, Alessandro M.; DeConto, Robert M.

2015-04-01

Reconstructions of the Antarctic ice sheet over long timescales (i.e. Myrs) require estimates of bedrock elevation through time. Ice sheet models have accounted, with varying levels of sophistication, for changes in the bedrock elevation due to glacial isostatic adjustment (GIA), but they have neglected other processes that may perturb topography. One notable example is dynamic topography, the deflection of the solid surface of the Earth due to convective flow within the mantle. Numerically predicted changes in dynamic topography have been used to correct paleo shorelines for this departure from eustasy, but the effect of such changes on ice sheet stability is unknown. In this study we use numerical predictions of time-varying dynamic topography to reconstruct bedrock elevation below the Antarctic ice sheet during the mid Pliocene warm period (~3 Ma). Moreover, we couple this reconstruction to a three-dimensional ice sheet model to explore the impact of dynamic topography on the evolution of the Antarctic ice sheet since the Pliocene. Our modeling indicates significant uplift in the area of the Transantarctic Mountains (TAM) and the adjacent Wilkes basin. This predicted uplift, which is at the lower end of geological inferences of uplift of the TAM, implies a lower elevation of the basin in the Pliocene. Relative to simulations that do not include dynamic topography, the lower elevation leads to a smaller Antarctic Ice Sheet volume and a more significant retreat of the grounding line in the Wilkes basin, both of which are consistent with offshore sediment core data. We conclude that reconstructions of the Antarctic Ice Sheet during the mid-Pliocene warm period should be based on bedrock elevation models that include the impact of both GIA and dynamic topography.

Exploring changes in vertical ice extent along the margin of the East Antarctic Ice Sheet in western Dronning Maud Land - initial results of the MAGIC-DML collaboration

NASA Astrophysics Data System (ADS)

Lifton, N. A.; Newall, J. C.; Fredin, O.; Glasser, N. F.; Fabel, D.; Rogozhina, I.; Bernales, J.; Prange, M.; Sams, S.; Eisen, O.; Hättestrand, C.; Harbor, J.; Stroeven, A. P.

2017-12-01

Numerical ice sheet models constrained by theory and refined by comparisons with observational data are a central component of work to address the interactions between the cryosphere and changing climate, at a wide range of scales. Such models are tested and refined by comparing model predictions of past ice geometries with field-based reconstructions from geological, geomorphological, and ice core data. However, on the East Antarctic Ice sheet, there are few empirical data with which to reconstruct changes in ice sheet geometry in the Dronning Maud Land (DML) region. In addition, there is poor control on the regional climate history of the ice sheet margin, because ice core locations, where detailed reconstructions of climate history exist, are located on high inland domes. This leaves numerical models of regional glaciation history in this near-coastal area largely unconstrained. MAGIC-DML is an ongoing Swedish-US-Norwegian-German-UK collaboration with a focus on improving ice sheet models by combining advances in numerical modeling with filling critical data gaps that exist in our knowledge of the timing and pattern of ice surface changes on the western Dronning Maud Land margin. A combination of geomorphological mapping using remote sensing data, field investigations, cosmogenic nuclide surface exposure dating, and numerical ice-sheet modeling are being used in an iterative manner to produce a comprehensive reconstruction of the glacial history of western Dronning Maud Land. We will present an overview of the project, as well as field observations and preliminary in situ cosmogenic nuclide measurements from the 2016/17 expedition.

Phenomenological Model of Current Sheet Canting in Pulsed Electromagnetic Accelerators

NASA Technical Reports Server (NTRS)

Markusic, Thomas; Choueiri, E. Y.

2003-01-01

The phenomenon of current sheet canting in pulsed electromagnetic accelerators is the departure of the plasma sheet (that carries the current) from a plane that is perpendicular to the electrodes to one that is skewed, or tipped. Review of pulsed electromagnetic accelerator literature reveals that current sheet canting is a ubiquitous phenomenon - occurring in all of the standard accelerator geometries. Developing an understanding of current sheet canting is important because it can detract from the propellant sweeping capabilities of current sheets and, hence, negatively impact the overall efficiency of pulsed electromagnetic accelerators. In the present study, it is postulated that depletion of plasma near the anode, which results from axial density gradient induced diamagnetic drift, occurs during the early stages of the discharge, creating a density gradient normal to the anode, with a characteristic length on the order of the ion skin depth. Rapid penetration of the magnetic field through this region ensues, due to the Hall effect, leading to a canted current front ahead of the initial current conduction channel. In this model, once the current sheet reaches appreciable speeds, entrainment of stationary propellant replenishes plasma in the anode region, inhibiting further Hall-convective transport of the magnetic field; however, the previously established tilted current sheet remains at a fairly constant canting angle for the remainder of the discharge cycle, exerting a transverse J x B force which drives plasma toward the cathode and accumulates it there. This proposed sequence of events has been incorporated into a phenomenological model. The model predicts that canting can be reduced by using low atomic mass propellants with high propellant loading number density; the model results are shown to give qualitative agreement with experimentally measured canting angle mass dependence trends.

Extensive retreat and re-advance of the West Antarctic Ice Sheet during the Holocene.

PubMed

Kingslake, J; Scherer, R P; Albrecht, T; Coenen, J; Powell, R D; Reese, R; Stansell, N D; Tulaczyk, S; Wearing, M G; Whitehouse, P L

2018-06-01

To predict the future contributions of the Antarctic ice sheets to sea-level rise, numerical models use reconstructions of past ice-sheet retreat after the Last Glacial Maximum to tune model parameters 1 . Reconstructions of the West Antarctic Ice Sheet have assumed that it retreated progressively throughout the Holocene epoch (the past 11,500 years or so) 2-4 . Here we show, however, that over this period the grounding line of the West Antarctic Ice Sheet (which marks the point at which it is no longer in contact with the ground and becomes a floating ice shelf) retreated several hundred kilometres inland of today's grounding line, before isostatic rebound caused it to re-advance to its present position. Our evidence includes, first, radiocarbon dating of sediment cores recovered from beneath the ice streams of the Ross Sea sector, indicating widespread Holocene marine exposure; and second, ice-penetrating radar observations of englacial structure in the Weddell Sea sector, indicating ice-shelf grounding. We explore the implications of these findings with an ice-sheet model. Modelled re-advance of the grounding line in the Holocene requires ice-shelf grounding caused by isostatic rebound. Our findings overturn the assumption of progressive retreat of the grounding line during the Holocene in West Antarctica, and corroborate previous suggestions of ice-sheet re-advance 5 . Rebound-driven stabilizing processes were apparently able to halt and reverse climate-initiated ice loss. Whether these processes can reverse present-day ice loss 6 on millennial timescales will depend on bedrock topography and mantle viscosity-parameters that are difficult to measure and to incorporate into ice-sheet models.

Cascading Failures in Bi-partite Graphs: Model for Systemic Risk Propagation

PubMed Central

Huang, Xuqing; Vodenska, Irena; Havlin, Shlomo; Stanley, H. Eugene

2013-01-01

As economic entities become increasingly interconnected, a shock in a financial network can provoke significant cascading failures throughout the system. To study the systemic risk of financial systems, we create a bi-partite banking network model composed of banks and bank assets and propose a cascading failure model to describe the risk propagation process during crises. We empirically test the model with 2007 US commercial banks balance sheet data and compare the model prediction of the failed banks with the real failed banks after 2007. We find that our model efficiently identifies a significant portion of the actual failed banks reported by Federal Deposit Insurance Corporation. The results suggest that this model could be useful for systemic risk stress testing for financial systems. The model also identifies that commercial rather than residential real estate assets are major culprits for the failure of over 350 US commercial banks during 2008–2011. PMID:23386974

Isochronal Ice Sheet Model: a New Approach to Tracer Transport by Explicitly Tracing Accumulation Layers

NASA Astrophysics Data System (ADS)

Born, A.; Stocker, T. F.

2014-12-01

The long, high-resolution and largely undisturbed depositional record of polar ice sheets is one of the greatest resources in paleoclimate research. The vertical profile of isotopic and other geochemical tracers provides a full history of depositional and dynamical variations. Numerical simulations of this archive could afford great advances both in the interpretation of these tracers as well as to help improve ice sheet models themselves, as show successful implementations in oceanography and atmospheric dynamics. However, due to the slow advection velocities, tracer modeling in ice sheets is particularly prone to numerical diffusion, thwarting efforts that employ straightforward solutions. Previous attemps to circumvent this issue follow conceptually and computationally extensive approaches that augment traditional Eulerian models of ice flow with a semi-Lagrangian tracer scheme (e.g. Clarke et al., QSR, 2005). Here, we propose a new vertical discretization for ice sheet models that eliminates numerical diffusion entirely. Vertical motion through the model mesh is avoided by mimicking the real-world ice flow as a thinning of underlying layers (see figure). A new layer is added to the surface at equidistant time intervals (isochronally). Therefore, each layer is uniquely identified with an age. Horizontal motion follows the shallow ice approximation using an implicit numerical scheme. Vertical diffusion of heat which is physically desirable is also solved implicitly. A simulation of a two-dimensional section through the Greenland ice sheet will be discussed.

Design and fabrication of titanium multi-wall Thermal Protection System (TPS) test panels

NASA Technical Reports Server (NTRS)

Blair, W.; Meaney, J. E., Jr.; Rosenthal, H. A.

1980-01-01

A titanium multiwall thermal protection system panel was designed. The panel is a nine sheet sandwich structure consisting of an upper and lower face sheet; four dimpled sheets, three septum sheets, and clips for attachment to a vehicle structure. An acceptable fabrication process was developed, and the panel design was verified through mechanical and thermal testing of component specimens. A design was completed which takes into consideration fabrication techniques, thermal properties, mechanical properties, and materials availability.

ISSM: Ice Sheet System Model

NASA Technical Reports Server (NTRS)

Larour, Eric; Schiermeier, John E.; Seroussi, Helene; Morlinghem, Mathieu

2013-01-01

In order to have the capability to use satellite data from its own missions to inform future sea-level rise projections, JPL needed a full-fledged ice-sheet/iceshelf flow model, capable of modeling the mass balance of Antarctica and Greenland into the near future. ISSM was developed with such a goal in mind, as a massively parallelized, multi-purpose finite-element framework dedicated to ice-sheet modeling. ISSM features unstructured meshes (Tria in 2D, and Penta in 3D) along with corresponding finite elements for both types of meshes. Each finite element can carry out diagnostic, prognostic, transient, thermal 3D, surface, and bed slope simulations. Anisotropic meshing enables adaptation of meshes to a certain metric, and the 2D Shelfy-Stream, 3D Blatter/Pattyn, and 3D Full-Stokes formulations capture the bulk of the ice-flow physics. These elements can be coupled together, based on the Arlequin method, so that on a large scale model such as Antarctica, each type of finite element is used in the most efficient manner. For each finite element referenced above, ISSM implements an adjoint. This adjoint can be used to carry out model inversions of unknown model parameters, typically ice rheology and basal drag at the ice/bedrock interface, using a metric such as the observed InSAR surface velocity. This data assimilation capability is crucial to allow spinning up of ice flow models using available satellite data. ISSM relies on the PETSc library for its vectors, matrices, and solvers. This allows ISSM to run efficiently on any parallel platform, whether shared or distrib- ISSM: Ice Sheet System Model NASA's Jet Propulsion Laboratory, Pasadena, California uted. It can run on the largest clusters, and is fully scalable. This allows ISSM to tackle models the size of continents. ISSM is embedded into MATLAB and Python, both open scientific platforms. This improves its outreach within the science community. It is entirely written in C/C++, which gives it flexibility in its design, and the power/speed that C/C++ allows. ISSM is svn (subversion) hosted, on a JPL repository, to facilitate its development and maintenance. ISSM can also model propagation of rifts using contact mechanics and mesh splitting, and can interface to the Dakota software. To carry out sensitivity analysis, mesh partitioning algorithms are available, based on the Scotch, Chaco, and Metis partitioners that ensure equal area mesh partitions can be done, which are then usable for sampling and local reliability methods.

Applications of Computer Simulation Methods in Plastic Forming Technologies for Magnesium Alloys

NASA Astrophysics Data System (ADS)

Zhang, S. H.; Zheng, W. T.; Shang, Y. L.; Wu, X.; Palumbo, G.; Tricarico, L.

2007-05-01

Applications of computer simulation methods in plastic forming of magnesium alloy parts are discussed. As magnesium alloys possess very poor plastic formability at room temperature, various methods have been tried to improve the formability, for example, suitable rolling process and annealing procedures should be found to produce qualified magnesium alloy sheets, which have the reduced anisotropy and improved formability. The blank can be heated to a warm temperature or a hot temperature; a suitable temperature field is designed, tools should be heated or the punch should be cooled; suitable deformation speed should be found to ensure suitable strain rate range. Damage theory considering non-isothermal forming is established. Various modeling methods have been tried to consider above situations. The following situations for modeling the forming process of magnesium alloy sheets and tubes are dealt with: (1) modeling for predicting wrinkling and anisotropy of sheet warm forming; (2) damage theory used for predicting ruptures in sheet warm forming; (3) modeling for optimizing of blank shape and dimensions for sheet warm forming; (4) modeling in non-steady-state creep in hot metal gas forming of AZ31 tubes.

Electron magnetic reconnection without ion coupling in Earth's turbulent magnetosheath

NASA Astrophysics Data System (ADS)

Phan, T. D.; Eastwood, J. P.; Shay, M. A.; Drake, J. F.; Sonnerup, B. U. Ö.; Fujimoto, M.; Cassak, P. A.; Øieroset, M.; Burch, J. L.; Torbert, R. B.; Rager, A. C.; Dorelli, J. C.; Gershman, D. J.; Pollock, C.; Pyakurel, P. S.; Haggerty, C. C.; Khotyaintsev, Y.; Lavraud, B.; Saito, Y.; Oka, M.; Ergun, R. E.; Retino, A.; Le Contel, O.; Argall, M. R.; Giles, B. L.; Moore, T. E.; Wilder, F. D.; Strangeway, R. J.; Russell, C. T.; Lindqvist, P. A.; Magnes, W.

2018-05-01

Magnetic reconnection in current sheets is a magnetic-to-particle energy conversion process that is fundamental to many space and laboratory plasma systems. In the standard model of reconnection, this process occurs in a minuscule electron-scale diffusion region1,2. On larger scales, ions couple to the newly reconnected magnetic-field lines and are ejected away from the diffusion region in the form of bi-directional ion jets at the ion Alfvén speed3-5. Much of the energy conversion occurs in spatially extended ion exhausts downstream of the diffusion region6. In turbulent plasmas, which contain a large number of small-scale current sheets, reconnection has long been suggested to have a major role in the dissipation of turbulent energy at kinetic scales7-11. However, evidence for reconnection plasma jetting in small-scale turbulent plasmas has so far been lacking. Here we report observations made in Earth's turbulent magnetosheath region (downstream of the bow shock) of an electron-scale current sheet in which diverging bi-directional super-ion-Alfvénic electron jets, parallel electric fields and enhanced magnetic-to-particle energy conversion were detected. Contrary to the standard model of reconnection, the thin reconnecting current sheet was not embedded in a wider ion-scale current layer and no ion jets were detected. Observations of this and other similar, but unidirectional, electron jet events without signatures of ion reconnection reveal a form of reconnection that can drive turbulent energy transfer and dissipation in electron-scale current sheets without ion coupling.

Electron magnetic reconnection without ion coupling in Earth's turbulent magnetosheath.

PubMed

Phan, T D; Eastwood, J P; Shay, M A; Drake, J F; Sonnerup, B U Ö; Fujimoto, M; Cassak, P A; Øieroset, M; Burch, J L; Torbert, R B; Rager, A C; Dorelli, J C; Gershman, D J; Pollock, C; Pyakurel, P S; Haggerty, C C; Khotyaintsev, Y; Lavraud, B; Saito, Y; Oka, M; Ergun, R E; Retino, A; Le Contel, O; Argall, M R; Giles, B L; Moore, T E; Wilder, F D; Strangeway, R J; Russell, C T; Lindqvist, P A; Magnes, W

2018-05-01

Magnetic reconnection in current sheets is a magnetic-to-particle energy conversion process that is fundamental to many space and laboratory plasma systems. In the standard model of reconnection, this process occurs in a minuscule electron-scale diffusion region 1,2 . On larger scales, ions couple to the newly reconnected magnetic-field lines and are ejected away from the diffusion region in the form of bi-directional ion jets at the ion Alfvén speed 3-5 . Much of the energy conversion occurs in spatially extended ion exhausts downstream of the diffusion region 6 . In turbulent plasmas, which contain a large number of small-scale current sheets, reconnection has long been suggested to have a major role in the dissipation of turbulent energy at kinetic scales 7-11 . However, evidence for reconnection plasma jetting in small-scale turbulent plasmas has so far been lacking. Here we report observations made in Earth's turbulent magnetosheath region (downstream of the bow shock) of an electron-scale current sheet in which diverging bi-directional super-ion-Alfvénic electron jets, parallel electric fields and enhanced magnetic-to-particle energy conversion were detected. Contrary to the standard model of reconnection, the thin reconnecting current sheet was not embedded in a wider ion-scale current layer and no ion jets were detected. Observations of this and other similar, but unidirectional, electron jet events without signatures of ion reconnection reveal a form of reconnection that can drive turbulent energy transfer and dissipation in electron-scale current sheets without ion coupling.

Summary of the SeaRISE Project's Experiments on Modeled Ice-Sheet Contributions to Future Sea Level: Linearities and Non-linearities

NASA Astrophysics Data System (ADS)

Bindschadler, Robert

2013-04-01

The SeaRISE (Sea-level Response to Ice Sheet Evolution) project achieved ice-sheet model ensemble responses to a variety of prescribed changes to surface mass balance, basal sliding and ocean boundary melting. Greenland ice sheet models are more sensitive than Antarctic ice sheet models to likely atmospheric changes in surface mass balance, while Antarctic models are most sensitive to basal melting of its ice shelves. An experiment approximating the IPCC's RCP8.5 scenario produces first century contributions to sea level of 22.3 and 7.3 cm from Greenland and Antarctica, respectively, with a range among models of 62 and 17 cm, respectively. By 200 years, these projections increase to 53.2 and 23.4 cm, respectively, with ranges of 79 and 57 cm. The considerable range among models was not only in the magnitude of ice lost, but also in the spatial pattern of response to identical forcing. Despite this variation, the response of any single model to a large range in the forcing intensity was remarkably linear in most cases. Additionally, the results of sensitivity experiments to single types of forcing (i.e., only one of the surface mass balance, or basal sliding, or ocean boundary melting) could be summed to accurately predict any model's result for an experiment when multiple forcings were applied simultaneously. This suggests a limited amount of feedback through the ice sheet's internal dynamics between these types of forcing over the time scale of a few centuries (SeaRISE experiments lasted 500 years).

Use of CMIP Atmospheric Boundary Conditions with ISMs

NASA Technical Reports Server (NTRS)

Cullather, Richard; Nowicki, Sophie

2017-01-01

Dynamical ice sheet models are being used in simulations of future sea level change resulting from changing glacier mass. One of the difficulties in doing so are the input conditions obtained from earth system models. These inputs can be of coarse spatial resolution, and may not represent surface melt in a future climate. I review various methods for overcoming this with the aim of promoting discussion among modelers.

Enhancing workability in sheet production of high silicon content electrical steel through large shear deformation

DOE PAGES

Kustas, Andrew B.; Johnson, David R.; Trumble, Kevin P.; ...

2018-07-01

Enhanced workability, as characterized by the magnitude and heterogeneity of accommodated plastic strains during sheet processing, is demonstrated in high Si content Fe-Si alloys containing 4 and 6.5 wt% Si using two single-step, simple-shear deformation techniques – peeling and large strain extrusion machining (LSEM). The model Fe-Si material system was selected for its intrinsically poor material workability, and well-known applications potential in next-generation electric machines. In a comparative study of the deformation characteristics of the shear processes with conventional rolling, two distinct manifestations of workability are observed. For rolling, the relatively diffuse and unconfined deformation zone geometry leads to crackingmore » at low strains, with sheet structures characterized by extensive deformation twinning and banding. Workpiece pre-heating is required to improve the workability in rolling. In contrast, peeling and LSEM produce continuous sheet at large plastic strains without cracking, the result of more confined deformation geometries that enhances the workability. Peeling, however, results in heterogeneous, shear-banded microstructures, pointing to a second type of workability issue – flow localization – that limits sheet processing. This shear banding is to a large extent facilitated by unrestricted flow at the sheet surface, unavoidable in peeling. With additional confinement of this free surface deformation and appropriately designed deformation zone geometry, LSEM is shown to suppress shear banding, resulting in continuous sheet with homogeneous microstructure. Thus LSEM is shown to produce the greatest enhancement in process workability for producing sheet. In conclusion, these workability findings are explained and discussed based on differences in process mechanics and deformation zone geometry.« less

Enhancing workability in sheet production of high silicon content electrical steel through large shear deformation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kustas, Andrew B.; Johnson, David R.; Trumble, Kevin P.

Enhanced workability, as characterized by the magnitude and heterogeneity of accommodated plastic strains during sheet processing, is demonstrated in high Si content Fe-Si alloys containing 4 and 6.5 wt% Si using two single-step, simple-shear deformation techniques – peeling and large strain extrusion machining (LSEM). The model Fe-Si material system was selected for its intrinsically poor material workability, and well-known applications potential in next-generation electric machines. In a comparative study of the deformation characteristics of the shear processes with conventional rolling, two distinct manifestations of workability are observed. For rolling, the relatively diffuse and unconfined deformation zone geometry leads to crackingmore » at low strains, with sheet structures characterized by extensive deformation twinning and banding. Workpiece pre-heating is required to improve the workability in rolling. In contrast, peeling and LSEM produce continuous sheet at large plastic strains without cracking, the result of more confined deformation geometries that enhances the workability. Peeling, however, results in heterogeneous, shear-banded microstructures, pointing to a second type of workability issue – flow localization – that limits sheet processing. This shear banding is to a large extent facilitated by unrestricted flow at the sheet surface, unavoidable in peeling. With additional confinement of this free surface deformation and appropriately designed deformation zone geometry, LSEM is shown to suppress shear banding, resulting in continuous sheet with homogeneous microstructure. Thus LSEM is shown to produce the greatest enhancement in process workability for producing sheet. In conclusion, these workability findings are explained and discussed based on differences in process mechanics and deformation zone geometry.« less

Constructing superconductors by graphene Chern-Simons wormholes

NASA Astrophysics Data System (ADS)

Capozziello, Salvatore; Pincak, Richard; Saridakis, Emmanuel N.

2018-03-01

We propose a new model which simulates the motion of free electrons in graphene by the evolution of strings on manifolds. In this model, molecules which constitute sheets of graphene are polygonal point-like structures which build (N + 1) -dimensional manifolds. By breaking the gravitational-analogue symmetry of graphene sheets, we show that two separated child sheets and a Chern-Simons bridge are produced giving rise to a wormhole. In this structure, free electrons are transmitted from one child sheet to the other producing superconductivity. An analogue between "effective gravitons" and "Cooper pairs" is found. In principle, this phenomenology provides the possibility to construct superconductor structures by using the analogue of cosmological models.

The use of platelet-rich fibrin combined with periodontal ligament and jaw bone mesenchymal stem cell sheets for periodontal tissue engineering

PubMed Central

Wang, Zhong-Shan; Feng, Zhi-Hong; Wu, Guo-Feng; Bai, Shi-Zhu; Dong, Yan; Chen, Fa-Ming; Zhao, Yi-Min

2016-01-01

Periodontal regeneration involves the restoration of at least three unique tissues: cementum, periodontal ligament tissue (PDL) and alveolar bone tissue. Here, we first isolated human PDL stem cells (PDLSCs) and jaw bone mesenchymal stem cells (JBMSCs). These cells were then induced to form cell sheets using an ascorbic acid-rich approach, and the cell sheet properties, including morphology, thickness and gene expression profile, were compared. Platelet-rich fibrin (PRF) derived from human venous blood was then fabricated into bioabsorbable fibrin scaffolds containing various growth factors. Finally, the in vivo potential of a cell-material construct based on PDLSC sheets, PRF scaffolds and JBMSC sheets to form periodontal tissue was assessed in a nude mouse model. In this model, PDLSC sheet/PRF/JBMSC sheet composites were placed in a simulated periodontal space comprising human treated dentin matrix (TDM) and hydroxyapatite (HA)/tricalcium phosphate (TCP) frameworks. Eight weeks after implantation, the PDLSC sheets tended to develop into PDL-like tissues, while the JBMSC sheets tended to produce predominantly bone-like tissues. In addition, the PDLSC sheet/PRF/JBMSC sheet composites generated periodontal tissue-like structures containing PDL- and bone-like tissues. Further improvements in this cell transplantation design may have the potential to provide an effective approach for future periodontal tissue regeneration. PMID:27324079

Free Wake Techniques for Rotor Aerodynamic Analylis. Volume 2: Vortex Sheet Models

NASA Technical Reports Server (NTRS)

Tanuwidjaja, A.

1982-01-01

Results of computations are presented using vortex sheets to model the wake and test the sensitivity of the solutions to various assumptions used in the development of the models. The complete codings are included.

Modeling Geoelectric Fields and Geomagnetically Induced Currents Around New Zealand to Explore GIC in the South Island's Electrical Transmission Network

NASA Astrophysics Data System (ADS)

Divett, T.; Ingham, M.; Beggan, C. D.; Richardson, G. S.; Rodger, C. J.; Thomson, A. W. P.; Dalzell, M.

2017-10-01

Transformers in New Zealand's South Island electrical transmission network have been impacted by geomagnetically induced currents (GIC) during geomagnetic storms. We explore the impact of GIC on this network by developing a thin-sheet conductance (TSC) model for the region, a geoelectric field model, and a GIC network model. (The TSC is composed of a thin-sheet conductance map with underlying layered resistivity structure.) Using modeling approaches that have been successfully used in the United Kingdom and Ireland, we applied a thin-sheet model to calculate the electric field as a function of magnetic field and ground conductance. We developed a TSC model based on magnetotelluric surveys, geology, and bathymetry, modified to account for offshore sediments. Using this representation, the thin sheet model gave good agreement with measured impedance vectors. Driven by a spatially uniform magnetic field variation, the thin-sheet model results in electric fields dominated by the ocean-land boundary with effects due to the deep ocean and steep terrain. There is a strong tendency for the electric field to align northwest-southeast, irrespective of the direction of the magnetic field. Applying this electric field to a GIC network model, we show that modeled GIC are dominated by northwest-southeast transmission lines rather than east-west lines usually assumed to dominate.

@NWTC Newsletter: Summer 2014 | Wind | NREL

Science.gov Websites

, Developmental Role in Major Wind Journal Boosting Wind Plant Power Output by 4%-5% through Coordinated Turbine . Part 2: Wind Farm Wake Models New Framework Transforms FAST Wind Turbine Modeling Tool (Fact Sheet ) Sensitivity Analysis of Wind Plant Performance to Key Turbine Design Parameters: A Systems Engineering

Inspiration & Insight - a tribute to Niels Reeh

NASA Astrophysics Data System (ADS)

Ahlstrom, A. P.; Vieli, A.

2009-12-01

Niels Reeh was highly regarded for his contributions to glaciology, specifically through his rigorous combination of numerical modelling and field observations. In 1966 he began his work on the application of beam mechanics to floating glaciers and ice shelves and throughout his life, Niels retained a strong interest in modelling glacier dynamics. In the early 1980s Niels developed a 3D-model for ice sheets and in the late 1980s an advanced flow-line model. Niels Reeh also took part in the early ice-core drilling efforts in Greenland and later pioneered the concept of retrieving similar records from the surface of the ice-sheet margin. Mass balance of glaciers and ice sheets was another theme in Niels Reeh’s research, with a number of important contributions and insights still used when teaching the subject to students. Niels developed elegant models for ablation and snow densification, notable for their applicability in large-scale ice-sheet models and studied the impact of climate change on ice sheets and glaciers. Niels also took his interest in ice-dynamics and mass balance into remote sensing and worked successfully on methods to utilize radar and laser data from airborne surveys and satellites in glaciology. In this, he pioneered the combination of field experiments, satellite observations and numerical modelling to solve problems on the Greenland Ice Sheet. In this presentation we will attempt to provide an overview of Niels Reeh’s many-facetted career in acknowledgement of his contributions to the field of glaciology.

The Cryosphere Model Comparison Tool (CmCt): Ice Sheet Model Validation and Comparison Tool for Greenland and Antarctica

NASA Astrophysics Data System (ADS)

Simon, E.; Nowicki, S.; Neumann, T.; Tyahla, L.; Saba, J. L.; Guerber, J. R.; Bonin, J. A.; DiMarzio, J. P.

2017-12-01

The Cryosphere model Comparison tool (CmCt) is a web based ice sheet model validation tool that is being developed by NASA to facilitate direct comparison between observational data and various ice sheet models. The CmCt allows the user to take advantage of several decades worth of observations from Greenland and Antarctica. Currently, the CmCt can be used to compare ice sheet models provided by the user with remotely sensed satellite data from ICESat (Ice, Cloud, and land Elevation Satellite) laser altimetry, GRACE (Gravity Recovery and Climate Experiment) satellite, and radar altimetry (ERS-1, ERS-2, and Envisat). One or more models can be uploaded through the CmCt website and compared with observational data, or compared to each other or other models. The CmCt calculates statistics on the differences between the model and observations, and other quantitative and qualitative metrics, which can be used to evaluate the different model simulations against the observations. The qualitative metrics consist of a range of visual outputs and the quantitative metrics consist of several whole-ice-sheet scalar values that can be used to assign an overall score to a particular simulation. The comparison results from CmCt are useful in quantifying improvements within a specific model (or within a class of models) as a result of differences in model dynamics (e.g., shallow vs. higher-order dynamics approximations), model physics (e.g., representations of ice sheet rheological or basal processes), or model resolution (mesh resolution and/or changes in the spatial resolution of input datasets). The framework and metrics could also be used for use as a model-to-model intercomparison tool, simply by swapping outputs from another model as the observational datasets. Future versions of the tool will include comparisons with other datasets that are of interest to the modeling community, such as ice velocity, ice thickness, and surface mass balance.

A Methodology for Assessing and Ranking Ballistic Missile Defense Technologies Using a System Performance Index

DTIC Science & Technology

2002-07-29

suggestions, and guidance concerning the technology assessment process. References 1. Using ACEIT for Total Ownership Cost Modeling and Analysis...2001 World Population Data Sheet, Population Reference Bureau, Washington, DC List of Acronyms ACEIT – Automated Cost Estimating Integrated

Impact of Basal Hydrology Near Grounding Lines: Results from the MISMIP-3D and MISMIP+ Experiments Using the Community Ice Sheet Model

NASA Astrophysics Data System (ADS)

Leguy, G.; Lipscomb, W. H.; Asay-Davis, X.

2017-12-01

Ice sheets and ice shelves are linked by the transition zone, the region where the grounded ice lifts off the bedrock and begins to float. Adequate resolution of the transition zone is necessary for numerically accurate ice sheet-ice shelf simulations. In previous work we have shown that by using a simple parameterization of the basal hydrology, a smoother transition in basal water pressure between floating and grounded ice improves the numerical accuracy of a one-dimensional vertically integrated fixed-grid model. We used a set of experiments based on the Marine Ice Sheet Model Intercomparison Project (MISMIP) to show that reliable grounding-line dynamics at resolutions 1 km is achievable. In this presentation we use the Community Ice Sheet Model (CISM) to demonstrate how the representation of basal lubrication impacts three-dimensional models using the MISMIP-3D and MISMIP+ experiments. To this end we will compare three different Stokes approximations: the Shallow Shelf Approximation (SSA), a depth-integrated higher-order approximation, and the Blatter-Pattyn model. The results from our one-dimensional model carry over to the 3-D models; a resolution of 1 km (and in some cases 2 km) remains sufficient to accurately simulate grounding-line dynamics.

Modeling protein homopolymeric repeats: possible polyglutamine structural motifs for Huntington's disease.

PubMed

Lathrop, R H; Casale, M; Tobias, D J; Marsh, J L; Thompson, L M

1998-01-01

We describe a prototype system (Poly-X) for assisting an expert user in modeling protein repeats. Poly-X reduces the large number of degrees of freedom required to specify a protein motif in complete atomic detail. The result is a small number of parameters that are easily understood by, and under the direct control of, a domain expert. The system was applied to the polyglutamine (poly-Q) repeat in the first exon of huntingtin, the gene implicated in Huntington's disease. We present four poly-Q structural motifs: two poly-Q beta-sheet motifs (parallel and antiparallel) that constitute plausible alternatives to a similar previously published poly-Q beta-sheet motif, and two novel poly-Q helix motifs (alpha-helix and pi-helix). To our knowledge, helical forms of polyglutamine have not been proposed before. The motifs suggest that there may be several plausible aggregation structures for the intranuclear inclusion bodies which have been found in diseased neurons, and may help in the effort to understand the structural basis for Huntington's disease.

Antarctic ice sheet thickness estimation using the horizontal-to-vertical spectral ratio method with single-station seismic ambient noise

NASA Astrophysics Data System (ADS)

Yan, Peng; Li, Zhiwei; Li, Fei; Yang, Yuande; Hao, Weifeng; Bao, Feng

2018-03-01

We report on a successful application of the horizontal-to-vertical spectral ratio (H / V) method, generally used to investigate the subsurface velocity structures of the shallow crust, to estimate the Antarctic ice sheet thickness for the first time. Using three-component, five-day long, seismic ambient noise records gathered from more than 60 temporary seismic stations located on the Antarctic ice sheet, the ice thickness measured at each station has comparable accuracy to the Bedmap2 database. Preliminary analysis revealed that 60 out of 65 seismic stations on the ice sheet obtained clear peak frequencies (f0) related to the ice sheet thickness in the H / V spectrum. Thus, assuming that the isotropic ice layer lies atop a high velocity half-space bedrock, the ice sheet thickness can be calculated by a simple approximation formula. About half of the calculated ice sheet thicknesses were consistent with the Bedmap2 ice thickness values. To further improve the reliability of ice thickness measurements, two-type models were built to fit the observed H / V spectrum through non-linear inversion. The two-type models represent the isotropic structures of single- and two-layer ice sheets, and the latter depicts the non-uniform, layered characteristics of the ice sheet widely distributed in Antarctica. The inversion results suggest that the ice thicknesses derived from the two-layer ice models were in good concurrence with the Bedmap2 ice thickness database, and that ice thickness differences between the two were within 300 m at almost all stations. Our results support previous finding that the Antarctic ice sheet is stratified. Extensive data processing indicates that the time length of seismic ambient noise records can be shortened to two hours for reliable ice sheet thickness estimation using the H / V method. This study extends the application fields of the H / V method and provides an effective and independent way to measure ice sheet thickness in Antarctica.

Evidence of local and regional freshening of Northeast Greenland coastal waters.

PubMed

Sejr, Mikael K; Stedmon, Colin A; Bendtsen, Jørgen; Abermann, Jakob; Juul-Pedersen, Thomas; Mortensen, John; Rysgaard, Søren

2017-10-13

The supply of freshwater to fjord systems in Greenland is increasing as a result of climate change-induced acceleration in ice sheet melt. However, insight into the marine implications of the melt water is impaired by lack of observations demonstrating the fate of freshwater along the Greenland coast and providing evaluation basis for ocean models. Here we present 13 years of summer measurements along a 120 km transect in Young Sound, Northeast Greenland and show that sub-surface coastal waters are decreasing in salinity with an average rate of 0.12 ± 0.05 per year. This is the first observational evidence of a significant freshening on decadal scale of the waters surrounding the ice sheet and comes from a region where ice sheet melt has been less significant. It implies that ice sheet dynamics in Northeast Greenland could be of key importance as freshwater is retained in southward flowing coastal currents thus reducing density of water masses influencing major deep water formation areas in the Subarctic Atlantic Ocean. Ultimately, the observed freshening could have implications for the Atlantic meridional overturning circulation.

Glacial removal of late Cenozoic subglacially emplaced volcanic edifices by the West Antarctic ice sheet

USGS Publications Warehouse

Behrendt, John C.; Blankenship, D.D.; Damaske, D.; Cooper, A. K.

1995-01-01

Local maxima of the horizontal gradient of pseudogravity from closely spaced aeromagnetic surveys over the Ross Sea, northwestern Ross Ice Shelf, and the West Antarctic ice sheet, reveal a linear magnetic rift fabric and numerous subcircular, high-amplitude anomalies. Geophysical data indicate two or three youthful volcanic edifices at widely separated areas beneath the sea and ice cover in the West Antarctic rift system. In contrast, we suggest glacial removal of edifices of volcanic sources of many more anomalies. Magnetic models, controlled by marine seismic reflection and radar ice-sounding data, allow us to infer that glacial removal of the associated late Cenozoic volcanic edifices (probably debris, comprising pillow breccias, and hyaloclastites) has occurred essentially concomitantly with their subglacial eruption. "Removal' of unconsolidated volcanic debris erupted beneath the ice is probably a more appropriate term than "erosion', given its fragmented, ice-contact origin. The exposed volcanoes may have been protected from erosion by the surrounding ice sheet because of more competent rock or high elevation above the ice sheet. -from Authors

Inferring Ice Thickness from a Glacier Dynamics Model and Multiple Surface Datasets.

NASA Astrophysics Data System (ADS)

Guan, Y.; Haran, M.; Pollard, D.

2017-12-01

The future behavior of the West Antarctic Ice Sheet (WAIS) may have a major impact on future climate. For instance, ice sheet melt may contribute significantly to global sea level rise. Understanding the current state of WAIS is therefore of great interest. WAIS is drained by fast-flowing glaciers which are major contributors to ice loss. Hence, understanding the stability and dynamics of glaciers is critical for predicting the future of the ice sheet. Glacier dynamics are driven by the interplay between the topography, temperature and basal conditions beneath the ice. A glacier dynamics model describes the interactions between these processes. We develop a hierarchical Bayesian model that integrates multiple ice sheet surface data sets with a glacier dynamics model. Our approach allows us to (1) infer important parameters describing the glacier dynamics, (2) learn about ice sheet thickness, and (3) account for errors in the observations and the model. Because we have relatively dense and accurate ice thickness data from the Thwaites Glacier in West Antarctica, we use these data to validate the proposed approach. The long-term goal of this work is to have a general model that may be used to study multiple glaciers in the Antarctic.

Simulation of climate, ice sheets and CO2 evolution during the last four glacial cycles with an Earth system model of intermediate complexity

NASA Astrophysics Data System (ADS)

Ganopolski, Andrey; Brovkin, Victor

2017-11-01

In spite of significant progress in paleoclimate reconstructions and modelling of different aspects of the past glacial cycles, the mechanisms which transform regional and seasonal variations in solar insolation into long-term and global-scale glacial-interglacial cycles are still not fully understood - in particular, in relation to CO2 variability. Here using the Earth system model of intermediate complexity CLIMBER-2 we performed simulations of the co-evolution of climate, ice sheets, and carbon cycle over the last 400 000 years using the orbital forcing as the only external forcing. The model simulates temporal dynamics of CO2, global ice volume, and other climate system characteristics in good agreement with paleoclimate reconstructions. These results provide strong support for the idea that long and strongly asymmetric glacial cycles of the late Quaternary represent a direct but strongly nonlinear response of the Northern Hemisphere ice sheets to orbital forcing. This response is strongly amplified and globalised by the carbon cycle feedbacks. Using simulations performed with the model in different configurations, we also analyse the role of individual processes and sensitivity to the choice of model parameters. While many features of simulated glacial cycles are rather robust, some details of CO2 evolution, especially during glacial terminations, are sensitive to the choice of model parameters. Specifically, we found two major regimes of CO2 changes during terminations: in the first one, when the recovery of the Atlantic meridional overturning circulation (AMOC) occurs only at the end of the termination, a pronounced overshoot in CO2 concentration occurs at the beginning of the interglacial and CO2 remains almost constant during the interglacial or even declines towards the end, resembling Eemian CO2 dynamics. However, if the recovery of the AMOC occurs in the middle of the glacial termination, CO2 concentration continues to rise during the interglacial, similar to the Holocene. We also discuss the potential contribution of the brine rejection mechanism for the CO2 and carbon isotopes in the atmosphere and the ocean during the past glacial termination.

Transient thermal analysis of a titanium multiwall thermal protection system

NASA Technical Reports Server (NTRS)

Blosser, M. L.

1982-01-01

The application of the SPAR thermal analyzer to the thermal analysis of a thermal protection system concept is discussed. The titanium multiwall thermal protection system concept consists of alternate flat and dimpled sheets which are joined together at the crests of the dimples and formed into 30 cm by 30 cm (12 in. by 12 in.) tiles. The tiles are mechanically attached to the structure. The complex tile geometry complicates thermal analysis. Three modes of heat transfer were considered: conduction through the gas inside the tile, conduction through the metal, and radiation between the various layers. The voids between the dimpled and flat sheets were designed to be small enough so that natural convection is insignificant (e.g., Grashof number 1000). A two step approach was used in the thermal analysis of the multiwall thermal protection system. First, an effective normal (through-the-thickness) thermal conductivity was obtained from a steady state analysis using a detailed SPAR finite element model of a small symmetric section of the multiwall tile. This effective conductivity was then used in simple one dimensional finite element models for preliminary analysis of several transient heat transfer problems.

Computation of Incompressible Potential Flow over an Airfoil Using a High Order Aerodynamic Panel Method Based on Circular Arc Panels.

DTIC Science & Technology

1982-08-01

Vortex Sheet Figure 4 - Properties of Singularity Sheets they may be used to model different types of flow. Transfer of boundary... Vortex Sheet Equivalence Singularity Behavior Using Green’s theorem it is clear that the problem of potential flow over a body can be modeled using ...that source, doublet, or vortex singularities can be used to model potential flow problems, and that the doublet and vortex singularities are

Assessing the formability of metallic sheets by means of localized and diffuse necking models

NASA Astrophysics Data System (ADS)

Comşa, Dan-Sorin; Lǎzǎrescu, Lucian; Banabic, Dorel

2016-10-01

The main objective of the paper consists in elaborating a unified framework that allows the theoretical assessment of sheet metal formability. Hill's localized necking model and the Extended Maximum Force Criterion proposed by Mattiasson, Sigvant, and Larsson have been selected for this purpose. Both models are thoroughly described together with their solution procedures. A comparison of the theoretical predictions with experimental data referring to the formability of a DP600 steel sheet is also presented by the authors.

Observational support for the current sheet catastrophe model of substorm current disruption

NASA Technical Reports Server (NTRS)

Burkhart, G. R.; Lopez, R. E.; Dusenbery, P. B.; Speiser, T. W.

1992-01-01

The principles of the current sheet catastrophe models are briefly reviewed, and observations of some of the signatures predicted by the theory are presented. The data considered here include AMPTE/CCE observations of fifteen current sheet disruption events. According to the model proposed here, the root cause of the current disruption is some process, as yet unknown, that leads to an increase in the k sub A parameter. Possible causes for the increase in k sub A are discussed.

Performance model for grid-connected photovoltaic inverters.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Boyson, William Earl; Galbraith, Gary M.; King, David L.

2007-09-01

This document provides an empirically based performance model for grid-connected photovoltaic inverters used for system performance (energy) modeling and for continuous monitoring of inverter performance during system operation. The versatility and accuracy of the model were validated for a variety of both residential and commercial size inverters. Default parameters for the model can be obtained from manufacturers specification sheets, and the accuracy of the model can be further refined using measurements from either well-instrumented field measurements in operational systems or using detailed measurements from a recognized testing laboratory. An initial database of inverter performance parameters was developed based on measurementsmore » conducted at Sandia National Laboratories and at laboratories supporting the solar programs of the California Energy Commission.« less

Buckling and stretching of thin viscous sheets

NASA Astrophysics Data System (ADS)

O'Kiely, Doireann; Breward, Chris; Griffiths, Ian; Howell, Peter; Lange, Ulrich

2016-11-01

Thin glass sheets are used in smartphone, battery and semiconductor technology, and may be manufactured by producing a relatively thick glass slab and subsequently redrawing it to a required thickness. The resulting sheets commonly possess undesired centerline ripples and thick edges. We present a mathematical model in which a viscous sheet undergoes redraw in the direction of gravity, and show that, in a sufficiently strong gravitational field, buckling is driven by compression in a region near the bottom of the sheet, and limited by viscous resistance to stretching of the sheet. We use asymptotic analysis in the thin-sheet, low-Reynolds-number limit to determine the centerline profile and growth rate of such a viscous sheet.

Ice stream activity scaled to ice sheet volume during Laurentide Ice Sheet deglaciation.

PubMed

Stokes, C R; Margold, M; Clark, C D; Tarasov, L

2016-02-18

The contribution of the Greenland and West Antarctic ice sheets to sea level has increased in recent decades, largely owing to the thinning and retreat of outlet glaciers and ice streams. This dynamic loss is a serious concern, with some modelling studies suggesting that the collapse of a major ice sheet could be imminent or potentially underway in West Antarctica, but others predicting a more limited response. A major problem is that observations used to initialize and calibrate models typically span only a few decades, and, at the ice-sheet scale, it is unclear how the entire drainage network of ice streams evolves over longer timescales. This represents one of the largest sources of uncertainty when predicting the contributions of ice sheets to sea-level rise. A key question is whether ice streams might increase and sustain rates of mass loss over centuries or millennia, beyond those expected for a given ocean-climate forcing. Here we reconstruct the activity of 117 ice streams that operated at various times during deglaciation of the Laurentide Ice Sheet (from about 22,000 to 7,000 years ago) and show that as they activated and deactivated in different locations, their overall number decreased, they occupied a progressively smaller percentage of the ice sheet perimeter and their total discharge decreased. The underlying geology and topography clearly influenced ice stream activity, but--at the ice-sheet scale--their drainage network adjusted and was linked to changes in ice sheet volume. It is unclear whether these findings can be directly translated to modern ice sheets. However, contrary to the view that sees ice streams as unstable entities that can accelerate ice-sheet deglaciation, we conclude that ice streams exerted progressively less influence on ice sheet mass balance during the retreat of the Laurentide Ice Sheet.

Knowledge synthesis of benefits and adverse effects of measles vaccination: the Lasbela balance sheet.

PubMed

Ledogar, Robert J; Fleming, John; Andersson, Neil

2009-10-14

In preparation for a cluster-randomized controlled trial of a community intervention to increase the demand for measles vaccination in Lasbela district of Pakistan, a balance sheet summarized published evidence on benefits and possible adverse effects of measles vaccination. The balance sheet listed: 1) major health conditions associated with measles; 2) the risk among the unvaccinated who contract measles; 3) the risk among the vaccinated; 4) the risk difference between vaccinated and unvaccinated; and 5) the likely net gain from vaccination for each condition. Two models revealed very different projections of net gain from measles vaccine. A Lasbela-specific combination of low period prevalence of measles among the unvaccinated, medium vaccination coverage and low vaccine efficacy rate, as revealed by the baseline survey, resulted in less-than-expected gains attributable to vaccination. Modelled on estimates where the vaccine had greater efficacy, the gains from vaccination would be more substantial. Specific local conditions probably explain the low rates among the unvaccinated while the high vaccine failure rate is likely due to weaknesses in the vaccination delivery system. Community perception of these realities may have had some role in household decisions about whether to vaccinate, although the major discouraging factor was inadequate access. The balance sheet may be useful as a communication tool in other circumstances, applied to up-to-date local evidence.

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.

Modelling large-scale ice-sheet-climate interactions at the last glacial inception

NASA Astrophysics Data System (ADS)

Browne, O. J. H.; Gregory, J. M.; Payne, A. J.; Ridley, J. K.; Rutt, I. C.

2010-05-01

In order to investigate the interactions between coevolving climate and ice-sheets on multimillenial timescales, a low-resolution atmosphere-ocean general circulation model (AOGCM) has been coupled to a three-dimensional thermomechanical ice-sheet model. We use the FAMOUS AOGCM, which is almost identical in formulation to the widely used HadCM3 AOGCM, but on account of its lower resolution (7.5° longitude × 5° latitude in the atmosphere, 3.75°× 2.5° in the ocean) it runs about ten times faster. We use the community ice-sheet model Glimmer at 20 km resolution, with the shallow ice approximation and an annual degree-day scheme for surface mass balance. With the FAMOUS-Glimmer coupled model, we have simulated the growth of the Laurentide and Fennoscandian ice sheets at the last glacial inception, under constant orbital forcing and atmospheric composition for 116 ka BP. Ice grows in both regions, totalling 5.8 m of sea-level equivalent in 10 ka, slower than proxy records suggest. Positive climate feedbacks reinforce this growth at local scales (order hundreds of kilometres), where changes are an order of magnitude larger than on the global average. The albedo feedback (higher local albedo means a cooler climate) is important in the initial expansion of the ice-sheet area. The topography feedback (higher surface means a cooler climate) affects ice-sheet thickness and is not noticeable for the first 1 ka. These two feedbacks reinforce each other. Without them, the ice volume is ~90% less after 10 ka. In Laurentia, ice expands initially on the Canadian Arctic islands. The glaciation of the islands eventually cools the nearby mainland climate sufficiently to produce a positive mass balance there. Adjacent to the ice-sheets, cloud feedbacks tend to reduce the surface mass balance and restrain ice growth; this is an example of a local feedback whose simulation requires a model that includes detailed atmospheric physics.

Optimization of CO2 laser cutting parameters on Austenitic type Stainless steel sheet

NASA Astrophysics Data System (ADS)

Parthiban, A.; Sathish, S.; Chandrasekaran, M.; Ravikumar, R.

2017-03-01

Thin AISI 316L stainless steel sheet widely used in sheet metal processing industries for specific applications. CO2 laser cutting is one of the most popular sheet metal cutting processes for cutting of sheets in different profile. In present work various cutting parameters such as laser power (2000 watts-4000 watts), cutting speed (3500mm/min - 5500 mm/min) and assist gas pressure (0.7 Mpa-0.9Mpa) for cutting of AISI 316L 2mm thickness stainless sheet. This experimentation was conducted based on Box-Behenken design. The aim of this work is to develop a mathematical model kerf width for straight and curved profile through response surface methodology. The developed mathematical models for straight and curved profile have been compared. The Quadratic models have the best agreement with experimental data, and also the shape of the profile a substantial role in achieving to minimize the kerf width. Finally the numerical optimization technique has been used to find out best optimum laser cutting parameter for both straight and curved profile cut.

Buckling of Aluminium Sheet Components

NASA Astrophysics Data System (ADS)

Hegadekatte, Vishwanath; Shi, Yihai; Nardini, Dubravko

Wrinkling is one of the major defects in sheet metal forming processes. It may become a serious obstacle to implementing the forming process and assembling the parts, and may also play a significant role in the wear of the tool. Wrinkling is essentially a local buckling phenomenon that results from compressive stresses (compressive instability) e.g., in the hoop direction for axi-symmetric systems such as beverage cans. Modern beverage can is a highly engineered product with a complex geometry. Therefore in order to understand wrinkling in such a complex system, we have started by studying wrinkling with the Yoshida buckling test. Further, we have studied the buckling of ideal and dented beverage cans under axial loading by laboratory testing. We have modelled the laboratory tests and also the imperfection sensitivity of the two systems using finite element method and the predictions are in qualitative agreement with experimental data.

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

NASA Astrophysics Data System (ADS)

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

2015-12-01

This paper reports about important upgrades of the Greenland Ice Sheet (GrIS) surface elevation and elevation-change database obtained with our Surface Elevation And Change detection (SERAC) software suite. We have developed SERAC to derive information from laser altimetry data, particularly time series of elevation changes and their partitioning into changes caused by ice dynamics. This allows direct investigation of ice dynamic processes that is much needed for improving the predictive power of ice sheet models. SERAC is different from most other change detection methods. It is based on detecting changes of surface patches, about 1 km by 1 km in size, rather than deriving elevation changes from individual laser points. The current database consists of ~100,000 time series with satellite laser altimetry data from ICESat, airborne laser observations obtained by NASA's Airborne Topographic Mapper (ATM) and the Land, Vegetation and Ice Sensor (LVIS). The upgrade is significant, because not only new observations from 2013 and 2014 have been added but also a number of improvements lead to a more comprehensive and consistent record of elevation-changes. First, we used the model that gives in addition to ice sheet also information about ice caps and glaciers (Rastner et al., 2012) for deciding if a laser point is on the ice sheet or ice cap. Then we added small gaps that exist in the ICESat GLA12 data set because the ice sheet mask is not wide enough. The new database is now more complete and will facilitate more accurate comparisons of mass balance studies obtained from the Gravity Recovery and Climate Experiment system (GRACE). For determining the part of a time series caused by ice dynamics we used the new firn compaction model and Surface Mass Balance (SMB) estimates from RACMO2.3. The new database spans the time period from 1993 to 2014. Adding new observations amounts to a spatial densification of the old record and at the same time extends the time domain by two years. Our presentation will show the improvement of the reconstruction of the total changes, those caused by SMB and ice dynamic during the ICESat mission (2003-2009). Moreover we will review changes on scales from individual outlet glaciers to drainage basins and the entire ice sheet.

Non-linear optical flow cytometry using a scanned, Bessel beam light-sheet.

PubMed

Collier, Bradley B; Awasthi, Samir; Lieu, Deborah K; Chan, James W

2015-05-29

Modern flow cytometry instruments have become vital tools for high-throughput analysis of single cells. However, as issues with the cellular labeling techniques often used in flow cytometry have become more of a concern, the development of label-free modalities for cellular analysis is increasingly desired. Non-linear optical phenomena (NLO) are of growing interest for label-free analysis because of the ability to measure the intrinsic optical response of biomolecules found in cells. We demonstrate that a light-sheet consisting of a scanned Bessel beam is an optimal excitation geometry for efficiently generating NLO signals in a microfluidic environment. The balance of photon density and cross-sectional area provided by the light-sheet allowed significantly larger two-photon fluorescence intensities to be measured in a model polystyrene microparticle system compared to measurements made using other excitation focal geometries, including a relaxed Gaussian excitation beam often used in conventional flow cytometers.

Evidence for elevated and spatially variable geothermal flux beneath the West Antarctic Ice Sheet

PubMed Central

Schroeder, Dustin M.; Blankenship, Donald D.; Young, Duncan A.; Quartini, Enrica

2014-01-01

Heterogeneous hydrologic, lithologic, and geologic basal boundary conditions can exert strong control on the evolution, stability, and sea level contribution of marine ice sheets. Geothermal flux is one of the most dynamically critical ice sheet boundary conditions but is extremely difficult to constrain at the scale required to understand and predict the behavior of rapidly changing glaciers. This lack of observational constraint on geothermal flux is particularly problematic for the glacier catchments of the West Antarctic Ice Sheet within the low topography of the West Antarctic Rift System where geothermal fluxes are expected to be high, heterogeneous, and possibly transient. We use airborne radar sounding data with a subglacial water routing model to estimate the distribution of basal melting and geothermal flux beneath Thwaites Glacier, West Antarctica. We show that the Thwaites Glacier catchment has a minimum average geothermal flux of ∼114 ± 10 mW/m2 with areas of high flux exceeding 200 mW/m2 consistent with hypothesized rift-associated magmatic migration and volcanism. These areas of highest geothermal flux include the westernmost tributary of Thwaites Glacier adjacent to the subaerial Mount Takahe volcano and the upper reaches of the central tributary near the West Antarctic Ice Sheet Divide ice core drilling site. PMID:24927578

Influence of nanotopography on periodontal ligament stem cell functions and cell sheet based periodontal regeneration

PubMed Central

Gao, Hui; Li, Bei; Zhao, Lingzhou; Jin, Yan

2015-01-01

Periodontal regeneration is an important part of regenerative medicine, with great clinical significance; however, the effects of nanotopography on the functions of periodontal ligament (PDL) stem cells (PDLSCs) and on PDLSC sheet based periodontal regeneration have never been explored. Titania nanotubes (NTs) layered on titanium (Ti) provide a good platform to study this. In the current study, the influence of NTs of different tube size on the functions of PDLSCs was observed. Afterward, an ectopic implantation model using a Ti/cell sheets/hydroxyapatite (HA) complex was applied to study the effect of the NTs on cell sheet based periodontal regeneration. The NTs were able to enhance the initial PDLSC adhesion and spread, as well as collagen secretion. With the Ti/cell sheets/HA complex model, it was demonstrated that the PDLSC sheets were capable of regenerating the PDL tissue, when combined with bone marrow mesenchymal stem cell (BMSC) sheets and HA, without the need for extra soluble chemical cues. Simultaneously, the NTs improved the periodontal regeneration result of the ectopically implanted Ti/cell sheets/HA complex, giving rise to functionally aligned collagen fiber bundles. Specifically, much denser collagen fibers, with abundant blood vessels as well as cementum-like tissue on the Ti surface, which well-resembled the structure of natural PDL, were observed in the NT5 and NT10 sample groups. Our study provides the first evidence that the nanotopographical cues obviously influence the functions of PDLSCs and improve the PDLSC sheet based periodontal regeneration size dependently, which provides new insight to the periodontal regeneration. The Ti/cell sheets/HA complex may constitute a good model to predict the effect of biomaterials on periodontal regeneration. PMID:26150714

Influence of nanotopography on periodontal ligament stem cell functions and cell sheet based periodontal regeneration.

PubMed

Gao, Hui; Li, Bei; Zhao, Lingzhou; Jin, Yan

2015-01-01

Periodontal regeneration is an important part of regenerative medicine, with great clinical significance; however, the effects of nanotopography on the functions of periodontal ligament (PDL) stem cells (PDLSCs) and on PDLSC sheet based periodontal regeneration have never been explored. Titania nanotubes (NTs) layered on titanium (Ti) provide a good platform to study this. In the current study, the influence of NTs of different tube size on the functions of PDLSCs was observed. Afterward, an ectopic implantation model using a Ti/cell sheets/hydroxyapatite (HA) complex was applied to study the effect of the NTs on cell sheet based periodontal regeneration. The NTs were able to enhance the initial PDLSC adhesion and spread, as well as collagen secretion. With the Ti/cell sheets/HA complex model, it was demonstrated that the PDLSC sheets were capable of regenerating the PDL tissue, when combined with bone marrow mesenchymal stem cell (BMSC) sheets and HA, without the need for extra soluble chemical cues. Simultaneously, the NTs improved the periodontal regeneration result of the ectopically implanted Ti/cell sheets/HA complex, giving rise to functionally aligned collagen fiber bundles. Specifically, much denser collagen fibers, with abundant blood vessels as well as cementum-like tissue on the Ti surface, which well-resembled the structure of natural PDL, were observed in the NT5 and NT10 sample groups. Our study provides the first evidence that the nanotopographical cues obviously influence the functions of PDLSCs and improve the PDLSC sheet based periodontal regeneration size dependently, which provides new insight to the periodontal regeneration. The Ti/cell sheets/HA complex may constitute a good model to predict the effect of biomaterials on periodontal regeneration.

Modeling the Alzheimer Abeta17-42 fibril architecture: tight intermolecular sheet-sheet association and intramolecular hydrated cavities.

PubMed

Zheng, Jie; Jang, Hyunbum; Ma, Buyong; Tsai, Chung-Jun; Nussinov, Ruth

2007-11-01

We investigate Abeta(17-42) protofibril structures in solution using molecular dynamics simulations. Recently, NMR and computations modeled the Abeta protofibril as a longitudinal stack of U-shaped molecules, creating an in-parallel beta-sheet and loop spine. Here we study the molecular architecture of the fibril formed by spine-spine association. We model in-register intermolecular beta-sheet-beta-sheet associations and study the consequences of Alzheimer's mutations (E22G, E22Q, E22K, and M35A) on the organization. We assess the structural stability and association force of Abeta oligomers with different sheet-sheet interfaces. Double-layered oligomers associating through the C-terminal-C-terminal interface are energetically more favorable than those with the N-terminal-N-terminal interface, although both interfaces exhibit high structural stability. The C-terminal-C-terminal interface is essentially stabilized by hydrophobic and van der Waals (shape complementarity via M35-M35 contacts) intermolecular interactions, whereas the N-terminal-N-terminal interface is stabilized by hydrophobic and electrostatic interactions. Hence, shape complementarity, or the "steric zipper" motif plays an important role in amyloid formation. On the other hand, the intramolecular Abeta beta-strand-loop-beta-strand U-shaped motif creates a hydrophobic cavity with a diameter of 6-7 A, allowing water molecules and ions to conduct through. The hydrated hydrophobic cavities may allow optimization of the sheet association and constitute a typical feature of fibrils, in addition to the tight sheet-sheet association. Thus, we propose that Abeta fiber architecture consists of alternating layers of tight packing and hydrated cavities running along the fibrillar axis, which might be possibly detected by high-resolution imaging.

Simulating the impact of glaciations on continental groundwater flow systems: 2. Model application to the Wisconsinian glaciation over the Canadian landscape

NASA Astrophysics Data System (ADS)

Lemieux, J.-M.; Sudicky, E. A.; Peltier, W. R.; Tarasov, L.

2008-09-01

A 3-D groundwater flow and brine transport numerical model of the entire Canadian landscape up to a depth of 10 km is constructed in order to capture the impacts of the Wisconsinian glaciation on the continental groundwater flow system. The numerical development of the model is presented in the companion paper of Lemieux et al. (2008b). Although the scale of the model prevents the use of a detailed geological model, commonly occurring geological materials that exhibit relatively consistent hydrogeological properties over the continent justify the simplifications while still allowing the capture of large-scale flow system trends. The model includes key processes pertaining to coupled groundwater flow and glaciation modeling, such a density-dependent (i.e., brine) flow, hydromechanical loading, subglacial infiltration, isostasy, and permafrost development. The surface boundary conditions are specified with the results of a glacial system model. The significant impact of the ice sheet on groundwater flow is evident by increases in the hydraulic head values below the ice sheet by as much as 3000 m down to a depth of 1.5 km into the subsurface. Results also indicate that the groundwater flow system after glaciation did not fully revert to its initial condition and that it is still recovering from the glaciation perturbation. This suggests that the current groundwater flow system cannot be interpreted solely on the basis of present-day boundary conditions and it is likely that several thousands of years of additional equilibration time will be necessary for the system to reach a new quasi-steady state. Finally, we find permafrost to have a large impact on the rate of dissipation of high hydraulic heads that build at depth and capturing its accurate distribution is important to explain the current hydraulic head distribution across the Canadian landscape.

Simulating Thin Sheets: Buckling, Wrinkling, Folding and Growth

NASA Astrophysics Data System (ADS)

Vetter, Roman; Stoop, Norbert; Wittel, Falk K.; Herrmann, Hans J.

2014-03-01

Numerical simulations of thin sheets undergoing large deformations are computationally challenging. Depending on the scenario, they may spontaneously buckle, wrinkle, fold, or crumple. Nature's thin tissues often experience significant anisotropic growth, which can act as the driving force for such instabilities. We use a recently developed finite element model to simulate the rich variety of nonlinear responses of Kirchhoff-Love sheets. The model uses subdivision surface shape functions in order to guarantee convergence of the method, and to allow a finite element description of anisotropically growing sheets in the classical Rayleigh-Ritz formalism. We illustrate the great potential in this approach by simulating the inflation of airbags, the buckling of a stretched cylinder, as well as the formation and scaling of wrinkles at free boundaries of growing sheets. Finally, we compare the folding of spatially confined sheets subject to growth and shrinking confinement to find that the two processes are equivalent.

An open source Bayesian Monte Carlo isotope mixing model with applications in Earth surface processes

NASA Astrophysics Data System (ADS)

Arendt, Carli A.; Aciego, Sarah M.; Hetland, Eric A.

2015-05-01

The implementation of isotopic tracers as constraints on source contributions has become increasingly relevant to understanding Earth surface processes. Interpretation of these isotopic tracers has become more accessible with the development of Bayesian Monte Carlo (BMC) mixing models, which allow uncertainty in mixing end-members and provide methodology for systems with multicomponent mixing. This study presents an open source multiple isotope BMC mixing model that is applicable to Earth surface environments with sources exhibiting distinct end-member isotopic signatures. Our model is first applied to new δ18O and δD measurements from the Athabasca Glacier, which showed expected seasonal melt evolution trends and vigorously assessed the statistical relevance of the resulting fraction estimations. To highlight the broad applicability of our model to a variety of Earth surface environments and relevant isotopic systems, we expand our model to two additional case studies: deriving melt sources from δ18O, δD, and 222Rn measurements of Greenland Ice Sheet bulk water samples and assessing nutrient sources from ɛNd and 87Sr/86Sr measurements of Hawaiian soil cores. The model produces results for the Greenland Ice Sheet and Hawaiian soil data sets that are consistent with the originally published fractional contribution estimates. The advantage of this method is that it quantifies the error induced by variability in the end-member compositions, unrealized by the models previously applied to the above case studies. Results from all three case studies demonstrate the broad applicability of this statistical BMC isotopic mixing model for estimating source contribution fractions in a variety of Earth surface systems.

Fact Sheet: Environmental Pathway Models-Ground-Water Modeling in Support of Remedial Decision Making at Sites Contaminated with Radioactive Material

EPA Pesticide Factsheets

This fact sheet was designed to be used by technical staff responsible for identifying and implementing flow and transport models to support cleanup decisions at hazardous and radioactive waste sites.

Fact Sheet: Documenting Ground-Water Models Selection at Site Contaminated with Radioactive Substance

EPA Pesticide Factsheets

This fact sheet summarizes the report by a joint Interagency Environmental Pathway Modeling Working Group. It was designed to be used by technical staff responsible for identifying and implementing flow and transport models to support cleanup decisions.

An approach to computing discrete adjoints for MPI-parallelized models applied to Ice Sheet System Model 4.11

NASA Astrophysics Data System (ADS)

Larour, Eric; Utke, Jean; Bovin, Anton; Morlighem, Mathieu; Perez, Gilberto

2016-11-01

Within the framework of sea-level rise projections, there is a strong need for hindcast validation of the evolution of polar ice sheets in a way that tightly matches observational records (from radar, gravity, and altimetry observations mainly). However, the computational requirements for making hindcast reconstructions possible are severe and rely mainly on the evaluation of the adjoint state of transient ice-flow models. Here, we look at the computation of adjoints in the context of the NASA/JPL/UCI Ice Sheet System Model (ISSM), written in C++ and designed for parallel execution with MPI. We present the adaptations required in the way the software is designed and written, but also generic adaptations in the tools facilitating the adjoint computations. We concentrate on the use of operator overloading coupled with the AdjoinableMPI library to achieve the adjoint computation of the ISSM. We present a comprehensive approach to (1) carry out type changing through the ISSM, hence facilitating operator overloading, (2) bind to external solvers such as MUMPS and GSL-LU, and (3) handle MPI-based parallelism to scale the capability. We demonstrate the success of the approach by computing sensitivities of hindcast metrics such as the misfit to observed records of surface altimetry on the northeastern Greenland Ice Stream, or the misfit to observed records of surface velocities on Upernavik Glacier, central West Greenland. We also provide metrics for the scalability of the approach, and the expected performance. This approach has the potential to enable a new generation of hindcast-validated projections that make full use of the wealth of datasets currently being collected, or already collected, in Greenland and Antarctica.

An Approach to Computing Discrete Adjoints for MPI-Parallelized Models Applied to the Ice Sheet System Model}

NASA Astrophysics Data System (ADS)

Perez, G. L.; Larour, E. Y.; Morlighem, M.

2016-12-01

Within the framework of sea-level rise projections, there is a strong need for hindcast validation of the evolution of polar ice sheets in a way that tightly matches observational records (from radar and altimetry observations mainly). However, the computational requirements for making hindcast reconstructions possible are severe and rely mainly on the evaluation of the adjoint state of transient ice-flow models. Here, we look at the computation of adjoints in the context of the NASA/JPL/UCI Ice Sheet System Model, written in C++ and designed for parallel execution with MPI. We present the adaptations required in the way the software is designed and written but also generic adaptations in the tools facilitating the adjoint computations. We concentrate on the use of operator overloading coupled with the AdjoinableMPI library to achieve the adjoint computation of ISSM. We present a comprehensive approach to 1) carry out type changing through ISSM, hence facilitating operator overloading, 2) bind to external solvers such as MUMPS and GSL-LU and 3) handle MPI-based parallelism to scale the capability. We demonstrate the success of the approach by computing sensitivities of hindcast metrics such as the misfit to observed records of surface altimetry on the North-East Greenland Ice Stream, or the misfit to observed records of surface velocities on Upernavik Glacier, Central West Greenland. We also provide metrics for the scalability of the approach, and the expected performance. This approach has the potential of enabling a new generation of hindcast-validated projections that make full use of the wealth of datasets currently being collected, or alreay collected in Greenland and Antarctica, such as surface altimetry, surface velocities, and/or gravity measurements.

Structure, burial history, and petroleum potential of frontal thrust belt and adjacent foreland, southwest Montana.

USGS Publications Warehouse

Perry, W.J.; Wardlaw, B.R.; Bostick, N.H.; Maughan, E.K.

1983-01-01

The frontal thrust belt in the Lima area of SW Montana consists of blind (nonsurfacing) thrusts of the Lima thrust system beneath the Lima anticline and the Tendoy thrust sheet to the W. The Tendoy sheet involves Mississippian through Cretaceous rocks of the SW-plunging nose of the Mesozoic Blacktail-Snowcrest uplift that are thrust higher (NE) onto the uplift. The front of the Tendoy sheet W of Lima locally has been warped by later compressive deformation which also involved synorogenic conglomerates of the structurally underlying Beaverhead Formation. To the N, recent extension faulting locally has dropped the front of the Tendoy sheet beneath Quaternary gravels. Rocks of the exposed Tendoy sheet have never been deeply buried, based on vitrinite relectance of = or <0.6%, conodont CAI (color alteration index) values that are uniformly 1, and on supporting organic geochemical data from Paleozoic rocks from the Tendoy thrust sheet. Directly above and W of the Tendoy sheet lie formerly more deeply buried rocks of the Medicine Lodge thrust system. Their greater burial depth is indicated by higher conodont CAI values. W-dipping post-Paleocene extension faults truncate much of the rear part of the Tendoy sheet and also separate the Medicine Lodge sheet from thrust sheets of the Beaverhead Range still farther W. -from Authors

Active control: an investigation method for combustion instabilities

NASA Astrophysics Data System (ADS)

Poinsot, T.; Yip, B.; Veynante, D.; Trouvé, A.; Samaniego, J. M.; Candel, S.

1992-07-01

Closed-loop active control methods and their application to combustion instabilities are discussed. In these methods the instability development is impeded with a feedback control loop: the signal provided by a sensor monitoring the flame or pressure oscillations is processed and sent back to actuators mounted on the combustor or on the feeding system. Different active control systems tested on a non-premixed multiple-flame turbulent combustor are described. These systems can suppress all unstable plane modes of oscillation (i.e. low frequency modes). The active instability control (AIC) also constitutes an original and powerful technique for studies of mechanisms leading to instability or resulting from the instability. Two basic applications of this kind are described. In the first case the flame is initially controlled with AIC, the feedback loop is then switched off and the growth of the instability is analysed through high speed Schlieren cinematography and simultaneous sound pressure and reaction rate measurements. Three phases are identified during th growth of the oscillations: (1) a linear phase where acoustic waves induce a flapping motion of the flame sheets without interaction between sheets, (2) a modulation phase, where flame sheets interact randomly and (3) a nonlinear phase where the flame sheets are broken and a limit cycle is reached. In the second case we investigate different types of flame extinctions associated with combustion instability. It is shown that pressure oscillations may lead to partial or total extinctions. Extinctions occur in various forms but usually follow a rapid growth of pressure oscillations. The flame is extinguished during the modulation phase observed in the initiation experiments. In these studies devoted to transient instability phenomena, the control system constitutes a unique investigation tool because it is difficult to obtain the same information by other means. Implications for modelling and prediction of combustion instabilities are discussed.

Development of oil canning index model for sheet metal forming products with large curvature

NASA Astrophysics Data System (ADS)

Kim, Honglae; Lee, Seonggi; Murugesan, Mohanraj; Hong, Seokmoo; Lee, Shanghun; Ki, Juncheol; Jung, Hunchul; Kim, Naksoo

2017-09-01

Oil canning is predominantly caused by unequal stretches and heterogeneous stress distributions in steel sheets, which affects the appearance of components and develop noise and vibration problems. This paper proposes the formulation of an Oil canning index (OCI) model that can predict the occurrence of oil canning in the sheet metal. To investigate the influence of material properties, we used electro-galvanized (EGI) and galvanized (GI) steel sheets with different thicknesses and processing conditions. Furthermore, this paper presents an appropriate experimental and numerical procedure for determining the sheet stiffness and indentation properties to evaluate the oil canning results. Experiments were carried out by varying the tensile force over different materials, thicknesses, and bead force. Comparison of the discrete results obtained from these experiments confirmed that the product shape characteristics, such as curvature, have a significant influence on the oil canning occurrence. Based on the results, we propose the new OCI model, which can effectively predict the oil canning occurrence owing to the shape curvature. Verification of the accuracy and usability of our model has been carried out by simulating the experiments that were done with the sheet metal. The authors observed a good agreement between the experimental and numerical results from the model. This research work can be considered as a very effective method for eliminating appearance defects from the automobile products.

Modelling heat conduction in polycrystalline hexagonal boron-nitride films

PubMed Central

Mortazavi, Bohayra; Pereira, Luiz Felipe C.; Jiang, Jin-Wu; Rabczuk, Timon

2015-01-01

We conducted extensive molecular dynamics simulations to investigate the thermal conductivity of polycrystalline hexagonal boron-nitride (h-BN) films. To this aim, we constructed large atomistic models of polycrystalline h-BN sheets with random and uniform grain configuration. By performing equilibrium molecular dynamics (EMD) simulations, we investigated the influence of the average grain size on the thermal conductivity of polycrystalline h-BN films at various temperatures. Using the EMD results, we constructed finite element models of polycrystalline h-BN sheets to probe the thermal conductivity of samples with larger grain sizes. Our multiscale investigations not only provide a general viewpoint regarding the heat conduction in h-BN films but also propose that polycrystalline h-BN sheets present high thermal conductivity comparable to monocrystalline sheets. PMID:26286820

Low cost light-sheet microscopy for whole brain imaging

NASA Astrophysics Data System (ADS)

Kumar, Manish; Nasenbeny, Jordan; Kozorovitskiy, Yevgenia

2018-02-01

Light-sheet microscopy has evolved as an indispensable tool in imaging biological samples. It can image 3D samples at fast speed, with high-resolution optical sectioning, and with reduced photobleaching effects. These properties make light-sheet microscopy ideal for imaging fluorophores in a variety of biological samples and organisms, e.g. zebrafish, drosophila, cleared mouse brains, etc. While most commercial turnkey light-sheet systems are expensive, the existing lower cost implementations, e.g. OpenSPIM, are focused on achieving high-resolution imaging of small samples or organisms like zebrafish. In this work, we substantially reduce the cost of light-sheet microscope system while targeting to image much larger samples, i.e. cleared mouse brains, at single-cell resolution. The expensive components of a lightsheet system - excitation laser, water-immersion objectives, and translation stage - are replaced with an incoherent laser diode, dry objectives, and a custom-built Arduino-controlled translation stage. A low-cost CUBIC protocol is used to clear fixed mouse brain samples. The open-source platforms of μManager and Fiji support image acquisition, processing, and visualization. Our system can easily be extended to multi-color light-sheet microscopy.

SPED light sheet microscopy: fast mapping of biological system structure and function

PubMed Central

Tomer, Raju; Lovett-Barron, Matthew; Kauvar, Isaac; Andalman, Aaron; Burns, Vanessa M.; Sankaran, Sethuraman; Grosenick, Logan; Broxton, Michael; Yang, Samuel; Deisseroth, Karl

2016-01-01

The goal of understanding living nervous systems has driven interest in high-speed and large field-of-view volumetric imaging at cellular resolution. Light-sheet microscopy approaches have emerged for cellular-resolution functional brain imaging in small organisms such as larval zebrafish, but remain fundamentally limited in speed. Here we have developed SPED light sheet microscopy, which combines large volumetric field-of-view via an extended depth of field with the optical sectioning of light sheet microscopy, thereby eliminating the need to physically scan detection objectives for volumetric imaging. SPED enables scanning of thousands of volumes-per-second, limited only by camera acquisition rate, through the harnessing of optical mechanisms that normally result in unwanted spherical aberrations. We demonstrate capabilities of SPED microscopy by performing fast sub-cellular resolution imaging of CLARITY mouse brains and cellular-resolution volumetric Ca2+ imaging of entire zebrafish nervous systems. Together, SPED light sheet methods enable high-speed cellular-resolution volumetric mapping of biological system structure and function. PMID:26687363

Wind and Water Power Fact Sheets | Wind | NREL

Science.gov Websites

Advanced Control Turbine Systems to Increase Performance, Decrease Structural Loading of Wind Turbines and and Water Power Fact Sheets Wind and Water Power Fact Sheets The capabilities for research at the National Wind Technology Center (NWTC) are numerous. Below you will find fact sheets about the many

Balance Mass Flux and Velocity Across the Equilibrium Line in Ice Drainage Systems of Greenland

NASA Technical Reports Server (NTRS)

Zwally, H. Jay; Giovinetto, Mario B.; Koblinsky, Chester J. (Technical Monitor)

2001-01-01

Estimates of balance mass flux and the depth-averaged ice velocity through the cross-section aligned with the equilibrium line are produced for each of six drainage systems in Greenland. (The equilibrium line, which lies at approximately 1200 m elevation on the ice sheet, is the boundary between the area of net snow accumulation at higher elevations and the areas of net melting at lower elevations around the ice sheet.) Ice drainage divides and six major drainage systems are delineated using surface topography from ERS (European Remote Sensing) radar altimeter data. The net accumulation rate in the accumulation zone bounded by the equilibrium line is 399 Gt/yr and net ablation rate in the remaining area is 231 Gt/yr. (1 GigaTon of ice is 1090 kM(exp 3). The mean balance mass flux and depth-averaged ice velocity at the cross-section aligned with the modeled equilibrium line are 0.1011 Gt kM(exp -2)/yr and 0.111 km/yr, respectively, with little variation in these values from system to system. The ratio of the ice mass above the equilibrium line to the rate of mass output implies an effective exchange time of approximately 6000 years for total mass exchange. The range of exchange times, from a low of 3 ka in the SE drainage system to 14 ka in the NE, suggests a rank as to which regions of the ice sheet may respond more rapidly to climate fluctuations.

Finite Element Modeling of the Buckling Response of Sandwich Panels

NASA Technical Reports Server (NTRS)

Rose, Cheryl A.; Moore, David F.; Knight, Norman F., Jr.; Rankin, Charles C.

2002-01-01

A comparative study of different modeling approaches for predicting sandwich panel buckling response is described. The study considers sandwich panels with anisotropic face sheets and a very thick core. Results from conventional analytical solutions for sandwich panel overall buckling and face-sheet-wrinkling type modes are compared with solutions obtained using different finite element modeling approaches. Finite element solutions are obtained using layered shell element models, with and without transverse shear flexibility, layered shell/solid element models, with shell elements for the face sheets and solid elements for the core, and sandwich models using a recently developed specialty sandwich element. Convergence characteristics of the shell/solid and sandwich element modeling approaches with respect to in-plane and through-the-thickness discretization, are demonstrated. Results of the study indicate that the specialty sandwich element provides an accurate and effective modeling approach for predicting both overall and localized sandwich panel buckling response. Furthermore, results indicate that anisotropy of the face sheets, along with the ratio of principle elastic moduli, affect the buckling response and these effects may not be represented accurately by analytical solutions. Modeling recommendations are also provided.

Sensitivity of Totten Glacier Ice Shelf extent and grounding line to oceanic forcing

NASA Astrophysics Data System (ADS)

Pelle, T.; Morlighem, M.; Choi, Y.

2017-12-01

Totten Glacier is a major outlet glacier of the East Antarctic Ice Sheet and has been shown to be vulnerable to ocean-induced melt in both its past and present states. The intrusion of warm, circumpolar deep water beneath the Totten Glacier Ice Shelf (TGIS) has been observed to accelerate ice shelf thinning and promote iceberg calving, a primary mechanism of mass discharge from Totten. As such, accurately simulating TGIS's ice front dynamics is crucial to the predictive capabilities of ice sheet models in this region. Here, we study the TGIS using the Ice Sheet System Model (ISSM) and test the applicability of three calving laws: Crevasse Formation calving, Eigen calving, and Tensile Stress calving. We simulate the evolution of Totten Glacier through 2100 under enhanced oceanic forcing in order to investigate both future changes in ice front dynamics and possible thresholds of instability. In addition, we artificially retreat Totten's ice front position and allow the model to proceed dynamically in order to analyze the response of the glacier to calving events. Our analyses show that Tensile Stress calving most accurately reproduces Totten Glacier's observed ice front position. Furthermore, unstable grounding line retreat is projected when Totten is simulated under stronger oceanic thermal forcing scenarios and when the calving front is significantly retreated.

Shape Transformations of Epithelial Shells

PubMed Central

Misra, Mahim; Audoly, Basile; Kevrekidis, Ioannis G.; Shvartsman, Stanislav Y.

2016-01-01

Regulated deformations of epithelial sheets are frequently foreshadowed by patterning of their mechanical properties. The connection between patterns of cell properties and the emerging tissue deformations is studied in multiple experimental systems, but the general principles remain poorly understood. For instance, it is in general unclear what determines the direction in which the patterned sheet is going to bend and whether the resulting shape transformation will be discontinuous or smooth. Here these questions are explored computationally, using vertex models of epithelial shells assembled from prismlike cells. In response to rings and patches of apical cell contractility, model epithelia smoothly deform into invaginated or evaginated shapes similar to those observed in embryos and tissue organoids. Most of the observed effects can be captured by a simpler model with polygonal cells, modified to include the effects of the apicobasal polarity and natural curvature of epithelia. Our models can be readily extended to include the effects of multiple constraints and used to describe a wide range of morphogenetic processes. PMID:27074691

Modeling MHD Stagnation Point Flow of Thixotropic Fluid with Non-uniform Heat Absorption/Generation

NASA Astrophysics Data System (ADS)

Hayat, Tasawar; Shah, Faisal; Khan, Muhammad Ijaz; Alsaedi, Ahmed; Yasmeen, Tabassum

2017-12-01

Here magnetohydrodynamic (MHD) stagnation point flow by nonlinear stretching sheet is discussed. Variable thickness of sheet is accounted. In addition non-uniform heat generation/absorption concept is retained. Numerical treatment to arising nonlinear system is presented. Shooting procedure is adopted for numerical treatment. Graphs and tables lead to physical description of results. It is observed that skin friction enhances for ( H a) and it decays for different rising values of ( K 1), ( K 2) and ( n). Further temperature gradient increases for higher estimation of (Pr) and decreases for larger ( H a). Major findings of present analysis are presented.

Remotely-sensed and in-situ observations of Greenland firn aquifers

NASA Astrophysics Data System (ADS)

Forster, R. R.; Miège, C.; Koenig, L.; Solomon, D. K.; Schmerr, N. C.; Miller, O. L.; Ligtenberg, S.; Montgomery, L. N.; Brucker, L.; Miller, J.; Legchenko, A.

2017-12-01

In 2011, prior to seasonal melt, our research team drilled into an unknown firn aquifer system in Southeast Greenland. Since 2013, we have conducted four field seasons, complemented with modeling and remote sensing to gain knowledge regarding firn aquifers and surrounding snow/firn/ice. We aim to provide a more complete picture of the system including formation conditions, controlling mechanisms, spatial and temporal changes, and connections with the larger ice sheet hydrologic system. This work summarizes remote sensing data since 1993 showing the spatial and temporal evolution of the aquifer extent. To complement the remote sensing and better characterize the firn aquifer in the field, we use a combination of three different geophysics methods. Ground penetrating radar provides us knowledge of the water table elevation and its variations, magnetic-resonance soundings give us the water volume held in the aquifer and the active seismic data allow us to locate the bottom of the aquifer. In addition, firn/ice-core stratigraphy suggests that the timing and evolution of the aquifer bottom is controlled by thermodynamics. Our compilation of remote sensing measurements point to a dynamic and expanding aquifer system. We found that firn aquifers have existed at least since 1993 (dataset start) in the high melt and high accumulation region of the South Eastern Greenland ice sheet. Firn aquifers are now growing toward the interior related to the warming air temperatures in the Arctic and more intense melt during summers. These remotely sensed observations and in-situ measurements are required to validate improved ice sheet mass balance models that incorporate firn aquifers. They are also needed to further investigate the potential of firn aquifer discharge to the glacier bed via crevasse hydrofracturing influencing ice dynamics.

Topical Application of a Silicone Gel Sheet with Verapamil Microparticles in a Rabbit Model of Hypertrophic Scar.

PubMed

Rha, Eun Young; Kim, Yun Ho; Kim, Tae-Jung; Yoo, Gyeol; Rhie, Jong Won; Kim, Hyun-Jung; Park, Il-Kyu

2016-01-01

The authors developed a novel treatment based on the topical application of a silicone gel sheet containing verapamil microparticles. The ability of these silicone gel sheets to inhibit hypertrophic scar in a rabbit ear wound model was examined. Ten New Zealand White rabbits with a total of 80 wounds in both ears were used in this study. The rabbits were divided into five groups (control; silicone gel sheet; and silicone gel sheet plus 0.25, 2.5, and 25 mg of verapamil per gram). Histopathologic findings were quantified. The mean scar elevation index, fibroblast counts, and capillary counts differed significantly among the five groups (p < 0.05). The median scar elevation index was significantly lower in the silicone gel sheet plus 2.5 mg of verapamil per gram group than in the silicone gel sheet group (1.2 versus 2.2). The median number of fibroblasts was significantly lower in the silicone gel sheet plus 0.25 mg of verapamil per gram group than in the silicone gel sheet group (172.5 versus 243). In the median number of capillary lumina, there was no significant difference between the silicone gel sheet group and the silicone gel sheet plus 0.25, 2.5, and 25 mg of verapamil per gram groups (28.5, 18, 20, and 18, respectively). Topical application of a silicone gel sheet with verapamil microparticles may be a novel, effective treatment method for hypertrophic scar, but its safety and efficacy in humans must be tested in clinical trials.

Note: Experimental observation of nano-channel pattern in light sheet laser interference nanolithography system

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mohan, Kavya; Mondal, Partha Pratim, E-mail: partha@iap.iisc.ernet.in

We experimentally observed nano-channel-like pattern in a light-sheet based interference nanolithography system. The optical system created nano-channel-like patterned illumination. Coherent counter-propagating light sheets are made to interfere at and near geometrical focus along the propagation z-axis. This results in the formation of nano-channel-like pattern (of size ≈ 300 nm and inter-channel periodicity of ≈337.5 nm) inside the sample due to constructive and destructive interference. In addition, the technique has the ability to generate large area patterning using larger light-sheets. Exciting applications are in the broad field of nanotechnology (nano-electronics and nano-fluidics).

Unsteady aerodynamics and vortex-sheet formation of a two-dimensional airfoil

NASA Astrophysics Data System (ADS)

Xia, X.; Mohseni, K.

2017-11-01

Unsteady inviscid flow models of wings and airfoils have been developed to study the aerodynamics of natural and man-made flyers. Vortex methods have been extensively applied to reduce the dimensionality of these aerodynamic models, based on the proper estimation of the strength and distribution of the vortices in the wake. In such modeling approaches, one of the most fundamental questions is how the vortex sheets are generated and released from sharp edges. To determine the formation of the trailing-edge vortex sheet, the classical Kutta condition can be extended to unsteady situations by realizing that a flow cannot turn abruptly around a sharp edge. This condition can be readily applied to a flat plate or an airfoil with cusped trailing edge since the direction of the forming vortex sheet is known to be tangential to the trailing edge. However, for a finite-angle trailing edge, or in the case of flow separation away from a sharp corner, the direction of the forming vortex sheet is ambiguous. To remove any ad-hoc implementation, the unsteady Kutta condition, the conservation of circulation, as well as the conservation laws of mass and momentum are coupled to analytically solve for the angle, strength, and relative velocity of the trailing-edge vortex sheet. The two-dimensional aerodynamic model together with the proposed vortex-sheet formation condition is verified by comparing flow structures and force calculations with experimental results for airfoils in steady and unsteady background flows.

Two-Dimensional Analysis of Conical Pulsed Inductive Plasma Thruster Performance

NASA Technical Reports Server (NTRS)

Hallock, A. K.; Polzin, K. A.; Emsellem, G. D.

2011-01-01

A model of the maximum achievable exhaust velocity of a conical theta pinch pulsed inductive thruster is presented. A semi-empirical formula relating coil inductance to both axial and radial current sheet location is developed and incorporated into a circuit model coupled to a momentum equation to evaluate the effect of coil geometry on the axial directed kinetic energy of the exhaust. Inductance measurements as a function of the axial and radial displacement of simulated current sheets from four coils of different geometries are t to a two-dimensional expression to allow the calculation of the Lorentz force at any relevant averaged current sheet location. This relation for two-dimensional inductance, along with an estimate of the maximum possible change in gas-dynamic pressure as the current sheet accelerates into downstream propellant, enables the expansion of a one-dimensional circuit model to two dimensions. The results of this two-dimensional model indicate that radial current sheet motion acts to rapidly decouple the current sheet from the driving coil, leading to losses in axial kinetic energy 10-50 times larger than estimations of the maximum available energy in the compressed propellant. The decreased available energy in the compressed propellant as compared to that of other inductive plasma propulsion concepts suggests that a recovery in the directed axial kinetic energy of the exhaust is unlikely, and that radial compression of the current sheet leads to a loss in exhaust velocity for the operating conditions considered here.

Planetary period modulations of Saturn's magnetotail current sheet during northern spring: Observations and modeling

NASA Astrophysics Data System (ADS)

Cowley, S. W. H.; Provan, G.

2017-06-01

We study Cassini magnetic field observations at Saturn on a sequence of passes through the near-equatorial magnetotail during 2015, focusing on dual modulation of the plasma/current sheet associated with northern and southern planetary period oscillations (PPOs). Previous study of inner magnetosphere PPOs during this northern spring interval showed that the southern system amplitude was generally half that of the northern during the first part of the year to late August, after which the southern amplitude weakened to less than one-fifth that of the northern. We examine four sequential tail passes in the earlier interval, during which prominent PPO-related tail field modulations were observed, with relative (beat) phases of the two PPO systems being near in phase, antiphase, and two opposite near-quadrature conditions. We find that the radial field displayed opposite "sawtooth" asymmetry modulations under opposite near-quadrature conditions, related to previous findings under equinoctial conditions with near-equal northern and southern PPO amplitudes, while modulations were near symmetric for in-phase and antiphase conditions, but with larger radial field modulations for in-phase and larger colatitudinal field modulations for antiphase. A simple physical mathematical model of dual modulation is developed, which provides reasonable correspondence with these data using one set of current sheet parameters while varying only the relative PPO phases, thus demonstrating that dual modulation can be discerned and modeled even when the northern and southern amplitudes differ by a factor of 2. No such effects were consistently discerned during the later interval when the amplitude ratio was >5.

Plasma Sheet Injections into the Inner Magnetosphere: Two-way Coupled OpenGGCM-RCM model results

NASA Astrophysics Data System (ADS)

Raeder, J.; Cramer, W. D.; Toffoletto, F.; Gilson, M. L.; Hu, B.

2017-12-01

Plasma sheet injections associated with low flux tube entropy bubbles have been found to be the primary means of mass transport from the plasma sheet to the inner magnetosphere. A two-way coupled global magnetosphere-ring current model, where the magnetosphere is modeled by the OpenGGCM MHD model and the ring current is modeled by the Rice Convection Model (RCM), is used to determine the frequency of association of bubbles with injections and inward plasma transport, as well as typical injection characteristics. Multiple geomagnetic storms and quiet periods are simulated to track and characterize inward flow behavior. Dependence on geomagnetic activity levels or drivers is also examined.

Implementation of virtual models from sheet metal forming simulation into physical 3D colour models using 3D printing

NASA Astrophysics Data System (ADS)

Junk, S.

2016-08-01

Today the methods of numerical simulation of sheet metal forming offer a great diversity of possibilities for optimization in product development and in process design. However, the results from simulation are only available as virtual models. Because there are any forming tools available during the early stages of product development, physical models that could serve to represent the virtual results are therefore lacking. Physical 3D-models can be created using 3D-printing and serve as an illustration and present a better understanding of the simulation results. In this way, the results from the simulation can be made more “comprehensible” within a development team. This paper presents the possibilities of 3D-colour printing with particular consideration of the requirements regarding the implementation of sheet metal forming simulation. Using concrete examples of sheet metal forming, the manufacturing of 3D colour models will be expounded upon on the basis of simulation results.

The multi-millennial Antarctic commitment to future sea-level rise

NASA Astrophysics Data System (ADS)

Golledge, N. R.; Kowalewski, D. E.; Naish, T. R.; Levy, R. H.; Fogwill, C. J.; Gasson, E. G. W.

2015-10-01

Atmospheric warming is projected to increase global mean surface temperatures by 0.3 to 4.8 degrees Celsius above pre-industrial values by the end of this century. If anthropogenic emissions continue unchecked, the warming increase may reach 8-10 degrees Celsius by 2300 (ref. 2). The contribution that large ice sheets will make to sea-level rise under such warming scenarios is difficult to quantify because the equilibrium-response timescale of ice sheets is longer than those of the atmosphere or ocean. Here we use a coupled ice-sheet/ice-shelf model to show that if atmospheric warming exceeds 1.5 to 2 degrees Celsius above present, collapse of the major Antarctic ice shelves triggers a centennial- to millennial-scale response of the Antarctic ice sheet in which enhanced viscous flow produces a long-term commitment (an unstoppable contribution) to sea-level rise. Our simulations represent the response of the present-day Antarctic ice-sheet system to the oceanic and climatic changes of four representative concentration pathways (RCPs) from the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. We find that substantial Antarctic ice loss can be prevented only by limiting greenhouse gas emissions to RCP 2.6 levels. Higher-emissions scenarios lead to ice loss from Antarctic that will raise sea level by 0.6-3 metres by the year 2300. Our results imply that greenhouse gas emissions in the next few decades will strongly influence the long-term contribution of the Antarctic ice sheet to global sea level.

The multi-millennial Antarctic commitment to future sea-level rise.

PubMed

Golledge, N R; Kowalewski, D E; Naish, T R; Levy, R H; Fogwill, C J; Gasson, E G W

2015-10-15

Atmospheric warming is projected to increase global mean surface temperatures by 0.3 to 4.8 degrees Celsius above pre-industrial values by the end of this century. If anthropogenic emissions continue unchecked, the warming increase may reach 8-10 degrees Celsius by 2300 (ref. 2). The contribution that large ice sheets will make to sea-level rise under such warming scenarios is difficult to quantify because the equilibrium-response timescale of ice sheets is longer than those of the atmosphere or ocean. Here we use a coupled ice-sheet/ice-shelf model to show that if atmospheric warming exceeds 1.5 to 2 degrees Celsius above present, collapse of the major Antarctic ice shelves triggers a centennial- to millennial-scale response of the Antarctic ice sheet in which enhanced viscous flow produces a long-term commitment (an unstoppable contribution) to sea-level rise. Our simulations represent the response of the present-day Antarctic ice-sheet system to the oceanic and climatic changes of four representative concentration pathways (RCPs) from the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. We find that substantial Antarctic ice loss can be prevented only by limiting greenhouse gas emissions to RCP 2.6 levels. Higher-emissions scenarios lead to ice loss from Antarctic that will raise sea level by 0.6-3 metres by the year 2300. Our results imply that greenhouse gas emissions in the next few decades will strongly influence the long-term contribution of the Antarctic ice sheet to global sea level.

MAGNETAR GIANT FLARES AND THEIR PRECURSORS-FLUX ROPE ERUPTIONS WITH CURRENT SHEETS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yu Cong; Huang Lei, E-mail: cyu@ynao.ac.cn, E-mail: muduri@shao.ac.cn

2013-07-10

We propose a catastrophic magnetospheric model for magnetar precursors and their successive giant flares. Axisymmetric models of the magnetosphere, which contain both a helically twisted flux rope and a current sheet, are established based on force-free field configurations. In this model, the helically twisted flux rope would lose its equilibrium and erupt abruptly in response to the slow and quasi-static variations at the ultra-strongly magnetized neutron star's surface. In a previous model without current sheets, only one critical point exists in the flux rope equilibrium curve. New features show up in the equilibrium curves for the flux rope when currentmore » sheets appear in the magnetosphere. The causal connection between the precursor and the giant flare, as well as the temporary re-entry of the quiescent state between the precursor and the giant flare, can be naturally explained. Magnetic energy would be released during the catastrophic state transitions. The detailed energetics of the model are also discussed. The current sheet created by the catastrophic loss of equilibrium of the flux rope provides an ideal place for magnetic reconnection. We point out the importance of magnetic reconnection for further enhancement of the energy release during eruptions.« less

Relative sea-level rise around East Antarctica during Oligocene glaciation

NASA Astrophysics Data System (ADS)

Stocchi, Paolo; Escutia, Carlota; Houben, Alexander J. P.; Vermeersen, Bert L. A.; Bijl, Peter K.; Brinkhuis, Henk; Deconto, Robert M.; Galeotti, Simone; Passchier, Sandra; Pollard, David; Brinkhuis, Henk; Escutia, Carlota; Klaus, Adam; Fehr, Annick; Williams, Trevor; Bendle, James A. P.; Bijl, Peter K.; Bohaty, Steven M.; Carr, Stephanie A.; Dunbar, Robert B.; Flores, Jose Abel; Gonzàlez, Jhon J.; Hayden, Travis G.; Iwai, Masao; Jimenez-Espejo, Francisco J.; Katsuki, Kota; Kong, Gee Soo; McKay, Robert M.; Nakai, Mutsumi; Olney, Matthew P.; Passchier, Sandra; Pekar, Stephen F.; Pross, Jörg; Riesselman, Christina; Röhl, Ursula; Sakai, Toyosaburo; Shrivastava, Prakash Kumar; Stickley, Catherine E.; Sugisaki, Saiko; Tauxe, Lisa; Tuo, Shouting; van de Flierdt, Tina; Welsh, Kevin; Yamane, Masako

2013-05-01

During the middle and late Eocene (~ 48-34Myr ago), the Earth's climate cooled and an ice sheet built up on Antarctica. The stepwise expansion of ice on Antarctica induced crustal deformation and gravitational perturbations around the continent. Close to the ice sheet, sea level rose despite an overall reduction in the mass of the ocean caused by the transfer of water to the ice sheet. Here we identify the crustal response to ice-sheet growth by forcing a glacial-hydro isostatic adjustment model with an Antarctic ice-sheet model. We find that the shelf areas around East Antarctica first shoaled as upper mantle material upwelled and a peripheral forebulge developed. The inner shelf subsequently subsided as lithosphere flexure extended outwards from the ice-sheet margins. Consequently the coasts experienced a progressive relative sea-level rise. Our analysis of sediment cores from the vicinity of the Antarctic ice sheet are in agreement with the spatial patterns of relative sea-level change indicated by our simulations. Our results are consistent with the suggestion that near-field processes such as local sea-level change influence the equilibrium state obtained by an ice-sheet grounding line.

Computational study of the shock driven instability of a multiphase particle-gas system

DOE Office of Scientific and Technical Information (OSTI.GOV)

None, None

This paper considers the interaction of a shock wave with a multiphase particle-gas system which creates an instability somewhat similar to the Richtmyer-Meshkov instability but with a larger parameter space. Because this parameter space is large, we only present an introductory survey of the effects of many of these parameters. We highlight the effects of particle-gas coupling, incident shock strength, particle size, effective system density differences, and multiple particle relaxation time effects. We focus on dilute flows with mass loading up to 40% and do not attempt to cover all parametric combinations. Instead, we vary one parameter at a timemore » leaving additional parametric combinations for future work. The simulations are run with the Ares code, developed at Lawrence Livermore National Laboratory, which uses a multiphase particulate transport method to model two-way momentum and energy coupling. A brief validation of these models is presented and coupling effects are explored. It is shown that even for small particles, on the order of 1μm, multi-phase coupling effects are important and diminish the circulation deposition on the interface by up to 25%. These coupling effects are shown to create large temperature deviations from the dusty gas approximation, up to 20% greater, especially at higher shock strengths. It is also found that for a multiphase instability, the vortex sheet deposited at the interface separates into two sheets. In conclusion, depending on the particle and particle-gas Atwood numbers, the instability may be suppressed or enhanced by the interactions of these two vortex sheets.« less

Computational study of the shock driven instability of a multiphase particle-gas system

DOE PAGES

None, None

2016-02-01

This paper considers the interaction of a shock wave with a multiphase particle-gas system which creates an instability somewhat similar to the Richtmyer-Meshkov instability but with a larger parameter space. Because this parameter space is large, we only present an introductory survey of the effects of many of these parameters. We highlight the effects of particle-gas coupling, incident shock strength, particle size, effective system density differences, and multiple particle relaxation time effects. We focus on dilute flows with mass loading up to 40% and do not attempt to cover all parametric combinations. Instead, we vary one parameter at a timemore » leaving additional parametric combinations for future work. The simulations are run with the Ares code, developed at Lawrence Livermore National Laboratory, which uses a multiphase particulate transport method to model two-way momentum and energy coupling. A brief validation of these models is presented and coupling effects are explored. It is shown that even for small particles, on the order of 1μm, multi-phase coupling effects are important and diminish the circulation deposition on the interface by up to 25%. These coupling effects are shown to create large temperature deviations from the dusty gas approximation, up to 20% greater, especially at higher shock strengths. It is also found that for a multiphase instability, the vortex sheet deposited at the interface separates into two sheets. In conclusion, depending on the particle and particle-gas Atwood numbers, the instability may be suppressed or enhanced by the interactions of these two vortex sheets.« less

Computational study of the shock driven instability of a multiphase particle-gas system

NASA Astrophysics Data System (ADS)

McFarland, Jacob A.; Black, Wolfgang J.; Dahal, Jeevan; Morgan, Brandon E.

2016-02-01

This paper considers the interaction of a shock wave with a multiphase particle-gas system which creates an instability similar in some ways to the Richtmyer-Meshkov instability but with a larger parameter space. As this parameter space is large, we only present an introductory survey of the effects of many of these parameters. We highlight the effects of particle-gas coupling, incident shock strength, particle size, effective system density differences, and multiple particle relaxation time effects. We focus on dilute flows with mass loading up to 40% and do not attempt to cover all parametric combinations. Instead, we vary one parameter at a time leaving additional parametric combinations for future work. The simulations are run with the Ares code, developed at Lawrence Livermore National Laboratory, which uses a multiphase particulate transport method to model two-way momentum and energy coupling. A brief validation of these models is presented and coupling effects are explored. It is shown that even for small particles, on the order of 1 μm, multi-phase coupling effects are important and diminish the circulation deposition on the interface by up to 25%. These coupling effects are shown to create large temperature deviations from the dusty gas approximation, up to 20% greater, especially at higher shock strengths. It is also found that for a multiphase instability, the vortex sheet deposited at the interface separates into two sheets. Depending on the particle and particle-gas Atwood numbers, the instability may be suppressed or enhanced by the interactions of these two vortex sheets.

Heinrich-type glacial surges in a low-order dynamical climate model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Verbitsky, M.; Saltzman, B.

1994-07-01

Recent studies suggest the occurrence of sporadic episodes during which the ice streams that discharge ice sheets become enormously active, producing large numbers of icebergs (reflected in North Atlantic sea cores as {open_quotes}Heinrich events{close_quotes}) and possibly causing the partial collapse of the ice sheets. To simulate the mechanism of implied internal thermo-hydrodynamical instability in the context of a more general paleoclimate dynamics model (PDM), a new sliding-catastrophe function that can account for ice-sheet surges in terms of the thickness, density, viscosity, heat-capacity. and heat-conductivity of ice is introduced. Analysis suggests these events might be of three possible kinds: the firstmore » occurs in periods of glacial maximum when temperature conditions on the ice surface are extremely cold, but internal friction within bottom boundary layer is also at its maximum and is strong enough to melt ice and cause its surge. The second may happen during an interglacial, when the ice thickness is small but relatively warm climate conditions on the upper surface of ice can be easily advected with the flow of ice to the bottom where even a small additional heating due to friction may cause melting. The third and, perhaps, most interesting type is one that may occur during ice sheet growth: in this period particles of ice reaching the bottom {open_quotes}remember{close_quotes} the warm temperature conditions of the previous interglacial and additional heating due to increasing friction associated with the growing ice sheet may again cause melting. This third introduces the interesting possibility that earlier CO{sub 2} concentrations may be as important for the present-day climate as its current value. According to our model the climate system seems more vulnerable to surges during the penultimate interglacial period than in present one contributing to an explanation of the recent results of the Greenland Ice Core Project. 18 refs., 3 figs., 1 tab.« less

The Antarctic Ice Sheet during the last Interglaciation: Insights from my Thesis

NASA Astrophysics Data System (ADS)

Whipple, Matthew; Lunt, Dan; Singarayer, Joy; Bradley, Sarah; Milne, Glenn; Wolff, Eric; Siddall, Mark

2015-04-01

The last interglaciation represents a period of warmer climates and higher sea levels, and a useful analogue to future climate. While many studies have focussed on the response of the Greenland Ice sheet, far less is known about the response of the Antarctic ice sheet. Here, I present the summarised results of my PhD thesis "Constraints on the minimum extent of the Antarctic ice sheet during the last interglaciation". Firstly, I cover the timings of interglaciation in Antarctica, and their differences with respect to the Northern Hemisphere timings, based on paleo sea level indicators, and oceanic temperature records. I move on to cover climate forcings, and how they influence the ice sheet, relative to present, and early Holocene. Secondly, I present thesis results, from looking at ice core stable water isotopes. These are compared with Isostatic and Climatic modelling results, for various different Ice sheet scenarios, as to the resulting Climate, from changes in Elevation, Temperature, Precipitation, and Sublimation, all contributing to the recorded stable water isotope record. Thirdly, I move on to looking at the mid-field relative sea level records, from Australia and Argentina. Using isostatic modelling, these are used to assess the relative contribution of the Eastern and Western Antarctic Ice sheets. Although data uncertainties result in us being to identify the contribution from West Antarctica. Overall, using model-data comparison, we find a lack of evidence for a substantial retreat of the Wilkes Subglacial basin. No data location is close enough to determine the existence of the marine based West Antarctic Ice sheet. Model uncertainty is unable to constrain evidence of variations in ice thickness in East Antarctica.

Why Europa's icy shell may convect, but ice sheets do not: a glaciological perspective

NASA Astrophysics Data System (ADS)

Bassis, J. N.

2016-12-01

Jupiter's moon Europa is covered in an icy shell that lies over a liquid ocean. Geological evidence and numerical models suggest that Europa's icy shell convects, providing the possibility that Europa may experience a form of plate tectonics and could even harbor life in its subsurface ocean. The hypothesis that Europa convects is supported by both models and geological evidence. Surprisingly, when we apply similar calculations and (assumptions) used by planetary scientists to infer convection in icy moons like Europa we find that these models also predict that vigorous convection should also occur in portions of our own terrestrial ice sheets and ice shelves where we have firm evidence to the contrary. We can explain the lack of convection within our own ice sheets by recognizing that instead of the diffusion creep limited rheology frequently invoked by planetary scientists, terrestrial ice undergoes power-law creep down to very low strain rates. Glaciological studies find that power-law creep is required to explain the structure of vertical strain rate near ice sheet divides and shape of the ice sheets near an ice divide. However, when we now apply a rheology that is consistent with terrestrial ice sheet dynamics to icy moon conditions, we find conditions are far less favorable for convection in icy moons, with only a very limited parameter regime where convection can occur. Given the many unknowns (grain size, impurities etc.) it is challenging to draw strong conclusions about the behavior of icy moons . Nonetheless, the lack of convection in terrestrial ice sheets provides an important constraint on the dynamics of icy moons and models that explain convection of icy moons should also explain the lack of convection on terrestrial ice sheets.

Surface water hydrology and the Greenland Ice Sheet

NASA Astrophysics Data System (ADS)

Smith, L. C.; Yang, K.; Pitcher, L. H.; Overstreet, B. T.; Chu, V. W.; Rennermalm, A. K.; Cooper, M. G.; Gleason, C. J.; Ryan, J.; Hubbard, A.; Tedesco, M.; Behar, A.

2016-12-01

Mass loss from the Greenland Ice Sheet now exceeds 260 Gt/year, raising global sea level by >0.7 mm annually. Approximately two-thirds of this total mass loss is now driven by negative ice sheet surface mass balance (SMB), attributed mainly to production and runoff of meltwater from the ice sheet surface. This new dominance of runoff as a driver of GrIS total mass loss will likely persist owing to anticipated further increases in surface melting, reduced meltwater storage in firn, and the waning importance of dynamical mass losses (ice calving) as the ice sheets retreat from their marine-terminating margins. It also creates the need and opportunity for integrative research pairing traditional surface water hydrology approaches with glaciology. As one example, we present a way to measure supraglacial "runoff" (i.e. specific discharge) at the supraglacial catchment scale ( 101-102 km2), using in situ measurements of supraglacial river discharge and high-resolution satellite/drone mapping of upstream catchment area. This approach, which is standard in terrestrial hydrology but novel for ice sheet science, enables independent verification and improvement of modeled SMB runoff estimates used to project sea level rise. Furthermore, because current SMB models do not consider the role of fluvial watershed processes operating on the ice surface, inclusion of even a simple surface routing model materially improves simulations of runoff delivered to moulins, the critical pathways for meltwater entry into the ice sheet. Incorporating principles of surface water hydrology and fluvial geomorphology and into glaciological models will thus aid estimates of Greenland meltwater runoff to the global ocean as well as connections to subglacial hydrology and ice sheet dynamics.

Projecting Antarctic ice discharge using response functions from SeaRISE ice-sheet models

NASA Astrophysics Data System (ADS)

Levermann, A.; Winkelmann, R.; Nowicki, S.; Fastook, J. L.; Frieler, K.; Greve, R.; Hellmer, H. H.; Martin, M. A.; Meinshausen, M.; Mengel, M.; Payne, A. J.; Pollard, D.; Sato, T.; Timmermann, R.; Wang, W. L.; Bindschadler, R. A.

2014-08-01

The largest uncertainty in projections of future sea-level change results from the potentially changing dynamical ice discharge from Antarctica. Basal ice-shelf melting induced by a warming ocean has been identified as a major cause for additional ice flow across the grounding line. Here we attempt to estimate the uncertainty range of future ice discharge from Antarctica by combining uncertainty in the climatic forcing, the oceanic response and the ice-sheet model response. The uncertainty in the global mean temperature increase is obtained from historically constrained emulations with the MAGICC-6.0 (Model for the Assessment of Greenhouse gas Induced Climate Change) model. The oceanic forcing is derived from scaling of the subsurface with the atmospheric warming from 19 comprehensive climate models of the Coupled Model Intercomparison Project (CMIP-5) and two ocean models from the EU-project Ice2Sea. The dynamic ice-sheet response is derived from linear response functions for basal ice-shelf melting for four different Antarctic drainage regions using experiments from the Sea-level Response to Ice Sheet Evolution (SeaRISE) intercomparison project with five different Antarctic ice-sheet models. The resulting uncertainty range for the historic Antarctic contribution to global sea-level rise from 1992 to 2011 agrees with the observed contribution for this period if we use the three ice-sheet models with an explicit representation of ice-shelf dynamics and account for the time-delayed warming of the oceanic subsurface compared to the surface air temperature. The median of the additional ice loss for the 21st century is computed to 0.07 m (66% range: 0.02-0.14 m; 90% range: 0.0-0.23 m) of global sea-level equivalent for the low-emission RCP-2.6 (Representative Concentration Pathway) scenario and 0.09 m (66% range: 0.04-0.21 m; 90% range: 0.01-0.37 m) for the strongest RCP-8.5. Assuming no time delay between the atmospheric warming and the oceanic subsurface, these values increase to 0.09 m (66% range: 0.04-0.17 m; 90% range: 0.02-0.25 m) for RCP-2.6 and 0.15 m (66% range: 0.07-0.28 m; 90% range: 0.04-0.43 m) for RCP-8.5. All probability distributions are highly skewed towards high values. The applied ice-sheet models are coarse resolution with limitations in the representation of grounding-line motion. Within the constraints of the applied methods, the uncertainty induced from different ice-sheet models is smaller than that induced by the external forcing to the ice sheets.

Numerical study of a Vlasov equation for systems with interacting particles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Herrera, Dianela; Curilef, Sergio

2015-03-10

We solve numerically the Vlasov equation for the self-gravitating sheet model. We used the method introduced by Cheng and Knorr [Comput Phys 22, 330-351 (1976)]. We discuss the quasi-stationary state for some thermodynamical observables, specifically the kinetic energy, whose trend is depicted for early evolution.

Fact Sheet: Best Practices Handbook for the Collection and Use of Solar Energy Applications; Best Practices Handbook for the Collection and Use of Solar Energy Applications (Fact Sheet), Energy Systems Integration (ESI), NREL (National Renewable Energy Laboratory)

DOE Office of Scientific and Technical Information (OSTI.GOV)

None

2015-06-01

This fact sheet presents highlights from the Best Practices Handbook for the Collection and Use of Solar Resource Data for Solar Energy Applications, which provides detailed information about solar resource data and the resulting data products needed for planning each stage of large concentrating solar power systems, from initial site selection to system operations.

Use of a spread sheet to calculate the current-density distribution produced in human and rat models by low-frequency electric fields.

PubMed

Hart, F X

1990-01-01

The current-density distribution produced inside irregularly shaped, homogeneous human and rat models by low-frequency electric fields is obtained by a two-stage finite-difference procedure. In the first stage the model is assumed to be equipotential. Laplace's equation is solved by iteration in the external region to obtain the capacitive-current densities at the model's surface elements. These values then provide the boundary conditions for the second-stage relaxation solution, which yields the internal current-density distribution. Calculations were performed with the Excel spread-sheet program on a Macintosh-II microcomputer. A spread sheet is a two-dimensional array of cells. Each cell of the sheet can represent a square element of space. Equations relating the values of the cells can represent the relationships between the potentials in the corresponding spatial elements. Extension to three dimensions is readily made. Good agreement was obtained with current densities measured on human models with both, one, or no legs grounded and on rat models in four different grounding configurations. The results also compared well with predictions of more sophisticated numerical analyses. Spread sheets can provide an inexpensive and relatively simple means to perform good, approximate dosimetric calculations on irregularly shaped objects.

Advances in modeling soil erosion after disturbance on rangelands

USDA-ARS?s Scientific Manuscript database

Research has been undertaken to develop process based models that predict soil erosion rate after disturbance on rangelands. In these models soil detachment is predicted as a combination of multiple erosion processes, rain splash and thin sheet flow (splash and sheet) detachment and concentrated flo...

Fact Sheet: A Technical Guide to Ground-Water Model Selection at Sites Contaminated with Radioactive Substances

EPA Pesticide Factsheets

This fact sheet summarizes the findings of a report drafted by a joint Interagency Environmental Pathway Modeling Working Group. It is to be used by technical staff responsible for implementing flow and transport models to support cleanup decisions.

Minimum and Maximum Potential Contributions to Future Sea Level Rise from Polar Ice Sheets

NASA Astrophysics Data System (ADS)

Deconto, R. M.; Pollard, D.

2017-12-01

New climate and ice-sheet modeling, calibrated to past changes in sea-level, is painting a stark picture of the future fate of the great polar ice sheets if greenhouse gas emissions continue unabated. This is especially true for Antarctica, where a substantial fraction of the ice sheet rests on bedrock more than 500-meters below sea level. Here, we explore the sensitivity of the polar ice sheets to a warming atmosphere and ocean under a range of future greenhouse gas emissions scenarios. The ice sheet-climate-ocean model used here considers time-evolving changes in surface mass balance and sub-ice oceanic melting, ice deformation, grounding line retreat on reverse-sloped bedrock (Marine Ice Sheet Instability), and newly added processes including hydrofracturing of ice shelves in response to surface meltwater and rain, and structural collapse of thick, marine-terminating ice margins with tall ice-cliff faces (Marine Ice Cliff Instability). The simulations improve on previous work by using 1) improved atmospheric forcing from a Regional Climate Model and 2) a much wider range of model physical parameters within the bounds of modern observations of ice dynamical processes (particularly calving rates) and paleo constraints on past ice-sheet response to warming. Approaches to more precisely define the climatic thresholds capable of triggering rapid and potentially irreversible ice-sheet retreat are also discussed, as is the potential for aggressive mitigation strategies like those discussed at the 2015 Paris Climate Conference (COP21) to substantially reduce the risk of extreme sea-level rise. These results, including physics that consider both ice deformation (creep) and calving (mechanical failure of marine terminating ice) expand on previously estimated limits of maximum rates of future sea level rise based solely on kinematic constraints of glacier flow. At the high end, the new results show the potential for more than 2m of global mean sea level rise by 2100, implying that physically plausible upper limits on future sea-level rise might need to be reconsidered.

Airborne Tomographic Swath Ice Sounding Processing System

NASA Technical Reports Server (NTRS)

Wu, Xiaoqing; Rodriquez, Ernesto; Freeman, Anthony; Jezek, Ken

2013-01-01

Glaciers and ice sheets modulate global sea level by storing water deposited as snow on the surface, and discharging water back into the ocean through melting. Their physical state can be characterized in terms of their mass balance and dynamics. To estimate the current ice mass balance, and to predict future changes in the motion of the Greenland and Antarctic ice sheets, it is necessary to know the ice sheet thickness and the physical conditions of the ice sheet surface and bed. This information is required at fine resolution and over extensive portions of the ice sheets. A tomographic algorithm has been developed to take raw data collected by a multiple-channel synthetic aperture sounding radar system over a polar ice sheet and convert those data into two-dimensional (2D) ice thickness measurements. Prior to this work, conventional processing techniques only provided one-dimensional ice thickness measurements along profiles.

Method and system for sensing and identifying foreign particles in a gaseous environment

NASA Technical Reports Server (NTRS)

Choi, Sang H. (Inventor); Park, Yeonjoon (Inventor)

2008-01-01

An optical method and system sense and identify a foreign particle in a gaseous environment. A light source generates light. An electrically-conductive sheet has an array of holes formed through the sheet. Each hole has a diameter that is less than one quarter of the light's wavelength. The sheet is positioned relative to the light source such that the light is incident on one face of the sheet. An optical detector is positioned adjacent the sheet's opposing face and is spaced apart therefrom such that a gaseous environment is adapted to be disposed there between. Alterations in the light pattern detected by the optical detector indicate the presence of a foreign particle in the holes or on the sheet, while a laser induced fluorescence (LIF) signature associated with the foreign particle indicates the identity of the foreign particle.

Efficient Flowline Simulations of Ice Shelf-Ocean Interactions: Sensitivity Studies with a Fully Coupled Model

NASA Technical Reports Server (NTRS)

Walker, Ryan Thomas; Holland, David; Parizek, Byron R.; Alley, Richard B.; Nowicki, Sophie M. J.; Jenkins, Adrian

2013-01-01

Thermodynamic flowline and plume models for the ice shelf-ocean system simplify the ice and ocean dynamics sufficiently to allow extensive exploration of parameters affecting ice-sheet stability while including key physical processes. Comparison between geophysically and laboratory-based treatments of ice-ocean interface thermodynamics shows reasonable agreement between calculated melt rates, except where steep basal slopes and relatively high ocean temperatures are present. Results are especially sensitive to the poorly known drag coefficient, highlighting the need for additional field experiments to constrain its value. These experiments also suggest that if the ice-ocean interface near the grounding line is steeper than some threshold, further steepening of the slope may drive higher entrainment that limits buoyancy, slowing the plume and reducing melting; if confirmed, this will provide a stabilizing feedback on ice sheets under some circumstances.

The effects of strain and stress state in hot forming of mg AZ31 sheet

NASA Astrophysics Data System (ADS)

Sherek, Paul A.; Carpenter, Alexander J.; Hector, Louis G.; Krajewski, Paul E.; Carter, Jon T.; Lasceski, Joshua; Taleff, Eric M.

Wrought magnesium alloys, such as AZ31 sheet, are of considerable interest for light-weighting of vehicle structural components. The poor room-temperature ductility of AZ31 sheet has been a hindrance to forming the complex part shapes necessary for practical applications. However, the outstanding formability of AZ31 sheet at elevated temperature provides an opportunity to overcome that problem. Complex demonstration components have already been produced at 450°C using gas-pressure forming. Accurate simulations of such hot, gas-pressure forming will be required for the design and optimization exercises necessary if this technology is to be implemented commercially. We report on experiments and simulations used to construct the accurate material constitutive models necessary for finite-element-method simulations. In particular, the effects of strain and stress state on plastic deformation of AZ31 sheet at 450°C are considered in material constitutive model development. Material models are validated against data from simple forming experiments.

Specific Amyloid Binding of Polybasic Peptides In Vivo Is Retained by β-Sheet Conformers but Lost in the Disrupted Coil and All D-Amino Acid Variants.

PubMed

Wall, Jonathan S; Williams, Angela; Richey, Tina; Stuckey, Alan; Wooliver, Craig; Christopher Scott, J; Donnell, Robert; Martin, Emily B; Kennel, Stephen J

2017-10-01

The heparin-reactive, helical peptide p5 is an effective amyloid imaging agent in mice with systemic amyloidosis. Analogs of p5 with modified secondary structure characteristics exhibited altered binding to heparin, synthetic amyloid fibrils, and amyloid extracts in vitro. Herein, we further study the effects of peptide helicity and chirality on specific amyloid binding using a mouse model of systemic inflammation-associated (AA) amyloidosis. Peptides with disrupted helical structure [p5 (coil) and p5 (Pro3) ], with an extended sheet conformation [p5 (sheet) ] or an all-D enantiomer [p5 (D) ], were chemically synthesized, radioiodinated, and their biodistribution studied in WT mice as well as transgenic animals with severe systemic AA amyloidosis. Peptide binding was assessed qualitatively by using small animal single-photon emission computed tomography/x-ray computed tomography imaging and microautoradiography and quantitatively using tissue counting. Peptides with reduced helical propensity, p5 (coil) and p5 (Pro3) , exhibited significantly reduced binding to AA amyloid-laden organs. In contrast, peptide p5 (D) was retained by non-amyloid-related ligands in the liver and kidneys of both WT and AA mice, but it also bound AA amyloid in the spleen. The p5 (sheet) peptide specifically bound AA amyloid in vivo and was not retained by healthy tissues in WT animals. Modification of amyloid-targeting peptides using D-amino acids should be performed cautiously due to the introduction of unexpected secondary pharmacologic effects. Peptides that adopt a helical structure, to align charged amino acid side chains along one face, exhibit specific reactivity with amyloid; however, polybasic peptides with a propensity for β-sheet conformation are also amyloid-reactive and may yield a novel class of amyloid-targeting agents for imaging and therapy.

Foam Core Shielding for Spacecraft

NASA Technical Reports Server (NTRS)

Adams, Marc

2007-01-01

A foam core shield (FCS) system is now being developed to supplant multilayer insulation (MLI) systems heretofore installed on spacecraft for thermal management and protection against meteoroid impacts. A typical FCS system consists of a core sandwiched between a face sheet and a back sheet. The core can consist of any of a variety of low-to-medium-density polymeric or inorganic foams chosen to satisfy application-specific requirements regarding heat transfer and temperature. The face sheet serves to shock and thereby shatter incident meteoroids, and is coated on its outer surface to optimize its absorptance and emittance for regulation of temperature. The back sheet can be dimpled to minimize undesired thermal contact with the underlying spacecraft component and can be metallized on the surface facing the component to optimize its absorptance and emittance. The FCS systems can perform better than do MLI systems, at lower mass and lower cost and with greater volumetric efficiency.

Role of ice-ocean interaction on glacier instability: Results from numerical modeling applied to Petermann Glacier (Invited)

NASA Astrophysics Data System (ADS)

Nick, F.; Hubbard, A.; Vieli, A.; van der Veen, C. J.; Box, J. E.; Bates, R.; Luckman, A. J.

2009-12-01

Calving of icebergs and bottom melting from ice shelves accounts for roughly half the ice transferred from the Greenland Ice Sheet into the surrounding ocean, and virtually all of the ice loss from the Antarctic Ice Sheet. Petermann Glacier (north Greenland) with its 16 km wide and 80 km long floating tongue, experiences massive bottom melting. We apply a numerical ice flow model using a physically-based calving criterion based on crevasse depth to investigate the contribution of processes such as bottom melting, sea ice or sikkusak disintegration, surface run off and iceberg calving to the mass balance and instability of Petermann Glacier and its ice shelf. Our modeling study provides insights into the role of ice-ocean interaction, and on how to incorporate calving in ice sheet models, improving our ability to predict future ice sheet change.

Role of ice-ocean interaction on glacier instability: Results from numerical modelling applied to Petermann Glacier

NASA Astrophysics Data System (ADS)

Nick, Faezeh M.; Hubbard, Alun; van der Veen, Kees; Vieli, Andreas

2010-05-01

Calving of icebergs and bottom melting from ice shelves accounts for roughly half the ice transferred from the Greenland Ice Sheet into the surrounding ocean, and virtually all of the ice loss from the Antarctic Ice Sheet. Petermann Glacier (north Greenland) with its 16 km wide and 80 km long floating tongue, experiences massive bottom melting. We apply a numerical ice flow model using a physically-based calving criterion based on crevasse depth to investigate the contribution of processes such as bottom melting, sea ice or sikkusak disintegration, surface run off and iceberg calving to the mass balance and instability of Petermann Glacier and its ice shelf. Our modelling study provides insights into the role of ice-ocean interaction, and on how to incorporate calving in ice sheet models, improving our ability to predict future ice sheet change.

Structure of the Magnetotail Current Sheet

NASA Technical Reports Server (NTRS)

Larson, Douglas J.; Kaufmann, Richard L.

1996-01-01

An orbit tracing technique was used to generate current sheets for three magnetotail models. Groups of ions were followed to calculate the resulting cross-tail current. Several groups then were combined to produce a current sheet. The goal is a model in which the ions and associated electrons carry the electric current distribution needed to generate the magnetic field B in which ion orbits were traced. The region -20 R(sub E) less than x less than - 14 R(sub E) in geocentric solar magnetospheric coordinates was studied. Emphasis was placed on identifying the categories of ion orbits which contribute most to the cross-tail current and on gaining physical insight into the manner by which the ions carry the observed current distribution. Ions that were trapped near z = 0, ions that magnetically mirrored throughout the current sheet, and ions that mirrored near the Earth all were needed. The current sheet structure was determined primarily by ion magnetization currents. Electrons of the observed energies carried relatively little cross-tail current in these quiet time current sheets. Distribution functions were generated and integrated to evaluate fluid parameters. An earlier model in which B depended only on z produced a consistent current sheet, but it did not provide a realistic representation of the Earth's middle magnetotail. In the present study, B changed substantially in the x and z directions but only weakly in the y direction within our region of interest. Plasmas with three characteristic particle energies were used with each of the magnetic field models. A plasma was found for each model in which the density, average energy, cross-tail current, and bulk flow velocity agreed well with satellite observations.

Structure of the Magnetotail Current Sheet

NASA Technical Reports Server (NTRS)

Larson, Douglas J.; Kaufmann, Richard L.

1996-01-01

An orbit tracing technique was used to generate current sheets for three magnetotail models. Groups of ions were followed to calculate the resulting cross-tail current. Several groups then were combined to produce a current sheet. The goal is a model in which the ions and associated electrons carry the electric current distribution needed to generate the magnetic field B in which ion orbits were traced. The region -20 R(E) less than x less than -14 R(E) in geocentric solar magnetospheric coordinates was studied. Emphasis was placed on identifying the categories of ion orbits which contribute most to the cross-tail current and on gaining physical insight into the manner by which the ions carry the observed current distribution. Ions that were trapped near z = 0, ions that magnetically mirrored throughout the current sheet, and ions that mirrored near the Earth all were needed. The current sheet structure was determined primarily by ion magnetization currents. Electrons of the observed energies carried relatively little cross-tail current in these quiet time current sheets. Distribution functions were generated and integrated to evaluate fluid parameters. An earlier model in which B depended only on z produced a consistent current sheet, but it did not provide a realistic representation of the Earth's middle magnetotail. In the present study, B changed substantially in the x and z directions but only weakly in the y direction within our region of interest. Plasmas with three characteristic particle energies were used with each of the magnetic field models. A plasma was found for each model in which the density, average energy, cross-tail current, and bulk flow velocity agreed well with satellite observations.

Modeling the evolution of the Laurentide Ice Sheet from MIS 3 to the Last Glacial Maximum: an approach using sea level modeling and ice flow dynamics

NASA Astrophysics Data System (ADS)

Weisenberg, J.; Pico, T.; Birch, L.; Mitrovica, J. X.

2017-12-01

The history of the Laurentide Ice Sheet since the Last Glacial Maximum ( 26 ka; LGM) is constrained by geological evidence of ice margin retreat in addition to relative sea-level (RSL) records in both the near and far field. Nonetheless, few observations exist constraining the ice sheet's extent across the glacial build-up phase preceding the LGM. Recent work correcting RSL records along the U.S. mid-Atlantic dated to mid-MIS 3 (50-35 ka) for glacial-isostatic adjustment (GIA) infer that the Laurentide Ice Sheet grew by more than three-fold in the 15 ky leading into the LGM. Here we test the plausibility of a late and extremely rapid glaciation by driving a high-resolution ice sheet model, based on a nonlinear diffusion equation for the ice thickness. We initialize this model at 44 ka with the mid-MIS 3 ice sheet configuration proposed by Pico et al. (2017), GIA-corrected basal topography, and mass balance representative of mid-MIS 3 conditions. These simulations predict rapid growth of the eastern Laurentide Ice Sheet, with rates consistent with achieving LGM ice volumes within 15 ky. We use these simulations to refine the initial ice configuration and present an improved and higher resolution model for North American ice cover during mid-MIS 3. In addition we show that assumptions of ice loads during the glacial phase, and the associated reconstructions of GIA-corrected basal topography, produce a bias that can underpredict ice growth rates in the late stages of the glaciation, which has important consequences for our understanding of the speed limit for ice growth on glacial timescales.