Sources and mobility of carbonate melts beneath cratons, with implications for deep carbon cycling, metasomatism and rift initiation

Science.gov (United States)

Tappe, Sebastian; Romer, Rolf L.; Stracke, Andreas; Steenfelt, Agnete; Smart, Katie A.; Muehlenbachs, Karlis; Torsvik, Trond H.

2017-05-01

Kimberlite and carbonatite magmas that intrude cratonic lithosphere are among the deepest probes of the terrestrial carbon cycle. Their co-existence on thick continental shields is commonly attributed to continuous partial melting sequences of carbonated peridotite at >150 km depths, possibly as deep as the mantle transition zone. At Tikiusaaq on the North Atlantic craton in West Greenland, approximately 160 Ma old ultrafresh kimberlite dykes and carbonatite sheets provide a rare opportunity to study the origin and evolution of carbonate-rich melts beneath cratons. Although their Sr-Nd-Hf-Pb-Li isotopic compositions suggest a common convecting upper mantle source that includes depleted and recycled oceanic crust components (e.g., negative ΔεHf coupled with > + 5 ‰ δ7Li), incompatible trace element modelling identifies only the kimberlites as near-primary low-degree partial melts (0.05-3%) of carbonated peridotite. In contrast, the trace element systematics of the carbonatites are difficult to reproduce by partial melting of carbonated peridotite, and the heavy carbon isotopic signatures (-3.6 to - 2.4 ‰ δ13C for carbonatites versus -5.7 to - 3.6 ‰ δ13C for kimberlites) require open-system fractionation at magmatic temperatures. Given that the oxidation state of Earth's mantle at >150 km depth is too reduced to enable larger volumes of 'pure' carbonate melt to migrate, it is reasonable to speculate that percolating near-solidus melts of carbonated peridotite must be silicate-dominated with only dilute carbonate contents, similar to the Tikiusaaq kimberlite compositions (e.g., 16-33 wt.% SiO2). This concept is supported by our findings from the North Atlantic craton where kimberlite and other deeply derived carbonated silicate melts, such as aillikites, exsolve their carbonate components within the shallow lithosphere en route to the Earth's surface, thereby producing carbonatite magmas. The relative abundances of trace elements of such highly

Constraints on mantle melt geometries from body wave attenuation in the Salton Trough and Snake River Plain

Science.gov (United States)

Byrnes, J. S.; Bezada, M.

2017-12-01

Melt can be retained in the mantle at triple junctions between grain boundaries, be spread in thin films along two-grain boundaries, or be organized by shear into elongate melt-rich bands. Which of these geometries is most prevalent is unknown. This ambiguity makes the interpretation of anomalous seismic velocities and quality factors difficult, since different geometries would result in different mechanical effects. Here, we compare observations of seismic attenuation beneath the Salton Trough and the Snake River Plain; two regions where the presence of melt has been inferred. The results suggest that seismic attenuation is diagnostic of melt geometry. We measure the relative attenuation of P waves from deep focus earthquakes using a time-domain method. Even though the two regions are underlain by comparably strong low-velocity anomalies, their attenuation signature is very different. The upper mantle beneath the Salton Trough is sufficiently attenuating that the presence of melt must lower Qp, while attenuation beneath the Snake River Plain is not anomalous with respect to surrounding regions. These seemingly contradictory results can be reconciled if different melt geometries characterize each region. SKS splitting from the Salton Trough suggests that melt is organized into melt-rich bands, while this is not the case for the Snake River Plain. We infer that beneath the Snake River Plain melt is retained at triple junctions between grain boundaries, a geometry that is not predicted to cause seismic attenuation. More elongate geometries beneath the Salton Trough may cause seismic attenuation via the melt-squirt mechanism. In light of these results, we conclude that prior observations of low seismic velocities with somewhat high quality factors beneath the East Pacific Rise and Southern California suggest that melt does not organize into elongate bands across much of the asthenosphere.

Mantle melting and melt refertilization beneath the Southwest Indian Ridge: Mineral composition of abyssal peridotites

Science.gov (United States)

Chen, Ling; Zhu, Jihao; Chu, Fengyou; Dong, Yan-hui; Liu, Jiqiang; Li, Zhenggang; Zhu, Zhimin; Tang, Limei

2017-04-01

As one of the slowest spreading ridges of the global ocean ridge system, the Southwest Indian Ridge (SWIR) is characterized by discontinued magmatism. The 53°E segment between the Gallieni fracture zone (FZ) (52°20'E) and the Gazelle FZ (53°30'E) is a typical amagmatic segment (crustal thickness 1cm) Opx, and Mg-rich mineral compositions akin to harzburgite xenoliths that sample old continental lithospheric mantle (Kelemen et al., 1998). Melt refertilization model shows that Group 2 peridotites were affected by an enriched low-degree partial melt from the garnet stability field. These results indicate that depleted mantle which experiences ancient melting event are more sensitive to melt refertilization, thus may reduce the melt flux, leading to extremely thin crust at 53°E segment. This research was granted by the National Basic Research Programme of China (973 programme) (grant No. 2013CB429705) and the Fundamental Research Funds of Second Institute of Oceanography, State Oceanic Administration (JG1603, SZ1507). References: Johnson K T M, Dick H J B, Shimizu N. Melting in the oceanic upper mantle: An ion microprobe study of diopsides in abyssal peridotites[J]. Journal of Geophysical Research, 1990, 95(B3):2661-2678. Kelemen P B, Hart S R, Bernstein S. Silica enrichment in the continental upper mantle via melt/rock reaction[J]. Earth & Planetary Science Letters, 1998, 164(1-2):387-406. Zhou H, Dick H J. Thin crust as evidence for depleted mantle supporting the Marion Rise.[J]. Nature, 2013, 494(7436):195-200.

Effects of acid conditions on element distribution beneath a sulphur basepad

International Nuclear Information System (INIS)

Sevigny, J.H.; Fennell, J.W.; Sharma, A.

1997-04-01

A reconnaissance-scale study was conducted to determine the extent of acid conditions beneath a sulphur basepad at Canadian Occidental's Balzac sour gas plant and to examine the effects of acid conditions on element distribution in the subsurface. Sulphur which is extracted from sour natural gas is stored in large blocks directly on the ground. The elemental sulphur will oxidize to H 2 SO 4 under aerobic conditions and with the proper microorganisms can result in possible removal of metals from the soil and transportation in the groundwater. The basepad at the sour gas plant is 36 years old and is covered by about 1 metre of elemental sulphur. EM31 terrain conductivity and electrical resistivity tomography geophysical surveys were conducted to determine aerial and subsurface bulk electrical conductivity. The objective was to locate the indurated layer using the geophysical techniques and soil boring. The extent of acid conditions beneath the sulphur block was determined. Migration rates for the site were also estimated. Results suggested that minimal soil and groundwater impact can be expected from sulphur blocks overlying properly buffered soils, and that synthetic liners beneath sulphur blocks may not be a necessary measure at sour gas plants in Alberta. 19 refs., 6 tabs., 6 figs., 5 appendices

Crustal Thickness Beneath Libya and the Origin of Partial Melt Beneath AS Sawda Volcanic Province From Receiver Function Constraints

Science.gov (United States)

Lemnifi, Awad A.; Elshaafi, Abdelsalam; Browning, John; Aouad, Nassib S.; El Ebaidi, Saad K.; Liu, Kelly K.; Gudmundsson, Agust

2017-12-01

This study investigates crustal thickness and properties within the Libyan region. Results obtained from 15 seismic stations belonging to the Libyan Center for Remote Sensing and Space Science are reported, in addition to 3 seismic stations publically available, using receiver functions. The results show crustal thicknesses ranging from 24 km to 36 km (with uncertainties ranging between ±0.10 km and ±0.90 km). More specifically, crustal thickness ranges from 32 km to 36 km in the southern portion of the Libyan territory then becomes thinner, between 24 km and 30 km, in the coastal areas of Libya and thinnest, between 24 km and 28 km, in the Sirt Basin. The observed high Vp/Vs value of 1.91 at one station located at the AS Sawda Volcanic Province in central Libya indicates the presence of either partial melt or an abnormally warm area. This finding suggests that magma reservoirs beneath the Libyan territory may still be partially molten and active, thereby posing significant earthquake and volcanic risks. The hypothesis of an active magma source is further demonstrated though the presence of asthenospheric upwelling and extension of the Sirt Basin. This study provides a new calculation of unconsolidated sediment layers by using the arrival time of the P to S converted phases. The results show sediments thicknesses of 0.4 km to 3.7 km, with the Vp/Vs values ranging from 2.2 to 4.8. The variations in crustal thickness throughout the region are correlated with surface elevation and Bouguer gravity anomalies, which suggest that they are isostatically compensated.

Imaging the Laguna del Maule Volcanic Field, central Chile using magnetotellurics: Evidence for crustal melt regions laterally-offset from surface vents and lava flows

Science.gov (United States)

Cordell, Darcy; Unsworth, Martyn J.; Díaz, Daniel

2018-04-01

low-frequency signals. The attenuation from C1 does not affect C3 or C4. At 1 km depth directly beneath LdM, a weak conductor (C2; 50%), silicic reservoir with 5 wt% H2O at 2 to 5 km depth beneath the inflation center is not supported by the MT data. However, a smaller (10 km3) eruptible volume could go undetected even with relatively high melt fraction (>50%). The location of large melt regions to the north has important implications for long-term volcanic hazards at LdMVF as well as other volcanoes as it raises the possibility that the vent distribution is not always indicative of the location of deeper source regions of melt.

Simulation of snow distribution and melt under cloudy conditions in an Alpine watershed

Directory of Open Access Journals (Sweden)

H.-Y. Li

2011-07-01

Full Text Available An energy balance method and remote-sensing data were used to simulate snow distribution and melt in an alpine watershed in northwestern China within a complete snow accumulation-melt period. The spatial energy budgets were simulated using meteorological observations and a digital elevation model of the watershed. A linear interpolation method was used to estimate the daily snow cover area under cloudy conditions, using Moderate Resolution Imaging Spectroradiometer (MODIS data. Hourly snow distribution and melt, snow cover extent and daily discharge were included in the simulated results. The root mean square error between the measured snow-water equivalent samplings and the simulated results is 3.2 cm. The Nash and Sutcliffe efficiency statistic (NSE between the measured and simulated discharges is 0.673, and the volume difference (Dv is 3.9 %. Using the method introduced in this article, modelling spatial snow distribution and melt runoff will become relatively convenient.

Short wavelength lateral variability of lithospheric mantle beneath the Middle Atlas (Morocco) as recorded by mantle xenoliths

Science.gov (United States)

El Messbahi, Hicham; Bodinier, Jean-Louis; Vauchez, Alain; Dautria, Jean-Marie; Ouali, Houssa; Garrido, Carlos J.

2015-05-01

The Middle Atlas is a region where xenolith-bearing volcanism roughly coincides with the maximum of lithospheric thinning beneath continental Morocco. It is therefore a key area to study the mechanisms of lithospheric thinning and constrain the component of mantle buoyancy that is required to explain the Moroccan topography. Samples from the two main xenolith localities, the Bou Ibalghatene and Tafraoute maars, have been investigated for their mineralogy, microstructures, crystallographic preferred orientation, and whole-rock and mineral compositions. While Bou Ibalghatene belongs to the main Middle Atlas volcanic field, in the 'tabular' Middle Atlas, Tafraoute is situated about 45 km away, on the North Middle Atlas Fault that separates the 'folded' Middle Atlas, to the South-East, from the 'tabular' Middle Atlas, to the North-West. Both xenolith suites record infiltration of sub-lithospheric melts that are akin to the Middle Atlas volcanism but were differentiated to variable degrees as a result of interactions with lithospheric mantle. However, while the Bou Ibalghatene mantle was densely traversed by high melt fractions, mostly focused in melt conduits, the Tafraoute suite records heterogeneous infiltration of smaller melt fractions that migrated diffusively, by intergranular porous flow. As a consequence the lithospheric mantle beneath Bou Ibalghaten was strongly modified by melt-rock interactions in the Cenozoic whereas the Tafraoute mantle preserves the record of extensional lithospheric thinning, most likely related to Mesozoic rifting. The two xenolith suites illustrate distinct mechanisms of lithospheric thinning: extensional thinning in Tafraoute, where hydrous incongruent melting triggered by decompression probably played a key role in favouring strain localisation, vs. thermal erosion in Bou Ibalghatene, favoured and guided by a dense network of melt conduits. Our results lend support to the suggestion that lithospheric thinning beneath the Atlas

Deep crustal melt plumbing of Bárðarbunga volcano, Iceland

Science.gov (United States)

Hudson, T. S.; White, R. S.; Greenfield, T.; Ágústsdóttir, T.; Brisbourne, A.; Green, R. G.

2017-09-01

Understanding magmatic plumbing within the Earth's crust is important for understanding volcanic systems and improving eruption forecasting. We discuss magma plumbing under Bárðarbunga volcano, Iceland, over a 4 year period encompassing the largest Icelandic eruption in 230 years. Microseismicity extends through the usually ductile region of the Earth's crust, from 7 to 22 km depth in a subvertical column. Moment tensor solutions for an example earthquake exhibits opening tensile crack behavior. This is consistent with the deep (>7 km) seismicity being caused by the movement of melt in the normally aseismic crust. The seismically inferred melt path from the mantle source is offset laterally from the center of the Bárðarbunga caldera by 12 km, rather than lying directly beneath it. It is likely that an aseismic melt feed also exists directly beneath the caldera and is aseismic due to elevated temperatures and pervasive partial melt under the caldera.

Sub-crustal seismic activity beneath Klyuchevskoy Volcano

Science.gov (United States)

Carr, M. J.; Droznina, S.; Levin, V. L.; Senyukov, S.

2013-12-01

Seismic activity is extremely vigorous beneath the Klyuchevskoy Volcanic Group (KVG). The unique aspect is the distribution in depth. In addition to upper-crustal seismicity, earthquakes take place at depths in excess of 20 km. Similar observations are known in other volcanic regions, however the KVG is unique in both the number of earthquakes and that they occur continuously. Most other instances of deep seismicity beneath volcanoes appear to be episodic or transient. Digital recording of seismic signals started at the KVG in early 2000s.The dense local network reliably locates earthquakes as small as ML~1. We selected records of 20 earthquakes located at depths over 20 km. Selection was based on the quality of the routine locations and the visual clarity of the records. Arrivals of P and S waves were re-picked, and hypocentral parameters re-established. Newl locations fell within the ranges outlined by historical seismicity, confirming the existence of two distinct seismically active regions. A shallower zone is at ~20 km depth, and all hypocenters are to the northeast of KVG, in a region between KVG and Shiveluch volcano. A deeper zone is at ~30 km, and all hypocenters cluster directly beneath the edifice of the Kyuchevskoy volcano. Examination of individual records shows that earthquakes in both zones are tectonic, with well-defined P and S waves - another distinction of the deep seismicity beneath KVG. While the upper seismic zone is unquestionably within the crust, the provenance of the deeper earthquakes is enigmatic. The crustal structure beneath KVG is highly complex, with no agreed-upon definition of the crust-mantle boundary. Rather, a range of values, from under 30 to over 40 km, exists in the literature. Similarly, a range of velocity structures has been reported. Teleseismic receiver functions (RFs) provide a way to position the earthquakes with respect to the crust-mantle boundary. We compare the differential travel times of S and P waves from deep

Modeling radar backscattering from melting snowflakes using spheroids with nonuniform distribution of water

International Nuclear Information System (INIS)

Tyynelä, Jani; Leinonen, Jussi; Moisseev, Dmitri; Nousiainen, Timo; Lerber, Annakaisa von

2014-01-01

In a number of studies it is reported that at the early stages, melting of aggregate snowflakes is enhanced at lower parts. In this paper, the manifestation of the resulting nonuniform distribution of water is studied for radar backscattering cross sections at C, Ku, Ka and W bands. The melting particles are described as spheroids with a mixture of water and air at the bottom part of the particle and a mixture of ice and air at the upper part. The radar backscattering is modeled using the discrete-dipole approximation in a horizontally pointing geometry. The results are compared to the T-matrix method, Mie theory, and the Rayleigh approximation using the Maxwell Garnett mixing formula. We find that the differential reflectivity and the linear depolarization ratio show systematic differences between the discrete-dipole approximation and the T-matrix method, but that the differences are relatively small. The horizontal cross sections show only small differences between the methods with the aspect ratio and the presence of resonance peaks having a larger effect on it than the nonuniform distribution of water. Overall, the effect of anisotropic distribution of water, reported for early stages of melting, is not significant for radar observations at the studied frequencies. -- Highlights: • We model backscattering from spheroidal melting snowflakes at C, Ku, Ka, and W bands. • We study the effect of anisotropic distribution of meltwater in the snow particles. • We find systematic, but relatively small differences for the backscattering properties. • We find that the aspect ratio and resonance peaks have a bigger effect than anisotropic distribution of water. • Anisotropic distribution of water is not significant for radar observations at early stages of melting

Formation of heterogeneous magmatic series beneath North Santorini, South Aegean island arc

DEFF Research Database (Denmark)

Bailey, John C; Jensen, E.S.; Hansen, A.

2008-01-01

magma formation beneath North Santorini throughout its 500 ka history is attributed to variable transfer of sedimentary components - either terrigenous or pelagic, as bulk sediments or high-temperature partial melts rather than fluids or low-temperature partial melts - from a rupture zone...... in the subducted slab to the overlying mantle. The three main magmatic series followed independent paths of assimilation of upper crustal materials during fractional crystallization. Assimilation was more pronounced at the basaltic stage. The long-lived histories of the three main magmatic series imply repetitive...... melting of isolated mantle regions, ascent of magmas through independent feeder systems, and their residence in separate crustal magma chambers....

Deformation mechanisms and melt nano-structures in experimentally deformed olivine-orthopyroxene rocks with low melt fractions

NARCIS (Netherlands)

Kloe, P.A. de

2001-01-01

The major part of the Earth’s upper mantle is thought to be solid, with some regions in the mantle where the rocks contain a small melt fraction These partially molten rocks are associated with important geological processes such as magma production beneath mid-oceanic ridges and may also play an

Magma heating by decompression-driven crystallization beneath andesite volcanoes.

Science.gov (United States)

Blundy, Jon; Cashman, Kathy; Humphreys, Madeleine

2006-09-07

Explosive volcanic eruptions are driven by exsolution of H2O-rich vapour from silicic magma. Eruption dynamics involve a complex interplay between nucleation and growth of vapour bubbles and crystallization, generating highly nonlinear variation in the physical properties of magma as it ascends beneath a volcano. This makes explosive volcanism difficult to model and, ultimately, to predict. A key unknown is the temperature variation in magma rising through the sub-volcanic system, as it loses gas and crystallizes en route. Thermodynamic modelling of magma that degasses, but does not crystallize, indicates that both cooling and heating are possible. Hitherto it has not been possible to evaluate such alternatives because of the difficulty of tracking temperature variations in moving magma several kilometres below the surface. Here we extend recent work on glassy melt inclusions trapped in plagioclase crystals to develop a method for tracking pressure-temperature-crystallinity paths in magma beneath two active andesite volcanoes. We use dissolved H2O in melt inclusions to constrain the pressure of H2O at the time an inclusion became sealed, incompatible trace element concentrations to calculate the corresponding magma crystallinity and plagioclase-melt geothermometry to determine the temperature. These data are allied to ilmenite-magnetite geothermometry to show that the temperature of ascending magma increases by up to 100 degrees C, owing to the release of latent heat of crystallization. This heating can account for several common textural features of andesitic magmas, which might otherwise be erroneously attributed to pre-eruptive magma mixing.

Vigorous lateral export of the meltwater outflow from beneath an Antarctic ice shelf.

Science.gov (United States)

Garabato, Alberto C Naveira; Forryan, Alexander; Dutrieux, Pierre; Brannigan, Liam; Biddle, Louise C; Heywood, Karen J; Jenkins, Adrian; Firing, Yvonne L; Kimura, Satoshi

2017-02-09

The instability and accelerated melting of the Antarctic Ice Sheet are among the foremost elements of contemporary global climate change. The increased freshwater output from Antarctica is important in determining sea level rise, the fate of Antarctic sea ice and its effect on the Earth's albedo, ongoing changes in global deep-ocean ventilation, and the evolution of Southern Ocean ecosystems and carbon cycling. A key uncertainty in assessing and predicting the impacts of Antarctic Ice Sheet melting concerns the vertical distribution of the exported meltwater. This is usually represented by climate-scale models as a near-surface freshwater input to the ocean, yet measurements around Antarctica reveal the meltwater to be concentrated at deeper levels. Here we use observations of the turbulent properties of the meltwater outflows from beneath a rapidly melting Antarctic ice shelf to identify the mechanism responsible for the depth of the meltwater. We show that the initial ascent of the meltwater outflow from the ice shelf cavity triggers a centrifugal overturning instability that grows by extracting kinetic energy from the lateral shear of the background oceanic flow. The instability promotes vigorous lateral export, rapid dilution by turbulent mixing, and finally settling of meltwater at depth. We use an idealized ocean circulation model to show that this mechanism is relevant to a broad spectrum of Antarctic ice shelves. Our findings demonstrate that the mechanism producing meltwater at depth is a dynamically robust feature of Antarctic melting that should be incorporated into climate-scale models.

Geological Mapping of Impact Melt Deposits at Lunar Complex Craters: New Insights into Morphological Diversity, Distribution and the Cratering Process

Science.gov (United States)

Dhingra, D.; Head, J. W., III; Pieters, C. M.

2014-12-01

We have completed high resolution geological mapping of impact melt deposits at the young lunar complex craters (wall and rim impact melt units and their relation to floor units have also been mapped. Among the distinctive features of these impact melt deposits are: 1) Impact Melt Wave Fronts: These are extensive (sometimes several kilometers in length) and we have documented their occurrence and distribution in different parts of the crater floor at Jackson and Tycho. These features emphasize melt mobility and style of emplacement during the modification stage of the craters. 2) Variations in Floor Elevations: Spatially extensive and coherent sections of crater floors have different elevations at all the three craters. The observed elevation differences could be caused by subsidence due to cooling of melt and/or structural failure, together with a contribution from regional slope. 3) Melt-Covered Megablocks: We also observe large blocks/rock-fragments (megablocks) covered in impact melt, which could be sections of collapsed wall or in some cases, subdued sections of central peaks. 4) Melt-Covered Central Peaks: Impact melt has also been mapped on the central peaks but varies in spatial extent among the craters. The presence of melt on peaks must be taken into account when interpreting peak mineralogy as exposures of deeper crust. 5) Boulder Distribution: Interesting trends are observed in the distribution of boulder units of various sizes; some impact melt units have spatially extensive boulders, while boulder distribution is very scarce in other units on the floor. We interpret these distributions to be influenced by a) the differential collapse of the crater walls during the modification stage, and b) the amount of relative melt volume retained in different parts of the crater floor. These observations provide important documentation of the morphological diversity and better understanding of the emplacement and final distribution of impact melt deposits.

Channelization of plumes beneath ice shelves

KAUST Repository

Dallaston, M.  C.; Hewitt, I. J.; Wells, A. J.

2015-01-01

© 2015 Cambridge University Press. We study a simplified model of ice-ocean interaction beneath a floating ice shelf, and investigate the possibility for channels to form in the ice shelf base due to spatial variations in conditions at the grounding line. The model combines an extensional thin-film description of viscous ice flow in the shelf, with melting at its base driven by a turbulent ocean plume. Small transverse perturbations to the one-dimensional steady state are considered, driven either by ice thickness or subglacial discharge variations across the grounding line. Either forcing leads to the growth of channels downstream, with melting driven by locally enhanced ocean velocities, and thus heat transfer. Narrow channels are smoothed out due to turbulent mixing in the ocean plume, leading to a preferred wavelength for channel growth. In the absence of perturbations at the grounding line, linear stability analysis suggests that the one-dimensional state is stable to initial perturbations, chiefly due to the background ice advection.

Channelization of plumes beneath ice shelves

KAUST Repository

Dallaston, M. C.

2015-11-11

© 2015 Cambridge University Press. We study a simplified model of ice-ocean interaction beneath a floating ice shelf, and investigate the possibility for channels to form in the ice shelf base due to spatial variations in conditions at the grounding line. The model combines an extensional thin-film description of viscous ice flow in the shelf, with melting at its base driven by a turbulent ocean plume. Small transverse perturbations to the one-dimensional steady state are considered, driven either by ice thickness or subglacial discharge variations across the grounding line. Either forcing leads to the growth of channels downstream, with melting driven by locally enhanced ocean velocities, and thus heat transfer. Narrow channels are smoothed out due to turbulent mixing in the ocean plume, leading to a preferred wavelength for channel growth. In the absence of perturbations at the grounding line, linear stability analysis suggests that the one-dimensional state is stable to initial perturbations, chiefly due to the background ice advection.

Dynamics of Melting and Melt Migration as Inferred from Incompatible Trace Element Abundance in Abyssal Peridotites

Science.gov (United States)

Peng, Q.; Liang, Y.

2008-12-01

To better understand the melting processes beneath the mid-ocean ridge, we developed a simple model for trace element fractionation during concurrent melting and melt migration in an upwelling steady-state mantle column. Based on petrologic considerations, we divided the upwelling mantle into two regions: a double- lithology upper region where high permeability dunite channels are embedded in a lherzolite/harzburgite matrix, and a single-lithology lower region that consists of partially molten lherzolite. Melt generated in the single lithology region migrates upward through grain-scale diffuse porous flow, whereas melt in the lherzolite/harzburgite matrix in the double-lithology region is allowed to flow both vertically through the overlying matrix and horizontally into its neighboring dunite channels. There are three key dynamic parameters in our model: degree of melting experienced by the single lithology column (Fd), degree of melting experienced by the double lithology column (F), and a dimensionless melt suction rate (R) that measures the accumulated rate of melt extraction from the matrix to the channel relative to the accumulated rate of matrix melting. In terms of trace element fractionation, upwelling and melting in the single lithology column is equivalent to non-modal batch melting (R = 0), whereas melting and melt migration in the double lithology region is equivalent to a nonlinear combination of non-modal batch and fractional melting (0 abyssal peridotite, we showed, with the help of Monte Carlo simulations, that it is difficult to invert for all three dynamic parameters from a set of incompatible trace element data with confidence. However, given Fd, it is quite possible to constrain F and R from incompatible trace element abundances in residual peridotite. As an illustrative example, we used the simple melting model developed in this study and selected REE and Y abundance in diopside from abyssal peridotites to infer their melting and melt migration

Asthenospheric percolation of alkaline melts beneath the St. Paul region (Central Atlantic Ocean)

Science.gov (United States)

Brunelli, Daniele; Seyler, Monique

2010-01-01

Two peridotite suites collected by submersible in the equatorial Atlantic Ocean (Hekinian et al., 2000) were studied for textures, modes, and in situ major and trace element compositions in pyroxenes. Dive SP12 runs along the immersed flank of the St. Peter and Paul Rocks islets where amphibole-bearing, ultramafic mylonites enriched in alkalies and incompatible elements are exposed (Roden et al., 1984), whereas dive SP03 sampled a small intra-transform spreading centre situated about 370 km east of the St. Peter and Paul Rocks. Both suites are characterized by undeformed, coarse-grained granular textures typical of abyssal peridotites, derived from residual mantle after ˜ 15% melting of a DMM source, starting in the garnet stability field. Trace element modelling, textures and lack of mineral zoning indicate that the residual peridotites were percolated, reacted and refertilized by ˜ 2.6% partially aggregated melts in the uppermost level of the melting region. This relatively large amount of refertilization is in agreement with the cold and thick lithosphere inferred by previous studies. Freezing of trapped melts occurred as the peridotite entered the conductive layer, resulting in late-stage crystallization of olivine, clinopyroxene, spinel, ± plagioclase. Chondrite-normalized REE patterns in clinopyroxenes from SP03 indicate that they last equilibrated with (ultra-) depleted partial melts. In contrast, REE concentrations in clinopyroxenes from SP12 display U and S shaped LREE-enriched patterns and the calculated compositions of the impregnating melts span the compositional range of the regional basalts, which vary from normal MORB to alkali basalt sometimes modified by chromatographic fractionation with no, or very limited, mineral reaction. Thus the mylonitic band forming the St. Peter and St. Paul Rocks ridge is not a fragment of subcontinental lithospheric mantle left behind during the opening of the Central Atlantic, nor the source of the alkaline basalts

Heterogeneous distribution of water in the mantle transition zone beneath United States inferred from seismic observations

Science.gov (United States)

Wang, Y.; Pavlis, G. L.; Li, M.

2017-12-01

The amount of water in the Earth's deep mantle is critical for the evolution of the solid Earth and the atmosphere. Mineral physics studies have revealed that Wadsleyite and Ringwoodite in the mantle transition zone could store several times the volume of water in the ocean. However, the water content and its distribution in the transition zone remain enigmatic due to lack of direct observations. Here we use seismic data from the full deployment of the Earthscope Transportable Array to produce 3D image of P to S scattering of the mantle transition zone beneath the United States. We compute the image volume from 141,080 pairs of high quality receiver functions defined by the Earthscope Automated Receiver Survey, reprocessed by the generalized iterative deconvolution method and imaged by the plane wave migration method. We find that the transition zone is filled with previously unrecognized small-scale heterogeneities that produce pervasive, negative polarity P to S conversions. Seismic synthetic modeling using a point source simulation method suggests two possible structures for these objects: 1) a set of randomly distributed blobs of slight difference in size, and 2) near vertical diapir structures from small scale convections. Combining with geodynamic simulations, we interpret the observation as compositional heterogeneity from small-scale, low-velocity bodies that are water enriched. Our results indicate there is a heterogeneous distribution of water through the entire mantle transition zone beneath the contiguous United States.

Experimental simulation of magma-carbonate interaction beneath Mt. Vesuvius, Italy

Science.gov (United States)

Jolis, E. M.; Freda, C.; Troll, V. R.; Deegan, F. M.; Blythe, L. S.; McLeod, C. L.; Davidson, J. P.

2013-11-01

We simulated the process of magma-carbonate interaction beneath Mt. Vesuvius in short duration piston-cylinder experiments under controlled magmatic conditions (from 0 to 300 s at 0.5 GPa and 1,200 °C), using a Vesuvius shoshonite composition and upper crustal limestone and dolostone as starting materials. Backscattered electron images and chemical analysis (major and trace elements and Sr isotopes) of sequential experimental products allow us to identify the textural and chemical evolution of carbonated products during the assimilation process. We demonstrate that melt-carbonate interaction can be extremely fast (minutes), and results in dynamic contamination of the host melt with respect to Ca, Mg and 87Sr/86Sr, coupled with intense CO2 vesiculation at the melt-carbonate interface. Binary mixing between carbonate and uncontaminated melt cannot explain the geochemical variations of the experimental charges in full and convection and diffusion likely also operated in the charges. Physical mixing and mingling driven by exsolving volatiles seems to be a key process to promote melt homogenisation. Our results reinforce hypotheses that magma-carbonate interaction is a relevant and ongoing process at Mt. Vesuvius and one that may operate not only on a geological, but on a human timescale.

The WAIS Melt Monitor: An automated ice core melting system for meltwater sample handling and the collection of high resolution microparticle size distribution data

Science.gov (United States)

Breton, D. J.; Koffman, B. G.; Kreutz, K. J.; Hamilton, G. S.

2010-12-01

Paleoclimate data are often extracted from ice cores by careful geochemical analysis of meltwater samples. The analysis of the microparticles found in ice cores can also yield unique clues about atmospheric dust loading and transport, dust provenance and past environmental conditions. Determination of microparticle concentration, size distribution and chemical makeup as a function of depth is especially difficult because the particle size measurement either consumes or contaminates the meltwater, preventing further geochemical analysis. Here we describe a microcontroller-based ice core melting system which allows the collection of separate microparticle and chemistry samples from the same depth intervals in the ice core, while logging and accurately depth-tagging real-time electrical conductivity and particle size distribution data. This system was designed specifically to support microparticle analysis of the WAIS Divide WDC06A deep ice core, but many of the subsystems are applicable to more general ice core melting operations. Major system components include: a rotary encoder to measure ice core melt displacement with 0.1 millimeter accuracy, a meltwater tracking system to assign core depths to conductivity, particle and sample vial data, an optical debubbler level control system to protect the Abakus laser particle counter from damage due to air bubbles, a Rabbit 3700 microcontroller which communicates with a host PC, collects encoder and optical sensor data and autonomously operates Gilson peristaltic pumps and fraction collectors to provide automatic sample handling, melt monitor control software operating on a standard PC allowing the user to control and view the status of the system, data logging software operating on the same PC to collect data from the melting, electrical conductivity and microparticle measurement systems. Because microparticle samples can easily be contaminated, we use optical air bubble sensors and high resolution ice core density

S-wave attenuation structure beneath the northern Izu-Bonin arc

Science.gov (United States)

Takahashi, Tsutomu; Obana, Koichiro; Kodaira, Shuichi

2016-04-01

To understand temperature structure or magma distribution in the crust and uppermost mantle, it is essential to know their attenuation structure. This study estimated the 3-D S-wave attenuation structure in the crust and uppermost mantle at the northern Izu-Bonin arc, taking into account the apparent attenuation due to multiple forward scattering. In the uppermost mantle, two areas of high seismic attenuation (high Q -1) imaged beneath the volcanic front were mostly colocated with low-velocity anomalies. This coincidence suggests that these high- Q -1 areas in low-velocity zones are the most likely candidates for high-temperature regions beneath volcanoes. The distribution of random inhomogeneities indicated the presence of three anomalies beneath the volcanic front: Two were in high- Q -1 areas but the third was in a moderate- Q -1 area, indicating a low correlation between random inhomogeneities and Q -1. All three anomalies of random inhomogeneities were rich in short-wavelength spectra. The most probable interpretation of such spectra is the presence of volcanic rock, which would be related to accumulated magma intrusion during episodes of volcanic activity. Therefore, the different distributions of Q -1 and random inhomogeneities imply that the positions of hot regions in the uppermost mantle beneath this arc have changed temporally; therefore, they may provide important constraints on the evolutionary processes of arc crust and volcanoes.

Comparisons of seismic and electromagnetic structures of the MELT area

Science.gov (United States)

Evans, R. L.; Hirth, G.; Forsyth, D.; Baba, K.; Chave, A.

2003-04-01

Both seismic and electromagnetic (EM) models from the MELT experiment show similar broad scale features in the mantle beneath the Southern EPR. In all EM models, the conductivity in the upper 50-60˜km is considerably higher to the west of the ridge than to the east. Similarly, seismic models of short period Love waves are asymmetric in velocity structure, with slower velocities to the west of the ridge within the upper 60˜km. Body wave data suggest a similar asymmetry, although the depth extent is not as well defined. West of the ridge, both the higher conductivities and lower velocities have been attributed to the presence of a small melt fraction, although the anomalous regions estimated from different techniques do not entirely agree. To the east, there is a rapid increase in resistivity and S-wave velocity, indicating that within 25˜km of the axis the mantle above 70˜km is both dry and melt-free. Further away from the ridge, the boundary between a conductive asthenospheric mantle and a resistive overlying mantle flattens, at a depth around 60-80˜km. Rayleigh wave inversions also show fairly flat velocity contours with a broad minimum centered at 60-80˜km. Both of these features are consistent with a transition from dry to damp mantle. Also away from the ridge, EM data, shear-wave splitting, and Rayleigh waves all require an azimuthally anisotropic mantle consistent with the a-axis of olivine being preferentially oriented horizontally and perpendicular to the ridge. Anisotropy in EM data suggests damp mantle conditions in the 100-200˜km depth range, with enhanced conduction along the a-axis of olivine. Rayleigh waves are most sensitive to shallower structure and require anisotropy in the upper 70˜km. In the uppermost 40˜km, the most conductive and lowest velocity regions are close to the axis but offset 5-10˜km to the west. Some anisotropic inversions recover a vertically conductive feature that could be interpreted as a few percent melt distributed in

Extensive, water-rich magma reservoir beneath southern Montserrat

Science.gov (United States)

Edmonds, M.; Kohn, S. C.; Hauri, E. H.; Humphreys, M. C. S.; Cassidy, M.

2016-05-01

South Soufrière Hills and Soufrière Hills volcanoes are 2 km apart at the southern end of the island of Montserrat, West Indies. Their magmas are distinct geochemically, despite these volcanoes having been active contemporaneously at 131-129 ka. We use the water content of pyroxenes and melt inclusion data to reconstruct the bulk water contents of magmas and their depth of storage prior to eruption. Pyroxenes contain up to 281 ppm H2O, with significant variability between crystals and from core to rim in individual crystals. The Al content of the enstatites from Soufrière Hills Volcano (SHV) is used to constrain melt-pyroxene partitioning for H2O. The SHV enstatite cores record melt water contents of 6-9 wt%. Pyroxene and melt inclusion water concentration pairs from South Soufriere Hills basalts independently constrain pyroxene-melt partitioning of water and produces a comparable range in melt water concentrations. Melt inclusions recorded in plagioclase and in pyroxene contain up to 6.3 wt% H2O. When combined with realistic melt CO2 contents, the depth of magma storage for both volcanoes ranges from 5 to 16 km. The data are consistent with a vertically protracted crystal mush in the upper crust beneath the southern part of Montserrat which contains heterogeneous bodies of eruptible magma. The high water contents of the magmas suggest that they contain a high proportion of exsolved fluids, which has implications for the rheology of the mush and timescales for mush reorganisation prior to eruption. A depletion in water in the outer 50-100 μm of a subset of pyroxenes from pumices from a Vulcanian explosion at Soufrière Hills in 2003 is consistent with diffusive loss of hydrogen during magma ascent over 5-13 h. These timescales are similar to the mean time periods between explosions in 1997 and in 2003, raising the possibility that the driving force for this repetitive explosive behaviour lies not in the shallow system, but in the deeper parts of a vertically

Real-time qualitative study of forsterite crystal - Melt lithium distribution by laser-induced breakdown spectroscopy

Science.gov (United States)

Lebedev, V. F.; Makarchuk, P. S.; Stepanov, D. N.

2017-11-01

A factor of lithium distribution between single-crystal forsterite (Cr,Li:Mg2SiO4) and its melt are studied by laser-induced breakdown spectroscopy. Lithium content in the crystalline phase is found to achieve a saturation at relatively low Li concentration in the melt (about 0.02%wt.). An algorithm and software are developed for real-time analysis of the studied spectra of lithium trace amounts at wide variation of the plasma radiation intensity. The analyzed plasma spectra processing method is based on the calculation of lithium emission part in the total emission of the target plasma for each recorded spectrum followed by the error estimation for the series of measurements in the normal distribution approximation.

Snow Dunes: A Controlling Factor of Melt Pond Distribution on Arctic Sea Ice

Science.gov (United States)

Petrich, Chris; Eicken, Hajo; Polashenski, Christopher M.; Sturm, Matthew; Harbeck, Jeremy P.; Perovich, Donald K.; Finnegan, David C.

2012-01-01

The location of snow dunes over the course of the ice-growth season 2007/08 was mapped on level landfast first-year sea ice near Barrow, Alaska. Landfast ice formed in mid-December and exhibited essentially homogeneous snow depths of 4-6 cm in mid-January; by early February distinct snow dunes were observed. Despite additional snowfall and wind redistribution throughout the season, the location of the dunes was fixed by March, and these locations were highly correlated with the distribution of meltwater ponds at the beginning of June. Our observations, including ground-based light detection and ranging system (lidar) measurements, show that melt ponds initially form in the interstices between snow dunes, and that the outline of the melt ponds is controlled by snow depth contours. The resulting preferential surface ablation of ponded ice creates the surface topography that later determines the melt pond evolution.

Characterization of ion distributions near the surface of sodium-containing and sodium-depleted calcium aluminosilicate glass melts

International Nuclear Information System (INIS)

Corrales, Louis R.; Du, Jincheng

2006-01-01

The distribution of cation and anion components of sodium containing calcium aluminosilicate glass was studied by classical molecular dynamics simulations in a high temperature melt in the bulk and at the vacuum-melt interface. A significant redistribution of the sodium and non-bridging oxygen ions was observed. Subsequently, a sodium depleted calcium aluminosilicate glass melt was simulated to determine the sensitivity of the redistribution of ions near the vacuum-melt interface to the presence of sodium ions. It is found that the thermodynamic equilibrium condition near a surface favors the enrichment of non-bridging oxygen ions that is closely associated with enrichment of the sodium ions

Neogene subduction beneath Java, Indonesia: Slab tearing and changes in magmatism

Science.gov (United States)

Cottam, Michael; Hall, Robert; Cross, Lanu; Clements, Benjamin; Spakman, Wim

2010-05-01

Java is a Neogene calc-alkaline volcanic island arc formed by the northwards subduction of the Indo-Australian Plate beneath Sundaland, the continental core of SE Asia. The island has a complex history of volcanism and displays unusual subduction characteristics. These characteristics are consistent with the subduction of a hole in the down going slab that was formed by the arrival of a buoyant oceanic plateau at the trench. Subduction beneath Java began in the Eocene. However, the position and character of the calc-alkaline arc has changed over time. An older Paleogene arc ceased activity in the Early Miocene. Volcanic activity resumed in the Late Miocene producing a younger arc to the north of the older arc, and continues to the present day. An episode of Late Miocene thrusting at about 7 Ma is observed throughout Java and appears to be linked to northward movement of the arc. Arc rocks display typical calc-alkaline characteristics and reflect melting of the mantle wedge and subducted sediments associated with high fluid fluxes. Between West Java and Bali the present arc-trench gap is unusually wide at about 300 km. Seismicity identifies subducted Indian Ocean lithosphere that dips north at about 20° between the trench and the arc and then dips more steeply at about 60-70° from 100 to 600 km depth. In East Java there is gap in seismicity between about 250 and 500 km. Seismic tomography shows that this gap is not an aseismic section of the subduction zone but a hole in the slab. East Java is also unusual in the presence of K-rich volcanoes, now inactive, to the north of the calc-alkaline volcanoes of the active arc. In contrast to the calc-alkaline volcanism of the main arc, these K-rich melts imply lower fluid fluxes and a different mantle source. We suggest that all these observations can be explained by the tearing of the subducting slab when a buoyant oceanic plateau arrived at the trench south of East Java at about 8 Ma. With the slab unable to subduct

Deformation in D″ Beneath North America From Anisotropy

Science.gov (United States)

Nowacki, A. J.; Wookey, J.; Kendall, J. M.

2009-12-01

same but with a tilted axis is possible (TTI) and would be consistent with inclusions of seismically-distinct material such as melt. TTI planes of isotropy dip south beneath Florida, southwest beneath western USA and southeast beneath Yucatan. However we test other slip systems in MgO, pv and ppv to determine if deformation in these phases can account for the observed anisotropy. The systems [100](010) and [1̅10](110) in ppv are consistent everywhere; pv is not beneath Yucatan. If we assume a general downwelling and displacement of mantle material in the seismically fast D″, corresponding to the impingement of slab material, slip along [100](010) seems more likely, with the possibility that slip along (110) as a transformation texture also occurs in the seismically fastest regions (Walte et al, GRL, 2009). With a new breed of detailed mantle deformation models, or experimental evidence of which system dominates, seismic anisotropy may be used to map deformation in D″ and provide greater insight into Earth's convecting interior.

The particle size distribution of fragmented melt debris from molten fuel coolant interactions

International Nuclear Information System (INIS)

Fletcher, D.F.

1984-04-01

Results are presented of a study of the types of statistical distributions which arise when examining debris from Molten Fuel Coolant Interactions. The lognormal probability distribution and the modifications of this distribution which result from the mixing of two distributions or the removal of some debris are described. Methods of fitting these distributions to real data are detailed. A two stage fragmentation model has been developed in an attempt to distinguish between the debris produced by coarse mixing and fine scale fragmentation. However, attempts to fit this model to real data have proved unsuccessful. It was found that the debris particle size distributions from experiments at Winfrith with thermite generated uranium dioxide/molybdenum melts were Upper Limit Lognormal. (U.K.)

Modelling of the controlled melt flow in a glass melting space – Its melting performance and heat losses

Czech Academy of Sciences Publication Activity Database

Jebavá, Marcela; Dyrčíková, Petra; Němec, Lubomír

2015-01-01

Roč. 430, DEC 15 (2015), s. 52-63 ISSN 0022-3093 Institutional support: RVO:67985891 Keywords : glass melt flow * mathematical modelling * energy distribution * space utilizatios * melting performance Subject RIV: JH - Ceramics, Fire-Resistant Materials and Glass Impact factor: 1.825, year: 2015

Steady distribution structure of point defects near crystal-melt interface under pulling stop of CZ Si crystal

Science.gov (United States)

Abe, T.; Takahashi, T.; Shirai, K.

2017-02-01

In order to reveal a steady distribution structure of point defects of no growing Si on the solid-liquid interface, the crystals were grown at a high pulling rate, which Vs becomes predominant, and the pulling was suddenly stopped. After restoring the variations of the crystal by the pulling-stop, the crystals were then left in prolonged contact with the melt. Finally, the crystals were detached and rapidly cooled to freeze point defects and then a distribution of the point defects of the as-grown crystals was observed. As a result, a dislocation loop (DL) region, which is formed by the aggregation of interstitials (Is), was formed over the solid-liquid interface and was surrounded with a Vs-and-Is-free recombination region (Rc-region), although the entire crystals had been Vs rich in the beginning. It was also revealed that the crystal on the solid-liquid interface after the prolonged contact with the melt can partially have a Rc-region to be directly in contact with the melt, unlike a defect distribution of a solid-liquid interface that has been growing. This experimental result contradicts a hypothesis of Voronkov's diffusion model, which always assumes the equilibrium concentrations of Vs and Is as the boundary condition for distribution of point defects on the growth interface. The results were disscussed from a qualitative point of view of temperature distribution and thermal stress by the pulling-stop.

Seismic Constraints on the Lithosphere-Asthenosphere Boundary Beneath the Izu-Bonin Area: Implications for the Oceanic Lithospheric Thinning

Science.gov (United States)

Cui, Qinghui; Wei, Rongqiang; Zhou, Yuanze; Gao, Yajian; Li, Wenlan

2018-01-01

The lithosphere-asthenosphere boundary (LAB) is the seismic discontinuity with negative velocity contrasts in the upper mantle. Seismic detections on the LAB are of great significance in understanding the plate tectonics, mantle convection and lithospheric evolution. In this paper, we study the LAB in the Izu-Bonin subduction zone using four deep earthquakes recorded by the permanent and temporary seismic networks of the USArray. The LAB is clearly revealed with sP precursors (sdP) through the linear slant stacking. As illustrated by reflected points of the identified sdP phases, the depth of LAB beneath the Izu-Bonin Arc (IBA) is about 65 km with a range of 60-68 km. The identified sdP phases with opposite polarities relative to sP phases have the average relative amplitude of 0.21, which means a 3.7% velocity drop and implies partial melting in the asthenosphere. On the basis of the crustal age data, the lithosphere beneath the IBA is located at the 1100 °C isotherm calculated with the GDH1 model. Compared to tectonically stable areas, such as the West Philippine Basin (WPB) and Parece Vela Basin (PVB) in the Philippine Sea, the lithosphere beneath the Izu-Bonin area shows the obvious lithospheric thinning. According to the geodynamic and petrological studies, the oceanic lithospheric thinning phenomenon can be attributed to the strong erosion of the small-scale convection in the mantle wedge enriched in volatiles and melts.

Thermal classification of lithospheric discontinuities beneath USArray

Science.gov (United States)

Hansen, Steven M.; Dueker, Ken; Schmandt, Brandon

2015-12-01

Broadband seismic data from the United States were processed into Ps and Sp receiver function image volumes for the purpose of constraining negative velocity gradients (NVG) at depths between the Moho and 200 km. Moho depth picks from the two independent datasets are in good agreement, however, large discrepancies in NVG picks occur and are attributed to free-surface multiples which obscure deep NVG arrivals in the Ps data. From the Sp data, shallow NVG are found west of the Rockies and in the central US while deep and sporadic NVG are observed beneath the Great Plains and northern Rockies. To aid the interpretation of the observed NVG arrivals, the mantle thermal field is estimated by mapping surface wave tomography velocities to temperature assuming an anelastic olivine model. The distribution of temperature versus NVG depth is bi-modal and displays two distinct thermal populations that are interpreted to represent both the lithosphere-asthenosphere boundary (LAB) and mid-lithosphere discontinuities (MLD). LAB arrivals occur in the western US at 60-85 km and 1200-1400 °C depth suggesting that they manifest partial melt near the base of the thermal plate. MLD arrivals primarily occur at 70-110 km depth and 700-900 °C and we hypothesize that these arrivals are caused by a low-velocity metasomatic layer containing phlogopite resulting from magma crystallization products that accumulate within long-lived thick lithosphere.

Seismic evidence of the lithosphere-asthenosphere boundary beneath Izu-Bonin area

Science.gov (United States)

Cui, H.; Gao, Y.; Zhou, Y.

2016-12-01

The lithosphere-asthenosphere boundary (LAB), separating the rigid lithosphere and the ductile asthenosphere layers, is the seismic discontinuity with the negative velocity contrast of the Earth's interior [Fischer et al., 2010]. The LAB has been also termed the Gutenberg (G) discontinuity that defines the top of the low velocity zone in the upper mantle [Gutenberg, 1959; Revenaugh and Jordan, 1991]. The seismic velocity, viscosity, resistivity and other physical parameters change rapidly with the depths across the boundary [Eaton et al., 2009]. Seismic detections on the LAB in subduction zone regions are of great help to understand the interactions between the lithosphere and asthenosphere layers and the geodynamic processes related with the slab subductions. In this study, the vertical broadband waveforms are collected from three deep earthquake events occurring from 2000 to 2014 with the focal depths of 400 600 km beneath the Izu-Bonin area. The waveform data is processed with the linear slant stack method [Zang and Zhou, 2002] to obtain the vespagrams in the relative travel-time to slowness domain and the stacked waveforms. The sP precursors reflected on the LAB (sLABP), which have the negative polarities with the amplitude ratios of 0.17 0.21 relative to the sP phases, are successfully extracted. Based on the one-dimensional modified velocity model (IASP91-IB), we obtain the distributions for six reflected points of the sLABP phases near the source region. Our results reveal that the LAB depths range between 58 and 65 km beneath the Izu-Bonin Arc, with the average depth of 62 km and the small topography of 7 km. Compared with the results of the tectonic stable areas in Philippine Sea [Kawakatsu et al., 2009; Kumar and Kawakatsu, 2011], the oceanic lithosphere beneath the Izu-Bonin Arc shows the obvious thinning phenomena. We infer that the lithospheric thinning is closely related with the partial melting, which is caused by the volatiles continuously released

Dynamics of upper mantle rocks decompression melting above hot spots under continental plates

Science.gov (United States)

Perepechko, Yury; Sorokin, Konstantin; Sharapov, Victor

2014-05-01

Numeric 2D simulation of the decompression melting above the hot spots (HS) was accomplished under the following conditions: initial temperature within crust mantle section was postulated; thickness of the metasomatized lithospheric mantle is determined by the mantle rheology and position of upper asthenosphere boundary; upper and lower boundaries were postulated to be not permeable and the condition for adhesion and the distribution of temperature (1400-2050°C); lateral boundaries imitated infinity of layer. Sizes and distribution of lateral points, their symmetry, and maximum temperature varied between the thermodynamic condition for existences of perovskite - majorite transition and its excess above transition temperature. Problem was solved numerically a cell-vertex finite volume method for thermo hydrodynamic problems. For increasing convergence of iterative process the method of lower relaxation with different value of relaxation parameter for each equation was used. The method of through calculation was used for the increase in the computing rate for the two-layered upper mantle - lithosphere system. Calculated region was selected as 700 x (2100-4900) km. The time step for the study of the asthenosphere dynamics composed 0.15-0.65 Ma. The following factors controlling the sizes and melting degree of the convective upper mantle, are shown: a) the initial temperature distribution along the section of upper mantleb) sizes and the symmetry of HS, c) temperature excess within the HS above the temperature on the upper and lower mantle border TB=1500-2000oC with 5-15% deviation but not exceed 2350oC. It is found, that appearance of decompression melting with HS presence initiate primitive mantle melting at TB > of 1600oC. Initial upper mantle heating influence on asthenolens dimensions with a constant HS size is controlled mainly by decompression melting degree. Thus, with lateral sizes of HS = 400 km the decompression melting appears at TB > 1600oC and HS

Eddy-resolving simulations of the Fimbul Ice Shelf cavity circulation: Basal melting and exchange with open ocean

Science.gov (United States)

Hattermann, T.; Smedsrud, L. H.; Nøst, O. A.; Lilly, J. M.; Galton-Fenzi, B. K.

2014-10-01

Melting at the base of floating ice shelves is a dominant term in the overall Antarctic mass budget. This study applies a high-resolution regional ice shelf/ocean model, constrained by observations, to (i) quantify present basal mass loss at the Fimbul Ice Shelf (FIS); and (ii) investigate the oceanic mechanisms that govern the heat supply to ice shelves in the Eastern Weddell Sea. The simulations confirm the low melt rates suggested by observations and show that melting is primarily determined by the depth of the coastal thermocline, regulating deep ocean heat fluxes towards the ice. Furthermore, the uneven distribution of ice shelf area at different depths modulates the melting response to oceanic forcing, causing the existence of two distinct states of melting at the FIS. In the simulated present-day state, only small amounts of Modified Warm Deep Water enter the continental shelf, and ocean temperatures beneath the ice are close to the surface freezing point. The basal mass loss in this so-called state of "shallow melting" is mainly controlled by the seasonal inflow of solar-heated surface water affecting large areas of shallow ice in the upper part of the cavity. This is in contrast to a state of "deep melting", in which the thermocline rises above the shelf break depth, establishing a continuous inflow of Warm Deep Water towards the deep ice. The transition between the two states is found to be determined by a complex response of the Antarctic Slope Front overturning circulation to varying climate forcings. A proper representation of these frontal dynamics in climate models will therefore be crucial when assessing the evolution of ice shelf basal melting along this sector of Antarctica.

X-ray fractography by using synchrotron radiation source. Residual stress distribution just beneath fatigue fracture surface

International Nuclear Information System (INIS)

Akita, Koichi; Yoshioka, Yasuo; Suzuki, Hiroshi; Sasaki, Toshihiko

2000-01-01

The residual stress distributions just beneath the fatigue fracture surface were measured using synchrotron radiation with three different wavelengths, i.e., three different penetration depths. The residual stress distributions were estimated from three kinds of diffraction data by the following process. First, a temporary residual stress distribution in the depth direction is assumed. Theoretical 2θ-sin 2 ψ diagrams for each wavelength, where each has a different penetration depth, are calculated by the cosψ method developed by one of the authors. The sum total of the differences between the theoretical and experimental values of the diffraction angle in 2θ-sin 2 ψ diagrams is calculated. This total value is minimized by changing the assumed stress distribution by the quasi-Newton optimization method. Finally, optimized 2θ-sin 2 ψ diagrams for each penetration depth and detailed stress distribution are determined. The true surface residual stress is obtained from this stress distribution. No effect of load ratio R (= P min /P max ) on the residual stresses of the fatigue fracture surfaces in low-carbon steels was observed when the sin 2 ψ method was used for stress measurement. However, the residual stresses became higher with increasing R when these were measured by the proposed method. On the basis of this, the stress intensity factor range, ΔK, can be estimated from the residual stress on the fatigue fracture surface. (author)

Modelling present-day basal melt rates for Antarctic ice shelves using a parametrization of buoyant meltwater plumes

Science.gov (United States)

Lazeroms, Werner M. J.; Jenkins, Adrian; Hilmar Gudmundsson, G.; van de Wal, Roderik S. W.

2018-01-01

Basal melting below ice shelves is a major factor in mass loss from the Antarctic Ice Sheet, which can contribute significantly to possible future sea-level rise. Therefore, it is important to have an adequate description of the basal melt rates for use in ice-dynamical models. Most current ice models use rather simple parametrizations based on the local balance of heat between ice and ocean. In this work, however, we use a recently derived parametrization of the melt rates based on a buoyant meltwater plume travelling upward beneath an ice shelf. This plume parametrization combines a non-linear ocean temperature sensitivity with an inherent geometry dependence, which is mainly described by the grounding-line depth and the local slope of the ice-shelf base. For the first time, this type of parametrization is evaluated on a two-dimensional grid covering the entire Antarctic continent. In order to apply the essentially one-dimensional parametrization to realistic ice-shelf geometries, we present an algorithm that determines effective values for the grounding-line depth and basal slope in any point beneath an ice shelf. Furthermore, since detailed knowledge of temperatures and circulation patterns in the ice-shelf cavities is sparse or absent, we construct an effective ocean temperature field from observational data with the purpose of matching (area-averaged) melt rates from the model with observed present-day melt rates. Our results qualitatively replicate large-scale observed features in basal melt rates around Antarctica, not only in terms of average values, but also in terms of the spatial pattern, with high melt rates typically occurring near the grounding line. The plume parametrization and the effective temperature field presented here are therefore promising tools for future simulations of the Antarctic Ice Sheet requiring a more realistic oceanic forcing.

Analysis of groundwater flow beneath ice sheets

Energy Technology Data Exchange (ETDEWEB)

Boulton, G. S.; Zatsepin, S.; Maillot, B. [Univ. of Edinburgh (United Kingdom). Dept. of Geology and Geophysics

2001-03-01

The large-scale pattern of subglacial groundwater flow beneath European ice sheets was analysed in a previous report. It was based on a two-dimensional flowline model. In this report, the analysis is extended to three dimensions by exploring the interactions between groundwater and tunnel flow. A theory is developed which suggests that the large-scale geometry of the hydraulic system beneath an ice sheet is a coupled, self-organising system. In this system the pressure distribution along tunnels is a function of discharge derived from basal meltwater delivered to tunnels by groundwater flow, and the pressure along tunnels itself sets the base pressure which determines the geometry of catchments and flow towards the tunnel. The large-scale geometry of tunnel distribution is a product of the pattern of basal meltwater production and the transmissive properties of the bed. The tunnel discharge from the ice margin of the glacier, its seasonal fluctuation and the sedimentary characteristics of eskers are largely determined by the discharge of surface meltwater which penetrates to the bed in the terminal zone. The theory explains many of the characteristics of esker systems and can account for tunnel valleys. It is concluded that the large-scale hydraulic regime beneath ice sheets is largely a consequence of groundwater/tunnel flow interactions and that it is essential similar to non-glacial hydraulic regimes. Experimental data from an Icelandic glacier, which demonstrates measured relationships between subglacial tunnel flow and groundwater flow during the transition from summer to winter seasons for a modern glacier, and which support the general conclusions of the theory is summarised in an appendix.

Analysis of groundwater flow beneath ice sheets

International Nuclear Information System (INIS)

Boulton, G. S.; Zatsepin, S.; Maillot, B.

2001-03-01

The large-scale pattern of subglacial groundwater flow beneath European ice sheets was analysed in a previous report. It was based on a two-dimensional flowline model. In this report, the analysis is extended to three dimensions by exploring the interactions between groundwater and tunnel flow. A theory is developed which suggests that the large-scale geometry of the hydraulic system beneath an ice sheet is a coupled, self-organising system. In this system the pressure distribution along tunnels is a function of discharge derived from basal meltwater delivered to tunnels by groundwater flow, and the pressure along tunnels itself sets the base pressure which determines the geometry of catchments and flow towards the tunnel. The large-scale geometry of tunnel distribution is a product of the pattern of basal meltwater production and the transmissive properties of the bed. The tunnel discharge from the ice margin of the glacier, its seasonal fluctuation and the sedimentary characteristics of eskers are largely determined by the discharge of surface meltwater which penetrates to the bed in the terminal zone. The theory explains many of the characteristics of esker systems and can account for tunnel valleys. It is concluded that the large-scale hydraulic regime beneath ice sheets is largely a consequence of groundwater/tunnel flow interactions and that it is essential similar to non-glacial hydraulic regimes. Experimental data from an Icelandic glacier, which demonstrates measured relationships between subglacial tunnel flow and groundwater flow during the transition from summer to winter seasons for a modern glacier, and which support the general conclusions of the theory is summarised in an appendix

Hot upwelling conduit beneath the Atlas Mountains, Morocco

Science.gov (United States)

Sun, Daoyuan; Miller, Meghan S.; Holt, Adam F.; Becker, Thorsten W.

2014-11-01

The Atlas Mountains of Morocco display high topography, no deep crustal root, and regions of localized Cenozoic alkaline volcanism. Previous seismic imaging and geophysical studies have implied a hot mantle upwelling as the source of the volcanism and high elevation. However, the existence, shape, and physical properties of an associated mantle anomaly are debated. Here we use seismic waveform analysis from a broadband deployment and geodynamic modeling to define the physical properties and morphology of the anomaly. The imaged low-velocity structure extends to ~200 km beneath the Atlas and appears ~350 K hotter than the ambient mantle with possible partial melting. It includes a lateral conduit, which suggests that the Quaternary volcanism arises from the upper mantle. Moreover, the shape and temperature of the imaged anomaly indicate that the unusually high topography of the Atlas Mountains is due to active mantle support.

Distribution of siderophile and other trace elements in melt rock at the Chicxulub impact structure

Science.gov (United States)

Schuraytz, B. C.; Lindstrom, D. J.; Martinez, R. R.; Sharpton, V. L.; Marin, L. E.

1994-01-01

Recent isotopic and mineralogical studies have demonstrated a temporal and chemical link between the Chicxulub multiring impact basin and ejecta at the Cretaceous-Tertiary boundary. A fundamental problem yet to be resolved, however, is identification of the projectile responsible for this cataclysmic event. Drill core samples of impact melt rock from the Chichxulub structure contain Ir and Os abundances and Re-Os isotopic ratios indicating the presence of up to approx. 3 percent meteoritic material. We have used a technique involving microdrilling and high sensitivity instrumental neutron activation analysis (INAA) in conjunction with electron microprobe analysis to characterize further the distribution of siderophile and other trace elements among phases within the C1-N10 melt rock.

Seismic Structure of the Shallow Mantle Beneath the Endeavor Segment of the Juan de Fuca Ridge

Science.gov (United States)

VanderBeek, B. P.; Toomey, D. R.; Hooft, E. E.; Wilcock, W. S.; Weekly, R. T.; Soule, D. C.

2013-12-01

We present tomographic images of the seismic structure of the shallow mantle beneath the intermediate-spreading Endeavor segment of the Juan de Fuca ridge. Our results provide insight into the relationship between magma supply from the mantle and overlying ridge crest processes. We use seismic energy refracted below the Moho (Pn), as recorded by the Endeavor tomography (ETOMO) experiment, to image the anisotropic and isotropic P wave velocity structure. The ETOMO experiment was an active source seismic study conducted in August 2009 as part of the RIDGE2000 science program. The experimental area extends 100 km along- and 60 km across-axis and encompasses active hydrothermal vent fields near the segment center, the eastern end of the Heck seamount chain, and two overlapping spreading centers (OSCs) at either end of the segment. Previous tomographic analyses of seismic arrivals refracted through the crust (Pg), and reflected off the Moho (PmP), constrain a three-dimensional starting model of crustal velocity and thickness. These Pg and PmP arrivals are incorporated in our inversion of Pn travel-time data to further constrain the isotropic and anisotropic mantle velocity structure. Preliminary results reveal three distinct mantle low-velocity zones, inferred as regions of mantle melt delivery to the base of the crust, that are located: (i) off-axis near the segment center, (ii) beneath the Endeavor-West Valley OSC, and (iii) beneath the Cobb OSC near Split Seamount. The mantle anomalies are located at intervals of ~30 to 40 km along-axis and the low velocity anomalies beneath the OSCs are comparable in magnitude to the one located near the segment center. The direction of shallow mantle flow is inferred from azimuthal variations in Pn travel-time residuals relative to a homogeneous isotropic mantle. Continuing analysis will focus on constraining spatial variations in the orientation of azimuthal anisotropy. On the basis of our results, we will discuss the transport of

Effect of re-melting on particle distribution and interface formation in SiC reinforced 2124Al matrix composite

Energy Technology Data Exchange (ETDEWEB)

Mandal, Durbadal, E-mail: durbadal73@yahoo.co.in [MEF Division, CSIR-National Metallurgical Laboratory, Jamshedpur 831007 (India); Viswanathan, Srinath [Dept of Metallurgical and Materials Engineering, University of Alabama, Tuscaloosa, AL (United States)

2013-12-15

The interface between metal matrix and ceramic reinforcement particles plays an important role in improving properties of the metal matrix composites. Hence, it is important to find out the interface structure of composite after re-melting. In the present investigation, the 2124Al matrix with 10 wt.% SiC particle reinforced composite was re-melted at 800 °C and 900 °C for 10 min followed by pouring into a permanent mould. The microstructures reveal that the SiC particles are distributed throughout the Al-matrix. The volume fraction of SiC particles varies from top to bottom of the composite plate and the difference increases with the decrease of re-melting temperature. The interfacial structure of re-melted 2124Al–10 wt.%SiC composite was investigated using scanning electron microscopy, an electron probe micro-analyzer, a scanning transmission electron detector fitted with scanning electron microscopy and an X-ray energy dispersive spectrometer. It is found that a thick layer of reaction product is formed at the interface of composite after re-melting. The experimental results show that the reaction products at the interface are associated with high concentration of Cu, Mg, Si and C. At re-melting temperature, liquid Al reacts with SiC to form Al{sub 4}C{sub 3} and Al–Si eutectic phase or elemental Si at the interface. High concentration of Si at the interface indicates that SiC is dissociated during re-melting. The X-ray energy dispersive spectrometer analyses confirm that Mg- and Cu-enrich phases are formed at the interface region. The Mg is segregated at the interface region and formed MgAl{sub 2}O{sub 4} in the presence of oxygen. The several elements identified at the interface region indicate that different types of interfaces are formed in between Al matrix and SiC particles. The Al–Si eutectic phase is formed around SiC particles during re-melting which restricts the SiC dissolution. - Highlights: • Re-melted composite shows homogeneous particle

Numerical simulation of the oxygen concentration distribution in silicon melt for different crystal lengths during Czochralski growth with a transverse magnetic field

Science.gov (United States)

Chen, Jyh-Chen; Chiang, Pei-Yi; Nguyen, Thi Hoai Thu; Hu, Chieh; Chen, Chun-Hung; Liu, Chien-Cheng

2016-10-01

A three-dimensional simulation model is used to study the oxygen concentration distribution in silicon crystal during the Czochralski growth process under a transverse uniform magnetic field. The flow, temperature, and oxygen concentration distributions inside the furnace are calculated for different crystal lengths. There is significant variation in the flow structure in the melt with the growth length. The results show that in the initial stages, there is a decrease in the oxygen concentration at the crystal-melt interface as the length of the growing crystal increases. As the crystal lengthens further, a minimum value is reached after which the oxygen concentration increases continuously. This trend is consistent with that shown in the experimental results. The variation of the oxygen concentration with the growth length is strongly related to the depth of the melt in the crucible and the flow structure inside the melt. Better uniformity of the axial oxygen concentration can be achieved by proper adjustment of the crucible rotation rate during the growth process.

Seasonal variation of ice melting on varying layers of debris of Lirung Glacier, Langtang Valley, Nepal

Directory of Open Access Journals (Sweden)

M. B. Chand

2015-05-01

Full Text Available Glaciers in the Himalayan region are often covered by extensive debris cover in ablation areas, hence it is essential to assess the effect of debris on glacier ice melt. Seasonal melting of ice beneath different thicknesses of debris on Lirung Glacier in Langtang Valley, Nepal, was studied during three seasons of 2013–14. The melting rates of ice under 5 cm debris thickness are 3.52, 0.09, and 0.85 cm d−1 during the monsoon, winter and pre-monsoon season, respectively. Maximum melting is observed in dirty ice (0.3 cm debris thickness and the rate decreases with the increase of debris thickness. The energy balance calculations on dirty ice and at 40 cm debris thickness show that the main energy source of ablation is net radiation. The major finding from this study is that the maximum melting occurs during the monsoon season than rest of the seasons.

Detailed Configuration of the Underthrusting Indian Lithosphere Beneath Western Tibet Revealed by Receiver Function Images

Science.gov (United States)

Xu, Qiang; Zhao, Junmeng; Yuan, Xiaohui; Liu, Hongbing; Pei, Shunping

2017-10-01

We analyze the teleseismic waveform data recorded by 42 temporary stations from the Y2 and ANTILOPE-1 arrays using the P and S receiver function techniques to investigate the lithospheric structure beneath western Tibet. The Moho is reliably identified as a prominent feature at depths of 55-82 km in the stacked traces and in depth migrated images. It has a concave shape and reaches the deepest location at about 80 km north of the Indus-Yarlung suture (IYS). An intracrustal discontinuity is observed at 55 km depth below the southern Lhasa terrane, which could represent the upper border of the eclogitized underthrusting Indian lower crust. Underthrusting of the Indian crust has been widely observed beneath the Lhasa terrane and correlates well with the Bouguer gravity low, suggesting that the gravity anomalies in the Lhasa terrane are induced by topography of the Moho. At 20 km depth, a midcrustal low-velocity zone (LVZ) is observed beneath the Tethyan Himalaya and southern Lhasa terrane, suggesting a layer of partial melts that decouples the thrust/fold deformation of the upper crust from the shortening and underthrusting in the lower crust. The Sp conversions at the lithosphere-asthenosphere boundary (LAB) can be recognized at depths of 130-200 km, showing that the Indian lithospheric mantle is underthrusting with a ramp-flat shape beneath southern Tibet and probably is detached from the lower crust immediately under the IYS. Our observations reconstruct the configuration of the underthrusting Indian lithosphere and indicate significant along strike variations.

Petrological Geodynamics of Mantle Melting I. AlphaMELTS + Multiphase Flow: Dynamic Equilibrium Melting, Method and Results

Directory of Open Access Journals (Sweden)

Massimiliano Tirone

2017-10-01

Full Text Available The complex process of melting in the Earth's interior is studied by combining a multiphase numerical flow model with the program AlphaMELTS which provides a petrological description based on thermodynamic principles. The objective is to address the fundamental question of the effect of the mantle and melt dynamics on the composition and abundance of the melt and the residual solid. The conceptual idea is based on a 1-D description of the melting process that develops along an ideal vertical column where local chemical equilibrium is assumed to apply at some level in space and time. By coupling together the transport model and the chemical thermodynamic model, the evolution of the melting process can be described in terms of melt distribution, temperature, pressure and solid and melt velocities but also variation of melt and residual solid composition and mineralogical abundance at any depth over time. In this first installment of a series of three contributions, a two-phase flow model (melt and solid assemblage is developed under the assumption of complete local equilibrium between melt and a peridotitic mantle (dynamic equilibrium melting, DEM. The solid mantle is also assumed to be completely dry. The present study addresses some but not all the potential factors affecting the melting process. The influence of permeability and viscosity of the solid matrix are considered in some detail. The essential features of the dynamic model and how it is interfaced with AlphaMELTS are clearly outlined. A detailed and explicit description of the numerical procedure should make this type of numerical models less obscure. The general observation that can be made from the outcome of several simulations carried out for this work is that the melt composition varies with depth, however the melt abundance not necessarily always increases moving upwards. When a quasi-steady state condition is achieved, that is when melt abundance does not varies significantly

Evolving magma storage conditions beneath Mount St. Helens inferred from chemical variations in melt inclusions from the 1980-1986 and current (2004-2006) eruptions: Chapter 33 in A volcano rekindled: the renewed eruption of Mount St. Helens, 2004-2006

Science.gov (United States)

Blundy, Jon; Cashman, Katharine V.; Berlo, Kim; Sherrod, David R.; Scott, William E.; Stauffer, Peter H.

2008-01-01

Major element, trace element, and volatile concentrations in 187 glassy melt inclusions and 25 groundmass glasses from the 1980-86 eruption of Mount St. Helens are presented, together with 103 analyses of touching FE-Ti oxide pairs from the same samples. These data are used to evaluate the temporal evolution of the magmatic plumbing system beneath the volcano during 1980-86 and so provide a framework in which to interpret analyses of melt inclusions from the current (2004-2006) eruption. Major and trace element concentrations of all melt inclusions lie at the high SiO2 end of the data array defined by eruptive products of the late Quaternary age from Mount St. Helens. For several major and trace elements, the glasses define a trend that is oblique to the whole-rock trend, indicating that different mineral assemblages were responsible for the two trends. The whole-rock trend can be ascribed to differentiation of hydrous basaltic parents in a deep-seated magma reservoir, probably at depths great enough to stabilize garnet. In contrast, the glass trends were generated by closed-system crystallization of the phenocryst and microlite mineral assemblages at low pressures. The dissolved H2O content of the melt inclusions from 1980-86, as measured by the ion microprobe, ranges from 0 to 6.7 wt. percent, with the highest values obtained from the plinian phase of May 18, 1980. Water contents decrease with increasing SiO2, consistent with decompression-driven crystallization. Preliminary data for dissolved CO2 in melt inclusions from the May 18 plinian phase from August 7, 1980, indicate that XH2O in a vapor phase was approximately constant at 0.80, irrespective of H2O content, suggestive of closed-system degassing with a high bubble fraction or gas streaming through the subvolcanic system. Temperature and f

Changes in flow of Crosson and Dotson ice shelves, West Antarctica, in response to elevated melt

Science.gov (United States)

Lilien, David A.; Joughin, Ian; Smith, Benjamin; Shean, David E.

2018-04-01

Crosson and Dotson ice shelves are two of the most rapidly changing outlets in West Antarctica, displaying both significant thinning and grounding-line retreat in recent decades. We used remotely sensed measurements of velocity and ice geometry to investigate the processes controlling their changes in speed and grounding-line position over the past 20 years. We combined these observations with inverse modeling of the viscosity of the ice shelves to understand how weakening of the shelves affected this speedup. These ice shelves have lost mass continuously since the 1990s, and we find that this loss results from increasing melt beneath both shelves and the increasing speed of Crosson. High melt rates persisted over the period covered by our observations (1996-2014), with the highest rates beneath areas that ungrounded during this time. Grounding-line flux exceeded basin-wide accumulation by about a factor of 2 throughout the study period, consistent with earlier studies, resulting in significant loss of grounded as well as floating ice. The near doubling of Crosson's speed in some areas during this time is likely the result of weakening of its margins and retreat of its grounding line. This speedup contrasts with Dotson, which has maintained its speed despite increasingly high melt rates near its grounding line, likely a result of the sustained competency of the shelf. Our results indicate that changes to melt rates began before 1996 and suggest that observed increases in melt in the 2000s compounded an ongoing retreat of this system. Advection of a channel along Dotson, as well as the grounding-line position of Kohler Glacier, suggests that Dotson experienced a change in flow around the 1970s, which may be the initial cause of its continuing retreat.

On melting criteria for complex plasma

International Nuclear Information System (INIS)

Klumov, Boris A

2011-01-01

The present paper considers melting criteria for a plasma crystal discovered in dust plasma in 1994. Separate discussions are devoted to three-dimensional (3D) and two-dimensional (2D) systems. In the 3D case, melting criteria are derived based on the properties of local order in a system of microparticles. The order parameters are constructed from the cumulative distributions of the microparticle probability distributions as functions of various rotational invariants. The melting criteria proposed are constructed using static information on microparticle positions: a few snapshots of the system that allow for the determination of particle coordinates are enough to determine the phase state of the system. It is shown that criteria obtained in this way describe well the melting and premelting of 3D complex plasmas. In 2D systems, a system of microparticles interacting via a screened Coulomb (i.e., Debye-Hueckel or Yukawa) potential is considered as an example, using molecular dynamics simulations. A number of new order parameters characterizing the melting of 2D complex plasmas are proposed. The order parameters and melting criteria proposed for 2D and 3D complex plasmas can be applied to other systems as well. (methodological notes)

Investigating the subsurface connection beneath Cerro Negro volcano and the El Hoyo Complex, Nicaragua

Science.gov (United States)

Venugopal, Swetha; Moune, Séverine; Williams-Jones, Glyn

2016-10-01

Cerro Negro, the youngest volcano along the Central American Volcanic Belt (CAVB), is a polygenetic cinder cone with relatively frequent basaltic eruptions. The neighbouring El Hoyo complex, of which Las Pilas is the dominant edifice, is a much larger and older complex with milder and less frequent eruptions. Previous studies have suggested a deep link beneath these two closely spaced volcanoes (McKnight, 1995; MacQueen, 2013). Melt inclusions were collected from various tephra samples in order to determine whether a connection exists and to delineate the features of this link. Major, volatile, and trace elemental compositions reveal a distinct geochemical continuum with Cerro Negro defining the primitive endmember and El Hoyo representing the evolved endmember. Magmatic conditions at the time of melt inclusion entrapment were estimated with major and volatile contents: 2.4 kbar and 1170 °C for Cerro Negro melts and 1.3 kbar and 1130 °C for El Hoyo melts with an overall oxygen fugacity at the NNO buffer. Trace element contents are distinct and suggest Cerro Negro magmas fractionally crystallise while El Hoyo magmas are a mix between primitive Cerro Negro melts and residual and evolved El Hoyo magma. Modelling of end member compositions with alphaMELTS confirms the unique nature of El Hoyo magmas as resulting from incremental mixing between Cerro Negro and residual evolved magma at 4 km depth. Combining all available literature data, this study presents a model of the interconnected subsurface plumbing system. This model considers the modern day analogue of the Lemptégy cinder cones in Massif Central, France and incorporates structurally controlled dykes. The main implications of this study are the classification of Cerro Negro as the newest conduit within the El Hoyo Complex as well as the potential re-activation of the El Hoyo edifice.

The Microwave Properties of Simulated Melting Precipitation Particles: Sensitivity to Initial Melting

Science.gov (United States)

Johnson, B. T.; Olson, W. S.; Skofronick-Jackson, G.

2016-01-01

A simplified approach is presented for assessing the microwave response to the initial melting of realistically shaped ice particles. This paper is divided into two parts: (1) a description of the Single Particle Melting Model (SPMM), a heuristic melting simulation for ice-phase precipitation particles of any shape or size (SPMM is applied to two simulated aggregate snow particles, simulating melting up to 0.15 melt fraction by mass), and (2) the computation of the single-particle microwave scattering and extinction properties of these hydrometeors, using the discrete dipole approximation (via DDSCAT), at the following selected frequencies: 13.4, 35.6, and 94.0GHz for radar applications and 89, 165.0, and 183.31GHz for radiometer applications. These selected frequencies are consistent with current microwave remote-sensing platforms, such as CloudSat and the Global Precipitation Measurement (GPM) mission. Comparisons with calculations using variable-density spheres indicate significant deviations in scattering and extinction properties throughout the initial range of melting (liquid volume fractions less than 0.15). Integration of the single-particle properties over an exponential particle size distribution provides additional insight into idealized radar reflectivity and passive microwave brightness temperature sensitivity to variations in size/mass, shape, melt fraction, and particle orientation.

Seismological evidence for a sub-volcanic arc mantle wedge beneath the Denali volcanic gap, Alaska

Science.gov (United States)

McNamara, D.E.; Pasyanos, M.E.

2002-01-01

Arc volcanism in Alaska is strongly correlated with the 100 km depth contour of the western Aluetian Wadati-Benioff zone. Above the eastern portion of the Wadati-Benioff zone however, there is a distinct lack of volcanism (the Denali volcanic gap). We observe high Poisson's ratio values (0.29-0.33) over the entire length of the Alaskan subduction zone mantle wedge based on regional variations of Pn and Sn velocities. High Poisson's ratios at this depth (40-70 km), adjacent to the subducting slab, are attributed to melting of mantle-wedge peridotites, caused by fluids liberated from the subducting oceanic crust and sediments. Observations of high values of Poisson's ratio, beneath the Denali volcanic gap suggest that the mantle wedge contains melted material that is unable to reach the surface. We suggest that its inability to migrate through the overlying crust is due to increased compression in the crust at the northern apex of the curved Denali fault.

Tin in granitic melts: The role of melting temperature and protolith composition

Science.gov (United States)

Wolf, Mathias; Romer, Rolf L.; Franz, Leander; López-Moro, Francisco Javier

2018-06-01

Granite bound tin mineralization typically is seen as the result of extreme magmatic fractionation and late exsolution of magmatic fluids. Mineralization, however, also could be obtained at considerably less fractionation if initial melts already had enhanced Sn contents. We present chemical data and results from phase diagram modeling that illustrate the dominant roles of protolith composition, melting conditions, and melt extraction/evolution for the distribution of Sn between melt and restite and, thus, the Sn content of melts. We compare the element partitioning between leucosome and restite of low-temperature and high-temperature migmatites. During low-temperature melting, trace elements partition preferentially into the restite with the possible exception of Sr, Cd, Bi, and Pb, that may be enriched in the melt. In high-temperature melts, Ga, Y, Cd, Sn, REE, Pb, Bi, and U partition preferentially into the melt whereas Sc, V, Cr, Co, Ni, Mo, and Ba stay in the restite. This contrasting behavior is attributed to the stability of trace element sequestering minerals during melt generation. In particular muscovite, biotite, titanite, and rutile act as host phases for Sn and, therefore prevent Sn enrichment in the melt as long as they are stable phases in the restite. As protolith composition controls both the mineral assemblage and modal contents of the various minerals, protolith composition eventually also controls the fertility of a rock during anatexis, restite mineralogy, and partitioning behavior of trace metals. If a particular trace element is sequestered in a phase that is stable during partial melting, the resulting melt is depleted in this element whereas the restite becomes enriched. Melt generation at high temperature may release Sn when Sn-hosts become unstable. If melt has not been lost before the breakdown of Sn-hosts, Sn contents in the melt will increase but never will be high. In contrast, if melt has been lost before the decomposition of Sn

Thin Crust and High Crustal Vp/Vs beneath the Central Armenia Plateau of the Lesser Caucasus

Science.gov (United States)

Tseng, T. L.; Lin, C. M.; Huang, B. S.; Karakhanyan, A.

2017-12-01

Armenia volcanic highland is part of the Lesser Caucasus directly connected with the East Anatolian Plateau to the west and Iranian Plateau to the east. Abundant Quaternary volcanoes in Armenia are the youngest among those associated with post-collision of Arabia-Eurasian since Miocene ( 11 Ma). In this study, teleseismic receiver functions were analyzed from a temporary array to constrain the crustal structures under Armenia and the vicinity. The results show that the Moho depth is shallowest beneath central Armenia where the estimated crustal thickness is 32 km with high averaged crustal Vp/Vs of 1.8-2.0 using H-κ technique. The high crustal Vp/Vs is distributed in a wider area but thin crust is confined more locally around stratovolcano Aragats, whose last eruption was about 0.5 Ma. High crustal Vp/Vs value approaching to 2.1 is found near East of volcano Ghegam complex and NW of volcano Ararat with last dated ages of 0.5 and <0.1 Ma, respectively. Such high Vp/Vs (2.0) cannot be explained without high mafic content and the presence of partial melt in the crust. The 1-D velocity models inverted demonstrate that the partial melt is more likely in the low-velocity layer of the lower crust. To support the unusually thin crust in central Armenia, it requires additional thermal buoyancy in the uppermost mantle which is consistent with regionally low Pn velocity found in previous studies. We propose that the volcanism here is facilitated by the stretches of lithosphere.

Migrating Toward Fully 4-D Geodynamical Models of Asthenospheric Circulation and Melt Production at Mid-Ocean Ridges

Science.gov (United States)

van Dam, L.; Kincaid, C. R.; Pockalny, R. A.; Sylvia, R. T.; Hall, P. S.

2017-12-01

Lateral migration of mid-ocean ridge spreading centers is a well-documented phenomenon leading to asymmetric melt production and the surficial expressions thereof. This form of plate motion has been difficult to incorporate into both numerical and analogue geodynamical models, and consequently, current estimates of time-dependent flow, material transport, and melting in the mantle beneath ridges are lacking. To address this, we have designed and built an innovative research apparatus that allows for precise and repeatable simulations of mid-ocean ridge spreading and migration. Three pairs of counter-rotating belts with adjustable lateral orientations are scaled to simulate spreading at, and flow beneath, three 600km wide ridge segments with up to 300km transform offsets. This apparatus is attached to a drive system that allows us to test a full range of axis-parallel to axis-normal migration directions, and is suspended above a reservoir of viscous glucose syrup, a scaled analogue for the upper mantle, and neutrally buoyant tracers. We image plate-driven flow in the syrup with high-resolution digital cameras and use particle image velocimetry methods to obtain information about transport pathlines and flow-induced anisotropy. Suites of experiments are run with and without ridge migration to determine the overall significance of migration on spatial and temporal characteristics of shallow mantle flow. Our experiments cover an expansive parameter space by including various spreading rates, migration speeds and directions, degrees of spreading asymmetry, transform-offset lengths, and upper mantle viscosity conditions. Preliminary results highlight the importance of modeling migratory plate forces. Mantle material exhibits a significant degree of lateral transport, particularly between ridge segments and towards the melt triangle. Magma supply to the melting region is highly complex; parcels of material do not necessarily move along fixed streamlines, rather, they can

Rapakivi texture formation via disequilibrium melting in a contact partial melt zone, Antarctica

Science.gov (United States)

Currier, R. M.

2017-12-01

In the McMurdo Dry Valleys of Antarctica, a Jurassic aged dolerite sill induced partial melting of granite in the shallow crust. The melt zone can be traced in full, from high degrees of melting (>60%) along the dolerite contact, to no apparent signs of melting, 10s of meters above the contact. Within this melt zone, the well-known rapakivi texture is found, arrested in various stages of development. High above the contact, and at low degrees of melting, K-feldspar crystals are slightly rounded and unmantled. In the lower half of the melt zone, mantles of cellular textured plagioclase appear on K-feldspar, and thicken towards the contact heat source. At the highest degrees of melting, cellular-textured plagioclase completely replaces restitic K-feldspar. Because of the complete exposure and intact context, the leading models of rapakivi texture formation can be tested against this system. The previously proposed mechanisms of subisothermal decompression, magma-mixing, and hydrothermal exsolution all fail to adequately describe rapakivi generation in this melt zone. Preferred here is a closed system model that invokes the production of a heterogeneous, disequilibrium melt through rapid heating, followed by calcium and sodium rich melt reacting in a peritectic fashion with restitic K-feldspar crystals. This peritectic reaction results in the production of plagioclase of andesine-oligoclase composition—which is consistent with not just mantles in the melt zone, but globally as well. The thickness of the mantle is diffusion limited, and thus a measure of the diffusive length scale of sodium and calcium over the time scale of melting. Thermal modeling provides a time scale of melting that is consistent with the thickness of observed mantles. Lastly, the distribution of mantled feldspars is highly ordered in this melt zone, but if it were mobilized and homogenized—mixing together cellular plagioclase, mantled feldspars, and unmantled feldspars—the result would be

Seismic structure of the lithosphere beneath NW Namibia: Impact of the Tristan da Cunha mantle plume

Science.gov (United States)

Yuan, Xiaohui; Heit, Benjamin; Brune, Sascha; Steinberger, Bernhard; Geissler, Wolfram H.; Jokat, Wilfried; Weber, Michael

2017-01-01

Northwestern Namibia, at the landfall of the Walvis Ridge, was affected by the Tristan da Cunha mantle plume during continental rupture between Africa and South America, as evidenced by the presence of the Etendeka continental flood basalts. Here we use data from a passive-source seismological network to investigate the upper mantle structure and to elucidate the Cretaceous mantle plume-lithosphere interaction. Receiver functions reveal an interface associated with a negative velocity contrast within the lithosphere at an average depth of 80 km. We interpret this interface as the relic of the lithosphere-asthenosphere boundary (LAB) formed during the Mesozoic by interaction of the Tristan da Cunha plume head with the pre-existing lithosphere. The velocity contrast might be explained by stagnated and "frozen" melts beneath an intensively depleted and dehydrated peridotitic mantle. The present-day LAB is poorly visible with converted waves, indicating a gradual impedance contrast. Beneath much of the study area, converted phases of the 410 and 660 km mantle transition zone discontinuities arrive 1.5 s earlier than in the landward plume-unaffected continental interior, suggesting high velocities in the upper mantle caused by a thick lithosphere. This indicates that after lithospheric thinning during continental breakup, the lithosphere has increased in thickness during the last 132 Myr. Thermal cooling of the continental lithosphere alone cannot produce the lithospheric thickness required here. We propose that the remnant plume material, which has a higher seismic velocity than the ambient mantle due to melt depletion and dehydration, significantly contributed to the thickening of the mantle lithosphere.

Anisotropy tomography beneath east-central China and its geodynamic implications

Science.gov (United States)

Jiang, G.; Zhang, G.

2017-12-01

The east-central China primary consists of the southeastern part of the North China Block (NCB), the Middle-Lower Yangtze Block (MLYB), the northern part of Cathaysia Block (CB) and the Qinling-Dabie-Sulu Orogen (QDSO) (Fig. 1). Previous studies have suggested that both the rich mineralization in MLYB and the ultra-high pressure metamorphic belts in QDSO are closely to the Cretaceous magmatism in the east-central China. For discussing the geodynamic process, we have used the teleseismic tomography to study the 3D P-wave velocity structure down to 800 km deep and proposed a double-slab subduction model. In the present study, we introduce another two parameters representing the azimuthal anisotropy based on the isotropy tomography. Compared with the SKS method, the anisotropy tomography can provide the velocity anisotropy structure in different depths. The new anisotropy results show that (1) high-velocity (high-V) anomalies exist beneath the Middle Yangtze Block (MYB) from 200 km to 700 km depths and beneath the Lower Yangtze Block from 500 km to 700 km depths, and (2) low-velocity (low-V) anomalies exist beneath the Lower Yangtze Block from 50 km to 200 km depths and beneath the CB from 300 km to 700 km depths, respectively, and (3) the fast directions of P-wave velocity at 50-100 km depths are chaotic, however they show some regular changes from 200 km to 600 km depths. At 200-km deep, the fast direction of the low-V beneath the LYB is nearly E-W-trending. With the depth increasing, the fast directions of the low-V beneath the CB from 300 km to 600 km depths change to NEE-trending. In other side, the fast directions of eastern part of the high-V beneath the MYB, close to the low-V beneath the CB, denote NW-trending from 300 km to 600 depths. Combing with previous studies, we explain the high-V and the low-V, mentioned above, as the ancient Yangtze Craton and the upwelling asthenospheric materials, respectively. In addition, the NE-trending fast directions in the

The effect of melting temperature and time on the TiC particles

Energy Technology Data Exchange (ETDEWEB)

Jiang Kun [Key Laboratory of Materials Liquid Structure and Heredity, Ministry of Education, Shandong University, Ji' nan 250061 (China); Liu Xiangfa, E-mail: xfliu@sdu.edu.c [Key Laboratory of Materials Liquid Structure and Heredity, Ministry of Education, Shandong University, Ji' nan 250061 (China)

2009-09-18

In the present work, the microstructure formation process and particle size distribution of TiC in Al-Ti-C master alloys are investigated by particle size analysis, which is based on the morphology characterizing from scanning electron microscopy (SEM). The TiC particle size distributions at different melting temperatures and during different melting times are researched. It is demonstrated that the TiC particle sizes increase with melting temperature and melting time elapsed. The micro size particles appear when the melting temperature is high enough.

The effect of melting temperature and time on the TiC particles

International Nuclear Information System (INIS)

Jiang Kun; Liu Xiangfa

2009-01-01

In the present work, the microstructure formation process and particle size distribution of TiC in Al-Ti-C master alloys are investigated by particle size analysis, which is based on the morphology characterizing from scanning electron microscopy (SEM). The TiC particle size distributions at different melting temperatures and during different melting times are researched. It is demonstrated that the TiC particle sizes increase with melting temperature and melting time elapsed. The micro size particles appear when the melting temperature is high enough.

Assessing the Climate Change Impact on Snow-Glacier Melting Dominated Basins in the Greater Himalaya Region Using a Distributed Glacio-Hydrologic Model

Science.gov (United States)

Wi, S.; Yang, Y. C. E.; Khalil, A.

2014-12-01

Glacier and snow melting is main source of water supply making a large contribution to streamflow of major river basins in the Greater Himalaya region including the Syr Darya, the Amu Darya, the Indus, the Ganges and the Brahmaputra basins. Due to the critical role of glacier and snow melting as water supply for both food production and hydropower generation in the region (especially during the low flow season), it is important to evaluate the vulnerability of snow and glacier melting streamflow to different climate conditions. In this study, a distributed glacio-hydrologic model with high resolution climate input is developed and calibrated that explicitly simulates all major hydrological processes and the glacier and snow dynamics for area further discretized by elevation bands. The distributed modeling structure and the glacier and snow modules provide a better understanding about how temperature and precipitation alterations are likely to affect current glacier ice reserves. Climate stress test is used to explore changes in the total streamflow change, snow/glacier melting contribution and glacier accumulation and ablation under a variety of different temperature and precipitation conditions. The latest future climate projections provided from the World Climate Research Programme's Coupled Model Intercomparison Project Phase 5 (CMIP5) is used to inform the possibility of different climate conditions.

Experience with melting beta and gamma contaminated metals

International Nuclear Information System (INIS)

Feaugas, J.; Laplante, D.; Puechlong, Y.; Barbusse, R.

1994-01-01

Following a description of the melting facility operated for purposes of decommissioning the G2 and G3 gas-cooled reactors at Marcoule, the physical and radiological characteristics of 4070 tonnes of metal processed to date in the furnace are discussed. Considerable data have been recorded regarding operating and measurement procedures; the results show that secondary wastes account for less than 5 wt% of the processed scrap metal, and that all the 137 Cs is transferred to the dust and slag. During the last two months of 1993, the ingot mold line was replaced by rails on which dollies carrying integral work-form molds can be moved into position beneath the casting ladle. (authors). 21 figs

Ex-vessel melt-coolant interactions in deep water pool: Studies and accident management for Swedish BWRs

International Nuclear Information System (INIS)

Sienicki, J.J.; Chu, C.C.; Spencer, B.W.; Frid, W.; Loewenhielm, G.

1993-01-01

In Swedish BWRs having an annular suppression pool, the lower drywell beneath the reactor vessel is flooded with water to mitigate against the effects of melt release into the drywell during a severe accident. The THIRMAL code has been used to analyze the effectiveness of the water pool to protect lower drywell penetrations by fragmenting and quenching the melt as it relocates downward through the water. Experiments have also been performed to investigate the benefits of adding surfactants to the water to reduce the likelihood of fine-scale debris formation from steam explosions. This paper presents an overview of the accident management approach and surfactant investigations together with results from the THIRMAL analyses

Magnetotelluric investigations of the lithosphere beneath the central Rae craton, mainland Nunavut, Canada

Science.gov (United States)

Spratt, Jessica E.; Skulski, Thomas; Craven, James A.; Jones, Alan G.; Snyder, David B.; Kiyan, Duygu

2014-03-01

New magnetotelluric soundings at 64 locations throughout the central Rae craton on mainland Nunavut constrain 2-D resistivity models of the crust and lithospheric mantle beneath three regional transects. Responses determined from colocated broadband and long-period magnetotelluric recording instruments enabled resistivity imaging to depths of > 300 km. Strike analysis and distortion decomposition on all data reveal a regional trend of 45-53°, but locally the geoelectric strike angle varies laterally and with depth. The 2-D models reveal a resistive upper crust to depths of 15-35 km that is underlain by a conductive layer that appears to be discontinuous at or near major mapped geological boundaries. Surface projections of the conductive layer coincide with areas of high grade, Archean metasedimentary rocks. Tectonic burial of these rocks and thickening of the crust occurred during the Paleoproterozoic Arrowsmith (2.3 Ga) and Trans-Hudson orogenies (1.85 Ga). Overall, the uppermost mantle of the Rae craton shows resistivity values that range from 3000 Ω m in the northeast (beneath Baffin Island and the Melville Peninsula) to 10,000 Ω m beneath the central Rae craton, to >50,000 Ω m in the south near the Hearne Domain. Near-vertical zones of reduced resistivity are identified within the uppermost mantle lithosphere that may be related to areas affected by mantle melt or metasomatism associated with emplacement of Hudsonian granites. A regional decrease in resistivities to values of 500 Ω m at depths of 180-220 km, increasing to 300 km near the southern margin of the Rae craton, is interpreted as the lithosphere-asthenosphere boundary.

Glaciation control of melting rates in the mantle: U-Th systematics of young basalts from Southern Siberia and Central Mongolia

Science.gov (United States)

Rasskazov, S.; Chebykin, E.

2012-04-01

Eastern Sayans, Siberia and Hangay, Central Mongolia are mountainous uplifts effected by Quaternary volcanism, but only the former area was covered by glaciers that were as thick as 500 m. Glaciation time intervals were marked by moraines and sub-glacial hyaloclastite-bearing volcanic edifices, whereas interglacial ones were exhibited by sub-aerial "valley" flows and cinder cones. To estimate temporal variations of maximum rates of melting and mantle upwelling in the glacial and glacial-free areas, we measured radionuclides of the U-Th system for 74 samples of the Middle-Late Pleistocene through Holocene basalts by ICP-MS technique (Chebykin et al. Russian Geol. Geophys. 2004. 45: 539-556) using mass-spectrometer Agilent 7500ce. The obtained U-Th isochron ages for the Pleistocene volcanic units in the age interval of the last 400 Kyr are mostly consistent with results of K-Ar dating. The measured (230Th/238U) ratios for the Holocene basalts from both areas are within the same range of 1.08-1.16 (parentheses denote units of activity), whereas the 50 Kyr lavas yield, respectively, the higher and lower initial (230Th0/238U) ratios (1.18-1.46 and 1.05-1.13). This discrepancy demonstrates contrast maximum rates of melting in conventional garnet peridotite sources. We suggest that this dynamical feature was provided by the abrupt Late Pleistocene deglaciation that caused the mantle decompression expressed by the earlier increasing melting beneath Eastern Sayans than beneath Hangay. In the last 400 Kyr, magmatic liquids from both Eastern Sayans and Hangay showed the overall temporal decreasing (230Th0/238U) (i.e. relative increasing rates of melting and upwelling of the mantle) with the systematically lower isotopic ratios (i.e. increased mantle activity) in the former area than in the latter. The 400 Kyr phonotephrites in Hangay showed elevated concentrations of Th (6-8 ppm) and Th/U (3.7-3.9). The high (230Th0/238U) (4.3-6.0) reflected slow fractional melting

Analysis of elementary process steps in industrial glass melting tanks: some ideas on innovations in industrial glass melting

NARCIS (Netherlands)

Beerkens, R.G.C.

2008-01-01

Conventional industrial glass furnaces show broad glass melt residence time distributions in the melting tanks and average residence times may be up to more than two days for high quality glass products, such as float glass or TV glass, despite the minimum residence times of 8-10 hours (or even less

Soil microbial respiration beneath Stipa tenacissima L. and in surrounding bare soil

Directory of Open Access Journals (Sweden)

Irena Novosádová

2011-01-01

Full Text Available Open steppes dominated by Stipa tenacissima L. constitute one of the most representative ecosystems of the semi-arid zones of Eastern Mediterranean Basin (Iberian Peninsula, North of Africa. Ecosystem functioning of these steppes is strongly related to the spatial pattern of grass tussocks. Soils beneath Stipa tenacissima L. grass show different fertility and different microclimatic conditions than in surrounding bare soil. The objective of this study was to assess the effect of Stipa tenacissima L. on the key soil microbial activities under controlled incubation conditions (basal and potential respiration. Basal and potential microbial respirations in the soils beneath Stipa tenacissima L. were, in general, not significantly different from the bare soils. The differences were less than 10%. Significantly less ethylene produced by microbial activity in soils beneath Stipa tenacissima L. after the addition of glucose could indicate the dependence of rhizospheric microbial communities on available carbon compounds. It can be concluded, that the soil respiration in semi-arid Mediterranean ecosystems is not necessarily associated with the patchy plant distribution and that some microbial activities characteristics can be unexpectedly homogenous.

Keweenaw hot spot: Geophysical evidence for a 1.1 Ga mantle plume beneath the Midcontinent Rift System

Science.gov (United States)

Hutchinson, D.R.; White, R.S.; Cannon, W.F.; Schulz, K.J.

1990-01-01

The Proterozoic Midcontinent Rift System of North America is remarkably similar to Phanerozoic rifted continental margins and flood basalt provinces. Like the younger analogues, the volcanism within this older rift can be explained by decompression melting and rapid extrusion of igneous material during lithospheric extension above a broad, asthenospheric, thermal anomaly which we call the Keweenaw hot spot. Great Lakes International Multidisciplinary Program on Crustal Evolution seismic reflection profiles constrain end-member models of melt thickness and stretching factors, which yield an inferred mantle potential temperature of 1500°–1570°C during rifting. Combined gravity modeling and subsidence calculations are consistent with stretching factors that reached 3 or 4 before rifting ceased, and much of the lower crust beneath the rift consists of relatively high density intruded or underplated synrift igneous material. The isotopic signature of Keweenawan volcanic rocks, presented in a companion paper by Nicholson and Shirey (this issue), is consistent with our model of passive rifting above an asthenospheric mantle plume.

A holistic model for the role of the axial melt lens at fast-spreading mid-ocean ridges

Science.gov (United States)

MacLeod, C. J.; Loocke, M. P.; Lissenberg, J. C. J.

2016-12-01

Axial melt lenses (AML) are melt or crystal mush1 bodies located at the dyke-gabbro transition beneath intermediate- and fast-spreading mid-ocean ridges (MORs)2,3. Although it is generally thought that AMLs play a major role in the storage and differentiation of mid-ocean ridge basalts (MORB)1, the melt compositions within the AML and its role in the accretion of the lower crust are heavily debated4-6. Here we present the first comprehensive study of the AML horizon at a fast-spreading MOR (Hess Deep, equatorial Pacific Ocean). We show that plagioclase and pyroxene within the AML are much too evolved to be in equilibrium with MORB, with mean An (54.85) and Mg# (65.01) consistent with derivation from basaltic andesite to andesite melts (Mg# 43-26). We propose that, in between decadal eruptions, the AML is predominantly crystal mush and is fed by small volumes of evolved interstitial melts. Short-lived, focused injection of primitive melt leads to mixing of primitive melts with the extant highly fractionated melt, and triggers eruptions. This model reconciles the paradoxical compositional mismatch between the volcanic and plutonic records with the geophysical characteristics of the AML, the short residence times of Pacific MORB phenocrysts, and the incompatible trace element over-enrichments in MORB. 1Marjanović, M. et al., 2015. Distribution of melt along the East Pacific Rise from 9°30' to 10°N from an amplitude variation with angle of incidence (AVA) technique. Geophys. J. Int. 203. 2Detrick, R. S. et al., 1987. Multi-channel seismic imaging of a crustal magma chamber along the EPR. Nature 326. 3Sinton, J. M. & Detrick, R. S., 1992. Mid-ocean ridge magma chambers. J. Geophys. Res. 97. 4Coogan, L. A., Thompson, G. & MacLeod, C. J., 2002. A textural and geochemical investigation of high level gabbros from the Oman ophiolite: implications for the role of the axial magma chamber at fast-spreading ridges. Lithos 63. 5Pan, Y. & Batiza, R., 2002. Mid-ocean ridge magma

Microstructure of selective laser melted nickel–titanium

International Nuclear Information System (INIS)

Bormann, Therese; Müller, Bert; Schinhammer, Michael; Kessler, Anja; Thalmann, Peter; Wild, Michael de

2014-01-01

In selective laser melting, the layer-wise local melting of metallic powder by means of a scanning focused laser beam leads to anisotropic microstructures, which reflect the pathway of the laser beam. We studied the impact of laser power, scanning speed, and laser path onto the microstructure of NiTi cylinders. Here, we varied the laser power from 56 to 100 W and the scanning speed from about 100 to 300 mm/s. In increasing the laser power, the grain width and length increased from (33 ± 7) to (90 ± 15) μm and from (60 ± 20) to (600 ± 200) μm, respectively. Also, the grain size distribution changed from uni- to bimodal. Ostwald-ripening of the crystallites explains the distinct bimodal size distributions. Decreasing the scanning speed did not alter the microstructure but led to increased phase transformation temperatures of up to 40 K. This was experimentally determined using differential scanning calorimetry and explained as a result of preferential nickel evaporation during the fabrication process. During selective laser melting of the NiTi shape memory alloy, the control of scanning speed allows restricted changes of the transformation temperatures, whereas controlling the laser power and scanning path enables us to tailor the microstructure, i.e. the crystallite shapes and arrangement, the extent of the preferred crystallographic orientation and the grain size distribution. - Highlights: • Higher laser powers during selective laser melting of NiTi lead to larger grains. • Selective laser melting of NiTi gives rise to preferred <111> orientation. • The observed Ni/Ti ratio depends on the exposure time. • Ostwald ripening explains the bimodal grain size distribution

Tailoring the thermal conductivity of the powder bed in Electron Beam Melting (EBM) Additive Manufacturing.

Science.gov (United States)

Smith, C J; Tammas-Williams, S; Hernandez-Nava, E; Todd, I

2017-09-05

Metallic powder bed additive manufacturing is capable of producing complex, functional parts by repeatedly depositing thin layers of powder particles atop of each other whilst selectively melting the corresponding part cross-section into each layer. A weakness with this approach arises when melting overhanging features, which have no prior melted material directly beneath them. This is due to the lower thermal conductivity of the powder relative to solid material, which as a result leads to an accumulation of heat and thus distortion. The Electron Beam Melting (EBM) process alleviates this to some extent as the powder must first be sintered (by the beam itself) before it is melted, which results in the added benefit of increasing the thermal conductivity. This study thus sought to investigate to what extent the thermal conductivity of local regions in a titanium Ti-6Al-4V powder bed could be varied by imparting more energy from the beam. Thermal diffusivity and density measurements were taken of the resulting sintered samples, which ranged from being loosely to very well consolidated. It was found that the calculated thermal conductivity at two temperatures, 40 and 730 °C, was more than doubled over the range of input energies explored.

Production, pathways and budgets of melts in mid-ocean ridges: An enthalpy based thermo-mechanical model

Science.gov (United States)

Mandal, Nibir; Sarkar, Shamik; Baruah, Amiya; Dutta, Urmi

2018-04-01

Using an enthalpy based thermo-mechanical model we provide a theoretical evaluation of melt production beneath mid-ocean ridges (MORs), and demonstrate how the melts subsequently develop their pathways to sustain the major ridge processes. Our model employs a Darcy idealization of the two-phase (solid-melt) system, accounting enthalpy (ΔH) as a function of temperature dependent liquid fraction (ϕ). Random thermal perturbations imposed in this model set in local convection that drive melts to flow through porosity controlled pathways with a typical mushroom-like 3D structure. We present across- and along-MOR axis model profiles to show the mode of occurrence of melt-rich zones within mushy regions, connected to deeper sources by single or multiple feeders. The upwelling of melts experiences two synchronous processes: 1) solidification-accretion, and 2) eruption, retaining a large melt fraction in the framework of mantle dynamics. Using a bifurcation analysis we determine the threshold condition for melt eruption, and estimate the potential volumes of eruptible melts (∼3.7 × 106 m3/yr) and sub-crustal solidified masses (∼1-8.8 × 106 m3/yr) on an axis length of 500 km. The solidification process far dominates over the eruption process in the initial phase, but declines rapidly on a time scale (t) of 1 Myr. Consequently, the eruption rate takes over the solidification rate, but attains nearly a steady value as t > 1.5 Myr. We finally present a melt budget, where a maximum of ∼5% of the total upwelling melt volume is available for eruption, whereas ∼19% for deeper level solidification; the rest continue to participate in the sub-crustal processes.

A linked lake system beneath Thwaites Glacier, West Antarctica reveals an efficient mechanism for subglacial water flow.

Science.gov (United States)

Smith, B. E.; Gourmelen, N.; Huth, A.; Joughin, I. R.

2016-12-01

In this presentation we show the results of a multi-sensor survey of a system of subglacial lakes beneath Thwaites Glacier, West Antarctica. This is the first substantial active (meaning draining or filling on annual time scales) lake system detected under the fast-flowing glaciers of the Amundsen Coast. Altimetry data show that over the 2013 calendar year, four subglacial lakes drained, essentially simultaneously, with the bulk of the drainage taking place over the course the first three months of the year. The largest of the lakes appears to have drained around 3.7 km3 of water, with the others each draining less than 1 km3. The high-resolution radar surveys conducted in this area by NASA's IceBridge program allow detailed analysis of the subglacial hydrologic potential, which shows that the potential map in this area is characterized by small closed basins that should not, under the common assumption that water flow is directed down the gradient of the hydropotential, allow long-range water transport. The lakes' discharge demonstrates that, at least in some cases, water can flow out of apparently closed hydropotential basins. Combining a basal-flow routing map with a map of basal melt production suggests that the largest drainage event could recur as often as every 22 years, provided that overflow or leakage of mapped hydropotential basins allows melt water transport to refill the lake. An analysis of ice-surface speed records both around the lakes and at the Thwaites grounding line shows small changes in ice speed, but none clearly associated with the drainage event, suggesting that, at least in this area where subglacial melt is abundant, the addition of further water to the subglacial hydrologic system need not have any significant effect on ice flow. It is likely that the main impact of the lake system on the glacier is that as an efficient mechanism to remove meltwater from the system, it drains water that would otherwise flow through less efficient

Bubble removal and sand dissolution in an electrically heated glass melting channel with defined melt flow examined by mathematical modelling

Czech Academy of Sciences Publication Activity Database

Hrbek, L.; Kocourková, P.; Jebavá, Marcela; Cincibusová, P.; Němec, Lubomír

2017-01-01

Roč. 456, JAN 15 (2017), s. 101-113 ISSN 0022-3093 Institutional support: RVO:67985891 Keywords : glass melt flow * mathematical modelling * energy distribution * space utilization * melting performance Subject RIV: JH - Ceramics, Fire-Resistant Materials and Glass OBOR OECD: Ceramics Impact factor: 2.124, year: 2016

Evidence of refilled chamber gas pressure enhancing cooling rate during melt spinning of a Zr50Cu40Al10 alloy

Directory of Open Access Journals (Sweden)

Hong-wang Yang

2015-07-01

Full Text Available The influence of the refilled gas pressure on the glass forming behaviour of one of the best ternary glass forming alloys Zr50Cu40Al10 was studied for the melt spinning process. The amorphicity of as-quenched ribbons was characterized by X-ray diffraction (XRD and differential scanning calorimetry (DSC. The refilled chamber atmospheric pressure is crucial to the cooling rate of melt spinning. At high vacuum, at pressure less than 0.0001 atm, fully crystalline fragments are obtained. Monolithic amorphous ribbons were only obtained at a gas pressure of 0.1 atm or higher. The extended contact length between thecribbons and the copper wheel contributes to the high cooling rate of melt spinning. Higher chamber gas pressure leads to more turbulence of liquid metal beneath the nozzle; therefore, lower pressure is preferable at practical melt spinning processes once glass forming conditions are fulfilled.

Bayesian estimation of core-melt probability

International Nuclear Information System (INIS)

Lewis, H.W.

1984-01-01

A very simple application of the canonical Bayesian algorithm is made to the problem of estimation of the probability of core melt in a commercial power reactor. An approximation to the results of the Rasmussen study on reactor safety is used as the prior distribution, and the observation that there has been no core melt yet is used as the single experiment. The result is a substantial decrease in the mean probability of core melt--factors of 2 to 4 for reasonable choices of parameters. The purpose is to illustrate the procedure, not to argue for the decrease

Melting relations and elemental distribution of portion of the system Fe-S-Si-O to 32 KB with planetary application

Science.gov (United States)

Huang, W. L.

1980-01-01

The melting relations and distribution of K and Cs in portions of the system was determined at high pressures. Ferrosilite is stable as a primary phase at high pressures because of the incongruent melting of ferrosilite to quartz plus liquid and the boundary between the one and two liquid fields on the joint Fe(1-x) O-FeS-SiO2 shifts away from silica with increasing pressures. Potassium K was found to have limited solubility in metal sulfide liquids at pressures up to 45 kb. The speculation that K may dissolve significantly in metal-metal sulfide liquids after undergoing first order isomorphic transition was tested by determining the distribution of Cs between sulfide and silicate liquids as an analogy to K. At 45 kb, 1400 C and 27 kb, 1300 C only limited amounts of Cs were detected in quench sulfide liquids even at pressures beyond the isomorphic transition of Cs.

A geochemical study of lithospheric mantle beneath Northern Victoria Land (Antarctica): main evidences from volatile content in ultramafic xenoliths

Science.gov (United States)

Correale, Alessandra; Pelorosso, Beatrice; Rizzo, Andrea Luca; Coltorti, Massimo; Italiano, Francesco; Bonadiman, Costanza

2017-04-01

A geochemical study of ultramafic xenoliths from Northern Victoria Land (Green Point, GP and Handler Ridge, HR), is carried out in order to investigate the features of the lithosphere mantle beneath the Western Antarctic Ridge System (WARS). The majority of samples is spinel anhydrous lherzolite with rare presence of secondary phases (secondary cpx and glass). Geothermobarometric calculations, based on the Fe/Mg distribution among the peridotite minerals reveal that Sub Continental Lithospheric Mantle (SCLM) beneath Handler Ridge records temperatures and redox conditions higher then Greene Point (P fixed at 15 Kbar). Moreover, geochemical models evidence that, GP mantle domain represents a residuum after ˜7 to 21 % of partial melting in the spinel stability field, which was variably affected by interaction with infiltrating melts, acting in different times, from at least Jurassic to Cenozoic (Pelorosso et al., 2016). Fluid inclusions (FI) entrapped in olivine and pyroxene crystals were investigated for elemental and isotopic contents of both, noble gases (He, Ne, Ar) and CO2. He, Ar and Ne concentrations range from 1.52×10-14 to 1.07×10-12, from 4.09×10-13 to 3.47×10-11and from 2.84×10-16 to 7.57×10-14 mol/g, respectively, while the CO2amounts are between 7.08×10-10 and 8.12×10-7 mol/g. The 3He/4He varies between 5.95 and 20.18 Ra (where Ra is the 3He/4He ratio of air), being the lowest and the highest values measured in the He-poorer samples. Post-eruptive input of cosmogenic 3He and radiogenic 4He seems to influence mainly the samples associated to a lower He concentrations, increasing and decreasing respectively their primordial 3He/4He values, that for all the other samples range between 6.76 and 7.45 Ra. This range reasonably reflects the isotope signature of mantle beneath the investigated areas. The 4He/40Ar* ratio corrected for atmospheric-derived contamination ranges between 0.004 and 0.39. The lowest 4He/40Ar* values (4He/40Ar*correspondence of

CO2-SO3-rich (carbonate-sulfate) melt/fluids in the lithosphere beneath El Hierro, Canary Islands.

Science.gov (United States)

Oglialoro, E.; Ferrando, S.; Malaspina, N.; Villa, I. M.; Frezzotti, M. L.

2015-12-01

Mantle xenoliths from the island of El Hierro, the youngest of the Canary Islands, have been studied to characterize fluxes of carbon in the lithosphere of an OIB volcanism region. Fifteen xenoliths (4-10 cm in diameter) were collected in a rift lava flow (15-41 ka) at a new xenolith locality in El Julan cliff (S-SW of the island). Peridotites consist of protogranular to porphyroblastic spinel harzburgites, lherzolites, and subordinate dunites. One spinel clinopyroxenite, and one olivine-websterite were also analyzed. Ultramafic xenoliths were classified as HEXO (harzburgite and dunite with exsolved orthopyroxene), HLCO (harzburgite and lherzolite containing orthopyroxene without visible exsolution lamellae), and HTR (transitional harzburgite with exsolved orthopyroxene porphyroclasts, and poikilitic orthopyroxene) following [1]. While HLCO and HTR peridotites contain mostly CO2 fluid inclusions, HEXO peridotites preserve an early association of melt/fluid inclusions containing dominantly carbonate/sulfate/silicate glass, evolving to carbonate/sulfate/phosphate/spinel aggregates, with exsolved CO2 (± carbonates, anhydrite and H2O). Chemical and Raman analyses identify dolomite, Mg-calcite, anhydrite, sulfohalite [Na6(SO4)2FCl] (± other anhydrous and hydrous alkali-sulfates), apatite, and Cr-spinel in the inclusions. Sulfides are noticeably absent. The microstructure and chemical composition of the metasomatic fluids indicate that the peridotites were infiltrated by a carbonate-sulfate-silicate melt/fluid enriched in CO2, H2O, and P. A mantle origin for this fluid is supported by high densities of CO2inclusions (> 1g/cm3), determined by Raman microspectroscopy and cross-checked by microthermometry. Consequently, El Julan peridotites provide the first evidence for liberating oxidized C and S fluxes from the Earth lithosphere in an OIB source region, and suggest that oxidation of sulfide to sulfate can occur during small-degree partial melting of the upper mantle

Bubble Formation in Basalt-like Melts

DEFF Research Database (Denmark)

Jensen, Martin; Keding, Ralf; Yue, Yuanzheng

2011-01-01

and their diameter. The variation in melting temperature has little influence on the overall bubble volume. However, the size distribution of the bubbles varies with the melting temperature. When the melt is slowly cooled, the bubble volume increases, implying decreased solubility of the gaseous species. Mass...... spectroscopy analysis of gases liberated during heating of the glass reveals that small bubbles contain predominantly CH4, CO and CO2, whereas large bubbles bear N2, SO2 and H2S. The methodology utilised in this work can, besides mapping the bubbles in a glass, be applied to shed light on the sources of bubble...

Application of the zone-melting technique to metal chelate systems-VI A new apparatus for zone-melting chromatography.

Science.gov (United States)

Maeda, S; Kobayashi, H; Ueno, K

1973-07-01

An improved apparatus has been constructed for zone-melting chromatography. An essential feature of the apparatus is that the length of the molten zone can be kept constant during a zone-melting operation, by employing heating and cooling compartments which are separated from each other by double partition plates. Each compartment is heated or cooled with jets of hot or cold air. The apparatus is suitable for organic materials melting in the range between 40 degrees and 180 degrees . The distribution of metal ion along the column after zone melting of copper acetylacetonate in 2-methoxynaphthalene was a smooth curve. The plot of the position of maximum concentration, x(max), against the number of zone passes, n, gave a relationship in accordance with theoretical prediction.

Impact of ice melting on distribution of particulate sterols in glacial fjords of Chilean Patagonia

Science.gov (United States)

Gutiérrez, Marcelo H.; Riquelme, Pablo; Pantoja, Silvio

2016-04-01

We analyzed variability in abundance and composition of sterols in waters of the fjord adjacent to glacier Jorge Montt, one of the fastest retreated glaciers in Patagonian Icefields. The study was carried out between August 2012 and November 2013 under different meltwater scenarios. Distribution of sterols in surface and bottom waters was determined by Gas Chromatography coupled to Mass Spectrometry. Sterol concentration ranged from 18 to 1726 ng/L in surface and bottom waters and was positive correlated with chlorophyll-a concentration. Under high melting conditions in austral summer, surface meltwaters showed high concentrations of sterols and were dominated by methylene-cholesterol, a representative sterol of centric diatoms. In the area near open ocean and in austral autumn, winter and spring in proglacial fjord, lower sterol concentrations in surface waters were accompanied by other microalgae sterols and an increase in relative abundance of plant sterols, evidencing a different source of organic matter. In autumn, when high meltwater flux was also evidenced, presence of stanols and an uncommon tri-unsaturated sterol suggests influence of meltwaters in composition of sterols in the downstream fjord. We conclude that ice melting can modify sterol composition by setting conditions for development of a singular phytoplankton population able to thrive in surface meltwater and by carrying glacier organic matter into Patagonian glacial fjords. In projected ice melting scenario, these changes in organic matter quantity and quality can potentially affect availability of organic substrates for heterotrophic activity and trophic status of glacial fjords. This research was funded by COPAS Sur-Austral (PFB-31)

Seismic Structure of Mantle Transition Zone beneath Northwest Pacific Subduction Zone and its Dynamic Implication

Science.gov (United States)

Li, J.; Guo, G.; WANG, X.; Chen, Q.

2017-12-01

The northwest Pacific subduction region is an ideal location to study the interaction between the subducting slab and upper mantle discontinuities. Various and complex geometry of the Pacific subducting slab can be well traced downward from the Kuril, Japan and Izu-Bonin trench using seismicity and tomography images (Fukao and Obayashi, 2013). Due to the sparse distribution of seismic stations in the sea, investigation of the deep mantle structure beneath the broad sea regions is very limited. In this study, we applied the well- developed multiple-ScS reverberations method (Wang et al., 2017) to analyze waveforms recorded by the Chinese Regional Seismic Network, the densely distributed temporary seismic array stations installed in east Asia. A map of the topography of the upper mantle discontinuities beneath the broad oceanic regions in northwest Pacific subduction zone is imaged. We also applied the receiver function analysis to waveforms recorded by stations in northeast China and obtain the detailed topography map beneath east Asia continental regions. We then combine the two kinds of topography of upper mantle discontinuities beneath oceanic and continental regions respectively, which are obtained from totally different methods. A careful image matching and spatial correlation is made in the overlapping study regions to calibrate results with different resolution. This is the first time to show systematically a complete view of the topography of the 410-km and 660-km discontinuities beneath the east Asia "Big mantle wedge" (Zhao and Ohtani, 2009) covering the broad oceanic and continental regions in the Northwestern Pacific Subduction zone. Topography pattern of the 660 and 410 is obtained and discussed. Especially we discovered a broad depression of the 410-km discontinuity covering more than 1000 km in lateral, which seems abnormal in the cold subducting tectonic environment. Based on plate tectonic reconstruction studies and HTHP mineral experiments, we

Radial viscous fingering of hot asthenosphere within the Icelandic plume beneath the North Atlantic Ocean

Science.gov (United States)

Schoonman, C. M.; White, N. J.; Pritchard, D.

2017-06-01

The Icelandic mantle plume has had a significant influence on the geologic and oceanographic evolution of the North Atlantic Ocean during Cenozoic times. Full-waveform tomographic imaging of this region shows that the planform of this plume has a complex irregular shape with significant shear wave velocity anomalies lying beneath the lithospheric plates at a depth of 100-200 km. The distribution of these anomalies suggests that about five horizontal fingers extend radially beneath the fringing continental margins. The best-imaged fingers lie beneath the British Isles and beneath western Norway where significant departures from crustal isostatic equilibrium have been measured. Here, we propose that these radial fingers are generated by a phenomenon known as the Saffman-Taylor instability. Experimental and theoretical analyses show that fingering occurs when a less viscous fluid is injected into a more viscous fluid. In radial, miscible fingering, the wavelength and number of fingers are controlled by the mobility ratio (i.e. the ratio of viscosities), by the Péclet number (i.e. the ratio of advective and diffusive transport rates), and by the thickness of the horizontal layer into which fluid is injected. We combine shear wave velocity estimates with residual depth measurements around the Atlantic margins to estimate the planform distribution of temperature and viscosity within a horizontal asthenospheric layer beneath the lithospheric plate. Our estimates suggest that the mobility ratio is at least 20-50, that the Péclet number is O (104), and that the asthenospheric channel is 100 ± 20 km thick. The existence and planform of fingering is consistent with experimental observations and with theoretical arguments. A useful rule of thumb is that the wavelength of fingering is 5 ± 1 times the thickness of the horizontal layer. Our proposal has been further tested by examining plumes of different vigor and planform (e.g. Hawaii, Cape Verde, Yellowstone). Our results

Smoke flow temperature beneath tunnel ceiling for train fire at subway station: Reduced-scale experiments and correlations

International Nuclear Information System (INIS)

Meng, Na; Wang, Qiang; Liu, Zhaoxia; Li, Xiao; Yang, He

2017-01-01

Highlights: • Reduced-scale experiments on train fire at subway station. • Smoke flow temperature beneath tunnel ceiling measured and correlated. • Effect of platform-tunnel conjunction door type on smoke temperature is clarified. - Abstract: This paper is to investigate the smoke flow temperature beneath tunnel ceiling for a train on fire stopping besides a subway station. Experiments were carried out in a reduced-scale (1:10) subway station model to study the maximum smoke temperature and the longitudinal temperature distribution beneath the tunnel ceiling by considering platform-tunnel conjunction doors of two types: the full-seal platform screen door (PSD) and the full-height safety door. For the maximum temperature beneath the tunnel ceiling, it is found to be well correlated non-dimensionally with heat release rate by a 3.65 and a 2.92 power law function for the full-seal platform screen door and the full-height safety door, respectively. For the longitudinal temperature distribution along the tunnel ceiling, it can be well correlated by an exponential function for both types of platform-tunnel conjunction doors. Concerning the effect of the door type, the maximum temperature is lower and the longitudinal temperature decays faster for full-height safety door than that for full-seal PSD. This is due to that with the full-height safety door, the effective width of the tunnel ceiling is widened, which results in more heat losses from the smoke flow to the ceiling.

Carbonate metasomatism and CO2 lithosphere-asthenosphere degassing beneath the western Mediterranean: An integrated model arising from petrological and geophysical data

International Nuclear Information System (INIS)

Frezzotti, Maria Luce; Peccerillo, Angelo; Panza, Giuliano

2009-03-01

We present an integrated petrological, geochemical, and geophysical model that offers an explanation for the present-day anomalously high non-volcanic deep (mantle derived) CO 2 emission in the Tyrrhenian region. We investigate how decarbonation or melting of carbonate-rich lithologies from a subducted lithosphere may affect the efficiency of carbon release in the lithosphere-asthenosphere system. We propose that melting of sediments and/or continental crust of the subducted Adriatic-Ionian (African) lithosphere at pressure greater than 4 GPa (130 km) may represent an efficient mean for carbon cycling into the upper mantle and into the exosphere in the Western Mediterranean area. Melting of carbonated lithologies, induced by the progressive rise of mantle temperatures behind the eastward retreating Adriatic-Ionian subducting plate, generates low fractions of carbonate-rich (hydrous-silicate) melts. Due to their low density and viscosity, such melts can migrate upward through the mantle, forming a carbonated partially molten CO 2 -rich mantle recorded by tomographic images in the depth range from 130 to 60 km. Upwelling in the mantle of carbonate-rich melts to depths less than 60 - 70 km, induces massive outgassing of CO 2 . Buoyancy forces, probably favored by fluid overpressures, are able to allow migration of CO 2 from the mantle to the surface, through deep lithospheric faults, and its accumulation beneath the Moho and within the lower crust. The present model may also explain CO 2 enrichment of the Etna active volcano. Deep CO 2 cycling is tentatively quantified in terms of conservative carbon mantle flux in the investigated area. (author)

Numerical simulation of fragmentation of hot metal and oxide melts with the computer code IVA3

International Nuclear Information System (INIS)

Mussa, S.; Tromm, W.

1994-01-01

The phenomena of fragmentation of melts caused by water-inlet from the bottom with the computer code IVA3/11,12,13/ are investigated. With the computer code IVA3 three-component-multiphase flows can be numerically simulated. Two geometrical models are used. Both consist of a cylindrical vessel for water lying beneath a cylindrical vessel for melt. The vessels are connected to each other through a hole. Steel and UO 2 melts are. The following parameters were varied: the type of the melt (steel,UO 2 ), the water supply pressure and the geometry of the hole in the bottom plate through which the water and melt vessels are connected. As results of the numerical simulations temperature and pressure versus time curves are plotted. Additionally the volume flow rates and the volume fractions of the various phases in the vessels and the increase in surface and enthalpy of the melt during the time of simulation are depicted. With steel melts the rate of fragmentation increases with increasing water pressure and melt temperature, whereby stable channels are formed in the melt layer showing a very low flow resistance for steam. With UO 2 the formations of channels are also observed. However, these channels are not so stable that they eventually break apart and lead to the fragmentation of the UO 2 melt in drops. The fragmentation of the steel melt in water vessel is less than that of UO 2 . No essential solidification of the melt is observed in the respective duration of the simulations. However, a small drop in the melt temperature is observed. With a slight or no water pressure the melt flows from the upper vessel into the water vessel via the connecting hole. The processes take place in a very slow manner and with such a low steam production so that despite the occuring pressure peaks no sign of steam explosions could be observed. (orig./HP) [de

Medium-scale melt-sodium fragmentation experiments

International Nuclear Information System (INIS)

Chu, T.Y.; Beattie, A.G.; Drotning, W.D.; Powers, D.A.

1979-01-01

The results of a series of fragmentation experiments involving up to 20 Kg of thermitically produced high temperature melts and 23 Kg of sodium are presented. Except for one experiment where some centimeter size particles are observed, the fragment distributions seem to be in the range of previous data. Spatial distribution of the fragments in the debris bed appears to be stratified. Scanning electron micrographs of fragments indicate fragmentation to be occurring in the molten state for the more intense interactions observed. Interaction data obtained show quiescent periods of 0.5 to 1.5 second between pressure pulses. The force impulse values per unit mass of melt seems to be in the same range as previous experiments

Mantle Convection beneath the Aegir Ridge, a Shadow in the Iceland Hotspot

Science.gov (United States)

Howell, S. M.; Ito, G.; Breivik, A. J.; Hanan, B. B.; Mjelde, R.; Sayit, K.; Vogt, P. R.

2012-12-01

The Iceland Hotspot has produced extensive volcanism spanning much of the ocean basin between Greenland and Norway, forming one of the world's largest igneous provinces. However, an apparent igneous "shadow" in hotspot activity is located at the fossil Aegir Ridge, which formed anomalously thin crust, despite this ridge being near the Iceland hotspot when it was active. The Aegir Ridge accommodated seafloor spreading northeast of present-day Iceland from the time of continental breakup at ~55 Ma until ~25 Ma, at which point spreading shifted west to the Kolbeinsey Ridge. To address the cause of the anomalously thin crust produced by the Aegir Ridge, we use three-dimensional numerical models to simulate the interaction between a mantle plume beneath the Iceland hotspot, rifting continental lithosphere, and the time-evolving North Atlantic ridge system. Two end-member hypotheses were investigated: (1) Material emanating from the Iceland mantle plume was blocked from reaching the Aegir Ridge by the thick lithosphere of the Jan Mayen Microcontinent as the Kolbeinsey Ridge began rifting it from Greenland at ~30 Ma, just east of the plume center; (2) Plume material was not blocked and did reach the Aegir Ridge, but had already experienced partial melting closer to the hotspot. This material was then unable to produce melt volumes at the Aegir Ridge comparable to those of pristine mantle. To test these hypotheses, we vary the volume flux and viscosity of the plume, and identify which conditions do and do not lead to the Aegir Ridge forming anomalously thin crust. Results show that the combination of plume material being drawn into the lithospheric channels beneath the Reykjanes Ridge and Kolbeinsey Ridge after their respective openings, and the impedance of plume flow by the Jan Mayen Microcontinent (hypothesis 1), can deprive the Aegir Ridge of plume influence. This leads to low crustal thicknesses that are comparable to those observed. We have yet to produce a model

Ex-vessel melt-coolant interactions in deep water pool: studies and accident management for Swedish BWRs

International Nuclear Information System (INIS)

Chu, C.C.; Sienicki, J.J.; Spencer, B.W.; Frid, W.; Loewenhielm, G.

1995-01-01

In Swedish BWRs having an annular suppression pool, the lower drywell beneath the reactor vessel is flooded with water to mitigate against the effects of melt release into the drywell during a severe accident. The THIRMAL-1 code has been used to analyze the effectiveness of the water pool to protect lower drywell penetrations by fragmenting and quenching the melt as it relocates downward through the water. Experiments have also been performed to investigate the benefits of adding surfactants to the water to reduce the likelihood of fine-scale debris formation from steam explosions. This paper presents an overview of the accident management approach and surfactant investigations together with results from the THIRMAL-1 analyses. A description of the modeling incorporated in THIRMAL-1 is also provided. (orig.)

New constraints on the crustal structure beneath northern Tyrrhenian Sea

Science.gov (United States)

Levin, V. L.; Park, J. J.

2009-12-01

We present new seismological data on the seismic structure beneath the Tyrrhenian Sea between Corsica and the coast of Italy. Teleseismic receiver functions from two Tyrrhenian islands (Elba and Gorgona) identify clear P-to-S mode-converted waves from two distinct interfaces, at ~20 and ~45 km depth. Both interfaces are characterized by an increase of seismic wavespeed with depth. Using a summation of direct and multiply-reflected body waves within the P wave coda we estimate the mean ratio of compressional and shear wave speeds above the 45 km interface to be 1.75-1.80. Using reflectivity computations in 1D layered models we develop a model of seismic wavespeed distribution that yields synthetic seismograms very similar to those observed. We apply a Ps-multiple summation procedure to the synthetic waveforms to further verify the match between observed and predicted wavefields. The lower layer of our model, between 20 and 45 km, has Vp ~ 7.5 km/sec, a value that can be ascribed to either very fast crustal rocks or very slow upper mantle rocks. The Vp/Vs ratio is ~1.8 in this intermediate layer. On the basis of a well-constrained downward increase in seismic wave speed beneath this second layer, we interpret it as the magmatically reworked lower crust, a lithology that has been proposed to explain high-Vp layers in the crustal roots of island-arc terranes and volcanically altered continental margins, as well as lower-crustal high-Vp features sometimes seen beneath continental rifts. The presence of a thick layer of high-Vp, but crustal, lithology beneath the Tyrrhenian Sea differs considerably from previous estimates that interpreted the interface at ~20 km as the Moho. Our new interpretation obviates a need for a crustal thickness change of over 20 km at the crest of the Apennines orogen. We propose an alteration in the properties of the lower crust instead. We argue that ongoing convergent subduction of the Adriatic lithospehre is not required beneath northern

Dehydration and melting experiments constrain the fate of subducted sediments

Science.gov (United States)

Johnson, Marie C.; Plank, Terry

2000-12-01

Geochemical tracers demonstrate that elements are cycled from subducted sediments into the arc melting regime at subduction zones, although the transfer mechanism is poorly understood. Are key elements (Th, Be, Rb) lost during sediment dehydration or is sediment melting required? To investigate this question, we conducted phase equilibria and trace element partitioning experiments on a pelagic red clay for conditions appropriate to the slab beneath arc volcanoes (2-4 GPa, 600°-1000°C). Using both piston cylinders and multianvils, we determined the solidus, phase stabilities, and major element compositions of coexisting phases. The solidus (H2O + Cl fluid-saturated) was located at 775 ± 25°C at 2 GPa, 810 ± 15°C at 3 GPa, and 1025 ± 25°C at 4 GPa with noevidence for complete miscibility between melt and fluid. This sediment composition produces a profusion of phases both above and below the solidus: garnet, jadeitic pyroxene, alkali-rich amphibole, phengite, biotite, magnetite, coesite, kyanite, apatite, zircon, Cl-rich fluids, and peraluminous to peralkaline granitic melts. At 2 GPa the phengite dehydration solidus is at 800°-825°C, while biotite breaks down between 850° and 900°C. To explore trace element partitioning across the solidus at 2 GPa, we used diamonds to trap fluids and melts. Both the bulk sediment residues and diamond traps were analyzed postexperiment by inductively coupled plasma-mass spectrometry (ICP-MS) and inductively coupled plasma-atomic emission spectrometry (ICP-AES) for 40 elements for which we calculated bulk partition coefficients (D = Csolid/Cfluid). Below the solidus, Rb, Sr, Ba, and Pb showed the greatest mobility (D ˜ 0.5-1.0), while at the solidus, Th and Be became notably partitioned into the melt (D values changing from >2.0 to oceanic crust dehydration) may provide new constraints on the next generation of thermal/geodynamical models of subduction zones.

Array-Based Receiver Function Analysis of the Subducting Juan de Fuca Plate Beneath the Mount St. Helens Region and its Implications for Subduction Geometry and Metamorphism

Science.gov (United States)

Mann, M. E.; Abers, G. A.; Creager, K. C.; Ulberg, C. W.; Crosbie, K.

2017-12-01

westward increase in wavespeed of the continental crust. The seismically-imaged surface of the subducting JdF slab at 68 km beneath MSH is the shallowest yet documented beneath an arc volcano. Combined with the inference of serpentinization in the mantle wedge, this geometry presents a problem in that vertical mantle melt migration seems unfeasible, yet mantle melts contribute to erupted MSH magmas.

Nature and extent of lava-flow aquifers beneath Pahute Mesa, Nevada Test Site

Energy Technology Data Exchange (ETDEWEB)

Prothro, L.B.; Drellack, S.L. Jr.

1997-09-01

Work is currently underway within the Underground Test Area subproject of the US Department of Energy/Nevada Operations Office Environmental Restoration Program to develop corrective action plans in support of the overall corrective action strategy for the Nevada Test Site as established in the Federal Facility Agreement and Consent Order (FFACO, 1996). A closure plan is currently being developed for Pahute Mesa, which has been identified in the FFACO as consisting of the Western and Central Pahute Mesa Corrective Action Units. Part of this effort requires that hydrogeologic data be compiled for inclusion in a regional model that will be used to predict a contaminant boundary for these Corrective Action Units. Hydrogeologic maps have been prepared for use in the model to define the nature and extent of aquifers and confining units that might influence the flow of contaminated groundwater from underground nuclear tests conducted at Pahute Mesa. Much of the groundwater flow beneath Pahute Mesa occurs within lava-flow aquifers. An understanding of the distribution and hydraulic character of these important hydrogeologic units is necessary to accurately model groundwater flow beneath Pahute Mesa. This report summarizes the results of a study by Bechtel Nevada geologists to better define the hydrogeology of lava-flow aquifers at Pahute Mesa. The purpose of this study was twofold: (1) aid in the development of the hydrostratigraphic framework for Pahute Mesa, and (2) provide information on the distribution and hydraulic character of lava-flow aquifers beneath Pahute Mesa for more accurate computer modeling of the Western and Central Pahute Mesa Corrective Action Units.

The coupled response to slope-dependent basal melting

Science.gov (United States)

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

2009-12-01

Ice shelf basal melting is likely to be strongly controlled by basal slope. If ice shelves steepen in response to intensified melting, it suggests instability in the coupled ice-ocean system. The dynamic response of ice shelves governs what stable morphologies are possible, and thus the influence of melting on buttressing and grounding line migration. Simulations performed using a 3-D ocean model indicate that a simple form of slope-dependent melting is robust under more complex oceanographic conditions. Here we utilize this parameterization to investigate the shape and grounding line evolution of ice shelves, using a shallow-shelf approximation-based model that includes lateral drag. The distribution of melting substantially affects the shape and aspect ratio of unbuttressed ice shelves. Slope-dependent melting thins the ice shelf near the grounding line, reducing velocities throughout the shelf. Sharp ice thickness gradients evolve at high melting rates, yet grounding lines remain static. In foredeepened, buttressed ice shelves, changes in grounding line flux allow two additional options: stable or unstable retreat. Under some conditions, slope-dependent melting results in stable configurations even at high melt rates.

Preliminary result of P-wave speed tomography beneath North Sumatera region

Energy Technology Data Exchange (ETDEWEB)

Jatnika, Jajat [Earth Science Study Program, Institute of Technology Bandung (Indonesia); Indonesian Meteorological, Climatological and Geophysical Agency (MCGA), Jakarta (Indonesia); Nugraha, Andri Dian, E-mail: nugraha@gf.itb.ac.id [Global Geophysical Research Group, Faculty of Mining and Petroleum Engineering, Insitute of Technology Bandung (Indonesia); Wandono [Indonesian Meteorological, Climatological and Geophysical Agency (MCGA), Jakarta (Indonesia)

2015-04-24

The structure of P-wave speed beneath the North Sumatra region was determined using P-wave arrival times compiled by MCGA from time periods of January 2009 to December 2012 combining with PASSCAL data for February to May 1995. In total, there are 2,246 local earthquake events with 10,666 P-wave phases from 63 stations seismic around the study area. Ray tracing to estimate travel time from source to receiver in this study by applying pseudo-bending method while the damped LSQR method was used for the tomographic inversion. Based on assessment of ray coverage, earthquakes and stations distribution, horizontal grid nodes was set up of 30×30 km2 for inside the study area and 80×80 km2 for outside the study area. The tomographic inversion results show low Vp anomaly beneath Toba caldera complex region and around the Sumatra Fault Zones (SFZ). These features are consistent with previous study. The low Vp anomaly beneath Toba caldera complex are observed around Mt. Pusuk Bukit at depths of 5 km down to 100 km. The interpretation is these anomalies may be associated with ascending hot materials from subduction processes at depths of 80 km down to 100 km. The obtained Vp structure from local tomography will give valuable information to enhance understanding of tectonic and volcanic in this study area.

Seasonal monitoring of melt and accumulation within the deep percolation zone of the Greenland Ice Sheet and comparison with simulations of regional climate modeling

Science.gov (United States)

Heilig, Achim; Eisen, Olaf; MacFerrin, Michael; Tedesco, Marco; Fettweis, Xavier

2018-06-01

Increasing melt over the Greenland Ice Sheet (GrIS) recorded over the past several years has resulted in significant changes of the percolation regime of the ice sheet. It remains unclear whether Greenland's percolation zone will act as a meltwater buffer in the near future through gradually filling all pore space or if near-surface refreezing causes the formation of impermeable layers, which provoke lateral runoff. Homogeneous ice layers within perennial firn, as well as near-surface ice layers of several meter thickness have been observed in firn cores. Because firn coring is a destructive method, deriving stratigraphic changes in firn and allocation of summer melt events is challenging. To overcome this deficit and provide continuous data for model evaluations on snow and firn density, temporal changes in liquid water content and depths of water infiltration, we installed an upward-looking radar system (upGPR) 3.4 m below the snow surface in May 2016 close to Camp Raven (66.4779° N, 46.2856° W) at 2120 m a.s.l. The radar is capable of quasi-continuously monitoring changes in snow and firn stratigraphy, which occur above the antennas. For summer 2016, we observed four major melt events, which routed liquid water into various depths beneath the surface. The last event in mid-August resulted in the deepest percolation down to about 2.3 m beneath the surface. Comparisons with simulations from the regional climate model MAR are in very good agreement in terms of seasonal changes in accumulation and timing of onset of melt. However, neither bulk density of near-surface layers nor the amounts of liquid water and percolation depths predicted by MAR correspond with upGPR data. Radar data and records of a nearby thermistor string, in contrast, matched very well for both timing and depth of temperature changes and observed water percolations. All four melt events transferred a cumulative mass of 56 kg m-2 into firn beneath the summer surface of 2015. We find that

P-wave velocity structure beneath the northern Antarctic Peninsula

Science.gov (United States)

Park, Y.; Kim, K.; Jin, Y.

2010-12-01

We have imaged tomographically the tree-dimensional velocity structure of the upper mantle beneath the northern Antarctic Peninsula using teleseismic P waves. The data came from the seven land stations of the Seismic Experiment in Patagonia and Antarctica (SEPA) campaigned during 1997-1999, a permanent IRIS/GSN station (PMSA), and 3 seismic stations installed at scientific bases, Esperanza (ESPZ), Jubany (JUBA), and King Sejong (KSJ), in South Shetland Islands. All of the seismic stations are located in coast area, and the signal to noise ratios (SNR) are very low. The P-wave model was inverted from 95 earthquakes resulting in 347 ray paths with P- and PKP-wave arrivals. The inverted model shows a strong low velocity anmaly beneath the Bransfield Strait, and a fast anomaly beneath the South Shetland Islands. The low velocity anomaly beneath the Bransfield might be due to a back arc extension, and the fast velocity anomaly beneath the South Shetland Islands could indicates the cold subducted slab.

Petrological Geodynamics of Mantle Melting II. AlphaMELTS + Multiphase Flow: Dynamic Fractional Melting

Science.gov (United States)

Tirone, Massimiliano

2018-03-01

In this second installment of a series that aims to investigate the dynamic interaction between the composition and abundance of the solid mantle and its melt products, the classic interpretation of fractional melting is extended to account for the dynamic nature of the process. A multiphase numerical flow model is coupled with the program AlphaMELTS, which provides at the moment possibly the most accurate petrological description of melting based on thermodynamic principles. The conceptual idea of this study is based on a description of the melting process taking place along a 1-D vertical ideal column where chemical equilibrium is assumed to apply in two local sub-systems separately on some spatial and temporal scale. The solid mantle belongs to a local sub-system (ss1) that does not interact chemically with the melt reservoir which forms a second sub-system (ss2). The local melt products are transferred in the melt sub-system ss2 where the melt phase eventually can also crystallize into a different solid assemblage and will evolve dynamically. The main difference with the usual interpretation of fractional melting is that melt is not arbitrarily and instantaneously extracted from the mantle, but instead remains a dynamic component of the model, hence the process is named dynamic fractional melting (DFM). Some of the conditions that may affect the DFM model are investigated in this study, in particular the effect of temperature, mantle velocity at the boundary of the mantle column. A comparison is made with the dynamic equilibrium melting (DEM) model discussed in the first installment. The implications of assuming passive flow or active flow are also considered to some extent. Complete data files of most of the DFM simulations, four animations and two new DEM simulations (passive/active flow) are available following the instructions in the supplementary material.

A Comparative Study of Continental vs. Intraoceanic Arc Mantle Melting: Experimentally Determined Phase Relations of Hydrous, Primitive Melts

Science.gov (United States)

Weaver, S.; Johnston, A.; Wallace, P. J.

2009-12-01

It is widely recognized that H2O and other volatiles play a crucial role in mantle melting in subduction zones. This work is a comparative study focused on determining the H2O-undersaturated, near-liquidus phase relations for two primitive subduction related compositions with the goal of determining the P-T-H2O conditions of mantle melting beneath arcs. These samples, JR-28, a calc-alkaline basalt from Volcan Jorullo, Mexico, and ID-16, a tholeiitic basalt from Okmok Volcano, Aleutian Islands, have major element compositions that indicate they are primary, mantle-derived melts. H2O-undersaturated piston cylinder experiments have been carried out at upper mantle pressures and temperatures (1.0-2.0 GPa and 1100-1350°C). The near-liquidus mineralogy of these two compositions has been mapped in P-T- H2O space in order to constrain the conditions under which these melts are multiply saturated with a mantle residue (lherzolite or harzburgite). Previous studies of dissolved volatiles in olivine-hosted melt inclusions have provided an estimate of pre-eruptive H2O-contents for JR-28 at ≥5 wt% H2O and experiments have been carried out accordingly. Preliminary results for JR-28 at 5 wt% H2O show olivine ± Cr-rich spinel on the liquidus at 1.0 GPa and enstatite as the liquidus phase at higher pressures (1.3 to 2.0 GPa). Ca-rich pyroxene appears in only one experiment 50°C below the liquidus at 1.5 GPa. These data show that JR-28 melts are multiply saturated with a harzburgite assemblage at ~1175°C and ~1.2 GPa at 5 wt% H2O. Experiments at 7 wt% H2O show similar results, although the olivine/Cr-spinel stability field expands at the expense of the enstatite stability field. Consequently, the olivine-enstatite cotectic is shifted to higher pressures and slightly cooler temperatures. The relatively high SiO2 content in the bulk rock (~52 wt% SiO2) supports the hypothesis that JR-28 last equilibrated with a depleted or harzburgite residue rather than a more fertile mantle

Network topology of olivine-basalt partial melts

Science.gov (United States)

Skemer, Philip; Chaney, Molly M.; Emmerich, Adrienne L.; Miller, Kevin J.; Zhu, Wen-lu

2017-07-01

The microstructural relationship between melt and solid grains in partially molten rocks influences many physical properties, including permeability, rheology, electrical conductivity and seismic wave speeds. In this study, the connectivity of melt networks in the olivine-basalt system is explored using a systematic survey of 3-D X-ray microtomographic data. Experimentally synthesized samples with 2 and 5 vol.% melt are analysed as a series of melt tubules intersecting at nodes. Each node is characterized by a coordination number (CN), which is the number of melt tubules that intersect at that location. Statistically representative volumes are described by coordination number distributions (CND). Polyhedral grains can be packed in many configurations yielding different CNDs, however widely accepted theory predicts that systems with small dihedral angles, such as olivine-basalt, should exhibit a predominant CN of four. In this study, melt objects are identified with CN = 2-8, however more than 50 per cent are CN = 4, providing experimental verification of this theoretical prediction. A conceptual model that considers the role of heterogeneity in local grain size and melt fraction is proposed to explain the formation of nodes with CN ≠ 4. Correctly identifying the melt network topology is essential to understanding the relationship between permeability and porosity, and hence the transport properties of partial molten mantle rocks.

The effect of polycrystalline rod insertion in a low Prandtl number melt for continuous Czochralski system

Science.gov (United States)

Nam, Phil-Ouk; Son, Seung-Suk; Yi, Kyung-Woo

2010-04-01

The increased wafer size results in greater instabilities and complexities within the silicon melt, and melt flow control through the application of magnetic fields is not adequate to stabilize the melt. Therefore, continuous Czochralski systems are being studied as a solution to these issues, with higher productivity and no change in size. The purpose of this study is to observe the effects of polycrystalline rod insertion on the melt for a continuous Czochralski system. In order to observe flow patterns within the melt both broadly and specifically, we employ experimentation on a model system in tandem with numerical simulation. The rod insertion do not significantly affect near the crystal edge. In the melt height from 0.14 to 0.09 m, an asymmetric temperature distributions arise when the crystal rotation is counterclockwise direction (-15 rpm) and the crucible rotation is clockwise direction (3 rpm). The axis-symmetrical temperature distribution is formed at lower melt heights (0.08 and 0.07 m). When the melt height is 0.07 m, the axis-symmetric temperature distribution is maintained even after the rod insertion.

GLASS MELTING PHENOMENA, THEIR ORDERING AND MELTING SPACE UTILISATION

Directory of Open Access Journals (Sweden)

Němec L.

2013-12-01

Full Text Available Four aspects of effective glass melting have been defined – namely the fast kinetics of partial melting phenomena, a consideration of the melting phenomena ordering, high utilisation of the melting space, and effective utilisation of the supplied energy. The relations were defined for the specific melting performance and specific energy consumption of the glass melting process which involve the four mentioned aspects of the process and indicate the potentials of effective melting. The quantity “space utilisation” has been treated in more detail as an aspect not considered in practice till this time. The space utilisation was quantitatively defined and its values have been determined for the industrial melting facility by mathematical modelling. The definitions of the specific melting performance and specific energy consumption have been used for assessment of the potential impact of a controlled melt flow and high space utilisation on the melting process efficiency on the industrial scale. The results have shown that even the partial control of the melt flow, leading to the partial increase of the space utilisation, may considerably increase the melting performance, whereas a decrease of the specific energy consumption was determined to be between 10 - 15 %.

Hurst's Exponent Determination for Radial Distribution Functions of In, Sn and In-40 wt%Sn Melt

International Nuclear Information System (INIS)

Zhou Yong-Zhi; Li Mei; Geng Hao-Ran; Yang Zhong-Xi; Sun Chun-Jing

2011-01-01

Hurst's exponent of radial distribution functions (RDFs) within the short-range scope of In, Sn and In-40 wt % Sn melts are determined by the rescaled range analysis method. Hurst's exponents H are between 0.94 and 0.97, which display long-range dependence. Within short-range scope, the number of particles from a reference particle belongs to fractional Brownian motion. After RDF serials are randomly scrambled, Hurst's exponents all dramatically dropped, which proves long-range dependence. H irregularly varies as the temperature rises, but the change tendency is not consistent with the correlation radius r c . (general)

Numerical simulation of hot-melt extrusion processes for amorphous solid dispersions using model-based melt viscosity.

Science.gov (United States)

Bochmann, Esther S; Steffens, Kristina E; Gryczke, Andreas; Wagner, Karl G

2018-03-01

Simulation of HME processes is a valuable tool for increased process understanding and ease of scale-up. However, the experimental determination of all required input parameters is tedious, namely the melt rheology of the amorphous solid dispersion (ASD) in question. Hence, a procedure to simplify the application of hot-melt extrusion (HME) simulation for forming amorphous solid dispersions (ASD) is presented. The commercial 1D simulation software Ludovic ® was used to conduct (i) simulations using a full experimental data set of all input variables including melt rheology and (ii) simulations using model-based melt viscosity data based on the ASDs glass transition and the physical properties of polymeric matrix only. Both types of HME computation were further compared to experimental HME results. Variation in physical properties (e.g. heat capacity, density) and several process characteristics of HME (residence time distribution, energy consumption) among the simulations and experiments were evaluated. The model-based melt viscosity was calculated by using the glass transition temperature (T g ) of the investigated blend and the melt viscosity of the polymeric matrix by means of a T g -viscosity correlation. The results of measured melt viscosity and model-based melt viscosity were similar with only few exceptions, leading to similar HME simulation outcomes. At the end, the experimental effort prior to HME simulation could be minimized and the procedure enables a good starting point for rational development of ASDs by means of HME. As model excipients, Vinylpyrrolidone-vinyl acetate copolymer (COP) in combination with various APIs (carbamazepine, dipyridamole, indomethacin, and ibuprofen) or polyethylene glycol (PEG 1500) as plasticizer were used to form the ASDs. Copyright © 2017 Elsevier B.V. All rights reserved.

Bathymetry and ocean properties beneath Pine Island Glacier revealed by Autosub3 and implications for recent ice stream evolution (Invited)

Science.gov (United States)

Jenkins, A.; Dutrieux, P.; McPhail, S.; Perrett, J.; Webb, A.; White, D.; Jacobs, S. S.

2009-12-01

The Antarctic ice sheet, which represents the largest of all potential contributors to sea level rise, appears to be losing mass at a rate that has accelerated over recent decades. Ice loss is focussed in a number of key drainage basins where dynamical changes in the outlet glaciers have led to increased discharge. The synchronous response of several independent glaciers, coupled with the observation that thinning is most rapid over their floating termini, is generally taken as an indicator that the changes have been driven from the ocean. Some of the most significant changes have been observed on Pine Island Glacier, where thinning, acceleration and grounding line retreat have all been observed, primarily through satellite remote sensing. Even during the relatively short satellite record, rates of change have been observed to increase. Between 20th and 30th January 2009 the Autosub3 autonomous underwater vehicle was deployed from host ship RVIB Nathaniel B Palmer on six sorties into the ocean cavity beneath Pine Island Glacier. Total track length was 887 km (taking 167 hours) of which 510 km (taking 94 hours) were beneath the glacier. Some of the main aims were to map both the seabed beneath and the underside of the glacier and to investigate how warm Circumpolar Deep Water (CDW) flows beneath Pine Island Glacier and determines its melt rate. Among the instruments carried by Autosub-3 were a Seabird CTD, with dual conductivity and temperature sensors plus a dissolved oxygen sensor and a transmissometer, a multi-beam echosounder that could be configured to look up or down, and two Acoustic Doppler Current Profilers (ADCPs): an upward-looking 300 kHz instrument and a downward-looking 150 kHz instrument, providing a record of ice draft and seabed depth along the vehicle track. The ADCP data reveal an apparently continuous ridge with an undulating crest that extends across the cavity about 30km in from the current ice front. This topographic feature blocks CDW inflow

Uranium-series disequilibria of inflated sections of the Juan de Fuca Ridge: Implications for mantle melting

Science.gov (United States)

Dreyer, B. M.; Gill, J. B.; Ramos, F. C.; Clague, D. A.; Scott, S. R.

2010-12-01

U-Th disequilibria are reported for the two inflated portions (defined by bathymetric highs) of the Juan de Fuca Ridge (JdFR): Axial Seamount and the northern Endeavour segment. Both have broad axis-centered bathymetric plateaus, commonly attributed to the influence of the adjacent Heckle and Cobb melt anomalies, respectively. We explore structural and geochemical contrasts between them that imply fundamental differences in magma plumbing and/or transport processes. The depth to the axial magma chamber (AMC) within the JdFR crust is shallowest beneath Axial Seamount and deepest and most variable beneath Endeavour. Lavas from Endeavour include the most enriched and diverse compositions of the JdFR. Endeavour N-MORBs are most similar to Axial basalts in K2O/TiO2, La/Yb, Na8, and Fe8 although most Axial basalts have lower MgO. Major element trends suggest clinopyroxene saturation at higher MgO at Endeavour. Additional basalt types from Endeavour (i.e., those with K2O/TiO2 >0.15), the West Valley segment to the north, and Southwest Seamount to the west share similar enrichments in incompatible trace elements (Th, Nb) and radiogenic-Pb. Similar characteristics are absent from basalts from the adjacent Heck and Heckle seamount chains, which are highly-depleted N-MORBs, precluding the hypothesis that thickened and inflated crust at Endeavour is associated with increased melt supply due to transit over the seamount source. In contrast, Axial basalts are more chemically homogeneous, and share selected geochemical characteristics with the adjacent Cobb seamount chain. New uranium-series data suggest fundamental differences in melting parameters between inflated and non-inflated portions of the JdFR. Average Th/U at Endeavour (3.03 ± 6, n=10) is nearly indistinguishable from Axial (2.83 ± 9, n=17), but both are distinct from elsewhere on the JdFR (~2.1-2.5). That is, basalts erupted from regions of inflated crust have higher Th/U. Despite high overall compositional

Extraction of scandium by organic substance melts

International Nuclear Information System (INIS)

Gladyshev, V.P.; Lobanov, F.I.; Zebreva, A.I.; Andreeva, N.N.; Manuilova, O.A.; Il'yukevich, Yu.A.

1984-01-01

Regularities of scandium extraction by the melts of octadecanicoic acid, n-carbonic acids of C 17 -C 20 commerical fraction and mixtures of tributylphosphate (TBP) with paraffin at (70+-1) deg C have been studied. The optimum conditions for scandium extraction in the melt of organic substances are determined. A scheme of the extraction by the melts of higher carbonic acids at ninitial metal concentrations of 10 -5 to 10 -3 mol/l has been suggested. The scandium compound has been isolated in solid form, its composition having been determined. The main advantages of extraction by melts are as follows: a possibility to attain high distribution coefficients, distinct separation of phases after extraction, the absence of emulsions, elimination of employing inflammable and toxic solvents, a possibility of rapid X-ray fluorescence determinatinon of scandium directly in solid extract

Controllable irregular melting induced by atomic segregation in bimetallic clusters with fabricating different initial configurations

International Nuclear Information System (INIS)

Li Guojian; Liu Tie; Wang Qiang; Lue Xiao; Wang Kai; He Jicheng

2010-01-01

The melting process of Co, Co-Cu and Co-Ni clusters with different initial configurations is studied in molecular dynamics by a general embedded atom method. An irregular melting, at which energy decreases as the temperature increase near the melting point, is found in the onion-like Co-Cu-Co clusters, but not in the mixed Co-Cu and onion-like Co-Ni-Co clusters. From the analysis of atomic distributions and energy variation, the results indicate the irregular melting is induced by Cu atomic segregation. Furthermore, this melting can be controlled by doping hetero atoms with different surface energies and controlling their distributions.

Gamma irradiation of melt processed biomedical PDLLA/HAP nanocomposites

International Nuclear Information System (INIS)

Dadbin, Susan; Kheirkhah, Yahya

2014-01-01

Poly(D-L lactide) PDLLA/hydroxyapatite (HAP) nanocomposites at various compositions were prepared by melt-compounding process and then subjected to gamma irradiation at a dose of 30 kGy. The morphology of the nanocomposites, characterized by transmission electron microscopy (TEM), displayed HAP nanoparticles at various sizes ranging from 10 to 100 nm distributed almost evenly within the polymer matrix. Differential scanning calorimetric (DSC) analysis of the irradiated nanocomposites showed an increase in the degree of crystallinity along with a melting peak split. The double melting peak suggested formation of different crystalline structures in the radiation exposed nanocomposites. Also the cold crystallization peak shifted to lower temperatures and became much sharper upon irradiation, indicating higher crystallization rate. The irradiated nanocomposites showed lower tensile strength and elongation at break, suggesting occurrence of some chain scission reactions in the PLA. - Highlights: • Biomedical polylactic acid/hydroxyapatite nanocomposites prepared by melt-compounding were gamma irradiated. • Transmission electron microscopy showed hydroxyapatite nanoparticles evenly distributed within polylactic acid ranging from 10 to 100 nm. • A halo appeared around hydroxyapatite particles showing interfacial interactions between polylactic acid and the particles. • Double melting peak appeared for polylactic acid in DSC thermograms upon gamma irradiation of the nanocomposites

Entangled Polymer Melts in Extensional Flow

DEFF Research Database (Denmark)

Hengeller, Ludovica

Many commercial materials derived from synthetic polymers exhibit a complex response under different processing operations such as fiber formation, injection moulding,film blowing, film casting or coatings. They can be processed both in the solid or in the melted state. Often they may contain two...... or more different polymers in addition to additives, fillers or solvents in order to modify the properties of the final product. Usually, it is also desired to improve the processability. For example the supplement of a high molecular weight component improves the stability in elongational flows....... Understanding the behaviour of polymer melts and solutions in complex non-linearflows is crucial for the design of polymeric materials and polymer processes. Through rheological characterization, in shear and extensional flow, of model polymer systems,i.e. narrow molar mass distribution polymer melts...

Computation and measurement of air temperature distribution of an industrial melt blowing die

Directory of Open Access Journals (Sweden)

Wu Li-Li

2014-01-01

Full Text Available The air flow field of the dual slot die on an HDF-6D melt blowing non-woven equipment is computed numerically. A temperature measurement system is built to measure air temperatures. The computation results tally with the measured results proving the correctness of the computation. The results have great valuable significance in the actual melt blowing production.

Deformation, static recrystallization, and reactive melt transport in shallow subcontinental mantle xenoliths (Tok Cenozoic volcanic field, SE Siberia)

Science.gov (United States)

Tommasi, Andréa; Vauchez, Alain; Ionov, Dmitri A.

2008-07-01

Partial melting and reactive melt transport may change the composition, microstructures, and physical properties of mantle rocks. Here we explore the relations between deformation and reactive melt transport through detailed microstructural analysis and crystallographic orientation measurements in spinel peridotite xenoliths that sample the shallow lithospheric mantle beneath the southeastern rim of the Siberian craton. These xenoliths have coarse-grained, annealed microstructures and show petrographic and chemical evidence for variable degrees of reaction with silicate melts and fluids, notably Fe-enrichment and crystallization of metasomatic clinopyroxene (cpx). Olivine crystal preferred orientations (CPO) range from strong to weak. [010]-fiber patterns, characterized by a point concentration of [010] normal to the foliation and by dispersion of [100] in the foliation plane with a weak maximum parallel to the lineation, predominate relative to the [100]-fiber patterns usually observed in lithospheric mantle xenoliths and peridotite massifs. Variations in olivine CPO patterns or intensity are not correlated with modal and chemical compositions. This, together with the analysis of microstructures, suggests that reactive melt percolation postdated both deformation and static recrystallization. Preferential crystallization of metasomatic cpx along (010) olivine grain boundaries points to an influence of the preexisting deformation fabrics on melt transport, with higher permeability along the foliation. Similarity between orthopyroxene (opx) and cpx CPO suggests that cpx orientations may be inherited from those of opx during melt-rock reaction. As observed in previous studies, reactive melt transport does not weaken olivine CPO and seismic anisotropy in the upper mantle, except in melt accumulation domains. In contrast, recovery and selective grain growth during static recrystallization may lead to development of [010]-fiber olivine CPO and, if foliations are

Lithospheric Layering beneath the Contiguous United States Constrained by S-to-P Receiver Functions

Science.gov (United States)

Liu, L.; Liu, K. H.; Kong, F.; Gao, S. S.

2017-12-01

The greatly-improved spatial coverage of broadband seismic stations as a result of the deployment of the EarthScope Transportable Array (TA) stations and the diversity of tectonic environments in the contiguous United States provide a unique opportunity to investigate the depth variation and nature of intra-lithospheric interfaces in different tectonic regimes. A total of 284,121 high-quality S-to-P receiver functions (SRFs) are obtained from 3,809 broadband seismic stations in the TA and other permanent and temporary deployments in the contiguous United States. The SRFs are computed using frequency domain deconvolution, and are stacked in consecutive circles with a radius of 2°. They are converted to depth series after move-out corrections using the IASP91 Earth model. Similar to previous SRF studies, a robust negative arrival, representing a sharp discontinuity of velocity reduction with depth, is visible in virtually all the stacked traces in the depth range of 30-110 km. Beneath the western US, the depth of this discontinuity is 69±17 km, and beneath the eastern US, it ranges from 75 to 90 km, both of which are comparable to the depth of the tomographically-determined lithosphere-asthenosphere boundary (LAB). In contrast, the depth of the discontinuity beneath the central US is 83±10 km which is significantly smaller than the 250 km LAB depth determined by seismic surface wave tomography. Based on previous seismic tomography, shear-wave splitting and mantle xenolith studies, we interpret this discontinuity as the top of a frozen-in layer of volatile-rich melt beneath the central US. The observations and the discrepancy between the SRF and seismic tomography results for the central US as well as the amplitude of the corresponding arrival on the SRFs may be explained by spatial variations of the thickness of the transitional layer between the "pure" lithosphere and the "pure" asthenosphere. Under this hypothesis, the consistency between the results from the

Formation and interpretation of eskers beneath retreating ice sheets

Science.gov (United States)

Creyts, T. T.; Hewitt, I.

2017-12-01

The retreat of the ice sheets during the Pleistocene left large and spectacular subglacial features exposed. Understanding these features gives us insight into how the ice sheets retreated, how meltwater influenced retreat, and can help inform our understanding of potential future rates of ice sheet retreat. Among these features, eskers, long sinuous ridges primarily composed of clastic sediments, lack a detailed explanation of how surface melt rates and ice sheet retreat rates influence their growth and spatial distribution. Here, we develop a theory for esker formation based on the initial work of Rothlisberger modified for sediment transport and inclusion of surface meltwater forcing. The primary subglacial ingredients include water flow through subglacial tunnels with the addition of mass balances for sediment transport. We show how eskers when water flow slows below a critical stress for sediment motion. This implies that eskers are deposited in a localized region near the snout of the ice sheet. Our findings suggest that very long eskers form sequentially as the ice front retreats. The position of the esker follows the path of the channel mouth through time, which does not necessarily coincide with the instantaneous route of the feeding channel. However, in most cases, we expect those locations to be similar. The role of surface meltwater and the climatology associated with the forcing is crucial to the lateral spacing of the eskers. We predict that high surface melt rates lead to narrower catchments but that the greater extent of the ablation area means that channels are likely larger. At the same time, for a given channel size (and hence sediment flux), the size of a deposited esker depends on a margin retreat rate. Hence, the size of the eskers is related delicately to the balance between surface melt rates and margin retreat rates. We discuss how our theory can be combined with observed esker distributions to infer the relationship between these two rates

MELTS_Excel: A Microsoft Excel-based MELTS interface for research and teaching of magma properties and evolution

Science.gov (United States)

Gualda, Guilherme A. R.; Ghiorso, Mark S.

2015-01-01

thermodynamic modeling software MELTS is a powerful tool for investigating crystallization and melting in natural magmatic systems. Rhyolite-MELTS is a recalibration of MELTS that better captures the evolution of silicic magmas in the upper crust. The current interface of rhyolite-MELTS, while flexible, can be somewhat cumbersome for the novice. We present a new interface that uses web services consumed by a VBA backend in Microsoft Excel©. The interface is contained within a macro-enabled workbook, where the user can insert the model input information and initiate computations that are executed on a central server at OFM Research. Results of simple calculations are shown immediately within the interface itself. It is also possible to combine a sequence of calculations into an evolutionary path; the user can input starting and ending temperatures and pressures, temperature and pressure steps, and the prevailing oxidation conditions. The program shows partial updates at every step of the computations; at the conclusion of the calculations, a series of data sheets and diagrams are created in a separate workbook, which can be saved independently of the interface. Additionally, the user can specify a grid of temperatures and pressures and calculate a phase diagram showing the conditions at which different phases are present. The interface can be used to apply the rhyolite-MELTS geobarometer. We demonstrate applications of the interface using an example early-erupted Bishop Tuff composition. The interface is simple to use and flexible, but it requires an internet connection. The interface is distributed for free from http://melts.ofm-research.org.

Thermal behavior and densification mechanism during selective laser melting of copper matrix composites: Simulation and experiments

International Nuclear Information System (INIS)

Dai, Donghua; Gu, Dongdong

2014-01-01

Highlights: • Thermal behavior and densification activity during SLM of composites are simulated. • Temperature distributions and melt pool dimensions during SLM are disclosed. • Motion behaviors of gaseous bubbles in laser induced melt pool are elucidated. • Simulation results show good agreement with the obtained experimental results. - Abstract: Simulation of temperature distribution and densification process of selective laser melting (SLM) WC/Cu composite powder system has been performed, using a finite volume method (FVM). The transition from powder to solid, the surface tension induced by temperature gradient, and the movement of laser beam power with a Gaussian energy distribution are taken into account in the physical model. The effect of the applied linear energy density (LED) on the temperature distribution, melt pool dimensions, behaviors of gaseous bubbles and resultant densification activity has been investigated. It shows that the temperature distribution is asymmetric with respect to the laser beam scanning area. The center of the melt pool does not locate at the center of the laser beam but slightly shifts towards the side of the decreasing X-axis. The dimensions of the melt pool are in sizes of hundreds of micrometers and increase with the applied LED. For an optimized LED of 17.5 kJ/m, an enhanced efficiency of gas removal from the melt pool is realized, and the maximum relative density of laser processed powder reaches 96%. As the applied LED surpasses 20 kJ/m, Marangoni flow tends to retain the entrapped gas bubbles. The flow pattern has a tendency to deposit the gas bubbles at the melt pool bottom or to agglomerate gas bubbles by the rotating flow in the melt pool, resulting in a higher porosity in laser processed powder. The relative density and corresponding pore size and morphology are experimentally acquired, which are in a good agreement with the results predicted by simulation

Emerging melt quality control solution technologies for aluminium melt

Directory of Open Access Journals (Sweden)

Arturo Pascual, Jr

2009-11-01

Full Text Available The newly developed “MTS 1500” Melt Treatment System is performing the specifi cally required melt treatment operations like degassing, cleaning, modification and/or grain refinement by an automated process in one step and at the same location. This linked process is saving time, energy and metal losses allowing - by automated dosage of the melt treatment agents - the production of a consistent melt quality batch after batch. By linking the MTS Metal Treatment System with sensors operating on-line in the melt, i.e., with a hydrogen sensor “Alspek H”, a fully automated control of parts of the process chain like degassing is possible. This technology does guarantee a pre-specifi ed and documented melt quality in each melt treatment batch. Furthermore, to ensure that castings are consistent and predictable there is a growing realization that critical parameters such as metal cleanliness must be measured prior to casting. There exists accepted methods for measuring the cleanliness of an aluminum melt but these can be both slow and costly. A simple, rapid and meaningful method of measuring and bench marking the cleanliness of an aluminum melt has been developed to offer the foundry a practical method of measuring melt cleanliness. This paper shows the structure and performance of the integrated MTS melt treatment process and documents achieved melt quality standards after degassing, cleaning, modifi cation and grain refi nement operations under real foundry conditions. It also provides an insight on a melt cleanliness measuring device “Alspek MQ” to provide foundry men better tools in meeting the increasing quality and tighter specifi cation demand from the industry.

Depth variations of P-wave azimuthal anisotropy beneath East Asia

Science.gov (United States)

Wei, W.; Zhao, D.; Xu, J.

2017-12-01

We present a new P-wave anisotropic tomographic model beneath East Asia by inverting a total of 1,488,531 P wave arrival-time data recorded by the regional seismic networks in East Asia and temporary seismic arrays deployed on the Tibetan Plateau. Our results provide important new insights into the subducting Indian, Pacific and Philippine Sea plates and mantle dynamics in East Asia. Our tomographic images show that the northern limit of the subducting Indian plate has reached the Jinsha River suture in eastern Tibet. A striking variation of P-wave azimuthal anisotropy is revealed in the Indian lithosphere: the fast velocity direction (FVD) is NE-SW beneath the Indian continent, whereas the FVD is arc parallel beneath the Himalaya and Tibetan Plateau, which may reflect re-orientation of minerals due to lithospheric extension, in response to the India-Eurasia collision. The FVD in the subducting Philippine Sea plate beneath the Ryukyu arc is NE-SW(trench parallel), which is consistent with the spreading direction of the West Philippine Basin during its initial opening stage, suggesting that it may reflect the fossil anisotropy. A circular pattern of FVDs is revealed around the Philippine Sea slab beneath SE China. We suggest that it reflects asthenospheric strain caused by toroidal mantle flow around the edge of the subducting slab. We find a striking variation of the FVD with depth in the subducting Pacific slab beneath the Northeast Japan arc. It may be caused by slab dehydration that changed elastic properties of the slab with depth. The FVD in the mantle wedge beneath the Northeast Japan and Ryukyu arcs is trench normal, which reflects subduction-induced convection. Beneath the Kuril and Izu-Bonin arcs where oblique subduction occurs, the FVD in the mantle wedge is nearly normal to the moving direction of the downgoing Pacific plate, suggesting that the oblique subduction together with the complex slab morphology have disturbed the mantle flow.

A multi-component evaporation model for beam melting processes

Science.gov (United States)

Klassen, Alexander; Forster, Vera E.; Körner, Carolin

2017-02-01

In additive manufacturing using laser or electron beam melting technologies, evaporation losses and changes in chemical composition are known issues when processing alloys with volatile elements. In this paper, a recently described numerical model based on a two-dimensional free surface lattice Boltzmann method is further developed to incorporate the effects of multi-component evaporation. The model takes into account the local melt pool composition during heating and fusion of metal powder. For validation, the titanium alloy Ti-6Al-4V is melted by selective electron beam melting and analysed using mass loss measurements and high-resolution microprobe imaging. Numerically determined evaporation losses and spatial distributions of aluminium compare well with experimental data. Predictions of the melt pool formation in bulk samples provide insight into the competition between the loss of volatile alloying elements from the irradiated surface and their advective redistribution within the molten region.

Evolution of ocean-induced ice melt beneath Zachariæ Isstrøm, Northeast Greenland combining observations and an ocean general circulation model from 1978 to present

Science.gov (United States)

Cai, C.; Rignot, E. J.; Menemenlis, D.; Millan, R.; Bjørk, A. A.; Khan, S. A.; Charolais, A.

2017-12-01

Zachariæ Isstrøm, a major ice stream in northeast Greenland, lost a large fraction of its ice shelf during the last decade. We study the evolution of subaqueous melting of its floating section from 1978 to present. The ice shelf melt rate depends on thermal forcing from warm, salty, subsurface ocean waters of Atlantic origin (AW), the mixing of AW with fresh, buoyant subglacial discharge at the calving margin, and the shape of the sub-ice-shelf cavity. Subglacial discharge doubled as a result of enhanced ice sheet runoff caused by warmer air temperatures. Ocean thermal forcing has increased due to enhanced advection of AW. Using an Eulerian method, MEaSUREs ice velocity, Operation IceBridge (OIB) ice thickness, and RACMO2.3 surface balance data, we evaluate the ice shelf melt rate in 1978, 1999 and 2010. The melt rate doubled from 1999 to 2010. Using a Lagrangian method with World View imagery, we map the melt rate in detail from 2011 to 2016. We compare the results with 2D simulations from the Massachusetts Institute of Technology general circulation model (MITgcm), at a high spatial resolution (20-m horizontal and 40-m vertical grid spacing), using OIB ice thickness and sub-ice-shelf cavity for years 1978, 1996, 2010 and 2011, combined with in-situ ocean temperature/salinity data from Ocean Melting Greenland (OMG) 2017. We find that winter melt rates are 2 3 times smaller than summer rates and melt rates increase by one order magnitude during the transition from ice shelf termination to near-vertical calving wall termination. As the last remaining bits of floating ice shelf disappear, ice-ocean interaction will therefore play an increasing role in driving the glacier retreat into its marine-based basin. This work was performed under a contract with NASA Cryosphere Program at UC Irvine and Caltech's Jet Propulsion Laboratory.

Volatile diffusion in silicate melts and its effects on melt inclusions

Directory of Open Access Journals (Sweden)

P. Scarlato

2005-06-01

Full Text Available A compendium of diffusion measurements and their Arrhenius equations for water, carbon dioxide, sulfur, fluorine, and chlorine in silicate melts similar in composition to natural igneous rocks is presented. Water diffusion in silicic melts is well studied and understood, however little data exists for melts of intermediate to basic compositions. The data demonstrate that both the water concentration and the anhydrous melt composition affect the diffusion coefficient of water. Carbon dioxide diffusion appears only weakly dependent, at most, on the volatilefree melt composition and no effect of carbon dioxide concentration has been observed, although few experiments have been performed. Based upon one study, the addition of water to rhyolitic melts increases carbon dioxide diffusion by orders of magnitude to values similar to that of 6 wt% water. Sulfur diffusion in intermediate to silicic melts depends upon the anhydrous melt composition and the water concentration. In water-bearing silicic melts sulfur diffuses 2 to 3 orders of magnitude slower than water. Chlorine diffusion is affected by both water concentration and anhydrous melt composition; its values are typically between those of water and sulfur. Information on fluorine diffusion is rare, but the volatile-free melt composition exerts a strong control on its diffusion. At the present time the diffusion of water, carbon dioxide, sulfur and chlorine can be estimated in silicic melts at magmatic temperatures. The diffusion of water and carbon dioxide in basic to intermediate melts is only known at a limited set of temperatures and compositions. The diffusion data for rhyolitic melts at 800°C together with a standard model for the enrichment of incompatible elements in front of growing crystals demonstrate that rapid crystal growth, greater than 10-10 ms-1, can significantly increase the volatile concentrations at the crystal-melt interface and that any of that melt trapped

Magma transport and olivine crystallization depths in Kīlauea's east rift zone inferred from experimentally rehomogenized melt inclusions

Science.gov (United States)

Tuohy, Robin M.; Wallace, Paul J.; Loewen, Matthew W.; Swanson, Donald A.; Kent, Adam J. R.

2016-07-01

Concentrations of H2O and CO2 in olivine-hosted melt inclusions can be used to estimate crystallization depths for the olivine host. However, the original dissolved CO2 concentration of melt inclusions at the time of trapping can be difficult to measure directly because in many cases substantial CO2 is transferred to shrinkage bubbles that form during post-entrapment cooling and crystallization. To investigate this problem, we heated olivine from the 1959 Kīlauea Iki and 1960 Kapoho (Hawai'i) eruptions in a 1-atm furnace to temperatures above the melt inclusion trapping temperature to redissolve the CO2 in shrinkage bubbles. The measured CO2 concentrations of the experimentally rehomogenized inclusions (⩽590 ppm for Kīlauea Iki [n = 10]; ⩽880 ppm for Kapoho, with one inclusion at 1863 ppm [n = 38]) overlap with values for naturally quenched inclusions from the same samples, but experimentally rehomogenized inclusions have higher within-sample median CO2 values than naturally quenched inclusions, indicating at least partial dissolution of CO2 from the vapor bubble during heating. Comparison of our data with predictions from modeling of vapor bubble formation and published Raman data on the density of CO2 in the vapor bubbles suggests that 55-85% of the dissolved CO2 in the melt inclusions at the time of trapping was lost to post-entrapment shrinkage bubbles. Our results combined with the Raman data demonstrate that olivine from the early part of the Kīlauea Iki eruption crystallized at <6 km depth, with the majority of olivine in the 1-3 km depth range. These depths are consistent with the interpretation that the Kīlauea Iki magma was supplied from Kīlauea's summit magma reservoir (∼2-5 km depth). In contrast, olivine from Kapoho, which was the rift zone extension of the Kīlauea Iki eruption, crystallized over a much wider range of depths (∼1-16 km). The wider depth range requires magma transport during the Kapoho eruption from deep beneath the summit

Age Distribution of Lunar Impact-Melt Rocks in Apollo Drive-Tube 68001/2

Science.gov (United States)

Curran, N. M.; Bower, D. M.; Frasl, B.; Cohen, B. A.

2018-01-01

Apollo 16 double-drive tube 68001 /68002 provides impact and volcanic materials along a depth of approximately 60 cm in five compositional distinct units. 68001 /2 offers the potential to study distinct populations of impact melts with depth to understand how 'gardening' affects these samples. We will use unbiased major-element chemistry, mineralogy, and age to understand the impact history of Apollo 16 landing site. The study demonstrates the techniques that landed missions require to identify lithologies of interest (e.g., impact melts).

Structure of dense shock-melted alkali halides: Evidence for a continuous pressure-induced structural transition in the melt

International Nuclear Information System (INIS)

Ross, M.; Rogers, F.J.

1985-01-01

Hypernetted-chain equation calculations have been made for the ion-ion pair distribution functions in shock-melted CsI, CsBr, KBr, KCl, NaCl, and LiF. The results show that the melt undergoes a gradual pressure-induced structural change from an open NaCl-like structure with six nearest neighbors of opposite charge to one that has a rare-gas close-packed-like arrangement containing about 12 neighbors of mixed charge. These effects are most pronounced for the larger ions in which the short-range repulsions are stronger relative to long-range Coulomb attractions

Double melting in polytetrafluoroethylene γ-irradiated above its melting point

International Nuclear Information System (INIS)

Serov, S.A.; Khatipov, S.A.; Sadovskaya, N.V.; Tereshenkov, A.V.; Chukov, N.A.

2012-01-01

Highlights: ► PTFE irradiation leads to formation of double melting peaks in DSC curves. ► This is connected to dual crystalline morphology typical for PTFE. ► Two crystalline types exist in the PTFE irradiated in the melt. - Abstract: PTFE irradiation above its melting point leads to formation of double melting and crystallization peaks in DSC curves. Splitting of melting peaks is connected to dual crystalline morphology typical for PTFE irradiated in the melt. According to electron microscopy, two crystalline types with different size and packing density exist in the irradiated PTFE.

Corium melt researches at VESTA test facility

Directory of Open Access Journals (Sweden)

Hwan Yeol Kim

2017-10-01

Full Text Available VESTA (Verification of Ex-vessel corium STAbilization and VESTA-S (-small test facilities were constructed at the Korea Atomic Energy Research Institute in 2010 to perform various corium melt experiments. Since then, several tests have been performed for the verification of an ex-vessel core catcher design for the EU-APR1400. Ablation tests of an impinging ZrO2 melt jet on a sacrificial material were performed to investigate the ablation characteristics. ZrO2 melt in an amount of 65–70 kg was discharged onto a sacrificial material through a well-designed nozzle, after which the ablation depths were measured. Interaction tests between the metallic melt and sacrificial material were performed to investigate the interaction kinetics of the sacrificial material. Two types of melt were used: one is a metallic corium melt with Fe 46%, U 31%, Zr 16%, and Cr 7% (maximum possible content of U and Zr for C-40, and the other is a stainless steel (SUS304 melt. Metallic melt in an amount of 1.5–2.0 kg was delivered onto the sacrificial material, and the ablation depths were measured. Penetration tube failure tests were performed for an APR1400 equipped with 61 in-core instrumentation penetration nozzles and extended tubes at the reactor lower vessel. ZrO2 melt was generated in a melting crucible and delivered down into an interaction crucible where the test specimen is installed. To evaluate the tube ejection mechanism, temperature distributions of the reactor bottom head and in-core instrumentation penetration were measured by a series of thermocouples embedded along the specimen. In addition, lower vessel failure tests for the Fukushima Daiichi nuclear power plant are being performed. As a first step, the configuration of the molten core in the plant was investigated by a melting and solidification experiment. Approximately 5 kg of a mixture, whose composition in terms of weight is UO2 60%, Zr 10%, ZrO2 15%, SUS304 14%, and B4C 1%, was melted in a

Greenland iceberg melt variability from high-resolution satellite observations

Directory of Open Access Journals (Sweden)

E. M. Enderlin

2018-02-01

Full Text Available Iceberg discharge from the Greenland Ice Sheet accounts for up to half of the freshwater flux to surrounding fjords and ocean basins, yet the spatial distribution of iceberg meltwater fluxes is poorly understood. One of the primary limitations for mapping iceberg meltwater fluxes, and changes over time, is the dearth of iceberg submarine melt rate estimates. Here we use a remote sensing approach to estimate submarine melt rates during 2011–2016 for 637 icebergs discharged from seven marine-terminating glaciers fringing the Greenland Ice Sheet. We find that spatial variations in iceberg melt rates generally follow expected patterns based on hydrographic observations, including a decrease in melt rate with latitude and an increase in melt rate with iceberg draft. However, we find no longitudinal variations in melt rates within individual fjords. We do not resolve coherent seasonal to interannual patterns in melt rates across all study sites, though we attribute a 4-fold melt rate increase from March to April 2011 near Jakobshavn Isbræ to fjord circulation changes induced by the seasonal onset of iceberg calving. Overall, our results suggest that remotely sensed iceberg melt rates can be used to characterize spatial and temporal variations in oceanic forcing near often inaccessible marine-terminating glaciers.

Soil property control of biogeochemical processes beneath two subtropical stormwater infiltration basins.

Science.gov (United States)

O'Reilly, Andrew M; Wanielista, Martin P; Chang, Ni-Bin; Harris, Willie G; Xuan, Zhemin

2012-01-01

Substantially different biogeochemical processes affecting nitrogen fate and transport were observed beneath two stormwater infiltration basins in north-central Florida. Differences are related to soil textural properties that deeply link hydroclimatic conditions with soil moisture variations in a humid, subtropical climate. During 2008, shallow groundwater beneath the basin with predominantly clayey soils (median, 41% silt+clay) exhibited decreases in dissolved oxygen from 3.8 to 0.1 mg L and decreases in nitrate nitrogen (NO-N) from 2.7 mg L to soils (median, 2% silt+clay), aerobic conditions persisted from 2007 through 2009 (dissolved oxygen, 5.0-7.8 mg L), resulting in NO-N of 1.3 to 3.3 mg L in shallow groundwater. Enrichment of δN and δO of NO combined with water chemistry data indicates denitrification beneath the clayey basin and relatively conservative NO transport beneath the sandy basin. Soil-extractable NO-N was significantly lower and the copper-containing nitrite reductase gene density was significantly higher beneath the clayey basin. Differences in moisture retention capacity between fine- and coarse-textured soils resulted in median volumetric gas-phase contents of 0.04 beneath the clayey basin and 0.19 beneath the sandy basin, inhibiting surface/subsurface oxygen exchange beneath the clayey basin. Results can inform development of soil amendments to maintain elevated moisture content in shallow soils of stormwater infiltration basins, which can be incorporated in improved best management practices to mitigate NO impacts. Copyright © by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America, Inc.

Elastic and Anelastic Structure Beneath Eurasia

National Research Council Canada - National Science Library

Ekstrom, Goran

1997-01-01

The primary objective of this work has been to map the variations of elastic mantle properties beneath Eurasia over horizontal length scales of approximately 1000-1500 kilometers and vertial length...

Melting method for miscellaneous radioactive solid waste and melting furnace

International Nuclear Information System (INIS)

Osaki, Toru; Furukawa, Hirofumi; Uda, Nobuyoshi; Katsurai, Kiyomichi

1998-01-01

A vessel containing miscellaneous solid wastes is inserted in a crucible having a releasable material on the inner surface, they are induction-heated from the outside of the crucible by way of low temperature heating coils to melt low melting point materials in the miscellaneous wastes within a temperature range at which the vessel does not melt. Then, they are induction-heated by way of high temperature heating coils to melt the vessel and not yet melted materials, those molten materials are cooled, solidified molten material and the releasable material are taken out, and then the crucible is used again. Then, the crucible can be used again, so that it can be applied to a large scaled melting furnace which treats wastes by a unit of drum. In addition, since the cleaning of the used crucible and the application of the releasable material can be conducted without interrupting the operation of the melting furnace, the operation cycle of the melting furnace can be shortened. (N.H.)

The Rock Record of Seismic Nucleation: examples from pseudotachylites beneath the Whipple Detachment Fault, eastern California

Science.gov (United States)

Ortega-Arroyo, D.; Behr, W. M.; Gentry, E.

2017-12-01

The mechanisms that lead to nucleation and dynamic weakening in the middle crust are not well understood. Proposed mechanisms include flash heating of asperities, thermal pressurization of pore fluids, dynamic instabilities, and fracture interactions. We investigate this issue in the rock record using exhumed mid-crustal rocks exposed beneath the Whipple Detachment fault (WDF) in eastern CA. Analysis of pseudotachylites (PS) beneath the WDF, representing paleo-earthquakes, reveal two types: Type 1 PS exhibit little to no precursory cataclasis and are concentrated along shear bands at the margins of feldspar-rich lenses embedded in more quartz-rich domains. These appear synkinematic with S-C fabrics in the surrounding mylonites and they exhibit finely dynamically recrystallized grains in quartz at their margins, suggesting coeval ductile deformation. By contrast, Type 2 PS occur along the principal slip surface of a brittle shear zone and show evidence for precursory cataclasis, brecciation, and fracturing. Some cataclasites inject into the host rock, forming eddies along the boundary with the PS. Slip appears to localize progressively into a 2 cm thick fault core, with PS concentrated primarily in the interior- the presence of solidified melt and fluidized cataclasite as clasts within the fault core suggests multiple slip events are preserved. We interpret the two types of pseudotachylites to represent different conditions and mechanisms of earthquake nucleation near the brittle-ductile transition (BDT). Type 1 PS are interpreted to represent nucleation in deeper sections of the BDT by failure along mineralogically-controlled stress concentrations hosted within an otherwise viscously deforming mylonite. Our data suggest that these do not develop into large-magnitude EQ's because seismic slip is dampened into the surrounding quartz-rich viscous matrix; instead they may represent deep microseismicity and/or seismic tremor. By contrast, Type 2 PS are interpreted to

The interaction of a core melt with concrete

International Nuclear Information System (INIS)

Reimann, M.; Holleck, H.; Skokan, A.; Perinic, D.

1977-01-01

In its fourth phase, a hypothetic core melt interacts with the concrete of the reactor foundation. This phase may last several days. Experimental laboratory investigations and theoretical models on the basis of model experiments aim at determining the time curve of the temperature of the core melt in order to quantify the processes up to the solidification of the melt and the end of concrete destroyal. Material interactions: 1) The two phases of the core melt, oxidic and metallic, remain separate for a long period of time. In dependence of the degree of oxidation of the system, the elemental distribution and, in particular, the fission products in the melt may be assessed. 2) The changes in the material values of the core melt in dependence of the temperature curve may be qualitatively assessed. 3) The solidification temperature of the oxidic phase of the core melt may be given in dependence of (UO 2 + ZrO 2 ) content. Thermal interactions: 1) The ratio vertical/radial erosion, which determines the cavity shape, is described in the correct order of magnitude by the extended film model. 2) The correct order of magnitude of the erosion rates is described by the concrete destruction model coupled with the film model. 3) The effects of the different concrete destruction enthalpies and concrete compositions (amount of gaseous decomposition products) may be estimated by the model calculations. (orig./HP) [de

Core melt retention and cooling concept of the ERP

Energy Technology Data Exchange (ETDEWEB)

Weisshaeupl, H [SIEMENS/KWU, Erlangen (Germany); Yvon, M [Nuclear Power International, Paris (France)

1996-12-01

For the French/German European Pressurized Water Reactor (EPR) mitigative measures to cope with the event of a severe accident with core melt down are considered already at the design stage. Following the course of a postulated severe accident with reactor pressure vessel melt through one of the most important features of a future design must be to stabilize and cool the melt within the containment by dedicated measures. This measures should - as far as possible - be passive. One very promising solution for core melt retention seems to be a large enough spreading of the melt on a high temperature resistant protection layer with water cooling from above. This is the favorite concept for the EPR. In dealing with the retention of a molten core outside of the RPV several ``steps`` from leaving the RPV to finally stabilize the melt have to gone through. These steps are: collection of the melt; transfer of the melt; distribution of the melt; confining; cooling and stabilization. The technical features for the EPR solution of a large spreading of the melt are: Dedicated spreading chamber outside the reactor pit (area about 150 m{sup 2}); high temperature resistant protection layers (e.g. Zirconia bricks) at the bottom and part of the lateral structures (thus avoiding melt concrete interaction); reactor pit and spreading compartment are connected via a discharge channel which has a slope to the spreading area and is closed by a steel plate, which will resist the core melt for a certain time in order to allow a collection of the melt; the spreading compartments is connected with the In-Containment Refuelling Water Storage Tank (IRWST) with pipes for water flooding after spreading. These pipes are closed and will only be opened by the hot melt itself. It is shown how the course of the different steps mentioned above is processed and how each of these steps is automatically and passively achieved. (Abstract Truncated)

The COMET-L3 experiment on long-term melt. Concrete interaction and cooling by surface flooding

International Nuclear Information System (INIS)

Alsmeyer, H.; Cron, T.; Fluhrer, B.; Messemer, G.; Miassoedov, A.; Schmidt-Stiefel, S.; Wenz, T.

2007-02-01

The COMET-L3 experiment considers the long-term situation of corium/concrete interaction in an anticipated core melt accident of a light-water-reactor, after the metal melt is layered beneath the oxide melt. The experimental focus is on cavity formation in the basemat and the risk of long term basemat penetration. The experiment investigates the two-dimensional concrete erosion in a cylindrical crucible fabricated from siliceous concrete in the first phase of the test, and the influence of surface flooding in the second phase. Decay heating in the two-component metal and oxide melt is simulated by sustained induction heating of the metal phase that is overlaid by the oxide melt. The inner diameter of the concrete crucible was 60 cm, the initial mass of the melt was 425 kg steel and 211 kg oxide at 1665 C, resulting in a melt height of 450 mm. The net power to the metal melt was about 220 kW from 0 s to 1880 s, when the maximum erosion limit of the crucible was reached and heating was terminated. In the initial phase of the test (less than 100 s), the overheated, highly agitated metal melt causes intense interaction with the concrete, which leads to fast decrease of the initial melt overheat and reduction of the initially high concrete erosion rate. Thereafter, under quasistationary conditions until about 800 s, the erosion by the metal melt slows down to some 0.07 mm/s into the axial direction. Lateral erosion is a factor 3 smaller. Video observation of the melt surface shows an agitated melt with ongoing gas release from the decomposing concrete. Several periods of more intense gas release, gas driven splashing, and release of crusts from the concrete interface indicate the existence and iterative break-up of crusts that probably form at the steel/concrete interface. Surface flooding of the melt is initiated at 800 s by a shower from the crucible head with 0.375 litre water/s. Flooding does not lead to strong melt/water interactions, and no entrapment reactions or

Phenomenological studies on melt-structure-water interactions (MSWI) during severe accidents

International Nuclear Information System (INIS)

Sehgal, B.R.; Yang, Z.L.; Haraldsson, H.O.; Nourgaliev, R.R.; Konovalikhin, M.; Paladino, D.; Gubaidullin, A.A.; Kolb, G.; Theerthan, A.

2000-05-01

This is the annual report for the work performed in 1999 in the research project Melt-Structure-Water Interactions During Severe Accidents in LWRs, under the auspices of the APRI Project, jointly funded by SKI, HSK, USNRC and the Swedish and Finnish power companies. The emphasis of the work is placed on phenomena and properties which govern the fragmentation and breakup of melt jets and droplets, melt spreading and coolability, and thermal and mechanical loadings of a pressure vessel during melt-vessel interaction. We believe that significant technical advances have been achieved during the course of these studies. It was found that: The coolant temperature has significant influence on the characteristics of debris fragments produced from the breakup of an oxidic melt jet. At low subcooling the fragments are relatively large and irregular compared to the smaller particles produced at high subcooling. The melt jet density has considerable effect on the fragment size produced. As the melt density increases the fragment size becomes smaller. The mass mean size of the debris changes proportionally to the square root of the coolant to melt density ratio. The melt superheat has little effect on the debris particle size distribution produced during the melt jet fragmentation. The impingement velocity of the jet has significant impact on the fragmentation process. At lower jet velocity the melt fragments agglomerate and form a cake of large size debris. When the jet velocity is increased more complete fragmentation is obtained. The scaling methodology for melt spreading, developed during 1998, has been further validated against almost all of the spreading experimental data available so far. Experimental results for the dryout heat flux of homogeneous particulate debris beds with top flooding compare well with the Lipinski correlation. For the stratified particle beds, the fine particle layer resting on the top of another particle layer dominates the dryout processes

Phenomenological studies on melt-structure-water interactions (MSWI) during severe accidents

Energy Technology Data Exchange (ETDEWEB)

Sehgal, B.R.; Yang, Z.L.; Haraldsson, H.O.; Nourgaliev, R.R.; Konovalikhin, M.; Paladino, D.; Gubaidullin, A.A.; Kolb, G.; Theerthan, A. [Royal Inst. of Tech., Stockholm (Sweden). Div. of Nuclear Power Safety

2000-05-01

This is the annual report for the work performed in 1999 in the research project Melt-Structure-Water Interactions During Severe Accidents in LWRs, under the auspices of the APRI Project, jointly funded by SKI, HSK, USNRC and the Swedish and Finnish power companies. The emphasis of the work is placed on phenomena and properties which govern the fragmentation and breakup of melt jets and droplets, melt spreading and coolability, and thermal and mechanical loadings of a pressure vessel during melt-vessel interaction. We believe that significant technical advances have been achieved during the course of these studies. It was found that: The coolant temperature has significant influence on the characteristics of debris fragments produced from the breakup of an oxidic melt jet. At low subcooling the fragments are relatively large and irregular compared to the smaller particles produced at high subcooling. The melt jet density has considerable effect on the fragment size produced. As the melt density increases the fragment size becomes smaller. The mass mean size of the debris changes proportionally to the square root of the coolant to melt density ratio. The melt superheat has little effect on the debris particle size distribution produced during the melt jet fragmentation. The impingement velocity of the jet has significant impact on the fragmentation process. At lower jet velocity the melt fragments agglomerate and form a cake of large size debris. When the jet velocity is increased more complete fragmentation is obtained. The scaling methodology for melt spreading, developed during 1998, has been further validated against almost all of the spreading experimental data available so far. Experimental results for the dryout heat flux of homogeneous particulate debris beds with top flooding compare well with the Lipinski correlation. For the stratified particle beds, the fine particle layer resting on the top of another particle layer dominates the dryout processes

Crustal structure beneath Eastern Greenland

DEFF Research Database (Denmark)

Reiche, Sönke; Thybo, H.; Kaip, G.

2011-01-01

is recorded by 350 Reftek Texan receivers for 10 equidistant shot points along the profile. We use forward ray tracing modelling to construct a two-dimensional velocity model from the observed travel times. These results show the first images of the subsurface velocity structure beneath the Greenland ice...

Throughfall and its spatial variability beneath xerophytic shrub canopies within water-limited arid desert ecosystems

Science.gov (United States)

Zhang, Ya-feng; Wang, Xin-ping; Hu, Rui; Pan, Yan-xia

2016-08-01

Throughfall is known to be a critical component of the hydrological and biogeochemical cycles of forested ecosystems with inherently temporal and spatial variability. Yet little is understood concerning the throughfall variability of shrubs and the associated controlling factors in arid desert ecosystems. Here we systematically investigated the variability of throughfall of two morphological distinct xerophytic shrubs (Caragana korshinskii and Artemisia ordosica) within a re-vegetated arid desert ecosystem, and evaluated the effects of shrub structure and rainfall characteristics on throughfall based on heavily gauged throughfall measurements at the event scale. We found that morphological differences were not sufficient to generate significant difference (P < 0.05) in throughfall between two studied shrub species under the same rainfall and meteorological conditions in our study area, with a throughfall percentage of 69.7% for C. korshinskii and 64.3% for A. ordosica. We also observed a highly variable patchy pattern of throughfall beneath individual shrub canopies, but the spatial patterns appeared to be stable among rainfall events based on time stability analysis. Throughfall linearly increased with the increasing distance from the shrub base for both shrubs, and radial direction beneath shrub canopies had a pronounced impact on throughfall. Throughfall variability, expressed as the coefficient of variation (CV) of throughfall, tended to decline with the increase in rainfall amount, intensity and duration, and stabilized passing a certain threshold. Our findings highlight the great variability of throughfall beneath the canopies of xerophytic shrubs and the time stability of throughfall pattern among rainfall events. The spatially heterogeneous and temporally stable throughfall is expected to generate a dynamic patchy distribution of soil moisture beneath shrub canopies within arid desert ecosystems.

Comparative Study on Two Melting Simulation Methods: Melting Curve of Gold

International Nuclear Information System (INIS)

Liu Zhong-Li; Li Rui; Sun Jun-Sheng; Zhang Xiu-Lu; Cai Ling-Cang

2016-01-01

Melting simulation methods are of crucial importance to determining melting temperature of materials efficiently. A high-efficiency melting simulation method saves much simulation time and computational resources. To compare the efficiency of our newly developed shock melting (SM) method with that of the well-established two-phase (TP) method, we calculate the high-pressure melting curve of Au using the two methods based on the optimally selected interatomic potentials. Although we only use 640 atoms to determine the melting temperature of Au in the SM method, the resulting melting curve accords very well with the results from the TP method using much more atoms. Thus, this shows that a much smaller system size in SM method can still achieve a fully converged melting curve compared with the TP method, implying the robustness and efficiency of the SM method. (paper)

Experimental Investigation of Concrete Runway Snow Melting Utilizing Heat Pipe Technology

Directory of Open Access Journals (Sweden)

Fengchen Chen

2018-01-01

Full Text Available A full scale snow melting system with heat pipe technology is built in this work, which avoids the negative effects on concrete structure and environment caused by traditional deicing chemicals. The snow melting, ice-freezing performance and temperature distribution characteristics of heat pipe concrete runway were discussed by the outdoor experiments. The results show that the temperature of the concrete pavement is greatly improved with the heat pipe system. The environment temperature and embedded depth of heat pipe play a dominant role among the decision variables of the snow melting system. Heat pipe snow melting pavement melts the snow completely and avoids freezing at any time when the environment temperature is below freezing point, which is secure enough for planes take-off and landing. Besides, the exportation and recovery of geothermal energy indicate that this system can run for a long time. This paper will be useful for the design and application of the heat pipe used in the runway snow melting.

Experimental Investigation of Concrete Runway Snow Melting Utilizing Heat Pipe Technology.

Science.gov (United States)

Chen, Fengchen; Su, Xin; Ye, Qing; Fu, Jianfeng

2018-01-01

A full scale snow melting system with heat pipe technology is built in this work, which avoids the negative effects on concrete structure and environment caused by traditional deicing chemicals. The snow melting, ice-freezing performance and temperature distribution characteristics of heat pipe concrete runway were discussed by the outdoor experiments. The results show that the temperature of the concrete pavement is greatly improved with the heat pipe system. The environment temperature and embedded depth of heat pipe play a dominant role among the decision variables of the snow melting system. Heat pipe snow melting pavement melts the snow completely and avoids freezing at any time when the environment temperature is below freezing point, which is secure enough for planes take-off and landing. Besides, the exportation and recovery of geothermal energy indicate that this system can run for a long time. This paper will be useful for the design and application of the heat pipe used in the runway snow melting.

Method and apparatus for improved melt flow during continuous strip casting

Science.gov (United States)

Follstaedt, Donald W.; King, Edward L.; Schneider, Ken C.

1991-11-12

The continuous casting of metal strip using the melt overflow process is improved by controlling the weir conditions in the nozzle to provide a more uniform flow of molten metal across the width of the nozzle and reducing the tendency for freezing of metal along the interface with refractory surfaces. A weir design having a sloped rear wall and tapered sidewalls and critical gap controls beneath the weir has resulted in the drastic reduction in edge tearing and a significant improvement in strip uniformity. The floor of the container vessel is preferably sloped and the gap between the nozzle and the rotating substrate is critically controlled. The resulting flow patterns observed with the improved casting process have reduced thermal gradients in the bath, contained surface slag and eliminated undesirable solidification near the discharge area by increasing the flow rates at those points.

Termination of light-water reactor core-melt accidents with a chemical core catcher: the core-melt source reduction system (COMSORS)

International Nuclear Information System (INIS)

Forsberg, C.W.; Parker, G.W.; Rudolph, J.C.; Osborne-Lee, I.W.; Kenton, M.A.

1996-09-01

The Core-Melt Source Reduction System (COMSORS) is a new approach to terminate light-water reactor core melt accidents and ensure containment integrity. A special dissolution glass is placed under the reactor vessel. If core debris is released onto the glass, the glass melts and the debris dissolves into the molten glass, thus creating a homogeneous molten glass. The molten glass, with dissolved core debris, spreads into a wide pool, distributing the heat for removal by radiation to the reactor cavity above or by transfer to water on top of the molten glass. Expected equilibrium glass temperatures are approximately 600 degrees C. The creation of a low-temperature, homogeneous molten glass with known geometry permits cooling of the glass without threatening containment integrity. This report describes the technology, initial experiments to measure key glass properties, and modeling of COMSORS operations

Olivine/melt transition metal partitioning, melt composition, and melt structure—Melt polymerization and Qn-speciation in alkaline earth silicate systems

Science.gov (United States)

Mysen, Bjorn O.

2008-10-01

The two most abundant network-modifying cations in magmatic liquids are Ca 2+ and Mg 2+. To evaluate the influence of melt structure on exchange of Ca 2+ and Mg 2+ with other geochemically important divalent cations ( m-cations) between coexisting minerals and melts, high-temperature (1470-1650 °C), ambient-pressure (0.1 MPa) forsterite/melt partitioning experiments were carried out in the system Mg 2SiO 4-CaMgSi 2O 6-SiO 2 with ⩽1 wt% m-cations (Mn 2+, Co 2+, and Ni 2+) substituting for Ca 2+ and Mg 2+. The bulk melt NBO/Si-range ( NBO/Si: nonbridging oxygen per silicon) of melt in equilibrium with forsterite was between 1.89 and 2.74. In this NBO/Si-range, the NBO/Si(Ca) (fraction of nonbridging oxygens, NBO, that form bonds with Ca 2+, Ca 2+- NBO) is linearly related to NBO/Si, whereas fraction of Mg 2+- NBO bonds is essentially independent of NBO/Si. For individual m-cations, rate of change of KD( m-Mg) with NBO/Si(Ca) for the exchange equilibrium, mmelt + Mg olivine ⇌ molivine + Mg melt, is linear. KD( m-Mg) decreases as an exponential function of increasing ionic potential, Z/ r2 ( Z: formal electrical charge, r: ionic radius—here calculated with oxygen in sixfold coordination around the divalent cations) of the m-cation. The enthalpy change of the exchange equilibrium, Δ H, decreases linearly with increasing Z/ r2 [Δ H = 261(9)-81(3)· Z/ r2 (Å -2)]. From existing information on (Ca,Mg)O-SiO 2 melt structure at ambient pressure, these relationships are understood by considering the exchange of divalent cations that form bonds with nonbridging oxygen in individual Qn-species in the melts. The negative ∂ KD( m-Mg) /∂( Z/ r2) and ∂(Δ H)/∂( Z/ r2) is because increasing Z/ r2 is because the cations forming bonds with nonbridging oxygen in increasingly depolymerized Qn-species where steric hindrance is decreasingly important. In other words, principles of ionic size/site mismatch commonly observed for trace and minor elements in crystals, also

Role of melt behavior in modifying oxidation distribution using an interface incorporated model in selective laser melting of aluminum-based material

Energy Technology Data Exchange (ETDEWEB)

Gu, Dongdong, E-mail: dongdonggu@nuaa.edu.cn; Dai, Donghua [College of Materials Science and Technology, Nanjing University of Aeronautics and Astronautics, Yudao Street 29, Nanjing 210016 (China); Institute of Additive Manufacturing (3D Printing), Nanjing University of Aeronautics and Astronautics, Yudao Street 29, Nanjing 210016 (China)

2016-08-28

A transient three dimensional model for describing the molten pool dynamics and the response of oxidation film evolution in the selective laser melting of aluminum-based material is proposed. The physical difference in both sides of the scan track, powder-solid transformation and temperature dependent physical properties are taken into account. It shows that the heat energy tends to accumulate in the powder material rather than in the as-fabricated part, leading to the formation of the asymmetrical patterns of the temperature contour and the attendant larger dimensions of the molten pool in the powder phase. As a higher volumetric energy density is applied (≥1300 J/mm{sup 3}), a severe evaporation is produced with the upward direction of velocity vector in the irradiated powder region while a restricted operating temperature is obtained in the as-fabricated part. The velocity vector continuously changes from upward direction to the downward one as the scan speed increases from 100 mm/s to 300 mm/s, promoting the generation of the debris of the oxidation films and the resultant homogeneous distribution state in the matrix. For the applied hatch spacing of 50 μm, a restricted remelting phenomenon of the as-fabricated part is produced with the upward direction of the convection flow, significantly reducing the turbulence of the thermal-capillary convection on the breaking of the oxidation films, and therefore, the connected oxidation films through the neighboring layers are typically formed. The morphology and distribution of the oxidation are experimentally acquired, which are in a good agreement with the results predicted by simulation.

XCT analysis of the influence of melt strategies on defect population in Ti–6Al–4V components manufactured by Selective Electron Beam Melting

International Nuclear Information System (INIS)

Tammas-Williams, S.; Zhao, H.; Léonard, F.; Derguti, F.; Todd, I.; Prangnell, P.B.

2015-01-01

Selective Electron Beam Melting (SEBM) is a promising powder bed Additive Manufacturing technique for near-net-shape manufacture of high-value titanium components. However without post-manufacture HIPing the fatigue life of SEBM parts is currently dominated by the presence of porosity. In this study, the size, volume fraction, and spatial distribution of the pores in model samples have been characterised in 3D, using X-ray Computed Tomography, and correlated to the process variables. The average volume fraction of the pores (< 0.2%) was measured to be lower than that usually observed in competing processes, such as selective laser melting, but a strong relationship was found with the different beam strategies used to contour, and infill by hatching, a part section. The majority of pores were found to be small spherical gas pores, concentrated in the infill hatched region; this was attributed to the lower energy density and less focused beam used in the infill strategy allowing less opportunity for gas bubbles to escape the melt pool. Overall, increasing the energy density or focus of the beam was found to correlate strongly to a reduction in the level of gas porosity. Rarer irregular shaped pores were mostly located in the contour region and have been attributed to a lack of fusion between powder particles. - Graphical abstract: Display Omitted - Highlights: • Vast majority of defects detected were small spherical gas pores. • Gas bubbles trapped in the powder granules expand and coalesce in the melt pool. • Pores have been shown not to be randomly distributed. • Larger and deeper melt pools give more opportunity for gas to escape. • Minor changes to melt strategy result in significant reductions in pore population

XCT analysis of the influence of melt strategies on defect population in Ti–6Al–4V components manufactured by Selective Electron Beam Melting

Energy Technology Data Exchange (ETDEWEB)

Tammas-Williams, S., E-mail: Samuel.tammas-wiliams@manchester.ac.uk [School of Materials, University of Manchester, Manchester M13 9PL (United Kingdom); Department of Materials Science and Engineering, University of Sheffield, Sheffield S1 3JD (United Kingdom); Zhao, H. [School of Materials, University of Manchester, Manchester M13 9PL (United Kingdom); Department of Materials Science and Engineering, University of Sheffield, Sheffield S1 3JD (United Kingdom); Léonard, F. [School of Materials, University of Manchester, Manchester M13 9PL (United Kingdom); Derguti, F.; Todd, I. [Department of Materials Science and Engineering, University of Sheffield, Sheffield S1 3JD (United Kingdom); Prangnell, P.B. [School of Materials, University of Manchester, Manchester M13 9PL (United Kingdom)

2015-04-15

Selective Electron Beam Melting (SEBM) is a promising powder bed Additive Manufacturing technique for near-net-shape manufacture of high-value titanium components. However without post-manufacture HIPing the fatigue life of SEBM parts is currently dominated by the presence of porosity. In this study, the size, volume fraction, and spatial distribution of the pores in model samples have been characterised in 3D, using X-ray Computed Tomography, and correlated to the process variables. The average volume fraction of the pores (< 0.2%) was measured to be lower than that usually observed in competing processes, such as selective laser melting, but a strong relationship was found with the different beam strategies used to contour, and infill by hatching, a part section. The majority of pores were found to be small spherical gas pores, concentrated in the infill hatched region; this was attributed to the lower energy density and less focused beam used in the infill strategy allowing less opportunity for gas bubbles to escape the melt pool. Overall, increasing the energy density or focus of the beam was found to correlate strongly to a reduction in the level of gas porosity. Rarer irregular shaped pores were mostly located in the contour region and have been attributed to a lack of fusion between powder particles. - Graphical abstract: Display Omitted - Highlights: • Vast majority of defects detected were small spherical gas pores. • Gas bubbles trapped in the powder granules expand and coalesce in the melt pool. • Pores have been shown not to be randomly distributed. • Larger and deeper melt pools give more opportunity for gas to escape. • Minor changes to melt strategy result in significant reductions in pore population.

Anisotropy of the upper mantle beneath the equatorial part of the Mid-Atlantic Ridge

Science.gov (United States)

Kendall, J. M.; Rychert, C.; Harmon, N.; Tharimena, S.; Agius, M. R.

2017-12-01

It has been long-known that the mantle beneath ocean spreading centres is anisotropic, holding the signature of the formation of new oceanic lithosphere and its coupling with the underlying convecting asthenosphere. Numerical studies have suggested that there should be significant differences between the anisotropy at slow versus fast spreading centres, but there is little observational evidence to calibrate these simulations, especially at slow spreading centres. Near the ridge axis, the anisotropic effects of melt versus the lattice preferred orientation of minerals is not well understood. Finally, the mantle flow near ridge-transform interactions is also poorly understood. Here we present observations of SKS splitting in a region of the Mid-Atlantic Ridge near the equator and offset by the Romanche and Chain Fracture Zones. An array of 37 ocean-bottom seismometers were deployed for a year in depths of up to nearly 6000m, with the aim of studying the nature of the lithosphere-asthenosphere boundary as it forms (the PiLAB - Passive Imaging of the lithosphere-asthenosphere boundary - experiment). Stations were deployed on crust that varies from newly formed to 80 My old. We analyse 40 teleseismic events of magnitude greater than 5.8 and with epicentral distances between 88 and 130 degrees. The ocean-bottom is a noisy environment and a range of filters are used to isolate the SKS, SKKS, and related signals. Furthermore, stacking splitting error envelopes is used to improve confidence in the splitting parameters. Many of the splitting measurements show an orientation parallel to the direction of plate spreading, as expected, but variability in the orientation of the anisotropy increases towards the ridge axis. The magnitude of the anisotropy is also quite variable and suggests larger delay times near the ridge axis. Off-axis anisotropy is interpreted in terms of deformation of peridotite due to mantle flow. Near the ridge axis, the effect of ridge-parallel melt

Electrical structure beneath the Hangai Dome, Mongolia, from magnetotelluric data

Science.gov (United States)

Comeau, Matthew; Käufl, Johannes; Becken, Michael; Kuvshinov, Alexey; Demberel, Sodnomsambuu; Sukhbaatar, Usnikh; Batmagnai, Erdenechimeg; Tserendug, Shoovdor; Nasan, Ochir

2017-04-01

The Hangai Dome in west-central Mongolia is an unusual high-elevation intra-continental plateau located far from tectonic plate boundaries and characterized by dispersed, low-volume, basaltic volcanism. This region is an ideal natural laboratory for studying intra-continental orogenic and magmatic processes resulting from crust-mantle interactions. The processes responsible for developing the Hangai Dome remain unexplained, due in part to a lack of high resolution geophysical data over the area. Here we present newly acquired broadband (0.008 - 3,000 s) magnetotelluric (MT) data from a large-scale ( 200 x 450 km) and high resolution (site spacing > 5 km) survey across the Hangai Dome. A total of 125 sites were collected and include full MT sites and telluric-only sites where inter-station transfer functions were computed. The MT data are used to generate an electrical resistivity model of the crust and upper mantle below the Hangai Dome. The model shows that the lower crust ( 30 - 50 km; below the brittle-ductile transition zone) beneath the Hangai Dome contains anomalous discrete pockets of low-resistivity ( 30 ohm-m) material that indicate the presence of local accumulations of fluids and/or low-percent partial melts. These anomalous regions appear to be spatially associated with the surface expressions of past volcanism, hydrothermal activity, and an increase in heat flow. They also correlate with observed crustal low-density and low-velocity anomalies. However they are in contrast to some geochemical and petrological studies which show long-lived crustal melt storage is impossible below the Hangai due to limited crustal assimilation and crustal contamination, arguing for a single parent-source at mantle depths. The upper mantle ( 6%) at this location. The results are consistent with modern geochemical and geophysical data, which show a thin lithosphere below the Hangai region. Furthermore the results agree with geodynamic models that require a low-heat flux

Shear Melting of a Colloidal Glass

Science.gov (United States)

Eisenmann, Christoph; Kim, Chanjoong; Mattsson, Johan; Weitz, David A.

2010-01-01

We use confocal microscopy to explore shear melting of colloidal glasses, which occurs at strains of ˜0.08, coinciding with a strongly non-Gaussian step size distribution. For larger strains, the particle mean square displacement increases linearly with strain and the step size distribution becomes Gaussian. The effective diffusion coefficient varies approximately linearly with shear rate, consistent with a modified Stokes-Einstein relationship in which thermal energy is replaced by shear energy and the length scale is set by the size of cooperatively moving regions consisting of ˜3 particles.

Soil microbial activities beneath Stipa tenacissima L. and in surrounding bare soil

Science.gov (United States)

Novosadová, I.; Ruiz Sinoga, J. D.; Záhora, J.; Fišerová, H.

2010-05-01

Open steppes dominated by Stipa tenacissima L. constitute one of the most representative ecosystems of the semi-arid zones of Eastern Mediterranean Basin (Iberian Peninsula, North of Africa). These steppes show a higher degree of variability in composition and structure. Ecosystem functioning is strongly related to the spatial pattern of grass tussocks. Soils beneath S. tenacissima grass show higher fertility and improved microclimatic conditions, favouring the formation of "resource islands" (Maestre et al., 2007). On the other hand in "resource islands" and in surrounding bare soil exists the belowground zone of influence. The competition for water and resources between plants and microorganisms is strong and mediated trough an enormous variety of exudates and resource depletion intended to regulate soil microbial communities in the rhizosphere, control herbivory, encourage beneficial symbioses, and change chemical and physical properties in soil (Pugnaire et Armas, 2008). Secondary compounds and allelopathy restrict other species growth and contribute to patchy plant distribution. Active root segregation affects not only neighbourś growth but also soil microbial activities. The objective of this study was to assess the effect of Stipa tenacissima on the key soil microbial activities under controlled incubation conditions (basal and potential respiration; net nitrogen mineralization). The experimental plots were located in the province Almería in Sierra de los Filabres Mountains near the village Gérgal (southeast Spain) in the small catchment which is situated between 1090 - 1165 m a.s.l. The area with extent of 82 000 m2 is affected by soil degradation. The climate is semiarid Mediterranean. The mean annual rainfall is of about 240 mm mostly concentrated in autumn and spring. The mean annual temperature is 13.9° C. The studied soil has a loam to sandy clay texture and is classified as Lithosol (FAO-ISRIC and ISSS, 1998). The vegetation of these areas is an

Freezing and melting line invariants of the Lennard-Jones system

DEFF Research Database (Denmark)

Costigliola, Lorenzo; Schrøder, Thomas; Dyre, Jeppe C.

2016-01-01

The invariance of several structural and dynamical properties of the Lennard-Jones (LJ) system along the freezing and melting lines is interpreted in terms of isomorph theory. First the freezing/melting lines of the LJ system are shown to be approximated by isomorphs. Then we show...... that the invariants observed along the freezing and melting isomorphs are also observed on other isomorphs in the liquid and crystalline phases. The structure is probed by the radial distribution function and the structure factor and dynamics are probed by the mean-square displacement, the intermediate scattering...... function, and the shear viscosity. Studying these properties with reference to isomorph theory explains why the known single-phase melting criteria hold, e.g., the Hansen–Verlet and the Lindemann criteria, and why the Andrade equation for the viscosity at freezing applies, e.g., for most liquid metals. Our...

Extensive crustal melting during craton destruction: Evidence from the Mesozoic magmatic suite of Junan, eastern North China Craton

Science.gov (United States)

Yang, Fan; Santosh, M.; Tang, Li

2018-05-01

The cratonic destruction associated with the Pacific plate subduction beneath the eastern North China Craton (NCC) shows a close relationship with the widespread magmatism during the Late Mesozoic. Here we investigate a suite of intrusive and extrusive magmatic rocks from the Junan region of the eastern NCC in order to evaluate the role of extensive crustal melting related to decratonization. We present petrological, geochemical, zircon U-Pb geochronological and Lu-Hf isotopic data to evaluate the petrogenesis, timing and tectonic significance of the Early Cretaceous magmatism. Zircon grains in the basalt from the extrusive suite of Junan show multiple populations with Neoproterozoic and Early Paleozoic xenocrystic grains ranging in age from 764 Ma to 495 Ma as well as Jurassic grains with an age range of 189-165 Ma. The dominant population of magmatic zircon grains in the syenite defines three major age peaks of 772 Ma, 132 Ma and 126 Ma. Zircons in the granitoids including alkali syenite, monzonite and granodiorite yield a tightly restricted age range of 124-130 Ma representing their emplacement ages. The Neoproterozoic (841-547 Ma) zircon grains from the basalt and the syenite possess εHf(t) values of -22.9 to -8.4 and from -18.8 to -17.3, respectively. The Early Paleozoic (523-494 Ma) zircons from the basalt and the syenite also show markedly negative εHf(t) values of -22.7 to -18.0. The dominant population of Early Cretaceous (134-121 Ma) zircon grains presented in all the samples also displays negative εHf(t) values range from -31.7 to -21.1, with TDM of 1653-2017 Ma and TDMC in the range of 2193-3187 Ma. Accordingly, the Lu-Hf data suggest that the parent magma was sourced through melting of Mesoarchean to Paleoproterozoic basement rocks. Geochemical data on the Junan magmatic suite display features similar to those associated with the arc magmatic rocks involving subduction-related components, with interaction of fluids and melts in the suprasubduction

Petrology and Wavespeeds in Central Tibet Indicate a Partially Melted Mica-Bearing Crust

Science.gov (United States)

Hacker, B. R.; Ritzwoller, M. H.; Xie, J.

2013-12-01

Mineralogist, 81, 202-212, 1996. Duret, F., N.M. Shapiro, Z. Cao, V. Levin, P. Molnar, and S. Roecker, Surface wave dispersion across Tibet: Direct evidence for radial anisotropy in the crust, Geophysical Research Letters, 37, doi:10.1029/2010GL043811, 2010. Hacker, B.R., E. Gnos, L. Ratschbacher, M. Grove, M. McWilliams, S.V. Sobolev, W. Jiang, and Z. Wu, Hot and dry xenoliths from the lower crust of Tibet, Science, 287, 2463-2466, 2000. Mechie, J., S.V. Sobolev, L. Ratschbacher, A.Y. Babeyko, G. Bock, A.G. Jones, K.D. Nelson, K.D. Solon, L.D. Brown, and W. Zhao, Precise temperature estimation in the Tibetan crust from seismic detection of the a-b quartz transition, Geology, 32, 601-604, 2004. Xie, J., M.H. Ritzwoller, W. Shen, Y. Yang, Y. Zheng, and L. Zhou, Crustal radial anisotropy across Eastern Tibet and the Western Yangtze Craton, Journal of Geophysical Research, in press, 2013. Xu, Z.J., X. Song, and L. Zhu, Crustal and uppermost mantle S velocity structure under Hi-CLIMB seismic array in central Tibetan Plateau from joint inversion of surface wave dispersion and receiver function data, Tectonophysics, 584, 209-220, 2013. Yang, Y., M.H. Ritzwoller, Y. Zheng, W. Shen, A.L. Levshin, and Z. Xie, A synoptic view of the distribution and connectivity of the mid-crustal low velocity zone beneath Tibet, Journal of Geophysical Research, 117, 10.1029/2011JB008810, 2012.

Lithospheric discontinuities beneath the U.S. Midcontinent - signatures of Proterozoic terrane accretion and failed rifting

Science.gov (United States)

Chen, Chen; Gilbert, Hersh; Fischer, Karen M.; Andronicos, Christopher L.; Pavlis, Gary L.; Hamburger, Michael W.; Marshak, Stephen; Larson, Timothy; Yang, Xiaotao

2018-01-01

Seismic discontinuities between the Moho and the inferred lithosphere-asthenosphere boundary (LAB) are known as mid-lithospheric discontinuities (MLDs) and have been ascribed to a variety of phenomena that are critical to understanding lithospheric growth and evolution. In this study, we used S-to-P converted waves recorded by the USArray Transportable Array and the OIINK (Ozarks-Illinois-Indiana-Kentucky) Flexible Array to investigate lithospheric structure beneath the central U.S. This region, a portion of North America's cratonic platform, provides an opportunity to explore how terrane accretion, cratonization, and subsequent rifting may have influenced lithospheric structure. The 3D common conversion point (CCP) volume produced by stacking back-projected Sp receiver functions reveals a general absence of negative converted phases at the depths of the LAB across much of the central U.S. This observation suggests a gradual velocity decrease between the lithosphere and asthenosphere. Within the lithosphere, the CCP stacks display negative arrivals at depths between 65 km and 125 km. We interpret these as MLDs resulting from the top of a layer of crystallized melts (sill-like igneous intrusions) or otherwise chemically modified lithosphere that is enriched in water and/or hydrous minerals. Chemical modification in this manner would cause a weak layer in the lithosphere that marks the MLDs. The depth and amplitude of negative MLD phases vary significantly both within and between the physiographic provinces of the midcontinent. Double, or overlapping, MLDs can be seen along Precambrian terrane boundaries and appear to result from stacked or imbricated lithospheric blocks. A prominent negative Sp phase can be clearly identified at 80 km depth within the Reelfoot Rift. This arrival aligns with the top of a zone of low shear-wave velocities, which suggests that it marks an unusually shallow seismic LAB for the midcontinent. This boundary would correspond to the top of a

Zircon reveals protracted magma storage and recycling beneath Mount St. Helens

Science.gov (United States)

Claiborne, L.L.; Miller, C.F.; Flanagan, D.M.; Clynne, M.A.; Wooden, J.L.

2010-01-01

Current data and models for Mount St. Helens volcano (Washington, United States) suggest relatively rapid transport from magma genesis to eruption, with no evidence for protracted storage or recycling of magmas. However, we show here that complex zircon age populations extending back hundreds of thousands of years from eruption age indicate that magmas regularly stall in the crust, cool and crystallize beneath the volcano, and are then rejuvenated and incorporated by hotter, young magmas on their way to the surface. Estimated dissolution times suggest that entrained zircon generally resided in rejuvenating magmas for no more than about a century. Zircon elemental compositions reflect the increasing influence of mafic input into the system through time, recording growth from hotter, less evolved magmas tens of thousands of years prior to the appearance of mafic magmas at the surface, or changes in whole-rock geochemistry and petrology, and providing a new, time-correlated record of this evolution independent of the eruption history. Zircon data thus reveal the history of the hidden, long-lived intrusive portion of the Mount St. Helens system, where melt and crystals are stored for as long as hundreds of thousands of years and interact with fresh influxes of magmas that traverse the intrusive reservoir before erupting. ?? 2010 Geological Society of America.

A dearth of intermediate melts at subduction zone volcanoes and the petrogenesis of arc andesites.

Science.gov (United States)

Reubi, Olivier; Blundy, Jon

2009-10-29

Andesites represent a large proportion of the magmas erupted at continental arc volcanoes and are regarded as a major component in the formation of continental crust. Andesite petrogenesis is therefore fundamental in terms of both volcanic hazard and differentiation of the Earth. Andesites typically contain a significant proportion of crystals showing disequilibrium petrographic characteristics indicative of mixing or mingling between silicic and mafic magmas, which fuels a long-standing debate regarding the significance of these processes in andesite petrogenesis and ultimately questions the abundance of true liquids with andesitic composition. Central to this debate is the distinction between liquids (or melts) and magmas, mixtures of liquids with crystals, which may or may not be co-genetic. With this distinction comes the realization that bulk-rock chemical analyses of petrologically complex andesites can lead to a blurred picture of the fundamental processes behind arc magmatism. Here we present an alternative view of andesite petrogenesis, based on a review of quenched glassy melt inclusions trapped in phenocrysts, whole-rock chemistry, and high-pressure and high-temperature experiments. We argue that true liquids of intermediate composition (59 to 66 wt% SiO(2)) are far less common in the sub-volcanic reservoirs of arc volcanoes than is suggested by the abundance of erupted magma within this compositional range. Effective mingling within upper crustal magmatic reservoirs obscures a compositional bimodality of melts ascending from the lower crust, and masks the fundamental role of silicic melts (>/=66 wt% SiO(2)) beneath intermediate arc volcanoes. This alternative view resolves several puzzling aspects of arc volcanism and provides important clues to the integration of plutonic and volcanic records.

Effects of Nanoparticles on Melting Process with Phase-Change Using the Lattice Boltzmann Method

KAUST Repository

Ibrahem, Ahmed M.; El-Amin, Mohamed; Sun, Shuyu

2017-01-01

-Gross-Krook (LBGK) is used to solve the problem of 1D melting by conduction. On the other hand, we use the model of multi-distribution functions (MDF) to calculate the density, the velocity and the temperature for the problem of 2D melting by free convection

Evaluation of Melt Behavior with initial Melt Velocity under SFR Severe Accidents

Energy Technology Data Exchange (ETDEWEB)

Heo, Hyo; Bang, In Cheol [UNIST, Ulsan (Korea, Republic of); Jerng, Dong Wook [Chung-Ang Univ, Seoul (Korea, Republic of)

2015-10-15

In the current Korean sodium-cooled fast reactor (SFR) program, early dispersion of the molten metallic fuel within a subchannel is suggested as one of the inherent safety strategies for the initiating phase of hypothetical core disruptive accident (HCDA). The safety strategy provides negative reactivity driven by the melt dispersal, so it could reduce the possibility of the recriticality event under a severe triple or more fault scenario for SFR. Since the behavior of the melt dispersion is unpredictable, it depends on the accident condition, particularly core region. While the voided coolant channel region is usually developed in the inner core, the unvoided coolant channel region is formed in the outer core. It is important to confirm the fuel dispersion with the core region, but there are not sufficient existing studies for them. From the existing studies, the coolant vapor pressure is considered as one of driving force to move the melt towards outside of the core. There is a complexity of the phenomena during intermixing of the melt with the coolant after the horizontal melt injections. It is too difficult to understand the several combined mechanisms related to the melt dispersion and the fragmentation. Thus, it could be worthwhile to study the horizontal melt injections at lower temperature as a preliminary study in order to identify the melt dispersion phenomena. For this reason, it is required to clarify whether the coolant vapor pressure is the driving force of the melt dispersion with the core region. The specific conditions to be well dispersed for the molten metallic fuel were discussed in the experiments with the simulant materials. The each melt behavior was compared to evaluate the melt dispersion under the coolant void condition and the boiling condition. As the results, the following results are remarked: 1. The upward melt dispersion did not occur for a given melt and coolant temperature in the nonboiling range. Over current range of conditions

Evaluation of Melt Behavior with initial Melt Velocity under SFR Severe Accidents

International Nuclear Information System (INIS)

Heo, Hyo; Bang, In Cheol; Jerng, Dong Wook

2015-01-01

In the current Korean sodium-cooled fast reactor (SFR) program, early dispersion of the molten metallic fuel within a subchannel is suggested as one of the inherent safety strategies for the initiating phase of hypothetical core disruptive accident (HCDA). The safety strategy provides negative reactivity driven by the melt dispersal, so it could reduce the possibility of the recriticality event under a severe triple or more fault scenario for SFR. Since the behavior of the melt dispersion is unpredictable, it depends on the accident condition, particularly core region. While the voided coolant channel region is usually developed in the inner core, the unvoided coolant channel region is formed in the outer core. It is important to confirm the fuel dispersion with the core region, but there are not sufficient existing studies for them. From the existing studies, the coolant vapor pressure is considered as one of driving force to move the melt towards outside of the core. There is a complexity of the phenomena during intermixing of the melt with the coolant after the horizontal melt injections. It is too difficult to understand the several combined mechanisms related to the melt dispersion and the fragmentation. Thus, it could be worthwhile to study the horizontal melt injections at lower temperature as a preliminary study in order to identify the melt dispersion phenomena. For this reason, it is required to clarify whether the coolant vapor pressure is the driving force of the melt dispersion with the core region. The specific conditions to be well dispersed for the molten metallic fuel were discussed in the experiments with the simulant materials. The each melt behavior was compared to evaluate the melt dispersion under the coolant void condition and the boiling condition. As the results, the following results are remarked: 1. The upward melt dispersion did not occur for a given melt and coolant temperature in the nonboiling range. Over current range of conditions

A Structural Molar Volume Model for Oxide Melts Part III: Fe Oxide-Containing Melts

Science.gov (United States)

Thibodeau, Eric; Gheribi, Aimen E.; Jung, In-Ho

2016-04-01

As part III of this series, the model is extended to iron oxide-containing melts. All available experimental data in the FeO-Fe2O3-Na2O-K2O-MgO-CaO-MnO-Al2O3-SiO2 system were critically evaluated based on the experimental condition. The variations of FeO and Fe2O3 in the melts were taken into account by using FactSage to calculate the Fe2+/Fe3+ distribution. The molar volume model with unary and binary model parameters can be used to predict the molar volume of the molten oxide of the Li2O-Na2O-K2O-MgO-CaO-MnO-PbO-FeO-Fe2O3-Al2O3-SiO2 system in the entire range of compositions, temperatures, and oxygen partial pressures from Fe saturation to 1 atm pressure.

Numerical and experimental investigation of the melt casting of explosives

Energy Technology Data Exchange (ETDEWEB)

Sun, Dawei; Garimella, Suresh V. [School of Mechanical Engineering, Purdue University, West Lafayette, IN 47907-2088 (United States); Singh, Sanjeev; Naik, Neelam [US Army Armaments Research, Development and Engineering Center, Picatinny Arsenal, NJ 07806 (United States)

2005-10-01

Melt casting of energetic materials is investigated, and a numerical model is formulated for the analysis of the coupled fluid flow, heat transfer, and stress fields involved in this phase-change process. The numerical model is based on a conservative multi block control volume method. The SIMPLE algorithm is employed along with an enthalpy method approach to model the solidification process. Results from the model are verified against analytical solutions, experimental results, and published numerical results for simplified cases. In the melt casting of RDX-binder mixtures, the very high viscosity of the melt limits the influence of melt convection. The impacts of different cooling conditions on the velocity, temperature and stress distributions, as well as on the solidification time, are discussed. The present model can be used to improve the quality of cast explosives, by optimizing and controlling the processing conditions. (Abstract Copyright [2005], Wiley Periodicals, Inc.)

Imaging Canary Island hotspot material beneath the lithosphere of Morocco and southern Spain

Science.gov (United States)

Miller, Meghan S.; O'Driscoll, Leland J.; Butcher, Amber J.; Thomas, Christine

2015-12-01

The westernmost Mediterranean has developed into its present day tectonic configuration as a result of complex interactions between late stage subduction of the Neo-Tethys Ocean, continental collision of Africa and Eurasia, and the Canary Island mantle plume. This study utilizes S receiver functions (SRFs) from over 360 broadband seismic stations to seismically image the lithosphere and uppermost mantle from southern Spain through Morocco and the Canary Islands. The lithospheric thickness ranges from ∼65 km beneath the Atlas Mountains and the active volcanic islands to over ∼210 km beneath the cratonic lithosphere in southern Morocco. The common conversion point (CCP) volume of the SRFs indicates that thinned lithosphere extends from beneath the Canary Islands offshore southwestern Morocco, to beneath the continental lithosphere of the Atlas Mountains, and then thickens abruptly at the West African craton. Beneath thin lithosphere between the Canary hot spot and southern Spain, including below the Atlas Mountains and the Alboran Sea, there are distinct pockets of low velocity material, as inferred from high amplitude positive, sub-lithospheric conversions in the SRFs. These regions of low seismic velocity at the base of the lithosphere extend beneath the areas of Pliocene-Quaternary magmatism, which has been linked to a Canary hotspot source via geochemical signatures. However, we find that this volume of low velocity material is discontinuous along strike and occurs only in areas of recent volcanism and where asthenospheric mantle flow is identified with shear wave splitting analyses. We propose that the low velocity structure beneath the lithosphere is material flowing sub-horizontally northeastwards beneath Morocco from the tilted Canary Island plume, and the small, localized volcanoes are the result of small-scale upwellings from this material.

Evidence of shallow positron traps in ion-implanted InP observed by maximum entropy reconstruction of positron lifetime distribution: a test of MELT

International Nuclear Information System (INIS)

Chen, Z.Q.; Wang, S.J.

1999-01-01

A newly developed maximum entropy method, which was realized by the computer program MELT introduced by Shukla et al., was used to analyze positron lifetime spectra measured in semiconductors. Several simulation studies were done to test the performance of this algorithm. Reliable reconstruction of positron lifetime distributions can be extracted at relatively lower counts, which shows the applicability and superiority of this method. Two positron lifetime spectra measured in ion-implanted p-InP(Zn) at 140 and 280 K, respectively were analyzed by this program. The lifetime distribution differed greatly for the two temperatures, giving direct evidence of the existence of shallow positron traps at low temperature

Two-dimensional model of laser alloying of binary alloy powder with interval of melting temperature

Science.gov (United States)

Knyzeva, A. G.; Sharkeev, Yu. P.

2017-10-01

The paper contains two-dimensional model of laser beam melting of powders from binary alloy. The model takes into consideration the melting of alloy in some temperature interval between solidus and liquidus temperatures. The external source corresponds to laser beam with energy density distributed by Gauss law. The source moves along the treated surface according to given trajectory. The model allows investigating the temperature distribution and thickness of powder layer depending on technological parameters.

Transient refractory material dissolution by a volumetrically-heated melt

Energy Technology Data Exchange (ETDEWEB)

Seiler, Jean Marie, E-mail: jean-marie.seiler@cea.fr [CEA, DEN, DTN, 17 Rue des Martyrs, 38054 Grenoble Cedex 9 (France); Ratel, Gilles [CEA, DEN, DTN, 17 Rue des Martyrs, 38054 Grenoble Cedex 9 (France); Combeau, Hervé [Institut Jean Lamour, UMR 7198, Lorraine University, Ecole des Mines de Nancy, Parc de Saurupt, 54042 Nancy Cedex (France); Gaus-Liu, Xiaoyang; Kretzschmar, Frank; Miassoedov, Alexei [Karlsruhe Institut of Technology, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen (Germany)

2014-12-15

Highlights: • We describe a test investigating ceramic dissolution by a molten non-eutectic melt. • The evolution of the interface temperature between melt and refractory is measured. • A theoretical model describing dissolution kinetics is proposed. • When dissolution stops, interface temperature is the liquidus temperature of the melt. - Abstract: The present work addresses the question of corium–ceramic interaction in a core catcher during a core-melt accident in a nuclear power plant. It provides an original insight into transient aspects concerning dissolution of refractory material by a volumetrically heated pool. An experiment with simulant material (LIVECERAM) is presented. Test results clearly show that dissolution of solid refractory material can occur in a non-eutectic melt at a temperature which is lower than the melting temperature of the refractory material. During the dissolution transient, the interface temperature rises above the liquidus temperature, corresponding to the instantaneous average composition of the melt pool. With constant power dissipation in the melt and external cooling of the core-catcher, a final steady-state situation is reached. Dissolution stops when the heat flux (delivered by the melt to the refractory) can be removed by conduction through the residual thickness of the ceramic, with T{sub interface} = T{sub liquidus} (calculated for the average composition of the final liquid pool). The final steady state corresponds to a uniform pool composition and uniform interface temperature distribution. Convection in the pool is governed by natural thermal convection and the heat flux distribution is therefore similar to what would be obtained for a single component pool. An interpretation of the experiment with two model-based approaches (0D and 1D) is presented. The mass transfer kinetics between the interface and the bulk is controlled by a diffusion sublayer within the boundary layer. During the dissolution transient

Seismic attenuation structure beneath Nazca Plate subduction zone in southern Peru

Science.gov (United States)

Jang, H.; Kim, Y.; Clayton, R. W.

2017-12-01

We estimate seismic attenuation in terms of quality factors, QP and QS using P and S phases, respectively, beneath Nazca Plate subduction zone between 10°S and 18.5°S latitude in southern Peru. We first relocate 298 earthquakes with magnitude ranges of 4.0-6.5 and depth ranges of 20-280 km. We measure t*, which is an integrated attenuation through the seismic raypath between the regional earthquakes and stations. The measured t* are inverted to construct three-dimensional attenuation structures of southern Peru. Checkerboard test results for both QP and QS structures ensure good resolution in the slab-dip transition zone between flat and normal slab subduction down to a depth of 200 km. Both QP and QS results show higher attenuation continued down to a depth of 50 km beneath volcanic arc and also beneath the Quimsachata volcano, the northernmost young volcano, located far east of the main volcanic front. We also observe high attenuation in mantle wedge especially beneath the normal subduction region in both QP and QS (100-130 in QP and 100-125 in QS) and slightly higher QP and QS beneath the flat-subduction and slab-dip transition regions. We plan to relate measured attenuation in the mantle wedge to material properties such as viscosity to understand the subduction zone dynamics.

A study on the particle melting by plasma spraying

International Nuclear Information System (INIS)

Jung, In Ha; Ji, C. G.; Bae, S. O.; Yoon, J. H.; Kwon, H. I.

2001-12-01

As a preliminary study for fabricating a thick and dense free standing type deposit, powder melting studies were carried out. Various morphologies and sizes of powder having the same chemical compositions were applied in particle melting experiments with varying systematic parameters. Through the study of powder melting by inductively coupled plasma, we can conclude as followings: Argon-hydrogen plasma gas with a higher plasma power gave good quality of splats and shown a higher density with a higher build-up rate. Reproducibility of the experiments appeared in the range of 99%. Degree of particle melting and its density just before impinging played a predominant role in the density of a deposit. Chamber pressure has an effect on degree of deformation of the splats, i.e. on the particle momentum. Completely melted particle showed a high deformation appearance. Build-up rate had a relation with a fraction of the fully melted particle, and this also closely associates with productivity and economical efficiency. For increasing the fraction of the fully melted particle, either increasing the power or limiting the particle size was recommended. Mean pore size and its distribution of a deposit seemed to have a relation with a viscosity of the melted powder, i.e. particle temperature, and also with a chamber pressure and spraying distances. Particle temperature may be governed by a plasma power, plasma gas property, probe position, and spraying distance in the present experimental range. Some results might be appeared with mutual interactions of the effects, for example, particle residence time and momentum with chamber pressure, particle temperature with chamber pressure, spraying distance and its size

A study on the particle melting by plasma spraying

Energy Technology Data Exchange (ETDEWEB)

Jung, In Ha; Ji, C. G.; Bae, S. O.; Yoon, J. H.; Kwon, H. I

2001-12-01

As a preliminary study for fabricating a thick and dense free standing type deposit, powder melting studies were carried out. Various morphologies and sizes of powder having the same chemical compositions were applied in particle melting experiments with varying systematic parameters. Through the study of powder melting by inductively coupled plasma, we can conclude as followings: Argon-hydrogen plasma gas with a higher plasma power gave good quality of splats and shown a higher density with a higher build-up rate. Reproducibility of the experiments appeared in the range of 99%. Degree of particle melting and its density just before impinging played a predominant role in the density of a deposit. Chamber pressure has an effect on degree of deformation of the splats, i.e. on the particle momentum. Completely melted particle showed a high deformation appearance. Build-up rate had a relation with a fraction of the fully melted particle, and this also closely associates with productivity and economical efficiency. For increasing the fraction of the fully melted particle, either increasing the power or limiting the particle size was recommended. Mean pore size and its distribution of a deposit seemed to have a relation with a viscosity of the melted powder, i.e. particle temperature, and also with a chamber pressure and spraying distances. Particle temperature may be governed by a plasma power, plasma gas property, probe position, and spraying distance in the present experimental range. Some results might be appeared with mutual interactions of the effects, for example, particle residence time and momentum with chamber pressure, particle temperature with chamber pressure, spraying distance and its size.

Magma transport and olivine crystallization depths in Kīlauea’s East Rift Zone inferred from experimentally rehomogenized melt inclusions

Science.gov (United States)

Tuohy, Robin M; Wallace, Paul J.; Loewen, Matthew W; Swanson, Don; Kent, Adam J R

2016-01-01

Concentrations of H2O and CO2 in olivine-hosted melt inclusions can be used to estimate crystallization depths for the olivine host. However, the original dissolved CO2concentration of melt inclusions at the time of trapping can be difficult to measure directly because in many cases substantial CO2 is transferred to shrinkage bubbles that form during post-entrapment cooling and crystallization. To investigate this problem, we heated olivine from the 1959 Kīlauea Iki and 1960 Kapoho (Hawai‘i) eruptions in a 1-atm furnace to temperatures above the melt inclusion trapping temperature to redissolve the CO2 in shrinkage bubbles. The measured CO2 concentrations of the experimentally rehomogenized inclusions (⩽590 ppm for Kīlauea Iki [n=10]; ⩽880 ppm for Kapoho, with one inclusion at 1863 ppm [n=38]) overlap with values for naturally quenched inclusions from the same samples, but experimentally rehomogenized inclusions have higher within-sample median CO2 values than naturally quenched inclusions, indicating at least partial dissolution of CO2 from the vapor bubble during heating. Comparison of our data with predictions from modeling of vapor bubble formation and published Raman data on the density of CO2 in the vapor bubbles suggests that 55-85% of the dissolved CO2 in the melt inclusions at the time of trapping was lost to post-entrapment shrinkage bubbles. Our results combined with the Raman data demonstrate that olivine from the early part of the Kīlauea Iki eruption crystallized at <6 km depth, with the majority of olivine in the 1-3 km depth range. These depths are consistent with the interpretation that the Kīlauea Iki magma was supplied from Kīlauea’s summit magma reservoir (∼2-5 km depth). In contrast, olivine from Kapoho, which was the rift zone extension of the Kīlauea Iki eruption, crystallized over a much wider range of depths (∼1-16 km). The wider depth range requires magma transport during the Kapoho eruption from deep beneath the

Hydrogeologic setting and ground water flow beneath a section of Indian River Bay, Delaware

Science.gov (United States)

Krantz, David E.; Manheim, Frank T.; Bratton, John F.; Phelan, Daniel J.

2004-01-01

The small bays along the Atlantic coast of the Delmarva Peninsula (Delaware, Maryland, and Virginia) are a valuable natural resource, and an asset for commerce and recreation. These coastal bays also are vulnerable to eutrophication from the input of excess nutrients derived from agriculture and other human activities in the watersheds. Ground water discharge may be an appreciable source of fresh water and a transport pathway for nutrients entering the bays. This paper presents results from an investigation of the physical properties of the surficial aquifer and the processes associated with ground water flow beneath Indian River Bay, Delaware. A key aspect of the project was the deployment of a new technology, streaming horizontal resistivity, to map the subsurface distribution of fresh and saline ground water beneath the bay. The resistivity profiles showed complex patterns of ground water flow, modes of mixing, and submarine ground water discharge. Cores, gamma and electromagnetic-induction logs, and in situ ground water samples collected during a coring operation in Indian River Bay verified the interpretation of the resistivity profiles. The shore-parallel resistivity lines show subsurface zones of fresh ground water alternating with zones dominated by the flow of salt water from the estuary down into the aquifer. Advective flow produces plumes of fresh ground water 400 to 600 m wide and 20 m thick that may extend more than 1 km beneath the estuary. Zones of dispersive mixing between fresh and saline ground water develop on the upper, lower, and lateral boundaries of the the plume. the plumes generally underlie small incised valleys that can be traced landward to stream draining the upland. The incised valleys are filled with 1 to 2 m of silt and peat that act as a semiconfining layer to restrict the downward flow of salt water from the estuary. Active circulation of both the fresh and saline ground water masses beneath the bay is inferred from the geophysical

Two magma bodies beneath the summit of Kilauea Volcano unveiled by isotopically distinct melt deliveries from the mantle

Science.gov (United States)

Pietruszka, Aaron J.; Heaton, Daniel E.; Marske, Jared P.; Garcia, Michael O.

2015-01-01

The summit magma storage reservoir of Kīlauea Volcano is one of the most important components of the magmatic plumbing system of this frequently active basaltic shield-building volcano. Here we use new high-precision Pb isotopic analyses of Kīlauea summit lavas—from 1959 to the active Halema‘uma‘u lava lake—to infer the number, size, and interconnectedness of magma bodies within the volcano's summit reservoir. From 1971 to 1982, the 206Pb/204Pb ratios of the lavas define two separate magma mixing trends that correlate with differences in vent location and/or pre-eruptive magma temperature. These relationships, which contrast with a single magma mixing trend for lavas from 1959 to 1968, indicate that Kīlauea summit eruptions since at least 1971 were supplied from two distinct magma bodies. The locations of these magma bodies are inferred to coincide with two major deformation centers identified by geodetic monitoring of the volcano's summit region: (1) the main locus of the summit reservoir ∼2–4 km below the southern rim of Kīlauea Caldera and (2) a shallower magma body 4 km3 of lava erupted), must therefore be sustained by a nearly continuous supply of new melt from the mantle. The model results show that a minimum of four compositionally distinct, mantle-derived magma batches were delivered to the volcano (at least three directly to the summit reservoir) since 1959. These melt inputs correlate with the initiation of energetic (1959 Kīlauea Iki) and/or sustained (1969–1974 Mauna Ulu, 1983-present Pu‘u ‘Ō‘ō and 2008-present Halema‘uma‘u) eruptions. Thus, Kīlauea's eruptive behavior is partly tied to the delivery of new magma batches from the volcano's source region within the Hawaiian mantle plume.

Numerical analysis of the effects of non-conventional laser beam geometries during laser melting of metallic materials

International Nuclear Information System (INIS)

Safdar, Shakeel; Li, Lin; Sheikh, M A

2007-01-01

Laser melting is an important industrial activity encountered in a variety of laser manufacturing processes, e.g. selective laser melting, welding, brazing, soldering, glazing, surface alloying, cladding etc. The majority of these processes are carried out by using either circular or rectangular beams. At present, the melt pool characteristics such as melt pool geometry, thermal gradients and cooling rate are controlled by the variation of laser power, spot size or scanning speed. However, the variations in these parameters are often limited by other processing conditions. Although different laser beam modes and intensity distributions have been studied to improve the process, no other laser beam geometries have been investigated. The effect of laser beam geometry on the laser melting process has received very little attention. This paper presents an investigation of the effects of different beam geometries including circular, rectangular and diamond shapes on laser melting of metallic materials. The finite volume method has been used to simulate the transient effects of a moving beam for laser melting of mild steel (EN-43A) taking into account Marangoni and buoyancy convection. The temperature distribution, melt pool geometry, fluid flow velocities and heating/cooling rates have been calculated. Some of the results have been compared with the experimental data

Crustal Structure beneath Alaska from Receiver Functions

Science.gov (United States)

Zhang, Y.; Li, A.

2017-12-01

The crustal structure in Alaska has not been well resolved due to the remote nature of much of the state. The USArray Transportable Array (TA), which is operating in Alaska and northwestern Canada, significantly increases the coverage of broadband seismic stations in the region and allows for a more comprehensive study of the crust. We have analyzed P-receiver functions from earthquake data recorded by 76 stations of the TA and AK networks. Both common conversion point (CCP) and H-K methods are used to estimate the mean crustal thickness. The results from the CCP stacking method show that the Denali fault marks a sharp transition from thick crust in the south to thin crust in the north. The thickest crust up to 52 km is located in the St. Elias Range, which has been formed by oblique collision between the Yakutat microplate and North America. A thick crust of 48 km is also observed beneath the eastern Alaska Range. These observations suggest that high topography in Alaska is largely compensated by the thick crust root. The Moho depth ranges from 28 km to 35 km beneath the northern lowlands and increases to 40-45 km under the Books Range. The preliminary crustal thickness from the H-K method generally agrees with that from the CCP stacking with thicker crust beneath high mountain ranges and thinner crust beneath lowlands and basins. However, the offshore part is not well constrained due to the limited coverage of stations. The mean Vp/Vs ratio is around 1.7 in the Yukon-Tanana terrane and central-northern Alaska. The ratio is about 1.9 in central and southern Alaska with higher values at the Alaska Range, Wrangell Mountains, and St. Elias Range. Further data analyses are needed for obtaining more details of the crustal structure in Alaska to decipher the origin and development of different tectonic terranes.

Experimental results for TiO2 melting and release using cold crucible melting

International Nuclear Information System (INIS)

Hong, S. W.; Min, B. T.; Park, I. G.; Kim, H. D.

2000-01-01

To simulate the severe accident phenomena using the real reactor material which melting point is about 2,800K, the melting and release method for materials with high melting point should be developed. This paper discusses the test results for TiO 2 materials using the cold crucible melting method to study the melting and release method of actual corium. To melt and release of few kg of TiO2, the experimental facility is manufactured through proper selection of design parameters such as frequency and capacity of R.F generator, crucible size and capacity of coolant. The melting and release of TiO 2 has been successfully performed in the cold crucible of 15cm in inner diameter and 30cm in height with 30kW RF power generator of 370 KHz. In the melt delivery experiment, about 2.6kg of molten TiO2, 60% of initial charged mass, is released. Rest of it is remained in the watercage in form of the rubble crust formed at the top of crucible and melt crust formed at the interface between the water-cage and melt. Especially, in the melt release test, the location of the working coil is important to make the thin crust at the bottom of the crucible

Research of Snow-Melt Process on a Heated Platform

Directory of Open Access Journals (Sweden)

Vasilyev Gregory P.

2016-01-01

Full Text Available The article has shown the results of experimental researches of the snow-melt on a heated platform-near building heat-pump snow-melt platform. The near-building (yard heat pump platforms for snow melt with the area up to 10-15 m2 are a basis of the new ideology of organization of the street cleaning of Moscow from snow in the winter period which supposes the creation in the megalopolis of the «distributed snow-melt system» (DSMS using non-traditional energy sources. The results of natural experimental researches are presented for the estimation of efficiency of application in the climatic conditions of Moscow of heat pumps in the snow-melt systems. The researches were conducted on a model sample of the near-building heat-pump platform which uses the low-potential thermal energy of atmospheric air. The conducted researches have confirmed experimentally in the natural conditions the possibility and efficiency of using of atmospheric air as a source of low-potential thermal energy for evaporation of the snow-melt heat pump systems in the climatic conditions of Moscow. The results of laboratory researches of snow-melt process on a heated horizontal platform are presented. The researches have revealed a considerable dependence of efficiency of the snow-melt process on its piling mode (form-building and the organization of the process of its piling mode (form-building and the organization of the process of its (snow mass heat exchange with the surface of the heated platform. In the process of researches the effect of formation of an «ice dome» under the melting snow mass called by the fact that in case of the thickness of snow loaded on the platform more than 10 cm the water formed from the melting snow while the contact with the heating surface don’t spread on it, but soaks into the snow, wets it due to capillary effect and freezes. The formation of «ice dome» leads to a sharp increase of snow-melt period and decreases the operating

Molecular dynamics simulation of melting of finite and infinite size silicene

OpenAIRE

Min, Tjun Kit; Yoon, Tiem Leong; Lim, Thong Leng

2017-01-01

We report the melting temperature of free-standing silicene by carrying out molecular dynamics (MD) simulation experiments using optimzed Stillinger-Weber (SW) potential by Zhang {\\it et al.}. The melting scenario of a free-standing silicene is well captured visually in our MD simulations. The data are systematically analyzed using a few qualitatively different indicators, including caloric curve, radial distribution function and a numerical indicator known as `global similarity index'. The o...

Energy Saving Melting and Revert Reduction Technology (E-SMARRT): Melting Efficiency Improvement

Energy Technology Data Exchange (ETDEWEB)

Principal Investigator Kent Peaslee; Co-PI’s: Von Richards, Jeffrey Smith

2012-07-31

Steel foundries melt recycled scrap in electric furnaces and typically consume 35-100% excess energy from the theoretical energy requirement required to pour metal castings. This excess melting energy is multiplied by yield losses during casting and finishing operations resulting in the embodied energy in a cast product typically being three to six times the theoretical energy requirement. The purpose of this research project was to study steel foundry melting operations to understand energy use and requirements for casting operations, define variations in energy consumption, determine technologies and practices that are successful in reducing melting energy and develop new melting techniques and tools to improve the energy efficiency of melting in steel foundry operations.

Estimation of Melt Ponds over Arctic Sea Ice using MODIS Surface Reflectance Data

Science.gov (United States)

Ding, Y.; Cheng, X.; Liu, J.

2017-12-01

Melt ponds over Arctic sea ice is one of the main factors affecting variability of surface albedo, increasing absorption of solar radiation and further melting of snow and ice. In recent years, a large number of melt ponds have been observed during the melt season in Arctic. Moreover, some studies have suggested that late spring to mid summer melt ponds information promises to improve the prediction skill of seasonal Arctic sea ice minimum. In the study, we extract the melt pond fraction over Arctic sea ice since 2000 using three bands MODIS weekly surface reflectance data by considering the difference of spectral reflectance in ponds, ice and open water. The preliminary comparison shows our derived Arctic-wide melt ponds are in good agreement with that derived by the University of Hamburg, especially at the pond distribution. We analyze seasonal evolution, interannual variability and trend of the melt ponds, as well as the changes of onset and re-freezing. The melt pond fraction shows an asymmetrical growth and decay pattern. The observed melt ponds fraction is almost within 25% in early May and increases rapidly in June and July with a high fraction of more than 40% in the east of Greenland and Beaufort Sea. A significant increasing trend in the melt pond fraction is observed for the period of 2000-2017. The relationship between melt pond fraction and sea ice extent will be also discussed. Key Words: melt ponds, sea ice, Arctic

Deep long-period earthquakes beneath Washington and Oregon volcanoes

Science.gov (United States)

Nichols, M.L.; Malone, S.D.; Moran, S.C.; Thelen, W.A.; Vidale, J.E.

2011-01-01

Deep long-period (DLP) earthquakes are an enigmatic type of seismicity occurring near or beneath volcanoes. They are commonly associated with the presence of magma, and found in some cases to correlate with eruptive activity. To more thoroughly understand and characterize DLP occurrence near volcanoes in Washington and Oregon, we systematically searched the Pacific Northwest Seismic Network (PNSN) triggered earthquake catalog for DLPs occurring between 1980 (when PNSN began collecting digital data) and October 2009. Through our analysis we identified 60 DLPs beneath six Cascade volcanic centers. No DLPs were associated with volcanic activity, including the 1980-1986 and 2004-2008 eruptions at Mount St. Helens. More than half of the events occurred near Mount Baker, where the background flux of magmatic gases is greatest among Washington and Oregon volcanoes. The six volcanoes with DLPs (counts in parentheses) are Mount Baker (31), Glacier Peak (9), Mount Rainier (9), Mount St. Helens (9), Three Sisters (1), and Crater Lake (1). No DLPs were identified beneath Mount Adams, Mount Hood, Mount Jefferson, or Newberry Volcano, although (except at Hood) that may be due in part to poorer network coverage. In cases where the DLPs do not occur directly beneath the volcanic edifice, the locations coincide with large structural faults that extend into the deep crust. Our observations suggest the occurrence of DLPs in these areas could represent fluid and/or magma transport along pre-existing tectonic structures in the middle crust. ?? 2010 Elsevier B.V.

Refining of high-temperature uranium melt by filtration through foam-ceramic filters

International Nuclear Information System (INIS)

Antsiferov, V.N.; Porozova, S.E.; Filippov, V.B.; Shtutsa, M.G.; Il'enko, E.V.; Kolotygina, N.S.

2004-01-01

An opportunity of applying foam-ceramic filters of corundum-mullite composition has been studied in refining natural uranium melts. Uranium melting conditions were chosen depending on technical characteristics of the foam ceramic filters. When their using, a portion of nonmetallic inclusions decreases by 20-30% (as little as 2.0-3.5% ingot weight), their size is reduced and their distribution in the ingot volume is equalized, contamination of uranium by the filter material being failed to be noticed. The parameters of foam-ceramic filters are optimized for provision of stable characteristics of uranium melt filtration process [ru

MELT-IIIB: an updated version of the melt code

International Nuclear Information System (INIS)

Tabb, K.K.; Lewis, C.H.; O'Dell, L.D.; Padilla, A. Jr.; Smith, D.E.; Wilburn, N.P.

1979-04-01

The MELT series is a reactor modeling code designed to investigate a wide variety of hypothetical accident conditions, particularly the transient overpower sequence. MELT-IIIB is the latest in the series

Large-scale global convection in the mantle beneath Australia from 55 Ma to now

International Nuclear Information System (INIS)

Zhang, M.

1999-01-01

Full text: The global-scale mantle convection cells in the asthenosphere are not geochemically homogeneous. The heterogeneity is most prominently reflected in the isotopic compositions (Pb-Sr-Nd) of the mid-ocean ridge basalts (MORB) that are direct partial melts from the underlying asthenosphere. Of particular relevance to Australia's geodynamic evolution from about 100 million years, are the distinctive geochemical signatures of the asthenosphere beneath the Pacific Ocean (Pacific MORB) and Indian Ocean (Indian MORB). Therefore, delineation of the boundary between the two distinct mantle reservoirs and any change in that boundary with time provide information about the patterns of global-scale asthenospheric mantle convection. This information has also allowed us to track large-scale mantle chemical reservoirs such as the distinctive Gondwana lithospheric mantle, and hence better understand the geodynamic evolution of the Australian continent from the time of Gondwana dispersal. Pb-Sr-Nd isotope data for Cenozoic basalts in eastern Australia (Zhang et al, 1999) indicate that Pacific-MORB type isotopic signatures characterise the lava-field basalts (55-14 Ma) in southeastern Australia, whereas Indian-MORB type isotopic signatures characterise younger basalts (6-0 Ma) from northeastern Australia. This discovery helps to constrain the changing locus of the major asthenospheric mantle convection cells represented by the Pacific and Indian MORB sources during and following the breakup of the eastern part of Gondwana, and locates, for the first time, the boundary of these convection cells beneath the Australian continent. This extends previous work in the SW Pacific back-arc basins (eg Hickey-Vargas et al., 1995) and the Southern Ocean (Lanyon et al., 1995) that indicates that the 1- and P-MORB mantle convection cells have been moving in opposite directions since the early Tertiary. These new data also indicate that the Indian-MORB source is a long-term asthenospheric

String-like cooperative motion in homogeneous melting.

Science.gov (United States)

Zhang, Hao; Khalkhali, Mohammad; Liu, Qingxia; Douglas, Jack F

2013-03-28

Despite the fundamental nature and practical importance of melting, there is still no generally accepted theory of this ubiquitous phenomenon. Even the earliest simulations of melting of hard discs by Alder and Wainwright indicated the active role of collective atomic motion in melting and here we utilize molecular dynamics simulation to determine whether these correlated motions are similar to those found in recent studies of glass-forming (GF) liquids and other condensed, strongly interacting, particle systems. We indeed find string-like collective atomic motion in our simulations of "superheated" Ni crystals, but other observations indicate significant differences from GF liquids. For example, we observe neither stretched exponential structural relaxation, nor any decoupling phenomenon, while we do find a boson peak, findings that have strong implications for understanding the physical origin of these universal properties of GF liquids. Our simulations also provide a novel view of "homogeneous" melting in which a small concentration of interstitial defects exerts a powerful effect on the crystal stability through their initiation and propagation of collective atomic motion. These relatively rare point defects are found to propagate down the strings like solitons, driving the collective motion. Crystal integrity remains preserved when the permutational atomic motions take the form of ring-like atomic exchanges, but a topological transition occurs at higher temperatures where the rings open to form linear chains similar in geometrical form and length distribution to the strings of GF liquids. The local symmetry breaking effect of the open strings apparently destabilizes the local lattice structure and precipitates crystal melting. The crystal defects are thus not static entities under dynamic conditions, such as elevated temperatures or material loading, but rather are active agents exhibiting a rich nonlinear dynamics that is not addressed in conventional "static

Effect of the distribution of saturated fatty acids in the melting and crystallization profiles of high-oleic high-stearic oils

International Nuclear Information System (INIS)

Bootello, M.A.; Garces, R.; Martinez-Force, E.; Salas, J.J.

2016-01-01

The composition and distribution of fatty acids in triacylglycerol (TAG) molecules are commonly considered as factors that determine the physical properties of a given oil or fat. The distribution of any fatty acid in fats and oils can be described through the α coefficient of asymmetry, which can be calculated from the TAG composition and fatty acid composition of the Sn-2 position of the TAGs determined through lipase hydrolysis. High-oleic high-stearic oils and fats are considered stable and healthy, and they are good substitutes for hydrogenated vegetable oils and palm fractions in many food products, such as spreads and confectionery. Here, different high-oleic high-stearic acid oils were formulated which contained different distributions of saturated fatty acids in their TAGs, while maintaining a similar fatty acid composition. The aim of this work was to discuss the possibility of using the α coefficient to predict the physical properties of fats in function of their chemical composition and their melting and crystallization behavior as examined by differential scanning calorimetry.

Drusen-like beneath retinal deposits in type II mesangiocapillary glomerulonephritis: a review

Directory of Open Access Journals (Sweden)

Miguel Hage Amaro

2015-02-01

Full Text Available The aim of this paper is to do a review of Drusen-like beneath retinal deposits in type II mesangiocapillary glomerulonephritis. Drusenlike beneath retinal deposits in type II mesangiocapillary glomerulonephritis appear to develop at an early age, often second decade of life different of drusen from age-related macular degeneration (AMD.Long term follow-up of the cases in this disease shows in the most of them, no progression of the of drusen-like beneath retinal deposits in type II mesangiocapillary glomerulonefritis, the most of subjects retain good visual acuity and no specific treatment is indicated.

Cloud screening and melt water detection over melting sea ice using AATSR/SLSTR

Science.gov (United States)

Istomina, Larysa; Heygster, Georg

2014-05-01

With the onset of melt in the Arctic Ocean, the fraction of melt water on sea ice, the melt pond fraction, increases. The consequences are: the reduced albedo of sea ice, increased transmittance of sea ice and affected heat balance of the system with more heat passing through the ice into the ocean, which facilitates further melting. The onset of melt, duration of melt season and melt pond fraction are good indicators of the climate state of the Arctic and its change. In the absence of reliable sea ice thickness retrievals in summer, melt pond fraction retrieval from satellite is in demand as input for GCM as an indicator of melt state of the sea ice. The retrieval of melt pond fraction with a moderate resolution radiometer as AATSR is, however, a non-trivial task due to a variety of subpixel surface types with very different optical properties, which give non-unique combinations if mixed. In this work this has been solved by employing additional information on the surface and air temperature of the pixel. In the current work, a concept of melt pond detection on sea ice is presented. The basis of the retrieval is the sensitivity of AATSR reflectance channels 550nm and 860nm to the amount of melt water on sea ice. The retrieval features extensive usage of a database of in situ surface albedo spectra. A tree of decisions is employed to select the feasible family of in situ spectra for the retrieval, depending on the melt stage of the surface. Reanalysis air temperature at the surface and brightness temperature measured by the satellite sensor are analyzed in order to evaluate the melting status of the surface. Case studies for FYI and MYI show plausible retrieved melt pond fractions, characteristic for both of the ice types. The developed retrieval can be used to process the historical AATSR (2002-2012) dataset, as well as for the SLSTR sensor onboard the future Sentinel-3 mission (scheduled for launch in 2015), to keep the continuity and obtain longer time sequence

UHMW Ziegler–Natta polyethylene: Synthesis, crystallization, and melt behavior

KAUST Repository

Atiqullah, Muhammad

2017-04-26

The fabrication of normal and UHMW PE end-products involves melting and crystallization of the polymer. Therefore, the melt behavior and crystallization of as-synthesized UHMW PE, and NMW PE and E-1-hexene copolymer have been studied using a new nonisothermal crystallization model, Flory\\'s equilibrium theory and ethylene sequence length distribution concept (SLD), Gibbs–Thompson equation, and DSC experiments. By using this approach, the effects of MW, 1-hexene incorporation, ethylene SLD, the level of undercooling θ, and crystal surface free energy D on crystallite stability, relative crystallinity α, instantaneous crystallinity χ, the crystallization kinetic triplet, crystallization entropy, and lamellar thickness distribution (LTD) have been evaluated. Consequently, this study reports insightful new results, interpretations, and explanations regarding the melting and crystallization of the aforementioned polymers. The UHMW PE results significantly differ from the NMW PE and E-1-hexene copolymer ones. Ethylene sequences shorter than the so called minimum crystallizable ethylene sequence length, irrespective of E-1-hexene copolymer MW, can also crystallize. Additionally, the polymer preparation shows that the catalyst coordination environment and symmetry, as well as achiral ethylene versus prochiral α-olefin steric encumbrance and competitive diffusion affect the synthesis of UHMW PE, particularly the corresponding UHMW copolymers.

Contaminated metallic melt volume reduction testing

International Nuclear Information System (INIS)

Deichman, J.L.

1981-01-01

Laboratory scale metallic melts (stainless steel) were accomplished in support of Decontamination and Decommissioning's (D and D) contaminated equipment volume reduction and Low-Level Lead Site Waste programs. Six laboratory scale melts made with contaminated stainless steel provided data that radionuclide distribution can be predicted when proper temperature rates and ranges are employed, and that major decontamination occurs with the use of designed slagging materials. Stainless steel bars were contaminated with plutonium, cobalt, cesium and europium. This study was limited to stainless steel, however, further study is desirable to establish data for other metals and alloys. This study represents a positive beginning in defining the feasibility of economical volume reduction or conversion from TRU waste forms to LLW forms for a large portion of approximately 50 thousand tons of contaminated metal waste now being stored at Hanford underground or in deactivated facilities

Study of formation mechanism of incipient melting in thixo-cast Al–Si–Cu–Mg alloys

Energy Technology Data Exchange (ETDEWEB)

Du, Kang, E-mail: du126kang@126.com; Zhu, Qiang, E-mail: zhu.qiang@grinm.com; Li, Daquan, E-mail: lidaquan@grinm.com; Zhang, Fan, E-mail: sk_zf@163.com

2015-08-15

Mechanical properties of thixo-cast Al–Si–Cu–Mg alloys can be enhanced by T61 heat treatment. Copper and magnesium atoms in aluminum matrix can form homogeneously distributed precipitations after solution and aging treatment which harden the alloys. However, microsegregation of these alloying elements could form numerous tiny multi-compound phases during solidification. These phases could cause incipient melting defects in subsequent heat treatment process and degrade the macro-mechanical properties of productions. This study is to present heterogeneous distribution of Cu, Si, and Mg elements and formation of incipient melting defects (pores). In this study, incipient melting pores that occurred during solution treatment at various temperatures, even lower than common melting points of various intermetallic phases, were identified, in terms of a method of investigating the same surface area in the samples before and after solution treatment in a vacuum environment. The results also show that the incipient melting mostly originates at the clusters with fine intermetallic particles while also some at the edge of block-like Al{sub 2}Cu. The fine particles were determined being Al{sub 2}Cu, Al{sub 5}Cu{sub 2}Mg{sub 8}Si{sub 6} and Al{sub 8}Mg{sub 3}FeSi{sub 2}. Tendency of the incipient melting decreases with decreases of the width of the clusters. The formation mechanism of incipient melting pores in solution treatment process was discussed using both the Fick law and the LSW theory. Finally, a criterion of solution treatment to avoid incipient melting pores for the thixo-cast alloys is proposed. - Highlights: • In-situ comparison technique was used to analysis the change of eutectic phases. • The ralationship between eutectic phase size and incipient melting was studied. • Teat treatment criterion for higher incipient melting resistance was proposed.

Study of formation mechanism of incipient melting in thixo-cast Al–Si–Cu–Mg alloys

International Nuclear Information System (INIS)

Du, Kang; Zhu, Qiang; Li, Daquan; Zhang, Fan

2015-01-01

Mechanical properties of thixo-cast Al–Si–Cu–Mg alloys can be enhanced by T61 heat treatment. Copper and magnesium atoms in aluminum matrix can form homogeneously distributed precipitations after solution and aging treatment which harden the alloys. However, microsegregation of these alloying elements could form numerous tiny multi-compound phases during solidification. These phases could cause incipient melting defects in subsequent heat treatment process and degrade the macro-mechanical properties of productions. This study is to present heterogeneous distribution of Cu, Si, and Mg elements and formation of incipient melting defects (pores). In this study, incipient melting pores that occurred during solution treatment at various temperatures, even lower than common melting points of various intermetallic phases, were identified, in terms of a method of investigating the same surface area in the samples before and after solution treatment in a vacuum environment. The results also show that the incipient melting mostly originates at the clusters with fine intermetallic particles while also some at the edge of block-like Al 2 Cu. The fine particles were determined being Al 2 Cu, Al 5 Cu 2 Mg 8 Si 6 and Al 8 Mg 3 FeSi 2 . Tendency of the incipient melting decreases with decreases of the width of the clusters. The formation mechanism of incipient melting pores in solution treatment process was discussed using both the Fick law and the LSW theory. Finally, a criterion of solution treatment to avoid incipient melting pores for the thixo-cast alloys is proposed. - Highlights: • In-situ comparison technique was used to analysis the change of eutectic phases. • The ralationship between eutectic phase size and incipient melting was studied. • Teat treatment criterion for higher incipient melting resistance was proposed

The extent of continental crust beneath the Seychelles

Science.gov (United States)

Hammond, J. O. S.; Kendall, J.-M.; Collier, J. S.; Rümpker, G.

2013-11-01

The granitic islands of the Seychelles Plateau have long been recognised to overlie continental crust, isolated from Madagascar and India during the formation of the Indian Ocean. However, to date the extent of continental crust beneath the Seychelles region remains unknown. This is particularly true beneath the Mascarene Basin between the Seychelles Plateau and Madagascar and beneath the Amirante Arc. Constraining the size and shape of the Seychelles continental fragment is needed for accurate plate reconstructions of the breakup of Gondwana and has implications for the processes of continental breakup in general. Here we present new estimates of crustal thickness and VP/VS from H-κ stacking of receiver functions from a year long deployment of seismic stations across the Seychelles covering the topographic plateau, the Amirante Ridge and the northern Mascarene Basin. These results, combined with gravity modelling of historical ship track data, confirm that continental crust is present beneath the Seychelles Plateau. This is ˜30-33 km thick, but with a relatively high velocity lower crustal layer. This layer thins southwards from ˜10 km to ˜1 km over a distance of ˜50 km, which is consistent with the Seychelles being at the edge of the Deccan plume prior to its separation from India. In contrast, the majority of the Seychelles Islands away from the topographic plateau show no direct evidence for continental crust. The exception to this is the island of Desroche on the northern Amirante Ridge, where thicker low density crust, consistent with a block of continental material is present. We suggest that the northern Amirantes are likely continental in nature and that small fragments of continental material are a common feature of plume affected continental breakup.

Solid-solid phase transformation via internal stress-induced virtual melting, significantly below the melting temperature. Application to HMX energetic crystal.

Science.gov (United States)

Levitas, Valery I; Henson, Bryan F; Smilowitz, Laura B; Asay, Blaine W

2006-05-25

We theoretically predict a new phenomenon, namely, that a solid-solid phase transformation (PT) with a large transformation strain can occur via internal stress-induced virtual melting along the interface at temperatures significantly (more than 100 K) below the melting temperature. We show that the energy of elastic stresses, induced by transformation strain, increases the driving force for melting and reduces the melting temperature. Immediately after melting, stresses relax and the unstable melt solidifies. Fast solidification in a thin layer leads to nanoscale cracking which does not affect the thermodynamics or kinetics of the solid-solid transformation. Thus, virtual melting represents a new mechanism of solid-solid PT, stress relaxation, and loss of coherence at a moving solid-solid interface. It also removes the athermal interface friction and deletes the thermomechanical memory of preceding cycles of the direct-reverse transformation. It is also found that nonhydrostatic compressive internal stresses promote melting in contrast to hydrostatic pressure. Sixteen theoretical predictions are in qualitative and quantitative agreement with experiments conducted on the PTs in the energetic crystal HMX. In particular, (a) the energy of internal stresses is sufficient to reduce the melting temperature from 551 to 430 K for the delta phase during the beta --> delta PT and from 520 to 400 K for the beta phase during the delta --> beta PT; (b) predicted activation energies for direct and reverse PTs coincide with corresponding melting energies of the beta and delta phases and with the experimental values; (c) the temperature dependence of the rate constant is determined by the heat of fusion, for both direct and reverse PTs; results b and c are obtained both for overall kinetics and for interface propagation; (d) considerable nanocracking, homogeneously distributed in the transformed material, accompanies the PT, as predicted by theory; (e) the nanocracking does not

Characterization of 316L Steel Cellular Dodecahedron Structures Produced by Selective Laser Melting

Directory of Open Access Journals (Sweden)

Konda Gokuldoss Prashanth

2016-10-01

Full Text Available The compression behavior of different 316L steel cellular dodecahedron structures with different density values were studied. The 316L steel structures produced using the selective laser melting process has four different geometries: single unit cells with and without the addition of base plates beneath and on top, and sandwich structures with multiple unit cells with different unit cell sizes. The relation between the relative compressive strength and the relative density was compared using different Gibson-Ashby models and with other published reports. The different aspects of the deformation and the mechanical properties were evaluated and the deformation at distinct loading levels was recorded. Finite element method (FEM simulations were carried out with the defined structures and the mechanical testing results were compared. The calculated theory, simulation estimation, and the observed experimental results are in good agreement.

Mapping magnetic lineaments and subsurface basement beneath ...

Indian Academy of Sciences (India)

65

studied the basement structures beneath parts of the Lower Benue Trough (LBT). Anudu et .... order vertical derivatives can be calculated respectively using the relations below: 145. ( ) ... minerals as in the case of the FVD-RTP-TMI (Figure 6).

Mantle transition zone beneath northeast China from P-receiver function

Science.gov (United States)

Zhang, R.; Wu, Q.

2015-12-01

We used receiver functions to examine lateral topographical variations on the 410- and 660-km beneath northeast China and particularly the Kuril-Japan arc junctions. Compared to other receiver functions studies, our analysis was based on greater station coverage of higher density by combining all recent seismic arrays so far deployed in northeast China. Our image shows that the 410-km is featured by a ~10-20 km uplift extending in the NNE direction beneath some areas of the Quaternary basaltic rocks distributed at Abaga and at Wudalianchi. The Clapeyron slope of the olivine phase transiton at 410-km suggests that the uplift is compatible with a negative thermal anomaly. We also confirm a significant depression of the 660 from the Changbai volcanism in the north to Korea in the south along the NW-SE direction. The depression is also accompanied by an uplift of the 660 to the west. The shallow 660-km discontinuity is also particularly detected beneath the Kuril-Japan arc junctions, while it was not detected before. The thermal anomaly at 410 km depth is most likely a remnant of a detached mantle lithosphere that recently sank to depth, thus providing robust evidence for the source and evolution of these basalts. The depression of the 660-km discontinuity may support that the subducting Pacific slab bends sharply and becomes stagnant when it meets strong resistance at a depth of about 670 km. After accumulation to a great extent the stagnant slab finally penetrates into the lower mantle. Combined with the previous triplicated studies, the shallow 660-km may suggest that descending Pacific slab at its leading and junction edges might be accommodated by a tearing near a depth of 660 km. Acknowledgements. Two liner seismic arrays were deployed by the Institute of Geophysics, China Earthquake Administration. The data of the permanent stations were provided by the Data Management Centre of China, National Seismic Network at the Institute of Geophysics, China Earthquake

Melting of Dense Sodium

International Nuclear Information System (INIS)

Gregoryanz, Eugene; Degtyareva, Olga; Hemley, Russell J.; Mao, Ho-kwang; Somayazulu, Maddury

2005-01-01

High-pressure high-temperature synchrotron diffraction measurements reveal a maximum on the melting curve of Na in the bcc phase at ∼31 GPa and 1000 K and a steep decrease in melting temperature in its fcc phase. The results extend the melting curve by an order of magnitude up to 130 GPa. Above 103 GPa, Na crystallizes in a sequence of phases with complex structures with unusually low melting temperatures, reaching 300 K at 118 GPa, and an increased melting temperature is observed with further increases in pressure

Energy Saving Melting and Revert Reduction Technology: Melting Efficiency in Die Casting Operations

Energy Technology Data Exchange (ETDEWEB)

David Schwam

2012-12-15

This project addressed multiple aspects of the aluminum melting and handling in die casting operations, with the objective of increasing the energy efficiency while improving the quality of the molten metal. The efficiency of melting has always played an important role in the profitability of aluminum die casting operations. Consequently, die casters need to make careful choices in selecting and operating melting equipment and procedures. The capital cost of new melting equipment with higher efficiency can sometimes be recovered relatively fast when it replaces old melting equipment with lower efficiency. Upgrades designed to improve energy efficiency of existing equipment may be well justified. Energy efficiency is however not the only factor in optimizing melting operations. Melt losses and metal quality are also very important. Selection of melting equipment has to take into consideration the specific conditions at the die casting shop such as availability of floor space, average quantity of metal used as well as the ability to supply more metal during peaks in demand. In all these cases, it is essential to make informed decisions based on the best available data.

U-series disequilibrium constraints on magma generation at the Jan Mayen hotspot

Science.gov (United States)

Rivers, E. R.; Chernow, R.; Elkins, L. J.; Sims, K. W.; Blichert-Toft, J.; Devey, C. W.

2013-12-01

The incompatible element-enriched magma source beneath the Jan Mayen Island hotspot influences melt generation on the adjacent northern Mid-Atlantic Ridge system and likely derives from either a small, local mantle plume, ancient Icelandic plume material emplaced in the mantle source, and/or sub-continental lithospheric mantle remnants emplaced locally by rifting of Greenland. The slow spreading Northern Kolbeinsey and Southern Mohns Ridges are immediately adjacent to Jan Mayen Island. Both have relatively shallow ridge axes, particularly the extremely shallow Eggvin Bank region of the Northern Kolbeinsey Ridge, which host anomalously large central volcanic edifices. We are currently collecting U-series disequilibrium and long-lived radiogenic isotope data for fresh, glassy mid-ocean ridge basalts from the Northern Kolbeinsey and Southern Mohns Ridge segments to better constrain source composition, depth of melting in the garnet peridotite stability field, solid mantle upwelling rates, and the nature of melt extraction beneath those segments. In particular, we are measuring isotopic data for geographically well-located samples collected from hummocky pillow basalt flows within the axial valley of the Northern Kolbeinsey Ridge segment as well as from the large volcanoes on both ridge segments, to further determine the role of the Jan Mayen hotspot in crustal construction on the Mid-Atlantic Ridge. Recently collected data show particularly high strontium isotope ratios consistent with trace element patterns that suggest a distinct local plume located beneath the Jan Mayen hotspot. A plume model for Jan Mayen is supported by new bathymetric imaging of adjacent ridge segments that reveals excess volcanism beneath the large axial volcanoes and a radial distribution of enrichment surrounding Jan Mayen Island. We predict that age-constrained U-series disequilibrium measurements will support active mantle upwelling focused beneath both Jan Mayen Island and the large axial

Partitioning ratio of depleted uranium during a melt decontamination by arc melting

International Nuclear Information System (INIS)

Min, Byeong Yeon; Choi, Wang Kyu; Oh, Won Zin; Jung, Chong Hun

2008-01-01

In a study of the optimum operational condition for a melting decontamination, the effects of the basicity, slag type and slag composition on the distribution of depleted uranium were investigated for radioactively contaminated metallic wastes of iron-based metals such as stainless steel (SUS 304L) in a direct current graphite arc furnace. Most of the depleted uranium was easily moved into the slag from the radioactive metal waste. The partitioning ratio of the depleted uranium was influenced by the amount of added slag former and the slag basicity. The composition of the slag former used to capture contaminants such as depleted uranium during the melt decontamination process generally consists of silica (SiO 2 ), calcium oxide (CaO) and aluminum oxide (Al 2 O 3 ). Furthermore, calcium fluoride (CaF 2 ), magnesium oxide (MgO), and ferric oxide (Fe 2 O 3 ) were added to increase the slag fluidity and oxidative potential. The partitioning ratio of the depleted uranium was increased as the amount of slag former was increased. Up to 97% of the depleted uranium was captured between the ingot phase and the slag phase. The partitioning ratio of the uranium was considerably dependent on the basicity and composition of the slag. The optimum condition for the removal of the depleted uranium was a basicity level of about 1.5. The partitioning ratio of uranium was high, exceeding 5.5x10 3 . The slag formers containing calcium fluoride (CaF 2 ) and a high amount of silica proved to be more effective for a melt decontamination of stainless steel wastes contaminated with depleted uranium

b-value distribution in and around Mt. Tarumae, Japan

Science.gov (United States)

Chiba, K.

2017-12-01

Mt. Tarumae is an active volcano located in southeastern Shikotsu caldera, Hokkaido, Japan. Recently, crustal expansion occurred in 1999-2000 and 2013 near the summit of Mt. Tarumae, with a M5.6 earthquake recorded west of the summit on 8 July 2014. In this study, I determined hypocenter distributions and then performed b-value analysis for the period between 1 August 2014 and 12 August 2016 to improve our understanding of the magma system geometry beneath the summit of Mt. Tarumae. Hypocenters are mainly distributed in two regions: 3 - 5 km west of Mt. Tarumae, and beneath the volcano. I then determined b-value distributions. Regions with relatively high b-values ( 1.3) are located at depths of -0.5 to 2.0 km beneath the summit and at depths greater than 6.0 km in the northwestern part at about 1.5 - 3.0 km from the summit, while a region with relatively low b-values ( 0.6) is located at depths of 2.0 - 6.0 km beneath the summit. Compared the b-value distributions with other geophysical observations, it was found that the high b-value region from -0.5 to 2.0 km depth corresponds to regions of lower resistivity, positive self-potential anomaly, and an inflation source observed in 1999-2000. It is thus inferred that this region is generated by crustal heterogeneity, a decrease in effective normal stress, and change of a frictional property due to the development of faults and fissures, and the circulation of hydrothermal fluids. On the other hand, the inflation source observed in 2013 was located near the boundary between the low b-value region beneath the summit and the deeper high b-value region in the northwestern part at about 1.5 - 3.0 km from the summit. Studies of other volcanoes suggest that such a high-b-value region likely corresponds to a magma chamber. From the deeper high b-value region estimated in this study, I am able to point out that the magma chamber is located to depths greater than 6.0 km in the northwestern part at about 1.5 - 3.0 km from the

Residence time modeling of hot melt extrusion processes.

Science.gov (United States)

Reitz, Elena; Podhaisky, Helmut; Ely, David; Thommes, Markus

2013-11-01

The hot melt extrusion process is a widespread technique to mix viscous melts. The residence time of material in the process frequently determines the product properties. An experimental setup and a corresponding mathematical model were developed to evaluate residence time and residence time distribution in twin screw extrusion processes. The extrusion process was modeled as the convolution of a mass transport process described by a Gaussian probability function, and a mixing process represented by an exponential function. The residence time of the extrusion process was determined by introducing a tracer at the extruder inlet and measuring the tracer concentration at the die. These concentrations were fitted to the residence time model, and an adequate correlation was found. Different parameters were derived to characterize the extrusion process including the dead time, the apparent mixing volume, and a transport related axial mixing. A 2(3) design of experiments was performed to evaluate the effect of powder feed rate, screw speed, and melt viscosity of the material on the residence time. All three parameters affect the residence time of material in the extruder. In conclusion, a residence time model was developed to interpret experimental data and to get insights into the hot melt extrusion process. Copyright © 2013 Elsevier B.V. All rights reserved.

Sorption of radionuclides from Pb-Bi melt. Report 1

International Nuclear Information System (INIS)

Konovalov, Eh.E.; Il'icheva, N.S.; Trifonova, O.E.

2015-01-01

Results of laboratory investigations of sorption and interfacial distribution of 54 Mn, 59 Fe, 60 Co, 106 Ru, 125 Sb, 137 Cs, 144 Ce, 154,155 Eu and 235,238 U radionuclides in the system Pb-Bi melt - steel surface are analyzed. It is shown that 106 Ru and 125 Sb are concentrated in Pb-Bi melt and other radionuclides with higher oxygen affinity are sorbed on oxide deposits on structural materials. Temperature dependences of sorption efficiency of radionuclides are studied. It is shown that there is sharp increase of this value for all radionuclides near the temperature range 350-400 deg C. Recommendations are given on the use of 106 Ru and 125 Sb as a reference for fuel element rupture detection system with radiometric monitoring of coolant melt samples and 137 Cs, 134 Cs, 134m Cs with radiometric monitoring of sorbing samples [ru

Fuel Rod Melt Progression Simulation Using Low-Temperature Melting Metal Alloy

International Nuclear Information System (INIS)

Seung Dong Lee; Suh, Kune Y.; GoonCherl Park; Un Chul Lee

2002-01-01

The TMI-2 accident and various severe fuel damage experiments have shown that core damage is likely to proceed through various states before the core slumps into the lower head. Numerous experiments were conducted to address when and how the core can lose its original geometry, what geometries are formed, and in what processes the core materials are transported to the lower plenum of the reactor pressure vessel. Core degradation progresses along the line of clad ballooning, clad oxidation, material interaction, metallic blockage, molten pool formation, melt progression, and relocation to the lower head. Relocation into the lower plenum may occur from the lateral periphery or from the bottom of the core depending upon the thermal and physical states of the pool. Determining the quantities and rate of molten material transfer to the lower head is important since significant amounts of molten material relocated to the lower head can threaten the vessel integrity by steam explosion and thermal and mechanical attack of the melt. In this paper the focus is placed on the melt flow regime on a cylindrical fuel rod utilizing the LAMDA (Lumped Analysis of Melting in Degrading Assemblies) facility at the Seoul National University. The downward relocation of the molten material is a combination of the external film flow and the internal pipe flow. The heater rods are 0.8 m long and are coated by a low-temperature melting metal alloy. The electrical internal heating method is employed during the test. External heating is adopted to simulate the exothermic Zircaloy-steam reaction. Tests are conducted in several quasi-steady-state conditions. Given the variable boundary conditions including the heat flux and the water level, observation is made for the melting location, progression, and the mass of molten material. Finally, the core melt progression model is developed from the visual inspection and quantitative analysis of the experimental data. As the core material relocates

Morphological indicators of a mascon beneath Ceres' largest crater, Kerwan

Science.gov (United States)

Bland, Michael T.; Ermakov, Anton; Raymond, Carol A.; Williams, David A.; Bowling, Tim J.; Preusker, F.; Park, Ryan S.; Marchi, Simone; Castillo-Rogez, Julie C.; Fu, R.R.; Russell, Christopher T.

2018-01-01

Gravity data of Ceres returned by the National Aeronautics and Space Administration's Dawn spacecraft is consistent with a lower density crust of variable thickness overlying a higher density mantle. Crustal thickness variations can affect the long‐term, postimpact modification of impact craters on Ceres. Here we show that the unusual morphology of the 280 km diameter crater Kerwan may result from viscous relaxation in an outer layer that thins substantially beneath the crater floor. We propose that such a structure is consistent with either impact‐induced uplift of the high‐density mantle beneath the crater or from volatile loss during the impact event. In either case, the subsurface structure inferred from the crater morphology is superisostatic, and the mass excess would result in a positive Bouguer anomaly beneath the crater, consistent with the highest‐degree gravity data from Dawn. Ceres joins the Moon, Mars, and Mercury in having basin‐associated gravity anomalies, although their origin may differ substantially.

Morphological Indicators of a Mascon Beneath Ceres's Largest Crater, Kerwan

Science.gov (United States)

Bland, M. T.; Ermakov, A. I.; Raymond, C. A.; Williams, D. A.; Bowling, T. J.; Preusker, F.; Park, R. S.; Marchi, S.; Castillo-Rogez, J. C.; Fu, R. R.; Russell, C. T.

2018-02-01

Gravity data of Ceres returned by the National Aeronautics and Space Administration's Dawn spacecraft is consistent with a lower density crust of variable thickness overlying a higher density mantle. Crustal thickness variations can affect the long-term, postimpact modification of impact craters on Ceres. Here we show that the unusual morphology of the 280 km diameter crater Kerwan may result from viscous relaxation in an outer layer that thins substantially beneath the crater floor. We propose that such a structure is consistent with either impact-induced uplift of the high-density mantle beneath the crater or from volatile loss during the impact event. In either case, the subsurface structure inferred from the crater morphology is superisostatic, and the mass excess would result in a positive Bouguer anomaly beneath the crater, consistent with the highest-degree gravity data from Dawn. Ceres joins the Moon, Mars, and Mercury in having basin-associated gravity anomalies, although their origin may differ substantially.

Transient shallow reservoirs beneath small eruptive centres: Constraints from Mg-Fe interdiffusion in olivine

Science.gov (United States)

Morgado, E.; Parada, M. A.; Morgan, D. J.; Gutiérrez, F.; Castruccio, A.; Contreras, C.

2017-11-01

Small eruptive centres commonly have more primitive lavas than those associated with stratovolcanoes, an observation that has been taken to indicate a short magma residence in the crust relative to those reservoirs below stratovolcanoes. The Caburgua cones of the Andean Southern Volcanic Zone from a basaltic small eruptive centre where this can be tested. Here, we use MELTS simulations, and the available thermobarometry data to determine the conditions of olivine crystal rim formation and the Mg-Fe diffusion modelling to determine the magma residence times of those rims in the crust. Results yield timescales varying from a few days to dozens of days, and if freezing is to be avoided, can only be explained by some form of storage or slow transport through at least one shallow magma body. The longest durations of magma residence seen in the olivine rim zones are up to 471 days. These timescales are shorter than those estimated (decadal) from the nearby, more-differentiated, and well-established stratovolcano, Villarrica, which has a dominantly basaltic andesite composition. For Caburgua cones, we propose the existence of a transient reservoir, in contrast to a long-lived reservoir such as that inferred beneath the adjacent Villarrica stratovolcano.

Postaccident heat removal. II. Heat transfer from an internally heated liquid to a melting solid

International Nuclear Information System (INIS)

Faw, R.E.; Baker, L. Jr.

1976-01-01

Microwave heating has been used in studies of heat transfer from a horizontal layer of internally heated liquid to a melting solid. Experiments were designed to simulate heat transfer and meltthrough processes of importance in the analysis of postaccident heat removal capabilities of nuclear reactors. Glycerin, heated by 2.45-GHz microwave radiation, was used to simulate molten fuel. Paraffin wax was used to simulate a melting barrier confining the fuel. Experimentally measured heat fluxes and melting rates were consistent with a model based on downward heat transfer by conduction through a stagnant liquid layer and upward heat transfer augmented by natural convection. Melting and displacement of the barrier material occurred by upward-moving droplets randomly distributed across the melting surface. Results indicated that the melting and displacement process had no effect on the heat transfer process

Evidence for early hunters beneath the Great Lakes.

Science.gov (United States)

O'Shea, John M; Meadows, Guy A

2009-06-23

Scholars have hypothesized that the poorly understood and rarely encountered archaeological sites from the terminal Paleoindian and Archaic periods associated with the Lake Stanley low water stage (10,000-7,500 BP) are lost beneath the modern Great Lakes. Acoustic and video survey on the Alpena-Amberley ridge, a feature that would have been a dry land corridor crossing the Lake Huron basin during this time period, reveals the presence of a series of stone features that match, in form and location, structures used for caribou hunting in both prehistoric and ethnographic times. These results present evidence for early hunters on the Alpena-Amberley corridor, and raise the possibility that intact settlements and ancient landscapes are preserved beneath Lake Huron.

Extreme incompatibility of helium during mantle melting: Evidence from undegassed mid-ocean ridge basalts

Science.gov (United States)

Graham, David W.; Michael, Peter J.; Shea, Thomas

2016-11-01

We report total helium concentrations (vesicles + glass) for a suite of thirteen ultradepleted mid-ocean ridge basalts (UD-MORBs) that were previously studied for volatile contents (CO2, H2O) plus major and trace elements. The selected basalts are undersaturated in CO2 + H2O at their depths of eruption and represent rare cases of undegassed MORBs. Sample localities from the Atlantic (2), Indian (1) and Pacific (7) Oceans collectively show excellent linear correlations (r2 = 0.75- 0.92) between the concentrations of helium and the highly incompatible elements C, K, Rb, Ba, Nb, Th and U. Three basalts from Gakkel Ridge in the Arctic were also studied but show anomalous behavior marked by excess lithophile trace element abundances. In the Atlantic-Pacific-Indian suite, incompatible element concentrations vary by factors of 3-4.3, while helium concentration varies by a factor of 13. The strong correlations between the concentrations of helium and incompatible elements are explained by helium behavior as the most incompatible element during mantle melting. Partial melting of an ultradepleted mantle source, formed as a residue of earlier melt extraction, accounts for the observed concentrations. The earlier melting event involved removal of a small degree melt (∼1%) at low but non-zero porosity (0.01-0.5%), leading to a small amount of melt retention that strongly leveraged the incompatible element budget of the ultradepleted mantle source. Equilibrium melting models that produce the range of trace element and helium concentrations from this source require a bulk solid/melt distribution coefficient for helium that is lower than that for other incompatible elements by about a factor of ten. Alternatively, the bulk solid/melt distribution coefficient for helium could be similar to or even larger than that for other incompatible elements, but the much larger diffusivity of helium in peridotite leads to its more effective incompatibility and efficient extraction from a

Estimating Net Primary Productivity Beneath Snowpack Using Snowpack Radiative Transfer Modeling and Global Satellite Data

Science.gov (United States)

Barber, D. E.; Peterson, M. C.

2002-05-01

Sufficient photosynthetically active radiation (PAR) penetrates snow for plants to grow beneath snowpack during late winter or early spring in tundra ecosystems. During the spring in this ecosystem, the snowpack creates an environment with higher humidity and less variable and milder temperatures than on the snow-free land. Under these conditions, the amount of PAR available is likely to be the limiting factor for plant growth. Current methods for determining net primary productivity (NPP) of tundra ecosystems do not account for this plant growth beneath snowpack, apparently resulting in underestimating plant production there. We are currently in the process of estimating the magnitude of this early growth beneath snow for tundra ecosystems. Our method includes a radiative transfer model that simulates diffuse and direct PAR penetrating snowpack based on downwelling PAR values and snow depth data from global satellite databases. These PAR levels are convolved with plant growth for vegetation that thrives beneath snowpacks, such as lichen. We expect to present the net primary production for Cladonia species (a common Arctic lichen) that has the capability of photosynthesizing at low temperatures beneath snowpack. This method may also be used to study photosynthesis beneath snowpacks in other hardy plants. Lichens are used here as they are common in snow-covered regions, flourish under snowpack, and provide an important food source for tundra herbivores (e.g. caribou). In addition, lichens are common in arctic-alpine environments and our results can be applied to these ecosystems as well. Finally, the NPP of lichen beneath snowpack is relatively well understood compared to other plants, making it ideal vegetation for this first effort at estimating the potential importance of photosynthesis at large scales. We are examining other candidate plants for their photosynthetic potential beneath snowpack at this time; however, little research has been done on this topic. We

Shock melting method to determine melting curve by molecular dynamics: Cu, Pd, and Al.

Science.gov (United States)

Liu, Zhong-Li; Zhang, Xiu-Lu; Cai, Ling-Cang

2015-09-21

A melting simulation method, the shock melting (SM) method, is proposed and proved to be able to determine the melting curves of materials accurately and efficiently. The SM method, which is based on the multi-scale shock technique, determines melting curves by preheating and/or prepressurizing materials before shock. This strategy was extensively verified using both classical and ab initio molecular dynamics (MD). First, the SM method yielded the same satisfactory melting curve of Cu with only 360 atoms using classical MD, compared to the results from the Z-method and the two-phase coexistence method. Then, it also produced a satisfactory melting curve of Pd with only 756 atoms. Finally, the SM method combined with ab initio MD cheaply achieved a good melting curve of Al with only 180 atoms, which agrees well with the experimental data and the calculated results from other methods. It turned out that the SM method is an alternative efficient method for calculating the melting curves of materials.

Shock melting method to determine melting curve by molecular dynamics: Cu, Pd, and Al

International Nuclear Information System (INIS)

Liu, Zhong-Li; Zhang, Xiu-Lu; Cai, Ling-Cang

2015-01-01

A melting simulation method, the shock melting (SM) method, is proposed and proved to be able to determine the melting curves of materials accurately and efficiently. The SM method, which is based on the multi-scale shock technique, determines melting curves by preheating and/or prepressurizing materials before shock. This strategy was extensively verified using both classical and ab initio molecular dynamics (MD). First, the SM method yielded the same satisfactory melting curve of Cu with only 360 atoms using classical MD, compared to the results from the Z-method and the two-phase coexistence method. Then, it also produced a satisfactory melting curve of Pd with only 756 atoms. Finally, the SM method combined with ab initio MD cheaply achieved a good melting curve of Al with only 180 atoms, which agrees well with the experimental data and the calculated results from other methods. It turned out that the SM method is an alternative efficient method for calculating the melting curves of materials

New constraints on the textural and geochemical evolution of the upper mantle beneath the Styrian basin

Science.gov (United States)

Aradi, Laszlo; Hidas, Károly; Zanetti, Alberto; János Kovács, István; Patkó, Levente; Szabó, Csaba

2016-04-01

, with [100]-fiber and orthorhombic symmetry appear in the high temperature (>1000 °C) xenoliths, which are thought to have an asthenospheric origin [3]. Based on our study, the subcontinental lithospheric mantle beneath the western part of the CPR is not as homogeneous as it was reported before. The shallower part of the mantle lithosphere contains peridotites, where the pervasive deformation and subsequent thermal recovery of the upper mantle was followed by melt percolation events causing extensive metasomatism. This research was granted by the Hungarian Science Foundation (OTKA, 78425 to Cs. Szabó). K. Hidas' research leading to these results was funded by the European Union Framework Programme 7 (EU-FP7) Marie Curie postdoctoral grant PIEF-GA-2012- 327226. References: [1]Szabó, C. et al. 2004. Tectonophysics, 393(1), 119-137. [2] Tommasi, A., Vauchez, A. 2015. Tectonophysics, 661, 11-37. [3] Kovács, I. et al. 2012. Tectonophysics, 514, 168-179.

Implications for carbon processing beneath the Greenland Ice Sheet from dissolved CO2 and CH4 concentrations of subglacial discharge

Science.gov (United States)

Pain, A.; Martin, J.; Martin, E. E.

2017-12-01

Subglacial carbon processes are of increasing interest as warming induces ice melting and increases fluxes of glacial meltwater into proglacial rivers and the coastal ocean. Meltwater may serve as an atmospheric source or sink of carbon dioxide (CO2) or methane (CH4), depending on the magnitudes of subglacial organic carbon (OC) remineralization, which produces CO2 and CH4, and mineral weathering reactions, which consume CO2 but not CH4. We report wide variability in dissolved CO2 and CH4 concentrations at the beginning of the melt season (May-June 2017) between three sites draining land-terminating glaciers of the Greenland Ice Sheet. Two sites, located along the Watson River in western Greenland, drain the Isunnguata and Russell Glaciers and contained 1060 and 400 ppm CO2, respectively. In-situ CO2 flux measurements indicated that the Isunnguata was a source of atmospheric CO2, while the Russell was a sink. Both sites had elevated CH4 concentrations, at 325 and 25 ppm CH4, respectively, suggesting active anaerobic OC remineralization beneath the ice sheet. Dissolved CO2 and CH4 reached atmospheric equilibrium within 2.6 and 8.6 km downstream of Isunnguata and Russell discharge sites, respectively. These changes reflect rapid gas exchange with the atmosphere and/or CO2 consumption via instream mineral weathering. The third site, draining the Kiagtut Sermiat in southern Greenland, had about half atmospheric CO2 concentrations (250 ppm), but approximately atmospheric CH4 concentrations (2.1 ppm). Downstream CO2 flux measurements indicated ingassing of CO2 over the entire 10-km length of the proglacial river. CO2 undersaturation may be due to more readily weathered lithologies underlying the Kiagtut Sermiat compared to Watson River sites, but low CH4 concentrations also suggest limited contributions of CO2 and CH4 from OC remineralization. These results suggest that carbon processing beneath the Greenland Ice Sheet may be more variable than previously recognized

Highly CO2-supersaturated melts in the Pannonian lithospheric mantle - A transient carbon reservoir?

Science.gov (United States)

Créon, Laura; Rouchon, Virgile; Youssef, Souhail; Rosenberg, Elisabeth; Delpech, Guillaume; Szabó, Csaba; Remusat, Laurent; Mostefaoui, Smail; Asimow, Paul D.; Antoshechkina, Paula M.; Ghiorso, Mark S.; Boller, Elodie; Guyot, François

2017-08-01

Subduction of carbonated crust is widely believed to generate a flux of carbon into the base of the continental lithospheric mantle, which in turn is the likely source of widespread volcanic and non-volcanic CO2 degassing in active tectonic intracontinental settings such as rifts, continental margin arcs and back-arc domains. However, the magnitude of the carbon flux through the lithosphere and the budget of stored carbon held within the lithospheric reservoir are both poorly known. We provide new constraints on the CO2 budget of the lithospheric mantle below the Pannonian Basin (Central Europe) through the study of a suite of xenoliths from the Bakony-Balaton Highland Volcanic Field. Trails of secondary fluid inclusions, silicate melt inclusions, networks of melt veins, and melt pockets with large and abundant vesicles provide numerous lines of evidence that mantle metasomatism affected the lithosphere beneath this region. We obtain a quantitative estimate of the CO2 budget of the mantle below the Pannonian Basin using a combination of innovative analytical and modeling approaches: (1) synchrotron X-ray microtomography, (2) NanoSIMS, Raman spectroscopy and microthermometry, and (3) thermodynamic models (Rhyolite-MELTS). The three-dimensional volumes reconstructed from synchrotron X-ray microtomography allow us to quantify the proportions of all petrographic phases in the samples and to visualize their textural relationships. The concentration of CO2 in glass veins and pockets ranges from 0.27 to 0.96 wt.%, higher than in typical arc magmas (0-0.25 wt.% CO2), whereas the H2O concentration ranges from 0.54 to 4.25 wt.%, on the low end for estimated primitive arc magmas (1.9-6.3 wt.% H2O). Trapping pressures for vesicles were determined by comparing CO2 concentrations in glass to CO2 saturation as a function of pressure in silicate melts, suggesting pressures between 0.69 to 1.78 GPa. These values are generally higher than trapping pressures for fluid inclusions

Upper Mantle Structure beneath Afar: inferences from surface waves.

Science.gov (United States)

Sicilia, D.; Montagner, J.; Debayle, E.; Lepine, J.; Leveque, J.; Cara, M.; Ataley, A.; Sholan, J.

2001-12-01

The Afar hotspot is related to one of the most important plume from a geodynamic point of view. It has been advocated to be the surface expression of the South-West African Superswell. Below the lithosphere, the Afar plume might feed other hotspots in central Africa (Hadiouche et al., 1989; Ebinger & Sleep, 1998). The processes of interaction between crust, lithosphere and plume are not well understood. In order to gain insight into the scientific issue, we have performed a surface-wave tomography covering the Horn of Africa. A data set of 1404 paths for Rayleigh waves and 473 paths for Love waves was selected in the period range 45-200s. They were collected from the permanent IRIS and GEOSCOPE networks and from the PASSCAL experiment, in Tanzania and Saudi Arabia. Other data come from the broadband stations deployed in Ethiopia and Yemen in the framework of the French INSU program ``Horn of Africa''. The results presented here come from a path average phase velocities obtained with a method based on a least-squares minimization (Beucler et al., 2000). The local phase velocity distribution and the azimuthal anisotropy were simultaneously retrieved by using the tomographic technique of Montagner (1986). A correction of the data is applied according to the crustal structure of the 3SMAC model (Nataf & Ricard, 1996). We find low velocities down to 200 km depth beneath the Red Sea, the Gulf of Aden, Afars, the Ethiopian Plateau and southern Arabia. High velocities are present in the eastern Arabia and the Tanzania Craton. The anisotropy beneath Afar seems to be complex, but enables to map the flow pattern at the interface lithosphere-asthenosphere. The results presented here are complementary to those obtained by Debayle et al. (2001) at upper-mantle transition zone depths using waveform inversion of higher Rayle igh modes.

Numerical Simulation and Optimization of the Melting Process of Phase Change Material inside Horizontal Annulus

Directory of Open Access Journals (Sweden)

Saiwei Li

2017-08-01

Full Text Available Latent heat storage (LHS technologies adopting phase change materials (PCMs are increasingly being used to bridge the spatiotemporal mismatch between energy production and demand, especially in industries like solar power, where strong cyclic fluctuations exist. The shell-and-tube configuration is among the most prevalent ones in LHS and thus draws special attention from researchers. This paper presents numerical investigations on the melting of PCM, a paraffin blend RT27, inside a horizontal annulus. The volume of fluid model was adopted to permit density changes with the solidification/melting model wherein natural convection was taken into account. The eccentricity and diameter of the inner tube, sub-cooling degree of the PCM, and the heating-surface temperature were considered as variables for study. Through the evaluation of the melting time and exergy efficiency, the optimal parameters of the horizontal annulus were obtained. The results showed that the higher the heating boundary temperature, the earlier the convection appeared and the shorter the melting time. Also, the different eccentricity and diameters of the inner tube influenced the annulus tube interior temperature distribution, which in turn determined the strength and distribution of the resulting natural convection, resulting in varying melting rates.

Organic micropollutants in snow. Distribution and behaviour during snowmelt

Energy Technology Data Exchange (ETDEWEB)

Herrmann, R.; Schoendorf, T.; Schrimpff, E.; Simmleit, N.

1988-03-01

The regional patterns of the concentrations of organic micropollutants can be explained by local emissions and enhanced wet and dry deposition of pollutants from atmospheric long-range transport especially in exposed elevations. During the melting process in deep snow covers, particle-bound pollutants with a high distribution coefficient will not be released until the final stage of snow melting in terms of a surge of high concentrations. Organic micropollutants with a small distribution coefficient, by contrast, are also dissolved and flushed out with the first melt water. As a result, this pollutant group features two concentration peaks: one in the first melt water and another in the last melt water. The melt water seeping into the soil and the underlying aquifers (e.g. in karst areas) very rapidly loses its load of pollutants by adsorption in the soil zone.

Research and development on the melting test of low-level radioactive miscellaneous solid waste

International Nuclear Information System (INIS)

Nakashio, Nobuyuki; Hoshi, Akiko; Kameo, Yutaka; Nakashima, Mikio

2007-02-01

The Nuclear Science Research Institute of the Japan Atomic Energy Agency constructed the Advanced Volume Reduction Facilities (AVRF) in February 2003 for treatment of low-level radioactive miscellaneous solid waste (LLW). The waste volume reduction is carried out by a high-compaction process or melting processes in the AVRF. In advance of operating the melting process in the AVRF, melting tests of simulated LLW with RI tracers ( 60 Co, 137 Cs and 152 Eu) have been conducted by using the plasma melter in pilot scale. Viscosity of molten waste, chemical composition and physical properties of solidified products and distribution of the tracers in each product were investigated in various melting conditions. It was confirmed that the viscosity of molten waste was able to be controlled by adjusting chemical composition of molten waste. The RI tracer were almost uniformly distributed in the solidified products. The retention of 137 Cs depended on the basicity (CaO/SiO 2 ) of the solidified products. The solidified product possessed satisfactory compressive strength. In the case of basicity less than 0.8, the leachability of RI tracers from the solidified products was less than or equal to that of a high-level vitrified waste. In this review, experimental results of the melting tests were discussed in order to contribute to actual treatment of LLW in the AVRF. (author)

Thermally driven gas flow beneath Yucca Mountain, Nevada

International Nuclear Information System (INIS)

Amter, S.; Lu, Ning; Ross, B.

1991-01-01

A coupled thermopneumatic model is developed for simulating heat transfer, rock-gas flow and carbon-14 travel time beneath Yucca Mountain, NV. The aim of this work is to understand the coupling of heat transfer and gas flow. Heat transfer in and near the potential repository region depends on several factors, including the geothermal gradient, climate, and local sources of heat such as radioactive wastes. Our numerical study shows that small temperature changes at the surface can change both the temperature field and the gas flow pattern beneath Yucca Mountain. A lateral temperature difference of 1 K is sufficient to create convection cells hundreds of meters in size. Differences in relative humidities between gas inside the mountain and air outside the mountain also significantly affect the gas flow field. 6 refs., 7 figs

Depleted subcontinental lithospheric mantle and its tholeiitic melt metasomatism beneath NE termination of the Eger Rift (Europe): the case study of the Steinberg (Upper Lusatia, SE Germany) xenoliths

Science.gov (United States)

Kukuła, Anna; Puziewicz, Jacek; Matusiak-Małek, Magdalena; Ntaflos, Theodoros; Büchner, Jörg; Tietz, Olaf

2015-12-01

The ca. 30 Ma Steinberg basanite occurs at the NE termination of the Eger (Ohře) Rift in the NW Bohemian Massif, Central Europe, and belongs to the Cenozoic alkaline Central European Volcanic Province. The basanite hosts a suite of mantle xenoliths, most of which are harzburgites containing relatively magnesian olivine (Fo 90.5-91.6) and Al-poor (0.04-0.13 a pfu) orthopyroxene (mg# 0.90-0.92). Some of these harzburgites also contain volumetrically minor clinopyroxene (mg# 0.92-0.95, Al 0.03-0.13 a pfu) and have U-shaped LREE-enriched REE patterns. The Steinberg harzburgites are typical for the Lower Silesian - Upper Lusatian domain of the European subcontinental lithospheric mantle. They represent residual mantle that has undergone extensive partial melting and was subsequently affected by mantle metasomatism by mixed carbonatite-silicate melts. The Steinberg xenolith suite comprises also dunitic xenoliths affected by metasomatism by melt similar to the host basanite, which lowered the Fo content in olivine to 87.6 %. This metasomatism happened shortly before xenolith entrainment in the erupting lava. One of the xenoliths is a wehrlite (olivine Fo 73 %, clinopyroxene mg# 0.83-0.85, subordinate orthopyroxene mg# 0.76-0.77). Its clinopyroxene REE pattern is flat and slightly LREE-depleted. This wehrlite is considered to be a tholeiitic cumulate. One of the studied harzburgites contains clinopyroxene with similar trace element contents to those in wehrlite. This type of clinopyroxene records percolation of tholeiitic melt through harzburgite. The tholeiitic melt might be similar to Cenozoic continental tholeiites occurring in the Central European Volcanic Province (e.g., Vogelsberg, Germany).

DEPENDENCY OF SULFATE SOLUBILITY ON MELT COMPOSITION AND MELT POLYMERIZATION

International Nuclear Information System (INIS)

JANTZEN, CAROL M.

2004-01-01

Sulfate and sulfate salts are not very soluble in borosilicate waste glass. When sulfate is present in excess it can form water soluble secondary phases and/or a molten salt layer (gall) on the melt pool surface which is purported to cause steam explosions in slurry fed melters. Therefore, sulfate can impact glass durability while formation of a molten salt layer on the melt pool can impact processing. Sulfate solubility has been shown to be compositionally dependent in various studies, (e.g. , B2O3, Li2O, CaO, MgO, Na2O, and Fe2O3 were shown to increase sulfate solubility while Al2O3 and SiO2 decreased sulfate solubility). This compositional dependency is shown to be related to the calculated melt viscosity at various temperatures and hence the melt polymerization

Imaging rifting at the lithospheric scale in the northern East African Rift using S-to-P receiver functions

Science.gov (United States)

Lavayssiere, A.; Rychert, C.; Harmon, N.; Keir, D.; Hammond, J. O. S.; Kendall, J. M.; Leroy, S. D.; Doubre, C.

2017-12-01

The lithosphere is modified during rifting by a combination of mechanical stretching, heating and potentially partial melt. We image the crust and upper mantle discontinuity structure beneath the northern East African Rift System (EARS), a unique tectonically active continental rift exposing along strike the transition from continental rifting in the Main Ethiopian rift (MER) to incipient seafloor spreading in Afar and the Red Sea. S-to-P receiver functions from 182 stations across the northern EARS were generated from 3688 high quality waveforms using a multitaper technique and then migrated to depth using a regional velocity model. Waveform modelling of data stacked in large conversion point bins confirms the depth and strength of imaged discontinuities. We image the Moho at 29.6±4.7 km depth beneath the Ethiopian plateaux with a variability in depth that is possibly due to lower crustal intrusions. The crust is 27.3±3.9 km thick in the MER and thinner in northern Afar, 17.5±0.7 km. The model requires a 3±1.2% reduction in shear velocity with increasing depth at 68.5±1.5 km beneath the Ethiopian plateaux, consistent with the lithosphere-asthenosphere boundary (LAB). We do not resolve a LAB beneath Afar and the MER. This is likely associated with partial melt near the base of the lithosphere, reducing the velocity contrast between the melt-intruded lithosphere and the partially molten asthenosphere. We identify a 4.5±0.7% increase in velocity with depth at 91±3 km beneath the MER. This change in velocity is consistent with the onset of melting found by previous receiver functions and petrology studies. Our results provide independent constraints on the depth of melt production in the asthenosphere and suggest melt percolation through the base of the lithosphere beneath the northernmost East African rift.

A numerical study of zone-melting process for the thermoelectric material of Bi2Te3

Science.gov (United States)

Chen, W. C.; Wu, Y. C.; Hwang, W. S.; Hsieh, H. L.; Huang, J. Y.; Huang, T. K.

2015-06-01

In this study, a numerical model has been established by employing a commercial software; ProCAST, to simulate the variation/distribution of temperature and the subsequent microstructure of Bi2Te3 fabricated by zone-melting technique. Then an experiment is conducted to measure the temperature variation/distribution during the zone-melting process to validate the numerical system. Also, the effects of processing parameters on crystallization microstructure such as moving speed and temperature of heater are numerically evaluated. In the experiment, the Bi2Te3 powder are filled into a 30mm diameter quartz cylinder and the heater is set to 800°C with a moving speed 12.5 mm/hr. A thermocouple is inserted in the Bi2Te3 powder to measure the temperature variation/distribution of the zone-melting process. The temperature variation/distribution measured by experiment is compared to the results of numerical simulation. The results show that our model and the experiment are well matched. Then the model is used to evaluate the crystal formation for Bi2Te3 with a 30mm diameter process. It's found that when the moving speed is slower than 17.5 mm/hr, columnar crystal is obtained. In the end, we use this model to predict the crystal formation of zone-melting process for Bi2Te3 with a 45 mm diameter. The results show that it is difficult to grow columnar crystal when the diameter comes to 45mm.

Melting of contaminated metallic waste

International Nuclear Information System (INIS)

Lee, Y.-S.; Cheng, S.-Y.; Kung, H.-T.; Lin, L.-F.

2004-01-01

Approximately 100 tons of contaminated metallic wastes were produced each year due to maintenance for each TPC's nuclear power reactor and it was roughly estimated that there will be 10,000 tons of metallic scraps resulted from decommissioning of each reactor in the future. One means of handling the contaminated metal is to melt it. Melting process owns not only volume reduction which saves the high cost of final disposal but also resource conservation and recycling benefits. Melting contaminated copper and aluminum scraps in the laboratory scale have been conducted at INER. A total of 546 kg copper condenser tubes with a specific activity of about 2.7 Bq/g was melted in a vacuum induction melting facility. Three types of products, ingot, slag and dust were derived from the melting process, with average activities of 0.10 Bq/g, 2.33 Bq/g and 84.3 Bq/g respectively. After the laboratory melting stage, a pilot plant with a 500 kg induction furnace is being designed to melt the increasingly produced contaminated metallic scraps from nuclear facilities and to investigate the behavior of different radionuclides during melting. (author)

First experimental observations on melting and chemical modification of volcanic ash during lightning interaction.

Science.gov (United States)

Mueller, S P; Helo, C; Keller, F; Taddeucci, J; Castro, J M

2018-01-23

Electrification in volcanic ash plumes often leads to syn-eruptive lightning discharges. High temperatures in and around lightning plasma channels have the potential to chemically alter, re-melt, and possibly volatilize ash fragments in the eruption cloud. In this study, we experimentally simulate temperature conditions of volcanic lightning in the laboratory, and systematically investigate the effects of rapid melting on the morphology and chemical composition of ash. Samples of different size and composition are ejected towards an artificially generated electrical arc. Post-experiment ash morphologies include fully melted spheres, partially melted particles, agglomerates, and vesiculated particles. High-speed imaging reveals various processes occurring during the short lightning-ash interactions, such as particle melting and rounding, foaming, and explosive particle fragmentation. Chemical analyses of the flash-melted particles reveal considerable bulk loss of Cl, S, P and Na through thermal vaporization. Element distribution patterns suggest convection as a key process of element transport from the interior of the melt droplet to rim where volatiles are lost. Modeling the degree of sodium loss delivers maximum melt temperatures between 3290 and 3490 K. Our results imply that natural lighting strikes may be an important agent of syn-eruptive morphological and chemical processing of volcanic ash.

Determination of the liquidus temperature of tin using the heat pulse-based melting and comparison with traditional methods

Science.gov (United States)

Joung, Wukchul; Park, Jihye; Pearce, Jonathan V.

2018-06-01

In this work, the liquidus temperature of tin was determined by melting the sample using the pressure-controlled loop heat pipe. Square wave-type pressure steps generated periodic 0.7 °C temperature steps in the isothermal region in the vicinity of the tin sample, and the tin was melted with controllable heat pulses from the generated temperature changes. The melting temperatures at specific melted fractions were measured, and they were extrapolated to the melted fraction of unity to determine the liquidus temperature of tin. To investigate the influence of the impurity distribution on the melting behavior, a molten tin sample was solidified by an outward slow freezing or by quenching to segregate the impurities inside the sample with concentrations increasing outwards or to spread the impurities uniformly, respectively. The measured melting temperatures followed the local solidus temperature variations well in the case of the segregated sample and stayed near the solidus temperature in the quenched sample due to the microscopic melting behavior. The extrapolated melting temperatures of the segregated and quenched samples were 0.95 mK and 0.49 mK higher than the outside-nucleated freezing temperature of tin (with uncertainties of 0.15 mK and 0.16 mK, at approximately 95% level of confidence), respectively. The extrapolated melting temperature of the segregated sample was supposed to be a closer approximation to the liquidus temperature of tin, whereas the quenched sample yielded the possibility of a misleading extrapolation to the solidus temperature. Therefore, the determination of the liquidus temperature could result in different extrapolated melting temperatures depending on the way the impurities were distributed within the sample, which has implications for the contemporary methodology for realizing temperature fixed points of the International Temperature Scale of 1990 (ITS-90).

Study on the Melting Point Depression of Tin Nanoparticles Manufactured by Modified Evaporation Method

Energy Technology Data Exchange (ETDEWEB)

Kim, Hyun Jin; Beak, Il Kwon; Kim, Kyu Han; Jang, Seok Pil [Korea Aerospace University, Goyang (Korea, Republic of)

2014-08-15

In the present study, the melting temperature depression of Sn nanoparticles manufactured using the modified evaporation method was investigated. For this purpose, a modified evaporation method with mass productivity was developed. Using the manufacturing process, Sn nanoparticles of 10 nm size was manufactured in benzyl alcohol solution to prevent oxidation. To examine the morphology and size distribution of the nanonoparticles, a transmission electron microscope was used. The melting temperature of the Sn nanoparticles was measured using a Differential scanning calorimetry (DSC) which can calculate the endothermic energy during the phase changing process and an X-ray photoelectron spectroscopy (XPS) used for observing the manufactured Sn nanoparticle compound. The melting temperature of the Sn nanoparticles was observed to be 129 ℃, which is 44 ℃ lower than that of the bulk material. Finally, the melting temperature was compared with the Gibbs Thomson and Lai's equations, which can predict the melting temperature according to the particle size. Based on the experimental results, the melting temperature of the Sn nanoparticles was found to match well with those recommended by the Lai's equation.

Ground-water quality beneath solid-waste disposal sites at anchorage, Alaska

Science.gov (United States)

Zenone, Chester; Donaldson, D.E.; Grunwaldt, J.J.

1975-01-01

Studies at three solid-waste disposal sites in the Anchorage area suggest that differences in local geohydrologic conditions influence ground-water quality. A leachate was detected in ground water within and beneath two sites where the water table is very near land surface and refuse is deposited either at or below the water table in some parts of the filled areas. No leachate was detected in ground water beneath a third site where waste disposal is well above the local water table.

Cumulates, Dykes and Pressure Solution in the Ice-Salt Mantle of Europa: Geological Consequences of Pressure Dependent Liquid Compositions and Volume Changes During Ice-Salt Melting Reactions.

Science.gov (United States)

Day, S.; Asphaug, E.; Bruesch, L.

2002-12-01

Water-salt analogue experiments used to investigate cumulate processes in silicate magmas, along with observations of sea ice and ice shelf behaviour, indicate that crystal-melt separation in water-salt systems is a rapid and efficient process even on scales of millimetres and minutes. Squeezing-out of residual melts by matrix compaction is also predicted to be rapid on geological timescales. We predict that the ice-salt mantle of Europa is likely to be strongly stratified, with a layered structure predictable from density and phase relationships between ice polymorphs, aqueous saline solutions and crystalline salts such as hydrated magnesium sulphates (determined experimentally by, inter alia, Hogenboom et al). A surface layer of water ice flotation cumulate will be separated from denser salt cumulates by a cotectic horizon. This cotectic horizon will be both the site of subsequent lowest-temperature melting and a level of neutral buoyancy for the saline melts produced. Initial melting will be in a narrow depth range owing to increasing melting temperature with decreasing pressure: the phase relations argue against direct melt-though to the surface unless vesiculation occurs. Overpressuring of dense melts due to volume expansion on cotectic melting is predicted to lead to lateral dyke emplacement and extension above the dyke tips. Once the liquid leaves the cotectic, melting of water ice will involve negative volume change. Impact-generated melts will drain downwards through the fractured zones beneath crater floors. A feature in the complex crater Mannan'an, with elliptical ring fractures around a conical depression with a central pit, bears a close resemblance to Icelandic glacier collapse cauldrons produced by subglacial eruptions. Other structures resembling Icelandic cauldrons occur along Europan banded structures, while resurgence of ice rubble within collapse structures may produce certain types of chaos region. More general contraction of the ice mantle

Recent Changes in Arctic Sea Ice Melt Onset, Freeze-Up, and Melt Season Length

Science.gov (United States)

Markus, Thorsten; Stroeve, Julienne C.; Miller, Jeffrey

2010-01-01

In order to explore changes and trends in the timing of Arctic sea ice melt onset and freeze-up and therefore melt season length, we developed a method that obtains this information directly from satellite passive microwave data, creating a consistent data set from 1979 through present. We furthermore distinguish between early melt (the first day of the year when melt is detected) and the first day of continuous melt. A similar distinction is made for the freeze-up. Using this method we analyze trends in melt onset and freeze-up for 10 different Arctic regions. In all regions except for the Sea of Okhotsk, which shows a very slight and statistically insignificant positive trend (O.4 days/decade), trends in melt onset are negative, i.e. towards earlier melt. The trends range from -1.0day/decade for the Bering Sea to -7.3 days/decade for the East Greenland Sea. Except for the Sea of Okhotsk all areas also show a trend towards later autumn freeze onset. The Chukchi/Beaufort Seas and Laptev/East Siberian Seas observe the strongest trends with 7 days/decade. For the entire Arctic, the melt season length has increased by about 20 days over the last 30 years. Largest trends of over 1O days/decade are seen for Hudson Bay, the East Greenland Sea the Laptev/East Siberian Seas, and the Chukchi/Beaufort Seas. Those trends are statistically significant a1 the 99% level.

Reaction of soda-lime-silica glass melt with water vapour at melting temperatures

Czech Academy of Sciences Publication Activity Database

Vernerová, Miroslava; Kloužek, Jaroslav; Němec, Lubomír

2015-01-01

Roč. 416, MAY 15 (2015), s. 21-30 ISSN 0022-3093 R&D Projects: GA TA ČR TA01010844 Institutional support: RVO:67985891 Keywords : glass melt * sulfate * water vapour * bubble nucleation * melt foaming * glass melting Subject RIV: JH - Ceramics, Fire-Resistant Materials and Glass Impact factor: 1.825, year: 2015

Transition metal ions in silicate melts. I. Manganese in sodium silicate melts

Energy Technology Data Exchange (ETDEWEB)

Nelson, C; White, W B

1980-01-01

Optical absorption spectra obtained on glasses quenched from sodium silicate melts show Mn/sup 3 +/ to be the dominant species for melts heated in air and Mn/sup 2 +/ to be the dominant species for melts heated at P/sub O/sub 2// = 10/sup -17/ bar. The absorption spectrum of Mn/sup 3 +/ consists of an intense band at 20,000 cm/sup -1/ with a 15,000 cm/sup -1/ satellite possibly arising from the Jahn-Teller effect. The independence of the spectrum from melt composition and the high band intensity is offered as evidence for a distinct Mn/sup 3 +/ complex in the melt. The spectrum of Mn/sup 2 +/ is weak and many expected bands are not observed. A two-band luminescence spectrum from Mn/sup 2 +/ has been tentatively interpreted as due to Mn/sup 2 +/ in interstitial sites in the network and Mn/sup 2 +/ coordiated by non-bridging oxygens.

Fine crustal and uppermost mantle S-wave velocity structure beneath the Tengchong volcanic area inferred from receiver function and surface-wave dispersion: constraints on magma chamber distribution

Science.gov (United States)

Li, Mengkui; Zhang, Shuangxi; Wu, Tengfei; Hua, Yujin; Zhang, Bo

2018-03-01

The Tengchong volcanic area is located in the southeastern margin of the collision zone between the Indian and Eurasian Plates. It is one of the youngest intraplate volcano groups in mainland China. Imaging the S-wave velocity structure of the crustal and uppermost mantle beneath the Tengchong volcanic area is an important means of improving our understanding of its volcanic activity and seismicity. In this study, we analyze teleseismic data from nine broadband seismic stations in the Tengchong Earthquake Monitoring Network. We then image the crustal and uppermost mantle S-wave velocity structure by joint analysis of receiver functions and surface-wave dispersion. The results reveal widely distributed low-velocity zones. We find four possible magma chambers in the upper-to-middle crust and one in the uppermost mantle. The chamber in the uppermost mantle locates in the depth range from 55 to 70 km. The four magma chambers in the crust occur at different depths, ranging from the depth of 7 to 25 km in general. They may be the heat sources for the high geothermal activity at the surface. Based on the fine crustal and uppermost mantle S-wave velocity structure, we propose a model for the distribution of the magma chambers.

FARO tests corium-melt cooling in water pool: Roles of melt superheat and sintering in sediment

Energy Technology Data Exchange (ETDEWEB)

Hwang, Gisuk [Department of Mechanical Engineering, Wichita State University, Wichita, KS 67260 (United States); Kaviany, Massoud [Department of Mechanical Engineering, University of Michigan, Ann Arbor, MI 48109 (United States); Division of Advance Nuclear Engineering, POSTECH, Pohang, Gyeongbuk 790-784 (Korea, Republic of); Moriyama, Kiyofumi [Division of Advance Nuclear Engineering, POSTECH, Pohang, Gyeongbuk 790-784 (Korea, Republic of); Park, Hyun Sun, E-mail: hejsunny@postech.ac.kr [Division of Advance Nuclear Engineering, POSTECH, Pohang, Gyeongbuk 790-784 (Korea, Republic of); Hwang, Byoungcheol; Lee, Mooneon; Kim, Eunho; Park, Jin Ho [Division of Advance Nuclear Engineering, POSTECH, Pohang, Gyeongbuk 790-784 (Korea, Republic of); Nasersharifi, Yahya [Department of Mechanical Engineering, Wichita State University, Wichita, KS 67260 (United States)

2016-08-15

Highlights: • The numerical approach for FARO experimental data is suggested. • The cooling mechanism of ex-vessel corium is suggested. • The predicted minimum pool depth for no cake formation is suggested. - Abstract: The FARO tests have aimed at understanding an important severe accident mitigation action in a light water reactor when the accident progresses from the reactor pressure vessel boundary. These tests have aimed to measure the coolability of a molten core material (corium) gravity dispersed as jet into a water pool, quantifying the loose particle diameter distribution and fraction converted to cake under range of initial melt superheat and pool temperature and depth. Under complete hydrodynamic breakup of corium and consequent sedimentation in the pool, the initially superheated corium can result in debris bed consisting of discrete solid particles (loose debris) and/or a solid cake at the bottom of the pool. The success of the debris bed coolability requires cooling of the cake, and this is controlled by the large internal resistance. We postulate that the corium cake forms when there is a remelting part in the sediment. We show that even though a solid shell forms around the melt particles transiting in the water pool due to film-boiling heat transfer, the superheated melt allows remelting of the large particles in the sediment (depending on the water temperature and the transit time) using the COOLAP (Coolability Analysis with Parametric fuel-cooant interaction models) code. With this remelting and its liquid-phase sintering of the non-remelted particles, we predict the fraction of the melt particles converting to a cake through liquid sintering. Our predictions are in good agreement with the existing results of the FARO experiments. We address only those experiments with pool depths sufficient/exceeding the length required for complete breakup of the molten jet. Our analysis of the fate of molten corium aimed at devising the effective

On high-pressure melting of tantalum

Science.gov (United States)

Luo, Sheng-Nian; Swift, Damian C.

2007-01-01

The issues related to high-pressure melting of Ta are discussed within the context of diamond-anvil cell (DAC) and shock wave experiments, theoretical calculations and common melting models. The discrepancies between the extrapolations of the DAC melting curve and the melting point inferred from shock wave experiments, cannot be reconciled either by superheating or solid-solid phase transition. The failure to reproduce low-pressure DAC melting curve by melting models such as dislocation-mediated melting and the Lindemann law, and molecular dynamics and quantum mechanics-based calculations, undermines their predictions at moderate and high pressures. Despite claims to the contrary, the melting curve of Ta (as well as Mo and W) remains inconclusive at high pressures.

Imaging Lithospheric-scale Structure Beneath Northern Altiplano in Southern Peru and Northern Bolivia

Science.gov (United States)

Kumar, A.; Wagner, L. S.; Beck, S. L.; Zandt, G.; Long, M. D.

2014-12-01

The northern Altiplano plateau of southern Peru and northern Bolivia is one of the highest topographic features on the Earth, flanked by Western and Eastern Cordillera along its margin. It has strongly influenced the local and far field lithospheric deformation since the early Miocene (Masek et al., 1994). Previous studies have emphasized the importance of both the crust and upper mantle in the evolution of Altiplano plateau (McQuarrie et al., 2005). Early tomographic and receiver function studies, south of 16° S, show significant variations in the crust and upper mantle properties in both perpendicular and along strike direction of the Altiplano plateau (Dorbath et. al., 1993; Myers et al., 1998; Beck and Zandt, 2002). In order to investigate the nature of subsurface lithospheric structure below the northern Altiplano, between 15-18° S, we have determined three-dimensional seismic tomography models for Vp and Vs using P and S-wave travel time data from two recently deployed local seismic networks of CAUGHT and PULSE. We also used data from 8 stations from the PERUSE network (PERU Subduction Experiment). Our preliminary tomographic models show a complex variation in the upper mantle velocity structure with depth, northwest and southeast of lake Titicaca. We see the following trend, at ~85 km depth, northwest of lake Titicaca: low Vp and Vs beneath the Western Cordillera, high Vs beneath the Altiplano and low Vp and Vs beneath the Eastern Cordillera. This low velocity anomaly, beneath Eastern Cordillera, seems to coincide with Kimsachata, a Holocene volcano in southern Peru. At depth greater than ~85 km: we find high velocity anomaly beneath the Western Cordillera and low Vs beneath the Altiplano. This high velocity anomaly, beneath Western Cordillera, coincides with the well-located Wadati-Benioff zone seismicity and perhaps represents the subducting Nazca slab. On the southeast of lake Titicaca, in northern Bolivia, we see a consistently high velocity anomaly

Bed-Deformation Experiments Beneath a Temperate Glacier

Science.gov (United States)

Iverson, N. R.; Hooyer, T. S.; Fischer, U. H.; Cohen, D.; Jackson, M.; Moore, P. L.; Lappegard, G.; Kohler, J.

2002-12-01

Fast flow of glaciers and genesis of glacial landforms are commonly attributed to shear deformation of subglacial sediment. Although models of this process abound, data gathered subglacially on the kinematics and mechanics of such deformation are difficult to interpret. Major difficulties stem from the necessity of either measuring deformation near glacier margins, where conditions may be abnormal, or at the bottoms of boreholes, where the scope of instrumentation is limited, drilling disturbs sediment, and local boundary conditions are poorly known. A different approach is possible at the Svartisen Subglacial Laboratory, where tunnels melted in the ice provide temporary human access to the bed of Engabreen, a temperate outlet glacier of the Svartisen Ice Cap in Norway. A trough (2 m x 1.5 m x 0.5 m deep) was blasted in the rock bed, where the glacier is 220 m thick and sliding at 0.1-0.2 m/d. During two spring field seasons, this trough was filled with 2.5 tons of simulated till. Instruments in the till recorded shear (tiltmeters), volume change, total normal stress, and pore-water pressure as ice moved across the till surface. Pore pressure was brought to near the total normal stress by feeding water to the base of the till with a high-pressure pump, operated in a rock tunnel 4 m below the bed surface. Results illustrate some fundamental aspects of bed deformation. Permanent shear deformation requires low effective normal stress and hence high pore-water pressure, owing to the frictional nature of till. Shear strain generally increases upward in the bed toward the glacier sole, consistent with previous measurements beneath thinner ice at glacier margins. At low effective normal stresses, ice sometimes decouples from underlying till. Overall, bed deformation accounts for 10-35 % of basal motion, although this range excludes shear in the uppermost 0.05 m of till where shear was not measured. Pump tests with durations ranging from seconds to hours highlight the need

The subcontinental mantle beneath southern New Zealand, characterised by helium isotopes in intraplate basalts and gas-rich springs

Science.gov (United States)

Hoke, L.; Poreda, R.; Reay, A.; Weaver, S. D.

2000-07-01

New helium isotope data measured in Cenozoic intraplate basalts and their mantle xenoliths are compared with present-day mantle helium emission on a regional scale from thermal and nonthermal gas discharges on the South Island of New Zealand and the offshore Chatham Islands. Cenozoic intraplate basaltic volcanism in southern New Zealand has ocean island basalt affinities but is restricted to continental areas and absent from adjacent Pacific oceanic crust. Its distribution is diffuse and widespread, it is of intermittent timing and characterised by low magma volumes. Most of the 3He/ 4He ratios measured in fluid inclusions in mantle xenocrysts and basalt phenocrysts such as olivine, garnet, and amphibole fall within the narrow range of 8.5 ± 1.5 Ra (Ra is the atmospheric 3He/ 4He ratio) with a maximum value of 11.5 Ra. This range is characteristic of the relatively homogeneous and degassed upper MORB-mantle helium reservoir. No helium isotope ratios typical of the lower less degassed mantle (>12 Ra), such as exemplified by the modern hot-spot region of Hawaii (with up to 32 Ra) were measured. Helium isotope ratios of less than 8 Ra are interpreted in terms of dilution of upper mantle helium with a radiogenic component, due to either age of crystallisation or small-scale mantle heterogeneities caused by mixing of crustal material into the upper mantle. The crude correlation between age of samples and helium isotopes with generally lower R/Ra values in mantle xenoliths compared with host rock phenocrysts and the in general depleted Nd and Sr isotope ratios and the light rare earth element enrichment of the basalts supports derivation of melts as small melt fractions from a depleted upper mantle, with posteruptive ingrowth of radiogenic helium as a function of lithospheric age. In comparison, the regional helium isotope survey of thermal and nonthermal gas discharges of the South Island of New Zealand shows that mantle 3He anomalies in general do not show an obvious

Ancient Continental Lithosphere Dislocated Beneath Ocean Basins Along the Mid-Lithosphere Discontinuity: A Hypothesis

Science.gov (United States)

Wang, Zhensheng; Kusky, Timothy M.; Capitanio, Fabio A.

2017-09-01

The documented occurrence of ancient continental cratonic roots beneath several oceanic basins remains poorly explained by the plate tectonic paradigm. These roots are found beneath some ocean-continent boundaries, on the trailing sides of some continents, extending for hundreds of kilometers or farther into oceanic basins. We postulate that these cratonic roots were left behind during plate motion, by differential shearing along the seismically imaged mid-lithosphere discontinuity (MLD), and then emplaced beneath the ocean-continent boundary. Here we use numerical models of cratons with realistic crustal rheologies drifting at observed plate velocities to support the idea that the mid-lithosphere weak layer fostered the decoupling and offset of the African continent's buoyant cratonic root, which was left behind during Meso-Cenozoic continental drift and emplaced beneath the Atlantic Ocean. We show that in some cratonic areas, the MLD plays a similar role as the lithosphere-asthenosphere boundary for accommodating lateral plate tectonic displacements.

Numerical simulation of electro-magnetic and flow fields of TiAl melt under electric field

Directory of Open Access Journals (Sweden)

Zhang Yong

2010-08-01

Full Text Available This article aims at building an electromagnetic and fluid model, based on the Maxwell equations and Navier-Stokes equations, in TiAl melt under two electric fields. FEM (Finite Element Method and APDL (ANSYS Parametric Design Language were employed to perform the simulation, model setup, loading and problem solving. The melt in molds of same cross section area with different flakiness ratio (i.e. width/depth under the load of sinusoidal current or pulse current was analyzed to obtain the distribution of electromagnetic field and flow field. The results show that the induced magnetic field occupies sufficiently the domain of the melt in the mold with a flakiness ratio of 5:1. The melt is driven bipolarly from the center in each electric field. It is also found that the pulse electric field actuates the TiAl melt to flow stronger than what the sinusoidal electric field does.

A numerical study of zone-melting process for the thermoelectric material of Bi2Te3

International Nuclear Information System (INIS)

Chen, W C; Wu, Y C; Hwang, W S; Hsieh, H L; Huang, J Y; Huang, T K

2015-01-01

In this study, a numerical model has been established by employing a commercial software; ProCAST, to simulate the variation/distribution of temperature and the subsequent microstructure of Bi 2 Te 3 fabricated by zone-melting technique. Then an experiment is conducted to measure the temperature variation/distribution during the zone-melting process to validate the numerical system. Also, the effects of processing parameters on crystallization microstructure such as moving speed and temperature of heater are numerically evaluated. In the experiment, the Bi 2 Te 3 powder are filled into a 30mm diameter quartz cylinder and the heater is set to 800°C with a moving speed 12.5 mm/hr. A thermocouple is inserted in the Bi 2 Te 3 powder to measure the temperature variation/distribution of the zone-melting process. The temperature variation/distribution measured by experiment is compared to the results of numerical simulation. The results show that our model and the experiment are well matched. Then the model is used to evaluate the crystal formation for Bi 2 Te 3 with a 30mm diameter process. It's found that when the moving speed is slower than 17.5 mm/hr, columnar crystal is obtained. In the end, we use this model to predict the crystal formation of zone-melting process for Bi 2 Te 3 with a 45 mm diameter. The results show that it is difficult to grow columnar crystal when the diameter comes to 45mm. (paper)

Melt inclusions: Chapter 6

Science.gov (United States)

,; Lowenstern, J. B.

2014-01-01

Melt inclusions are small droplets of silicate melt that are trapped in minerals during their growth in a magma. Once formed, they commonly retain much of their initial composition (with some exceptions) unless they are re-opened at some later stage. Melt inclusions thus offer several key advantages over whole rock samples: (i) they record pristine concentrations of volatiles and metals that are usually lost during magma solidification and degassing, (ii) they are snapshots in time whereas whole rocks are the time-integrated end products, thus allowing a more detailed, time-resolved view into magmatic processes (iii) they are largely unaffected by subsolidus alteration. Due to these characteristics, melt inclusions are an ideal tool to study the evolution of mineralized magma systems. This chapter first discusses general aspects of melt inclusions formation and methods for their investigation, before reviewing studies performed on mineralized magma systems.

Exploration of the fragmentation of laser shock-melted aluminum using x-ray backlighting

Directory of Open Access Journals (Sweden)

Lin Zhang

2016-05-01

Full Text Available The fragmentation of shock-melted metal material is an important scientific problem in shock physics and is suitable for experimentally investigating by the laser-driven x-ray backlighting technique. This letter reports on the exploration of laser shock-melted aluminum fragmentation by means of x-ray backlighting at the SGII high energy facility in China. High-quality and high-resolution radiographs with negligible motion blur were obtained and these images enabled analysis of the mass distribution of the fragmentation product.

High-pressure melting curve of KCl: Evidence against lattice-instability theories of melting

International Nuclear Information System (INIS)

Ross, M.; Wolf, G.

1986-01-01

We show that the large curvature in the T-P melting curve of KCl is the result of a reordering of the liquid to a more densely packed arrangement. As a result theories of melting, such as the instability model, which do not take into account the structure of the liquid fail to predict the correct pressure dependence of the melting curve

Electron beam melting of sponge titanium

International Nuclear Information System (INIS)

Kanayama, Hiroshi; Kusamichi, Tatsuhiko; Muraoka, Tetsuhiro; Onouye, Toshio; Nishimura, Takashi

1991-01-01

Fundamental investigations were done on electron beam (EB) melting of sponge titanium by using 80 kW EB melting furnace. Results obtained are as follows: (1) To increase the melting yield of titanium in EB melting of sponge titanium, it is important to recover splashed metal by installation of water-cooled copper wall around the hearth and to decrease evaporation loss of titanium by keeping the surface temperature of molten metal just above the melting temperature of titanium without local heating. (2) Specific power consumption of drip melting of pressed sponge titanium bar and hearth melting of sponge titanium are approximately 0.9 kWh/kg-Ti and 0.5-0.7 kWh/kg-Ti, respectively. (3) Ratios of the heat conducted to water-cooled mould in the drip melting and to water-cooled hearth in the hearth melting to the electron beam input power are 50-65% and 60-65%, respectively. (4) Surface defects of EB-melted ingots include rap which occurs when the EB output is excessively great, and transverse cracks when the EB output is excessively small. To prevent surface defects, the up-down withdrawal method is effective. (author)

Crustal accretion along the global mid-ocean ridge system based on basaltic glass and olivine-hosted melt inclusion compositions

Science.gov (United States)

Wanless, V. D.; Behn, M. D.

2015-12-01

The depth and distribution of crystallization at mid-ocean ridges controls the overall architecture of the oceanic crust, influences hydrothermal circulation, and determines geothermal gradients in the crust and uppermost mantle. Despite this, there is no overall consensus on how crystallization is distributed within the crust/upper mantle or how this varies with spreading rate. Here, we examine crustal accretion at mid-ocean ridges by combining crystallization pressures calculated from major element barometers on mid-ocean ridge basalt (MORB) glasses with vapor-saturation pressures from melt inclusions to produce a detailed map of crystallization depths and distributions along the global ridge system. We calculate pressures of crystallization from >11,500 MORB glasses from the global ridge system using two established major element barometers (1,2). Additionally, we use vapor-saturation pressures from >400 olivine-hosted melt inclusions from five ridges with variable spreading rates to constrain pressures and distributions of crystallization along the global ridge system. We show that (i) crystallization depths from MORB glasses increase and become less focused with decreasing spreading rate, (ii) maximum glass pressures are greater than the maximum melt inclusion pressure, which indicates that the melt inclusions do not record the deepest crystallization at mid-ocean ridges, and (iii) crystallization occurs in the lower crust/upper mantle at all ridges, indicating accretion is distributed throughout the crust at all spreading rates, including those with a steady-state magma lens. Finally, we suggest that the remarkably similar maximum vapor-saturation pressures (~ 3000 bars) in melt inclusion from all spreading rates reflects the CO2 content of the depleted upper mantle feeding the global mid-ocean ridge system. (1) Michael, P. & W. Cornell (1998), Journal of Geophysical Research, 103(B8), 18325-18356; (2) Herzberg, C. (2004), Journal of Petrology, 45(12), 2389.

Effect of Duration on Ti Grain Refinement of A356 and Melt Quality

Science.gov (United States)

Gürsoy, Özen; Erzi, Eray; Yüksel, Çağlar; Dispinar, Derya

Grain refinement of aluminium alloys increases fluidity and feedability; and thus higher mechanical properties and decreased porosity is achieved. Typically, various ratios of Ti-B is used as grain refiner. It is well known that due to the sedimentation, the effectiveness of the grain refinement decreases which is called the fading effect. In this work, this effect has been investigated by means of melt quality. Two different melting temperatures were selected (725 and 750C) and samples were cast into die and sand mould. After the addition of grain refiners, samples were collected at 10 minutes of interval. Metallographic examinations were carried out where microstructural change and porosity distribution were investigated. The results were correlated with bifilm index (i.e. melt quality).

Melting point of yttria

International Nuclear Information System (INIS)

Skaggs, S.R.

1977-06-01

Fourteen samples of 99.999 percent Y 2 O 3 were melted near the focus of a 250-W CO 2 laser. The average value of the observed melting point along the solid-liquid interface was 2462 +- 19 0 C. Several of these same samples were then melted in ultrahigh-purity oxygen, nitrogen, helium, or argon and in water vapor. No change in the observed temperature was detected, with the exception of a 20 0 C increase in temperature from air to helium gas. Post test examination of the sample characteristics, clarity, sphericity, and density is presented, along with composition. It is suggested that yttria is superior to alumina as a secondary melting-point standard

[Influence of implants prepared by selective laser melting on early bone healing].

Science.gov (United States)

Liu, J Y; Chen, F; Ge, Y J; Wei, L; Pan, S X; Feng, H L

2018-02-18

To evaluate the influence of the rough surface of dental implants prepared by selective laser melting (SLM) on early bone healing around titanium implants. A total of sixteen titanium implants were involved in our research, of which eight implants were prepared by SLM (TIXOS Cylindrical, Leader-Novaxa, Milan, Italy; 3.3 mm×10 mm, internal hex) and the other eight were sandblasted, large-grit and acid-etched (SLA) implants (IMPLUS Cylindrical, Leader-Novaxa, Milan, Italy; 3.3 mm×10 mm, internal hex). All of the dental implants were inserted into the healed extraction sockets of the mandible of two adult male Beagle dogs. Half of the dental implants were designed to be healed beneath the mucosa and the other half were intended to be healed transgingivally and were immediately loaded by acrylic resin bridge restoration. Three types of tetracycline fluorescent labels, namely calcein blue, alizarin complexone and calcein, were administered into the veins of the Beagle dogs 2, 4, and 8 weeks after implant placement respectively for fluorescent evaluation of newly formed bone peri-implant. Both Beagle dogs were euthanized 12 weeks after implant insertion and the mandible block specimens containing the titanium implants and surrounding bone and soft tissue of each dog were carefully sectioned and dissected. A total of 16 hard tissue slices were obtained and stained with toluidine blue for microscopic examination and histomorphometric measurements. Histological observation was made for each slice under light microscope and laser scanning confocal microscope (LSCM). Comparison on new bone formation around titanium implants of each group was made and mineral apposition rate (MAR) was calculated for each group. Dental implants prepared by selective laser melting had achieved satisfying osseointegration to surrounding bone tissue after the healing period of 12 weeks. Newly formed bone tissue was observed creeping on the highly porous surface of the SLM implant and growing

Measurement of snow interception and canopy effects on snow accumulation and melt in a mountainous maritime climate, Oregon, United States

Science.gov (United States)

Storck, Pascal; Lettenmaier, Dennis P.; Bolton, Susan M.

2002-11-01

The results of a 3 year field study to observe the processes controlling snow interception by forest canopies and under canopy snow accumulation and ablation in mountain maritime climates are reported. The field study was further intended to provide data to develop and test models of forest canopy effects on beneath-canopy snowpack accumulation and melt and the plot and stand scales. Weighing lysimeters, cut-tree experiments, and manual snow surveys were deployed at a site in the Umpqua National Forest, Oregon (elevation 1200 m). A unique design for a weighing lysimeter was employed that allowed continuous measurements of snowpack evolution beneath a forest canopy to be taken at a scale unaffected by variability in canopy throughfall. Continuous observations of snowpack evolution in large clearings were made coincidentally with the canopy measurements. Large differences in snow accumulation and ablation were observed at sites beneath the forest canopy and in large clearings. These differences were not well described by simple relationships between the sites. Over the study period, approximately 60% of snowfall was intercepted by the canopy (up to a maximum of about 40 mm water equivalent). Instantaneous sublimation rates exceeded 0.5 mm per hour for short periods. However, apparent average sublimation from the intercepted snow was less than 1 mm per day and totaled approximately 100 mm per winter season. Approximately 72 and 28% of the remaining intercepted snow was removed as meltwater drip and large snow masses, respectively. Observed differences in snow interception rate and maximum snow interception capacity between Douglas fir (Pseudotsuga menziesii), white fir (Abies concolor), ponderosa pine (Pinus ponderosa), and lodgepole pine (Pinus contorta) were minimal.

Method of melting solid waste

International Nuclear Information System (INIS)

Ootsuka, Katsuyuki; Mizuno, Ryokichi; Kuwana, Katsumi; Sawada, Yoshihisa; Komatsu, Fumiaki.

1982-01-01

Purpose: To enable the volume reduction treatment of a HEPA filter containing various solid wastes, particularly acid digestion residue, or an asbestos separator at a relatively low temperature range. Method: Solid waste to be heated and molten is high melting point material treated by ''acid digestion treatment'' for treating solid waste, e.g. a HEPA filter or polyvinyl chloride, etc. of an atomic power facility treated with nitric acid or the like. When this material is heated and molten by an electric furnace, microwave melting furnace, etc., boron oxide, sodium boride, sodium carbonate, etc. is added as a melting point lowering agent. When it is molten in this state, its melting point is lowered, and it becomes remarkably fluid, and the melting treatment is facilitated. Solidified material thus obtained through the melting step has excellent denseness and further large volume reduction rate of the solidified material. (Yoshihara, H.)

Size-dependent melting modes and behaviors of Ag nanoparticles: a molecular dynamics study

Science.gov (United States)

Liang, Tianshou; Zhou, Dejian; Wu, Zhaohua; Shi, Pengpeng

2017-12-01

The size-dependent melting behaviors and mechanisms of Ag nanoparticles (NPs) with diameters of 3.5-16 nm were investigated by molecular dynamics (MD). Two distinct melting modes, non-premelting and premelting with transition ranges of about 7-8 nm, for Ag NPs were demonstrated via the evolution of distribution and transition of atomic physical states during annealing. The small Ag NPs (3.5-7 nm) melt abruptly without a stable liquid shell before the melting point, which is characterized as non-premelting. A solid-solid crystal transformation is conducted through the migration of adatoms on the surface of Ag NPs with diameters of 3.5-6 nm before the initial melting, which is mainly responsible for slightly increasing the melting point of Ag NPs. On the other hand, surface premelting of Ag NPs with diameters of 8-16 nm propagates from the outer shell to the inner core with initial anisotropy and late isotropy as the temperature increases, and the close-packed facets {111} melt by a side-consumed way which is responsible for facets {111} melting in advance relative to the crystallographic plane {111}. Once a stable liquid shell is formed, its size-independent minimum thickness is obtained, and a three-layer structure of atomic physical states is set up. Lastly, the theory of point defect-pair (vacancy-interstitial) severing as the mechanism of formation and movement of the solid-liquid interface was also confirmed. Our study provides a basic understanding and theoretical guidance for the research, production and application of Ag NPs.

Uniform distribution of TiCp in TiCp/Zn-Al composites prepared by XDTM

Institute of Scientific and Technical Information of China (English)

王香; 马旭梁; 李庆芬; 曾松岩

2002-01-01

The prefabricated Al/TiC alloy with high TiC particle content was prepared by XDTM process. The uniform distribution process of TiC particles in the stationary zinc melt was studied and analyzed using self-made experimental equipment, and the model of the uniform distribution process was built. The results show that zinc diffuses into the prepared Al/TiC alloy after it is placed in the zinc melt at temperatures below the melting point of aluminum, which leads to the decrease of the liquidus temperature of Al-Zn alloy in the surface layer of Al/TiC alloy. When the liquidus temperature of Al-Zn alloy is equal to or below the temperature of zinc melt, Al-Zn alloy melts and TiC particles drop with it from the Al/TiC alloy and then transfer into the zinc melt and finally distribute uniformly in it.

Quantitative structure-property relationships for prediction of boiling point, vapor pressure, and melting point.

Science.gov (United States)

Dearden, John C

2003-08-01

Boiling point, vapor pressure, and melting point are important physicochemical properties in the modeling of the distribution and fate of chemicals in the environment. However, such data often are not available, and therefore must be estimated. Over the years, many attempts have been made to calculate boiling points, vapor pressures, and melting points by using quantitative structure-property relationships, and this review examines and discusses the work published in this area, and concentrates particularly on recent studies. A number of software programs are commercially available for the calculation of boiling point, vapor pressure, and melting point, and these have been tested for their predictive ability with a test set of 100 organic chemicals.

Thermodynamics of Oligonucleotide Duplex Melting

Science.gov (United States)

Schreiber-Gosche, Sherrie; Edwards, Robert A.

2009-01-01

Melting temperatures of oligonucleotides are useful for a number of molecular biology applications, such as the polymerase chain reaction (PCR). Although melting temperatures are often calculated with simplistic empirical equations, application of thermodynamics provides more accurate melting temperatures and an opportunity for students to apply…

Automatic Control of Silicon Melt Level

Science.gov (United States)

Duncan, C. S.; Stickel, W. B.

1982-01-01

A new circuit, when combined with melt-replenishment system and melt level sensor, offers continuous closed-loop automatic control of melt-level during web growth. Installed on silicon-web furnace, circuit controls melt-level to within 0.1 mm for as long as 8 hours. Circuit affords greater area growth rate and higher web quality, automatic melt-level control also allows semiautomatic growth of web over long periods which can greatly reduce costs.

Crustal structure beneath the southern Korean Peninsula from local earthquakes

Science.gov (United States)

Kim, Kwang-Hee; Park, Jung-Ho; Park, Yongcheol; Hao, Tian-Yao; Kim, Han-Joon

2017-05-01

The 3-D subsurface structure beneath the southern Korean Peninsula is poorly known, even though such information could be key in verifying or rejecting several competing models of the tectonic evolution of East Asia. We constructed a 3-D velocity model of the upper crust beneath the southern Korean Peninsula using 19 935 P-wave arrivals from 747 earthquakes recorded by high-density local seismic networks. Results show significant lateral and vertical variations: velocity increases from northwest to southeast at shallow depths, and significant velocity variations are observed across the South Korea Tectonic Line between the Okcheon Fold Belt and the Youngnam Massif. Collision between the North and South China blocks during the Early Cretaceous might have caused extensive deformation and the observed negative velocity anomalies in the region. The results of the tomographic inversion, combined with the findings of previous studies of Bouguer and isostatic gravity anomalies, indicate the presence of high-density material in the upper and middle crust beneath the Gyeongsang Basin in the southeastern Korean Peninsula. Although our results partially support the indentation tectonic model, it is still premature to discard other tectonic evolution models because our study only covers the southern half of the peninsula.

Experimental study of simulant melt stream-water thermal interaction in pool and narrow geometries

International Nuclear Information System (INIS)

Narayanan, K.S.; Jasmin Sudha, A.; Murthy, S.S.; Rao, E.H.V.M.; Lydia, G.; Das, S.K.; Harvey, J.; Kannan, S.E.

2005-01-01

Full text of publication follows: Small scale experiments were carried out to investigate the thermal interaction characteristics of a few kilograms of Sn Pb, Bi and Zn as hot melt, in the film boiling region of water in an attempt to simulate a coherent fuel coolant interaction during a postulated severe accident in a nuclear reactor. Melt stream solidification and detached debris generation were studied with different melt superheat up to 200 deg. C, at different coolant temperatures of 30 deg. C, 50 deg. C, 70 deg. C, 90 deg. C, in pool geometry and in long narrow coolant column. The material was heated in an Alumina crucible and poured through a hot stainless steel funnel with a nozzle diameter of 7.7 mm, into the coolant. A stainless steel plate was used to collect the solidified mass after the interaction. Temperature monitoring was done in the coolant column close to the melt stream. The melt stream movement inside the coolant was imaged using a video camera at 25 fps. Measured melt stream entry velocity was around 1.5 m/sec. For low melt superheat and low coolant temperature, solidified porous tree like structure extended from the collector plate up to the melt release point. For water temperature of 70 deg. C, the solidified bed height at the center was found to decrease with increase in the melt superheat up to 150 deg. C. Fragmentation was found to occur when the melt superheat exceeded 200 deg. C. Particle size distribution was obtained for the fragmented debris. In 1D geometry, with 50 deg. C superheat, columnar solidification was observed with no fine debris. The paper gives the details of the results obtained in the experiments and highlights the role of Rayleigh-Taylor, Kelvin-Helmholtz instabilities and the melt physical properties on the fragmentation kinetics. (authors)

Melting of polydisperse hard disks

NARCIS (Netherlands)

Pronk, S.; Frenkel, D.

2004-01-01

The melting of a polydisperse hard-disk system is investigated by Monte Carlo simulations in the semigrand canonical ensemble. This is done in the context of possible continuous melting by a dislocation-unbinding mechanism, as an extension of the two-dimensional hard-disk melting problem. We find

Long-lived melting of ancient lower crust of the North China Craton in response to paleo-Pacific plate subduction, recorded by adakitic rhyolite

Science.gov (United States)

Wang, Chao; Song, Shuguang; Niu, Yaoling; Allen, Mark B.; Su, Li; Wei, Chunjing; Zhang, Guibin; Fu, Bin

2017-11-01

Magmatism in eastern China in response to paleo-Pacific plate subduction during the Mesozoic was complex, and it is unclear how and when exactly the magmas formed via thinning and partial destruction of the continental lithosphere. To better understand this magmatism, we report the results of a geochronological and geochemical study of Early Cretaceous adakitic rhyolite (erupted at 125.4 ± 2.2 Ma) in the Xintaimen area within the eastern North China Craton (NCC). In situ zircon U-Pb dating shows that this adakitic rhyolite records a long ( 70 Myrs) and complicated period of magmatism with concordant 206Pb/238U ages from 193 Ma to 117 Ma. The enriched bulk rock Sr-Nd isotopic compositions of the Xintaimen adakitic rhyolite, as well as the enriched zircon Hf and O isotopic compositions, indicate that the magmas parental to the adakitic rhyolite were derived from partial melting of the Paleoproterozoic mafic lower crust, heated by mafic melts derived from the mantle during the paleo-Pacific plate subduction. A minor older basement component is indicated by the presence of captured Neoarchean to Early Paleoproterozoic zircons. The Mesozoic zircons have restricted Hf and O isotopic compositions irrespective of their ages, suggesting that they formed from similar sources at similar melting conditions. The Xintaimen adakitic rhyolite offers an independent line of evidence that the ancient lower crust of eastern China underwent a long period ( 70 Myrs) of destruction, melting or remelting, from 193 to 120 Ma, related to the subduction of the paleo-Pacific plate beneath eastern China.

Seismic velocity structure in the lower crust beneath the seismic belt in the San-in district, Southwest Japan

Science.gov (United States)

Tsuda, H.; Iio, Y.; Shibutani, T.

2017-12-01

In the San-in district in Southwest Japan, a linear distribution of the epicenters of microearthquakes is seen along the coast of the Japan Sea (Fig. 1). The linear distribution is known as the seismic belt in the San-in district. Large earthquakes also occurred in the seismic belt. What localizes the earthquake distribution in the San-in district which is located far from the plate boundary? We thought that the model proposed by Iio et al. (2002, 2004) could answer this question. The model is as follows. Viscosity is low in a part of the lower crust, which is called `weak zone'. Stress and strain are concentrated in the upper crust right above the weak zone, due to concentrated deformation in the weak zone, and thus earthquakes occur there. To verify whether the weak zone exists in the lower crust beneath the seismic belt, we estimated the seismic velocity structure there by travel-time tomography. We used the tomography program, FMTOMO (Rawlinson et al., 2006). For the model space, we set the latitude range of 33°-36°N, the longitude range of 131°-136°E (Fig. 1), and the depth range of 0-81 km. The grid intervals are 0.1°×0.1°×7 km. We used arrival times picked by Japan Meteorological Agency (JMA) for earthquakes that occurred in the study area. In addition, we used arrival times manually picked at stations in and around the San-in district for earthquakes that occurred within the Philippine Sea Slab, because they are not included in the JMA data. Since the seismic waves from those earthquakes to the stations in the San-in district pass through the lower crust beneath the San-in district, we expect that these data can improve the resolution there. We revealed that low velocity anomalies exist in the lower crust beneath the seismic belt (Fig. 1). It is inferred that the region of low velocity anomalies is characterized by low viscosity, since velocities of rocks decrease with temperature and/or water content. Therefore, the results of this study support

Imaging voids beneath bridge bent using electrical resistivity tomography.

Science.gov (United States)

2014-02-01

Five electrical resistivity tomography (ERT) profiles and borehole control were acquired beneath two bridges on the bank of the : Gasconade River in order to determine extension of the underground water-filled openings in rock encountered during a dr...

Depth-Dependent Earthquake Properties Beneath Long-Beach, CA: Implications for the Rheology at the Brittle-Ductile Transition Zone

Science.gov (United States)

Inbal, A.; Clayton, R. W.; Ampuero, J. P.

2015-12-01

Except for a few localities, seismicity along faults in southern California is generally confined to depths shallower than 15 km. Among faults hosting deep seismicity, the Newport-Inglewood Fault (NIF), which traverses the Los-Angeles basin, has an exceptionally mild surface expression and low deformation rates. Moreover, the NIF structure is not as well resolved as other, less well instrumented faults because of poor signal-to-noise ratio. Here we use data from three temporary dense seismic arrays, which were deployed for exploration purposes and contain up to several thousands of vertical geophones, to investigate the properties of deep seismicity beneath Long-Beach (LB), Compton and Santa-Fe Springs (SFS). The latter is located 15 km northeast of the NIF, presumably above a major detachment fault underthrusting the basin.Event detection is carried out using a new approach for microseismic multi-channel picking, in which downward-continued data are back-projected onto the volume beneath the arrays, and locations are derived from statistical analysis of back-projection images. Our technique reveals numerous, previously undetected events along the NIF, and confirms the presence of an active shallow structure gently dipping to the north beneath SFS. Seismicity characteristics vary along the NIF strike and dip. While LB seismicity is uncorrelated with the mapped trace of the NIF, Compton seismicity illuminates a sub-vertical fault that extends down to about 20 km. This result, along with the reported high flux of mantle Helium along the NIF (Boles et al., 2015), suggests that the NIF is deeply rooted and acts as a major conduit for mantle fluids. We find that the LB size distribution obeys the typical power-law at shallow depths, but falls off exponentially for events occurring below 20 km. Because deep seismicity occurs uniformly beneath LB, this transition is attributed to a reduction in seismic asperity density with increasing depth, consistent with a transition

Mesozoic mafic dikes from the Shandong Peninsula, North China Craton: Petrogenesis and tectonic implications

International Nuclear Information System (INIS)

Liu Shen; Hu Ruizhong; Zhao Junhong; Feng Caixia; Zou, Haibo

2006-01-01

Mesozoic mafic dikes are widely distributed in Luxi (Mengyin and Zichuan) and Jiaodong regions of the Shandong Peninsula, China, providing an opportunity of investigating the nature of the lost lithospheric mantle beneath the North China Craton (NCC). The mafic dikes are characterized by strong depletion in high field strength elements (HFSE), enrichment in light rare earth elements (LREE), highly variable Th/U ratios, high initial ( 87 Sr/ 86 Sr) i (0.7050-0.7099) and negative ε Nd (T) (-6.0 to -17.6). They were derived from melting of metasomatized portions of the subcontinental lithospheric mantle, followed by fractionation of clinopyroxenes. The similarity in Nd isotopic compositions between the Mengyin gabbro dikes and the Paleozoic peridotite xenoliths suggests that ancient lithospheric mantle was still retained at 120 Ma below Mengyin, although the ancient lithospheric mantle in many other places beneath NCC had been severely modified. There might be multiple enrichment events in the lithospheric mantle. An early-stage (before or during Paleozoic) rutile-rich metasomatism affected the lithospheric mantle below Mengyin, Jiaodong and Zichuan. Since then, the lithospheric mantle beneath Mengyin was isolated. A late-stage metasomatism by silicate melts modified the lithospheric mantle beneath Jiaodong and Zichuan but not Mengyin. The removal of the enriched lithospheric mantle and the generation of the mafic dikes may be mainly related to the convective overturn accompanying Jurassic-Cretaceous subduction of the paleo-Pacific plate. (author)

Melt cooling by bottom flooding: The experiment CometPC-H3. Ex-vessel core melt stabilization research

International Nuclear Information System (INIS)

Alsmeyer, H.; Cron, T.; Merkel, G.; Schmidt-Stiefel, S.; Tromm, W.; Wenz, T.

2003-03-01

The CometPC-H3 experiment was performed to investigate melt cooling by water addition to the bottom of the melt. The experiment was performed with a melt mass of 800 kg, 50% metal and 50% oxide, and 300 kW typical decay heat were simulated in the melt. As this was the first experiment after repair of the induction coil, attention was given to avoid overload of the induction coil and to keep the inductor voltage below critical values. Therefore, the height of the sacrificial concrete layer was reduced to 5 cm only, and the height of the porous concrete layers was also minimized to have a small distance and good coupling between heated melt and induction coil. After quite homogeneous erosion of the upper sacrificial concrete layer, passive bottom flooding started from the porous concrete after 220 s with 1.3 liter water/s. The melt was safely stopped, arrested and cooled. The porous, water filled concrete was only slightly attacked by the hot melt in the upper 25 mm of one sector of the coolant device. The peak cooling rate in the early contact phase of coolant water and melt was 4 MW/m 2 , and exceeded the decay heat by one order of magnitude. The cooling rate remarkably dropped, when the melt was covered by the penetrating water and a surface crust was formed. Volcanic eruptions from the melt during the solidification process were observed from 360 - 510 s and created a volcanic dome some 25 cm high, but had only minor effect on the generation of a porous structure, as the expelled melt solidified mostly with low porosity. Unfortunately, decay heat simulation in the melt was interrupted at 720 s by an incorrect safety signal, which excluded further investigation of the long term cooling processes. At that time, the melt was massively flooded by a layer of water, about 80 cm thick, and coolant water inflow was still 1 l/s. The melt had reached a stable situation: Downward erosion was stopped by the cooling process from the water filled, porous concrete layer. Top

Are diamond-bearing Cretaceous kimberlites related to shallow-angle subduction beneath western North America?

Science.gov (United States)

Currie, C. A.; Beaumont, C.

2009-05-01

The origin of deep-seated magmatism (in particular, kimberlites and lamproites) within continental plate interiors remains enigmatic in the context of plate tectonic theory. One hypothesis proposes a relationship between kimberlite occurrence and lithospheric subduction, such that a subducting plate releases fluids below a continental craton, triggering melting of the deep lithosphere and magmatism (Sharp, 1974; McCandless, 1999). This study provides a quantitative evaluation of this hypothesis, focusing on the Late Cretaceous- Eocene (105-50 Ma) kimberlites and lamproites of western North America. These magmas were emplaced along a corridor of Archean and Proterozoic lithosphere, 1000-1500 km inboard of the plate margin separating the subducting Farallon Plate and continental North America Plate. Kimberlite-lamproite magmatism coincides with tectonic events, including the Laramide orogeny, shut-down of the Sierra Nevada arc, and eastward migration of volcanism, that are commonly attributed to a change in Farallon Plate geometry to a shallow-angle trajectory (subduction that places the Farallon Plate beneath the western edge of the cratonic interior of North America. This geometry is consistent with the observed continental dynamic subsidence that lead to the development of the Western Interior Seaway. The models also show that the subducting plate has a cool thermal structure, and subducted hydrous minerals (serpentine, phengite and phlogopite) remain stable to more than 1200 km from the trench, where they may break down and release fluids that infiltrate the overlying craton lithosphere. This is supported by geochemical studies that indicate metasomatism of the Colorado Plateau and Wyoming craton mantle lithosphere by an aqueous fluid and/or silicate melt with a subduction signature. Through Cretaceous shallow-angle subduction, the Farallon Plate was in a position to mechanically and chemically interact with North American craton lithosphere at the time of

Model of interfacial melting

DEFF Research Database (Denmark)

Mouritsen, Ole G.; Zuckermann, Martin J.

1987-01-01

A two-dimensional model is proposed to describe systems with phase transitions which take place in terms of crystalline as well as internal degrees of freedom. Computer simulation of the model shows that the interplay between the two sets of degrees of freedom permits observation of grain-boundar......-boundary formation and interfacial melting, a nonequilibrium process by which the system melts at the boundaries of a polycrystalline domain structure. Lipid membranes are candidates for systems with pronounced interfacial melting behavior....

A Bed-Deformation Experiment Beneath Engabreen, Norway

Science.gov (United States)

Iverson, N. R.; Hooyer, T. S.; Fischer, U. H.; Cohen, D.; Jackson, M.; Moore, P. L.; Lappegard, G.; Kohler, J.

2001-12-01

Although deformation of sediment beneath ice masses may contribute to their motion and may sometimes enable fast glacier flow, both the kinematics and mechanics of deformation are controversial. This controversy stems, in part, from subglacial measurements that are difficult to interpret. Measurements have been made either beneath ice margins or remotely through boreholes with interpretive limitations caused by uncertain instrument position and performance, uncertain sediment thickness and bed geometry, and unknown disturbance of the bed and stress state by drilling. We have used a different approach made possible by the Svartisen Subglacial Laboratory, which enables human access to the bed of Engabreen, Norway, beneath 230 m of temperate ice. A trough (2 m x 1.5 m x 0.4 m deep) was blasted in the rock bed and filled with sediment (75 percent sand and gravel, 20 percent silt, 5 percent clay). Instruments were placed in the sediment to record shear deformation (tiltmeters), dilation and contraction, total normal stress, and pore-water pressure. Pore pressure was manipulated by feeding water to the base of the sediment with a high-pressure pump, operated in a rock tunnel 4 m below the bed surface. After irregular deformation during closure of ice on the sediment, shear deformation and volume change stopped, and total normal stress became constant at 2.2 MPa. Subsequent pump tests, which lasted several hours, induced pore-water pressures greater than 70 percent of the total normal stress and resulted in shear deformation over most of the sediment thickness with attendant dilation. Ice separated from the sediment when effective normal stress was lowest, arresting shear deformation. Displacement profiles during pump tests were similar to those observed by Boulton and co-workers at Breidamerkurjökull, Iceland, with rates of shear strain increasing upward toward the glacier sole. Such deformation does not require viscous deformation resistance and is expected in a

Evolution of the East Philippine Arc: experimental constraints on magmatic phase relations and adakitic melt formation

Science.gov (United States)

Coldwell, B.; Adam, J.; Rushmer, T.; MacPherson, C. G.

2011-10-01

Piston-cylinder experiments on a Pleistocene adakite from Mindanao in the Philippines have been used to establish near-liquidus and sub-liquidus phase relationships relevant to conditions in the East Philippines subduction zone. The experimental starting material belongs to a consanguineous suite of adakitic andesites. Experiments were conducted at pressures from 0.5 to 2 GPa and temperatures from 950 to 1,150°C. With 5 wt. % of dissolved H2O in the starting mix, garnet, clinopyroxene and orthopyroxene are liquidus phases at pressures above 1.5 GPa, whereas clinopyroxene and orthopyroxene are liquidus (or near-liquidus) phases at pressures 1.5 GPa) and subsequently involved the lower pressure fractionation of amphibole, plagioclase and subordinate clinopyroxene. Thus, the distinctive Y and HREE depletions of the andesitic adakites (which distinguish them from associated non-adakitic andesites) must be established relatively early in the fractionation process. Our experiments show that this early fractionation must have occurred at pressures >1.5 GPa and, thus, deeper than the Mindanao Moho. Published thermal models of the Philippine Sea Plate preclude a direct origin by melting of the subducting ocean crust. Thus, our results favour a model whereby basaltic arc melt underwent high-pressure crystal fractionation while stalled beneath immature arc lithosphere. This produced residual magma of adakitic character which underwent further fractionation at relatively low (i.e. crustal) pressures before being erupted.

Dynamic fragmentation of laser shock-melted tin: experiment and modelling

Energy Technology Data Exchange (ETDEWEB)

De Resseguier, T. [CNRS ENSMA, Lab Combust and Deton, F-86961 Futuroscope (France); Signor, L.; Dragon, A. [CNRS ENSMA, Mecan and Phys Mat Lab, F-86961 Futuroscope (France); Signor, L.; Roy, G. [CEA Valduc, 21 - Is-sur-Tille (France)

2010-07-01

Dynamic fragmentation of shock-loaded metals is an issue of considerable importance for both basic science and a variety of technological applications, such as pyrotechnics or inertial confinement fusion, the latter involving high energy laser irradiation of thin metallic shells. Whereas spall fracture in solid materials has been extensively studied for many years, little data can be found yet about the evolution of this phenomenon after partial or full melting on compression or on release. Here, we present an investigation of dynamic fragmentation in laser shock-melted tin, from the 'micro-spall' process (ejection of a cloud of fine droplets) occurring upon reflection of the compressive pulse from the target free surface, to the late rupture observed in the un-spalled melted layer (leading to the formation of larger spherical fragments). Experimental results consist of time-resolved velocity measurements and post-shock observations of recovered targets and fragments. They provide original information regarding the loss of tensile strength associated with melting, the cavitation mechanism likely to occur in the melted metal, the sizes of the subsequent fragments and their ejection velocities. A theoretical description based on an energetic approach adapted to the case of a liquid metal is implemented as a failure criterion in a one-dimensional hydro-code including a multi-phase equation of state for tin. The resulting predictions of the micro-spall process are compared with experimental data. In particular, the use of a new experimental technique to quantify the fragment size distributions leads to a much better agreement with theory than previously reported. Finally, a complementary approach focused on cavitation is proposed to evaluate the role of this phenomenon in the fragmentation of the melted metal. (authors)

Baseline mapping study of the Steed Pond aquifer and vadose zone beneath A/M Area, Savannah River Site, Aiken, South Carolina

International Nuclear Information System (INIS)

Jackson, D.G. Jr.

2000-01-01

This report presents the second phase of a baseline mapping project conducted for the Environmental Restoration Department (ERD) at Savannah River Site. The purpose of this second phase is to map the structure and distribution of mud (clay and silt-sized sediment) within the vadose zone beneath A/M Area. The results presented in this report will assist future characterization and remediation activities in the vadose zone and upper aquifer zones in A/M Area

Can Nano-Particle Melt below the Melting Temperature of Its Free Surface Partner?

International Nuclear Information System (INIS)

Sui Xiao-Hong; Qin Shao-Jing; Wang Zong-Guo; Kang Kai; Wang Chui-Lin

2015-01-01

The phonon thermal contribution to the melting temperature of nano-particles is inspected. The discrete summation of phonon states and its corresponding integration form as an approximation for a nano-particle or for a bulk system have been analyzed. The discrete phonon energy levels of pure size effect and the wave-vector shifts of boundary conditions are investigated in detail. Unlike in macroscopic thermodynamics, the integration volume of zero-mode of phonon for a nano-particle is not zero, and it plays an important role in pure size effect and boundary condition effect. We find that a nano-particle will have a rising melting temperature due to purely finite size effect; a lower melting temperature bound exists for a nano-particle in various environments, and the melting temperature of a nano-particle with free boundary condition reaches this lower bound. We suggest an easy procedure to estimation the melting temperature, in which the zero-mode contribution will be excluded, and only several bulk quantities will be used as input. We would like to emphasize that the quantum effect of discrete energy levels in nano-particles, which is not present in early thermodynamic studies on finite size corrections to melting temperature in small systems, should be included in future researches. (condensed matter: structural, mechanical, and thermal properties)

Ps mantle transition zone imaging beneath the Colorado Rocky Mountains: Evidence for an upwelling hydrous mantle

Science.gov (United States)

Zhang, Zhu; Dueker, Kenneth G.; Huang, Hsin-Hua

2018-06-01

We analyze teleseismic P-to-S conversions for high-resolution imaging of the mantle transition zone beneath the Colorado Rocky Mountains using data from a dense PASSCAL seismic broadband deployment. A total of 6,021 P-to-S converted receiver functions are constructed using a multi-channel minimum-phase deconvolution method and migrated using the common converted point technique with the 3-D teleseismic P- and S-wave tomography models of Schmandt and Humphreys (2010). The image finds that the average depths of the 410-km discontinuity (the 410) and 660-km discontinuity (the 660) at 408 ± 1.9 km and 649 ± 1.6 km respectively. The peak-to-peak topography of both discontinuities is 33 km and 27 km respectively. Additionally, prominent negative polarity phases are imaged both above and below the 410. To quantify the mean properties of the low-velocity layers about 410 km, we utilize double gradient layer models parameterization to fit the mean receiver function waveform. This waveform fitting is accomplished as a grid-search using anelastic synthetic seismograms. The best-fitting model reveals that the olivine-wadsleyite phase transformation width is 21 km, which is significantly larger than anhydrous mineral physics prediction (4-10 km) (Smyth and Frost, 2002). The findings of a wide olivine-wadsleyite phase transformation and the negative polarity phases above and below the 410, suggest that the mantle, at least in the 350-450 km depth range, is significantly hydrated. Furthermore, a conspicuous negative polarity phase below the 660 is imaged in high velocity region, we speculate the low velocity layer is due to dehydration flux melting in an area of convective downwelling. Our interpretation of these results, in tandem with the tomographic image of a Farallon slab segment at 800 km beneath the region (Schmandt and Humphreys, 2010), is that hydrous and upwelling mantle contributes to the high-standing Colorado Rocky Mountains.

Radiant heat evaluation of concrete: a study of the erosion of concrete due to surface heating

International Nuclear Information System (INIS)

Chu, T.Y.

1978-01-01

Experiments were carried out to investigate the erosion of concrete under high surface heat flux in connection with the core-melt/concrete interaction studies. The dominate erosion mechanism was found to be melting at the surface accompanied by chemical decomposition of the concrete beneath the melt-solid interface. The erosion process reaches a steady state after an initial transient. The steady state is characterized by an essentially constant erosion rate at the surface and a nonvarying (with respect to the moving melt interface) temperature distribution within the concrete. For the range of incident heat flux 64 W/cm 2 to 118 W/cm 2 , the corresponding steady state erosion rate varies from approximately 8 cm/hr to 23 cm/hr. A simple ablation/melting model is proposed for the erosion process. The model was found to be able to correlate all temperature responses at various depths from all tests at large times and for temperatures above approximately 250 0 C

Melt spreading code assessment, modifications, and initial application to the EPR core catcher design

International Nuclear Information System (INIS)

Farmer, M.T.; Basu, S.

2009-01-01

The Evolutionary Power Reactor (EPR) is a 1,600-MWe Pressurized Water Reactor (PWR) that is undergoing a design certification review by the U.S. Nuclear Regulatory Commission (NRC). The EPR severe accident design philosophy is predicated upon the fact that the projected power rating results in a narrow margin for in-vessel melt retention by external flooding. As a result, the design addresses ex-vessel core melt stabilization using a mitigation strategy that includes: 1) an external core melt retention system to temporarily hold core melt released from the vessel; 2) a layer of 'sacrificial' material that is admixed with the melt while in the core melt retention system; 3) a melt plug that, when failed, provides a pathway for the mixture to spread to a large core spreading chamber; and finally, 4) cooling and stabilization of the spread melt by controlled top and bottom flooding. The melt spreading process relies heavily on inertial flow of a low-viscosity admixed melt to a segmented spreading chamber, and assumes that the melt mass will be distributed to a uniform height in the chamber. The spreading phenomenon thus needs to be modeled properly in order to adequately assess the EPR design. The MELTSPREAD code, developed at Argonne National Laboratory, can model segmented, and both uniform and non-uniform spreading. The NRC is using MELTSPREAD to evaluate melt spreading in the EPR design. The development of MELTSPREAD ceased in the early 1990's, and so the code was first assessed against the more contemporary spreading database and code modifications, as warranted, were carried out before performing confirmatory plant calculations. This paper provides principle findings from the MELTSPREAD assessment activities and resulting code modifications, and also summarizes the results of initial scoping calculations for the EPR plant design and preliminary plant analyses, along with the plan for performing the final set of plant calculations including sensitivity studies

Force induced DNA melting

International Nuclear Information System (INIS)

Santosh, Mogurampelly; Maiti, Prabal K

2009-01-01

When pulled along the axis, double-strand DNA undergoes a large conformational change and elongates by roughly twice its initial contour length at a pulling force of about 70 pN. The transition to this highly overstretched form of DNA is very cooperative. Applying a force perpendicular to the DNA axis (unzipping), double-strand DNA can also be separated into two single-stranded DNA, this being a fundamental process in DNA replication. We study the DNA overstretching and unzipping transition using fully atomistic molecular dynamics (MD) simulations and argue that the conformational changes of double-strand DNA associated with either of the above mentioned processes can be viewed as force induced DNA melting. As the force at one end of the DNA is increased the DNA starts melting abruptly/smoothly above a critical force depending on the pulling direction. The critical force f m , at which DNA melts completely decreases as the temperature of the system is increased. The melting force in the case of unzipping is smaller compared to the melting force when the DNA is pulled along the helical axis. In the case of melting through unzipping, the double-strand separation has jumps which correspond to the different energy minima arising due to sequence of different base pairs. The fraction of Watson-Crick base pair hydrogen bond breaking as a function of force does not show smooth and continuous behavior and consists of plateaus followed by sharp jumps.

Melting in super-earths.

Science.gov (United States)

Stixrude, Lars

2014-04-28

We examine the possible extent of melting in rock-iron super-earths, focusing on those in the habitable zone. We consider the energetics of accretion and core formation, the timescale of cooling and its dependence on viscosity and partial melting, thermal regulation via the temperature dependence of viscosity, and the melting curves of rock and iron components at the ultra-high pressures characteristic of super-earths. We find that the efficiency of kinetic energy deposition during accretion increases with planetary mass; considering the likely role of giant impacts and core formation, we find that super-earths probably complete their accretionary phase in an entirely molten state. Considerations of thermal regulation lead us to propose model temperature profiles of super-earths that are controlled by silicate melting. We estimate melting curves of iron and rock components up to the extreme pressures characteristic of super-earth interiors based on existing experimental and ab initio results and scaling laws. We construct super-earth thermal models by solving the equations of mass conservation and hydrostatic equilibrium, together with equations of state of rock and iron components. We set the potential temperature at the core-mantle boundary and at the surface to the local silicate melting temperature. We find that ancient (∼4 Gyr) super-earths may be partially molten at the top and bottom of their mantles, and that mantle convection is sufficiently vigorous to sustain dynamo action over the whole range of super-earth masses.

Buckling instabilities of subducted lithosphere beneath the transition zone

NARCIS (Netherlands)

Ribe, N.M.; Stutzmann, E.; Ren, Y.; Hilst, R.D. van der

2007-01-01

A sheet of viscous fluid poured onto a surface buckles periodically to generate a pile of regular folds. Recent tomographic images beneath subduction zones, together with quantitative fluid mechanical scaling laws, suggest that a similar instability can occur when slabs of subducted oceanic

Oceanic provenance of lithospheric mantle beneath Lower Silesia (SW Poland) and the two kinds of its "Fe-metasomatism"

Science.gov (United States)

Puziewicz, Jacek; Matusiak-Małek, Magdalena; Ntaflos, Theodoros; Kukuła, Anna; Ćwiek, Mateusz

2016-04-01

Our recent studies (Puziewicz et al. 2015, IJES 104:1913-1924, and references therein) show that the subcontinental lithospheric mantle (SCLM) beneath Lower Silesia (SW Poland) and neighbouring part of Upper Lusatia (SE Germany) is dominated by harzburgites. Part of them contain small amounts of clinopyroxene which, despite its primary textural appearance, is a late addition to the protoliths which are residues after extensive (up to 30 %) partial melting. This clinopyroxene was added to the harzburgites in Cenozoic times by alkaline basaltic melts migrating upwards from their asthenospheric sources during rifting in the Variscan foreland of the Alpine-Carpathian chain. The pre-rifting history of the SCLM beneath the region is thus recorded in the olivine and orthopyroxene. The forsterite content in olivine divides the Lower Silesian harzburgites into two groups: A (olivine Fo 90.5 - 92.0), and B (olivine Fo 84.0 - 90.0; for data see Puziewicz et al. 2015, op. cit.). The Al content in orthopyroxene is low and similar in both A and part of B harzburgites, called B1 in the following. The orthopyroxene occurring in the B1 harzburgites contains typically 0.05 - 0.10 atoms of Al per formula unit (corresponding to 0.5 - 2.5 wt. % Al2O3), although slightly lower (down to 0.02 a pfu) and slightly higher (up to 0.13 a pfu) Al contents occur in subordinate number of samples. The Al content in the B1 orthopyroxene is not correlated with forsterite content in coexisting olivine. The B2 harzburgites occur only in one site (Księginki). They contain orthopyroxene which Al content exhibits negative correlation with forsterite content in coexisting olivine. The most Al -rich orthopyroxene (0.24 atoms of Al pfu, corresponding to ca. 5.7 wt % Al2O3) coexists with olivine Fo 86.5 in Księginki. The low contents of Al in orthopyroxene is specific for the Lower Silesian/Upper Lusatian domain of European lithospheric mantle. The Al-poor mantle domain below Lower Silesia and upper

Melting under shock compression

International Nuclear Information System (INIS)

Bennett, B.I.

1980-10-01

A simple model, using experimentally measured shock and particle velocities, is applied to the Lindemann melting formula to predict the density, temperature, and pressure at which a material will melt when shocked from room temperature and zero pressure initial conditions

Electric melting furnace of solidifying radioactive waste by utilizing magnetic field and melting method

International Nuclear Information System (INIS)

Igarashi, Hiroshi.

1990-01-01

An electric melting furnace for solidification of radioactive wastes utilizing magnetic fields in accordance with the present invention comprises a plurality of electrodes supplying AC current to molten glass in a glass melting furnace and a plurality of magnetic poles for generating AC magnetic fields. Interactions between the current and the magnetic field, generated forces in the identical direction in view of time in the molten glass. That is, forces for promoting the flow of molten glass in the melting furnace are resulted due to the Fleming's left-hand rule. As a result, the following effects can be obtained. (1) The amount of heat ransferred from the molten glass to the starting material layer on the molten surface is increased to improve the melting performance. (2) For an identical melting performance, the size and the weight of the melting furnace can be reduced to decrease the amount of secondary wastes when the apparatus-life is exhausted. (3) Bottom deposits can be suppressed and prevented from settling and depositing to the reactor bottom by the promoted flow in the layer. (4) Further, the size of auxiliary electrodes for directly supplying electric current to heat the molten glass near the reactor bottom can be decreased. (I.S.)

Finite element modeling of melting and fluid flow in the laser-heated diamond-anvil cell

Science.gov (United States)

Gomez-Perez, N.; Rodriguez, J. F.; McWilliams, R. S.

2017-04-01

The laser-heated diamond anvil cell is widely used in the laboratory study of materials behavior at high-pressure and high-temperature, including melting curves and liquid properties at extreme conditions. Laser heating in the diamond cell has long been associated with fluid-like motion in samples, which is routinely used to determine melting points and is often described as convective in appearance. However, the flow behavior of this system is poorly understood. A quantitative treatment of melting and flow in the laser-heated diamond anvil cell is developed here to physically relate experimental motion to properties of interest, including melting points and viscosity. Numerical finite-element models are used to characterize the temperature distribution, melting, buoyancy, and resulting natural convection in samples. We find that continuous fluid motion in experiments can be explained most readily by natural convection. Fluid velocities, peaking near values of microns per second for plausible viscosities, are sufficiently fast to be detected experimentally, lending support to the use of convective motion as a criterion for melting. Convection depends on the physical properties of the melt and the sample geometry and is too sluggish to detect for viscosities significantly above that of water at ambient conditions, implying an upper bound on the melt viscosity of about 1 mPa s when convective motion is detected. A simple analytical relationship between melt viscosity and velocity suggests that direct viscosity measurements can be made from flow speeds, given the basic thermodynamic and geometric parameters of samples are known.

Flow-induced correlation effects within a linear chain in a polymer melt

NARCIS (Netherlands)

Stepanyan, R.; Slot, J.J.M.; Molenaar, J.; Tchesnokov, M.A.

2005-01-01

A framework for a consistent description of the flow-induced correlation effects within a linear polymer chain in a melt is proposed. The formalism shows how correlations between chain segments in the flow can be incorporated into a hierarchy of distribution functions for tangent vectors. The

Molecular thermodynamics of polymer melts at interfaces

International Nuclear Information System (INIS)

Theodorou, D.N.

1988-09-01

A lattice model is developed for the prediction of structure and thermodynamic properties at free polymer melt surfaces and polymer melt/solid interfaces. Density variations in the interfacial region are taken into account by introducing voids in the lattice, in the spirit of the equation of state theory of Sanchez and Lacombe. Intramolecular energy (chain stiffness) effects are explicitly incorporated. The model is derived through a rigorous statistical mechanical and thermodynamic analysis, which is based on the concept of availability. Two cases are considered: ''full equilibrium,'' whereby the interfacial polymer is taken as free to exchange heat, work and mass with a bulk polymer phase at given temperature and pressure; and ''restricted equilibrium,'' whereby a thin polymer film is allowed to equilibrate locally in response to ambient temperature and pressure, but in which chains do not necessarily have the same chemical potential as in the unconstrained bulk. Techniques are developed for calculating surface tension, adhesion tension, density profiles, chain shape, bond orientation, as well as the distribution of segments of various orders in the interfacial region. 28 refs., 6 figs

Attenuation and Velocity Structure in Spain and Morocco: Distinguishing Between Water, Temperature, and Partial Melt

Science.gov (United States)

Bezada, M. J.; Humphreys, E.

2014-12-01

Temperature, melt fraction, and water content affect seismic velocity and attenuation differently. Both are sensitive to temperature, but velocity is more sensitive to melt fraction and attenuation is thought to be more sensitive to water content. For these reasons, combining attenuation measurements with tomographic imaging of velocity structure can help untangle these fields and better resolve lithospheric structure and physical state. We map variations in attenuation beneath Spain and northern Morocco using teleseismic data generated by more than a dozen teleseismic deep-focus earthquakes recorded on a dense array of stations. For each event, we first estimate the source from the best quality recordings. We then apply an attenuation operator to the source estimate, using a range of t* values, to match the record at each station. We invert for a smooth map of t* from the ensemble of measurements. The spatial patterns in t* correlate very well with the tectonic domains in Spain and Morocco. In particular, areas in Spain that resisted deformation during the Variscan and Alpine orogenies produce very little attenuation. Comparing the attenuation map with seismic velocity structure we find that, in Morocco, some areas with strong low-velocity anomalies and recent volcanism do not cause high attenuation. These observations suggest that water content is a more likely cause for seismic attenuation in the study area than temperature, and that the non-attenuative low-velocity anomalies in Morocco are produced by partial mel.

Magnetotelluric Exploration of the Aleutian Arc: Mantle Melt Generation and Migration beneath Okmok Caldera

Science.gov (United States)

Zelenak, Georgianna

In this thesis a Kremer-Grest polymer model was used to investigate the mechanical response of a polymer glass critically depending on the chain length. Molecular dynamic simulations were done for tensile deformation of various polymeric glasses. It was found that during the extension, polymer glasses showed different mechanical responses depending on their molecular weight distribution. Systems with enough long chains could undergo large extension, and systems dominated by short chains would show premature breakup. Detailed analyses showed that the bond length increased during necking on the ductile systems. These results could be understood in terms of the recent molecular model1 and demonstrate the role of chain networking.

Origin of migmatites by deformation-enhanced melt infiltration of orthogneiss: a new model based on quantitative microstructural analysis

Czech Academy of Sciences Publication Activity Database

Hasalová, P.; Schulmann, K.; Lexa, O.; Štípská, P.; Hrouda, F.; Ulrich, Stanislav; Haloda, J.; Týcová, P.

2008-01-01

Roč. 26, č. 1 (2008), s. 29-53 ISSN 0263-4929 Grant - others:GA AV ČR(CZ) IAA3111401; GA ČR(CZ) GA205/04/2065 Institutional research plan: CEZ:AV0Z30120515 Keywords : crystal size distribution * melt infiltration * melt topology * migmatites * quantitative textural analysis Subject RIV: DB - Geology ; Mineralogy Impact factor: 3.340, year: 2008

Upper Mantle Shear Wave Structure Beneath North America From Multi-mode Surface Wave Tomography

Science.gov (United States)

Yoshizawa, K.; Ekström, G.

2008-12-01

The upper mantle structure beneath the North American continent has been investigated from measurements of multi-mode phase speeds of Love and Rayleigh waves. To estimate fundamental-mode and higher-mode phase speeds of surface waves from a single seismogram at regional distances, we have employed a method of nonlinear waveform fitting based on a direct model-parameter search using the neighbourhood algorithm (Yoshizawa & Kennett, 2002). The method of the waveform analysis has been fully automated by employing empirical quantitative measures for evaluating the accuracy/reliability of estimated multi-mode phase dispersion curves, and thus it is helpful in processing the dramatically increasing numbers of seismic data from the latest regional networks such as USArray. As a first step toward modeling the regional anisotropic shear-wave velocity structure of the North American upper mantle with extended vertical resolution, we have applied the method to long-period three-component records of seismic stations in North America, which mostly comprise the GSN and US regional networks as well as the permanent and transportable USArray stations distributed by the IRIS DMC. Preliminary multi-mode phase-speed models show large-scale patterns of isotropic heterogeneity, such as a strong velocity contrast between the western and central/eastern United States, which are consistent with the recent global and regional models (e.g., Marone, et al. 2007; Nettles & Dziewonski, 2008). We will also discuss radial anisotropy of shear wave speed beneath North America from multi-mode dispersion measurements of Love and Rayleigh waves.

Melting in trivalent metal chlorides

International Nuclear Information System (INIS)

Saboungi, M.L.; Price, D.L.; Scamehorn, C.; Tosi, M.P.

1990-11-01

We report a neutron diffraction study of the liquid structure of YCl 3 and combine the structural data with macroscopic melting and transport data to contrast the behaviour of this molten salt with those of SrCl 2 , ZnCl 2 and AlCl 3 as prototypes of different melting mechanisms for ionic materials. A novel melting mechanism for trivalent metal chlorides, leading to a loose disordered network of edge-sharing octahedral units in the liquid phase, is thereby established. The various melting behaviours are related to bonding character with the help of Pettifor's phenomenological chemical scale. (author). 25 refs, 4 figs, 3 tabs

Tomography of the upper mantle beneath the African/Iberian collision zone

Science.gov (United States)

Mickael, B.; Nolet, G.; Villasenor, A.; Josep, G.; Thomas, C.

2013-12-01

During Cenozoic, geodynamics of the western Mediterranean domain has been characterized by a complex history of subduction of Mesozoic oceanic lithosphere. The final stage of these processes is proposed to have led to the development of the Calabria and Gibraltar arcs, whose formation is still under debate. In this study we take advantage of the dense broadband-station networks now available in Alborán Sea region, to develop a high-resolution 3D tomographic P velocity model of the upper mantle beneath the African/Iberian collision zone that will bring new constraints on the past dynamics of this zone. The model is based on 13200 teleseismic arrival times recorded between 2008 and 2012 at 279 stations for which cross-correlation delays are measured with a new technique in different frequency bands centered between 0.03 and 1.0 Hz, and interpreted using multiple frequency tomography. Our model shows, beneath Alborán Sea, a strong (~ 4%) fast vertically dipping anomaly observed to at least 650 km depth. The arched shape of this anomaly and its extent at depth are coherent with a lithospheric slab, thus favoring the hypothesis of a westward consumption of the Ligurian ocean slab by roll-back during Cenozoic. In addition to this fast anomaly in the deep upper-mantle, several high intensity slow anomalies are widely observed in the lithosphere and asthenosphere beneath Morocco and southern Spain. These anomalies are correlated at surface with the position of the orogens (Rif and Atlas) and with Cenozoic volcanic fields. We thus confirm the presence, beneath Morocco, of an anomalous (hot) upper mantle, with piece of evidence for a lateral connection with the Canary volcanic islands, likely indicating a lateral spreading of the Canary plume to the east.

Nutrient transport and transformation beneath an infiltration basin

Science.gov (United States)

Sumner, D.M.; Rolston, D.E.; Bradner, L.A.

1998-01-01

Field experiments were conducted to examine nutrient transport and transformation beneath an infiltration basin used for the disposal of treated wastewater. Removal of nitrogen from infiltrating water by denitrification was negligible beneath the basin, probably because of subsurface aeration as a result of daily interruptions in basin loading. Retention of organic nitrogen in the upper 4.6 m of the unsaturated zone (water table depth of approximately 11 m) during basin loading resulted in concentrations of nitrate as much as 10 times that of the applied treated wastewater, following basin 'rest' periods of several weeks, which allowed time for mineralization and nitrification. Approximately 90% of the phosphorus in treated wastewater was removed within the upper 4.6 m of the subsurface, primarily by adsorption reactions, with abundant iron and aluminum oxyhydroxides occurring as soil coatings. A reduction in the flow rate of infiltrating water arriving at the water table may explain the accumulation of relatively coarse (>0.45 ??m), organic forms of nitrogen and phosphorus slightly below the water table. Mineralization and nitrification reactions at this second location of organic nitrogen accumulation contributed to concentrations of nitrate as much as three times that of the applied treated wastewater. Phosphorus, which accumulated below the water table, was immobilized by adsorption or precipitation reactions during basin rest periods.Field experiments were conducted to examine nutrient transport and transformation beneath an infiltration basin used for the disposal of treated wastewater. Removal of nitrogen from infiltrating water by denitrification was negligible beneath the basin, probably because of subsurface aeration as a result of daily interruptions in basin loading. Retention of organic nitrogen in the upper 4.6 m of the unsaturated zone (water table depth of approximately 11 m) during basin loading resulted in concentrations of nitrate as much as 10

Fossil plume head beneath the Arabian lithosphere?

Science.gov (United States)

Stein, Mordechai; Hofmann, Albrecht W.

1992-12-01

Phanerozoic alkali basalts from Israel, which have erupted over the past 200 Ma, have isotopic compositions similar to PREMA ("prevalent mantle") with narrow ranges of initial ɛ Nd(T) = +3.9-+5.9; 87Sr/ 86Sr(T)= 0.70292-0.70334; 206Pb/ 204Pb(T)= 18.88-19.99; 207Pb/ 204Pb(T)= 15.58-15.70; and 208Pb/ 204Pb(T)= 38.42-39.57. Their Nb/U(43 ± 9) and Ce/Pb(26 ± 6) ratios are identical to those of normal oceanic basalts, demonstrating that the basalts are essentially free of crustal contamination. Overall, the basalts are chemically and isotopically indistinguishable from many ordinary plume basalts, but no plume track can be identified. We propose that these and other, similar, magmas from the Arabian plate originated from a "fossilized" head of a mantle plume, which was unable to penetrate the continental lithosphere and was therefore trapped and stored beneath it. The plume head was emplaced some time between the late Proterozoic crust formation and the initiation of the Phanerozoic magmatic cycles. Basalts from rift environments in other continental localities show similar geochemistry to that of the Arabian basalts and their sources may also represent fossil plume heads trapped below the continents. We suggest that plume heads are, in general, characterized by the PREMA isotopic mantle signature, because the original plume sources (which may have HIMU or EM-type composition) have been diluted by overlying mantle material, which has been entrained by the plume heads during ascent. On the Arabian plate, rifting and thinning of the lithosphere caused partial melting of the stored plume, which led to periodic volcanism. In the late Cenozoic, the lithosphere broke up and the Red Sea opened. N-MORB tholeiites are now erupting in the central trough of the Red Sea, where the lithosphere has moved apart and the fossil plume has been exhausted, whereas E-MORBs are erupting in the northern and southern troughs, still tapping the plume reservoir. Fossil plumes, which are

Evolution of deep crustal magma structures beneath Mount Baekdu volcano (MBV) intraplate volcano in northeast Asia

Science.gov (United States)

Rhie, J.; Kim, S.; Tkalcic, H.; Baag, S. Y.

2017-12-01

Heterogeneous features of magmatic structures beneath intraplate volcanoes are attributed to interactions between the ascending magma and lithospheric structures. Here, we investigate the evolution of crustal magmatic stuructures beneath Mount Baekdu volcano (MBV), which is one of the largest continental intraplate volcanoes in northeast Asia. The result of our seismic imaging shows that the deeper Moho depth ( 40 km) and relatively higher shear wave velocities (>3.8 km/s) at middle-to-lower crustal depths beneath the volcano. In addition, the pattern at the bottom of our model shows that the lithosphere beneath the MBV is shallower (interpret the observations as a compositional double layering of mafic underplating and a overlying cooled felsic structure due to fractional crystallization of asthenosphere origin magma. To achieve enhanced vertical and horizontal model coverage, we apply two approaches in this work, including (1) a grid-search based phase velocity measurement using real-coherency of ambient noise data and (2) a transdimensional Bayesian joint inversion using multiple ambient noise dispersion data.

Premixing and steam explosion phenomena in the tests with stratified melt-coolant configuration and binary oxidic melt simulant materials

Energy Technology Data Exchange (ETDEWEB)

Kudinov, Pavel, E-mail: pavel@safety.sci.kth.se; Grishchenko, Dmitry, E-mail: dmitry@safety.sci.kth.se; Konovalenko, Alexander, E-mail: kono@kth.se; Karbojian, Aram, E-mail: karbojan@kth.se

2017-04-01

Highlights: • Steam explosion in stratified melt-coolant configuration is studied experimentally. • Different binary oxidic melt simulant materials were used. • Five spontaneous steam explosions were observed. • Instability of melt-coolant interface and formation of premixing layer was observed. • Explosion strength is influenced by melt superheat and water subcooling. - Abstract: Steam explosion phenomena in stratified melt-coolant configuration are considered in this paper. Liquid corium layer covered by water on top can be formed in severe accident scenarios with (i) vessel failure and release of corium melt into a relatively shallow water pool; (ii) with top flooding of corium melt layer. In previous assessments of potential energetics in stratified melt-coolant configuration, it was assumed that melt and coolant are separated by a stable vapor film and there is no premixing prior to the shock wave propagation. This assumption was instrumental for concluding that the amount of energy that can be released in such configuration is not of safety importance. However, several recent experiments carried out in Pouring and Under-water Liquid Melt Spreading (PULiMS) facility with up to 78 kg of binary oxidic corium simulants mixtures have resulted in spontaneous explosions with relatively high conversion ratios (order of one percent). The instability of the melt-coolant interface, melt splashes and formation of premixing layer were observed in the tests. In this work, we present results of experiments carried out more recently in steam explosion in stratified melt-coolant configuration (SES) facility in order to shed some light on the premixing phenomena and assess the influence of the test conditions on the steam explosion energetics.

Melting of superheated molecular crystals

Science.gov (United States)

Cubeta, Ulyana; Bhattacharya, Deepanjan; Sadtchenko, Vlad

2017-07-01

Melting dynamics of micrometer scale, polycrystalline samples of isobutane, dimethyl ether, methyl benzene, and 2-propanol were investigated by fast scanning calorimetry. When films are superheated with rates in excess of 105 K s-1, the melting process follows zero-order, Arrhenius-like kinetics until approximately half of the sample has transformed. Such kinetics strongly imply that melting progresses into the bulk via a rapidly moving solid-liquid interface that is likely to originate at the sample's surface. Remarkably, the apparent activation energies for the phase transformation are large; all exceed the enthalpy of vaporization of each compound and some exceed it by an order of magnitude. In fact, we find that the crystalline melting kinetics are comparable to the kinetics of dielectric α-relaxation in deeply supercooled liquids. Based on these observations, we conclude that the rate of non-isothermal melting for superheated, low-molecular-weight crystals is limited by constituent diffusion into an abnormally dense, glass-like, non-crystalline phase.

Further studies on melting of radioactive metallic wastes from the dismantling of nuclear installations

International Nuclear Information System (INIS)

Diepenau, H.; Seidler, M.

1991-01-01

Melting of radioactive waste metal from the dismantling/refurbishing of nuclear installations is an acceptable way for nuclear waste recycling. This material can be used for the casting of qualified products such as type A- and type B-waste containers. The results of the melting facility -TAURUS- were used to build the industrial scale melting facility -CARLA- at Siempelkamp. The test results and the longterm-behaviour of the facility showed that the licensing conditions can be respected. The radiation exposure of workers was in the range of the admissible limit for non-exposed people. The radiation exposure of the environment is far below the value of the German Radiation Protection Law. The activity distribution within the product is homogeneous, so that its activity can be measured exactly before it is sent back in the nuclear area. By melting waste copper it is possible to respect the specific limits for unrestricted reuse, whereas for brass the limit for conditioned reuse in the industrial field was reached. Radioactive carbon can only be bound in form of small graphite lamellas or nodules in the cast iron; i.e. radioactive carbon can only be added to the melt as crushed material. During the research programme 2000 Mg of waste steel was melted at industrial scale and mainly products such as shielding blocks and waste containers were produced. 12 figs., 27 tabs., 6 refs

Comparison of partial structures of melts of superionic AgI and CuI and non-superionic AgCl

Energy Technology Data Exchange (ETDEWEB)

Kawakita, Yukinobu [Department of Physics, Faculty of Sciences, Kyushu University, 4-2-1 Ropponmatsu, Fukuoka 810-8560 (Japan); Tahara, Shuta [Department of Condensed Matter Chemistry and Physics, Graduate School of Sciences, Kyushu University, 4-2-1 Ropponmatsu, Chuo-ku, Fukuoka 810-8560 (Japan); Fujii, Hiroyuki [Department of Condensed Matter Chemistry and Physics, Graduate School of Sciences, Kyushu University, 4-2-1 Ropponmatsu, Chuo-ku, Fukuoka 810-8560 (Japan); Kohara, Shinji [Research and Utilization Division, Japan Synchrotron Radiation Research Institute (JASRI, SPring-8), 1-1-1 Koto, Sayo-cho, Sayo-gun, Hyogo 679-5198 (Japan); Takeda, Shin' ichi [Department of Physics, Faculty of Sciences, Kyushu University, 4-2-1 Ropponmatsu, Fukuoka 810-8560 (Japan)

2007-08-22

Neutron and high-energy x-ray diffraction analyses of molten AgI have been performed and the partial structures are discussed in detail with the aid of the structural modelling procedure of the reverse Monte Carlo (RMC) technique by comparison with those of molten CuI and AgCl. It is well known that AgI and CuI have a superionic solid phase below the melting point, in which the cations favour a tetrahedral configuration, while solid AgCl has a rock-salt structure with an octahedral environment around both Ag and Cl atoms. Even in the molten states, there is a significant difference between superionic and non-superionic melts. The cation is located on the triangular plain formed by three iodine ions in molten AgCl and CuI, while molten AgCl favours a 90 deg. Cl-Ag-Cl bond angle, which is understood to maintain a similar local environment to that in the solid state. The atomic configurations of the RMC model suggest that the cation distributions in superionic melts of CuI and AgI exhibit large fluctuations, while Ag ions in the non-superionic melts of AgCl are distributed much more uniformly.

Fragmentation and melting of the seasonal sea ice cover

Science.gov (United States)

Feltham, D. L.; Bateson, A.; Schroeder, D.; Ridley, J. K.; Aksenov, Y.

2017-12-01

Recent years have seen a rapid reduction in the summer extent of Arctic sea ice. This trend has implications for navigation, oil exploration, wildlife, and local communities. Furthermore the Arctic sea ice cover impacts the exchange of heat and momentum between the ocean and atmosphere with significant teleconnections across the climate system, particularly mid to low latitudes in the Northern Hemisphere. The treatment of melting and break-up processes of the seasonal sea ice cover within climate models is currently limited. In particular floes are assumed to have a uniform size which does not evolve with time. Observations suggest however that floe sizes can be modelled as truncated power law distributions, with different exponents for smaller and larger floes. This study aims to examine factors controlling the floe size distribution in the seasonal and marginal ice zone. This includes lateral melting, wave induced break-up of floes, and the feedback between floe size and the mixed ocean layer. These results are then used to quantify the proximate mechanisms of seasonal sea ice reduction in a sea ice—ocean mixed layer model. Observations are used to assess and calibrate the model. The impacts of introducing these processes to the model will be discussed and the preliminary results of sensitivity and feedback studies will also be presented.

Pressure melting and ice skating

Science.gov (United States)

Colbeck, S. C.

1995-10-01

Pressure melting cannot be responsible for the low friction of ice. The pressure needed to reach the melting temperature is above the compressive failure stress and, if it did occur, high squeeze losses would result in very thin films. Pure liquid water cannot coexist with ice much below -20 °C at any pressure and friction does not increase suddenly in that range. If frictional heating and pressure melting contribute equally, the length of the wetted contact could not exceed 15 μm at a speed of 5 m/s, which seems much too short. If pressure melting is the dominant process, the water films are less than 0.08 μm thick because of the high pressures.

Flocculation alters the distribution and flux of melt-water supplied sediments and nutrients in the Arctic

DEFF Research Database (Denmark)

Markussen, Thor Nygaard; Andersen, Thorbjørn Joest; Ernstsen, Verner Brandbyge

In the Arctic, thawing permafrost and increased melting of glaciers are important drivers for changes in fine-grained sediment supply and biogeochemical fluxes from land to sea. Flocculation of particles is a controlling factor for the magnitude of fluxes and deposition rates in the marine...... environment but comparatively little is known about the flocculation processes in the Arctic. We investigated flocculation dynamics from a melt-water river in the inner Disko Fjord, West Greenland. A novel, laser-illuminated camera system significantly improved the particle size measurement capabilities...... and settling tubes were sampled to enable sub-sampling of different floc size fractions. Flocculation was observed during periods with low turbulent shear and also at the front of the fresh water plume resulting in significant volumes of large sized flocs at depth below the plume. The floc sizes and volumes...

Argon Diffusion Measured in Rhyolite Melt at 100 MPa

Science.gov (United States)

Weldon, N.; Edwards, P. M.; Watkins, J. M.; Lesher, C. E.

2016-12-01

Argon diffusivity (D_{Ar} ) controls the rate and length scale of argon exchange between melt and gas phases and is used as a parameter to model noble gas fractionation during magma degassing. D_{Ar} may also be useful in geochronology to estimate the distribution of excess (non-radiogenic) atmospheric argon in lavas. Our measurements of D_{Ar} in molten anhydrous rhyolite near 1000 °C and 100 MPa add to the existing dataset. Using a rapid-quench cold seal pressure apparatus we exposed cylindrical charges drilled from a Miocene rhyolite flow near Buck Mtn., CA to a pure argon atmosphere resulting in a gradually lengthening argon concentration gradient between the saturated surface and the argon poor interior. Argon concentration was measured by electron microprobe along radial transects from the center to the surface of bisected samples. D_{Ar} was calculated for each transect by fitting relative argon concentration (as a function of distance from the surface) to Green's function (given each experiment's specific temperature, pressure and runtime). Variability (σ = 1.202{μm }^{2} /s) was smaller than in previous studies, but still greater than what is likely due to analytical or experimental uncertainty. We observed a symmetric geometric bias in the distribution of argon in our samples, possibly related to advective redistribution of argon accompanying the deformation of cylindrical charges into spheroids driven by surface tension. Average diffusivity, D_{Ar} = 4.791{μm }^{2} /s, is close to the predicted value, D_{Ar} = {μm }^{2} /s ( σ_{ \\bar{x} } = 1.576 {μm }^{2} /s), suggesting that Behrens and Zhang's (2001) empirical model is valid for anhydrous rhyolite melts to relatively higher temperatures and lower pressures. Behrens, H. and Y. Zhang (2001). "Ar diffusion in hydrous silicic melts: implications for volatile diffusion mechanisms and fractionation." Earth and Planetary Science Letters 192: 363-376.

Filament stretching rheometry of polymer melts

DEFF Research Database (Denmark)

Hassager, Ole; Nielsen, Jens Kromann; Rasmussen, Henrik Koblitz

2005-01-01

The Filament Stretching Rheometry (FSR) method developed by Sridhar, McKinley and coworkers for polymer solutions has been extended to be used also for polymer melts. The design of a melt-FSR will be described and differences to conventional melt elongational rheometers will be pointed out. Results...

Melting temperature of graphite

International Nuclear Information System (INIS)

Korobenko, V.N.; Savvatimskiy, A.I.

2001-01-01

Full Text: Pulse of electrical current is used for fast heating (∼ 1 μs) of metal and graphite specimens placed in dielectric solid media. Specimen consists of two strips (90 μm in thick) placed together with small gap so they form a black body model. Quasy-monocrystal graphite specimens were used for uniform heating of graphite. Temperature measurements were fulfilled with fast pyrometer and with composite 2-strip black body model up to melting temperature. There were fulfilled experiments with zirconium and tungsten of the same black body construction. Additional temperature measurements of liquid zirconium and liquid tungsten are made. Specific heat capacity (c P ) of liquid zirconium and of liquid tungsten has a common feature in c P diminishing just after melting. It reveals c P diminishing after melting in both cases over the narrow temperature range up to usual values known from steady state measurements. Over the next wide temperature range heat capacity for W (up to 5000 K) and Zr (up to 4100 K) show different dependencies of heat capacity on temperature in liquid state. The experiments confirmed a high quality of 2-strip black body model used for graphite temperature measurements. Melting temperature plateau of tungsten (3690 K) was used for pyrometer calibration area for graphite temperature measurement. As a result, a preliminary value of graphite melting temperature of 4800 K was obtained. (author)

In-situ observations of bubble growth in basaltic, andesitic and rhyodacitic melts

Science.gov (United States)

Masotta, M.; Ni, H.; Keppler, H.

2013-12-01

Bubble growth strongly affects the physical properties of degassing magmas and their eruption dynamics. Natural samples and products from quench experiments provide only a snapshot of the final state of volatile exsolution, leaving the processes occurring during its early stages unconstrained. In order to fill this gap, we present in-situ high-temperature observations of bubble growth in magmas of different compositions (basalt, andesite and rhyodacite) at 1100 to 1240 °C and 1 bar, obtained using a moissanite cell apparatus. The data show that nucleation occurs at very small degrees of supersaturaturation (bubbles occurring simultaneously with the nucleation of crystals. During the early stages of exsolution, melt degassing is the driving mechanism of bubble growth, with coalescence becoming increasingly important as exsolution progresses. Ostwald ripening occurs only at the end of the process and only in basaltic melt. The average bubble growth rate (GR) ranges from 3.4*10-6 to 5.2*10-7 mm/s, with basalt and andesite showing faster growth rates than rhyodacite. The bubble number density (NB) at nucleation ranges from 1.8*108 to 7.9*107 cm-3 and decreases exponentially over time. While the rhyodacite melt maintained a well-sorted bubble-size distribution (BSD) through time, the BSD's of basalt and andesite are much more inhomogeneous. Our experimental observations demonstrate that bubble growth cannot be ascribed to a single mechanism but is rather a combination of many processes, which depend on the physical properties of the melt. Depending on coalescence rate, annealing of bubbles following a single nucleation event can produce complex bubble size distributions. In natural samples, such BSD's may be misinterpreted as resulting from several separate nucleation events. Incipient crystallization upon cooling of a magma may allow bubble nucleation already at very small degrees of supersaturation and could therefore be an important trigger for volatile release and

Theoretical melting curve of caesium

International Nuclear Information System (INIS)

Simozar, S.; Girifalco, L.A.; Pennsylvania Univ., Philadelphia

1983-01-01

A statistical-mechanical model is developed to account for the complex melting curve of caesium. The model assumes the existence of three different species of caesium defined by three different electronic states. On the basis of this model, the free energy of melting and the melting curve are computed up to 60 kbar, using the solid-state data and the initial slope of the fusion curve as input parameters. The calculated phase diagram agrees with experiment to within the experimental error. Other thermodynamic properties including the entropy and volume of melting were also computed, and they agree with experiment. Since the theory requires only one adjustable constant, this is taken as strong evidence that the three-species model is satisfactory for caesium. (author)

Simulation of Groundwater Mounding Beneath Hypothetical Stormwater Infiltration Basins

Science.gov (United States)

Carleton, Glen B.

2010-01-01

Groundwater mounding occurs beneath stormwater management structures designed to infiltrate stormwater runoff. Concentrating recharge in a small area can cause groundwater mounding that affects the basements of nearby homes and other structures. Methods for quantitatively predicting the height and extent of groundwater mounding beneath and near stormwater Finite-difference groundwater-flow simulations of infiltration from hypothetical stormwater infiltration structures (which are typically constructed as basins or dry wells) were done for 10-acre and 1-acre developments. Aquifer and stormwater-runoff characteristics in the model were changed to determine which factors are most likely to have the greatest effect on simulating the maximum height and maximum extent of groundwater mounding. Aquifer characteristics that were changed include soil permeability, aquifer thickness, and specific yield. Stormwater-runoff variables that were changed include magnitude of design storm, percentage of impervious area, infiltration-structure depth (maximum depth of standing water), and infiltration-basin shape. Values used for all variables are representative of typical physical conditions and stormwater management designs in New Jersey but do not include all possible values. Results are considered to be a representative, but not all-inclusive, subset of likely results. Maximum heights of simulated groundwater mounds beneath stormwater infiltration structures are the most sensitive to (show the greatest change with changes to) soil permeability. The maximum height of the groundwater mound is higher when values of soil permeability, aquifer thickness, or specific yield are decreased or when basin depth is increased or the basin shape is square (and values of other variables are held constant). Changing soil permeability, aquifer thickness, specific yield, infiltration-structure depth, or infiltration-structure shape does not change the volume of water infiltrated, it changes the

Satellite-derived submarine melt rates and mass balance (2011-2015) for Greenland's largest remaining ice tongues

Science.gov (United States)

Wilson, Nat; Straneo, Fiammetta; Heimbach, Patrick

2017-12-01

Ice-shelf-like floating extensions at the termini of Greenland glaciers are undergoing rapid changes with potential implications for the stability of upstream glaciers and the ice sheet as a whole. While submarine melting is recognized as a major contributor to mass loss, the spatial distribution of submarine melting and its contribution to the total mass balance of these floating extensions is incompletely known and understood. Here, we use high-resolution WorldView satellite imagery collected between 2011 and 2015 to infer the magnitude and spatial variability of melt rates under Greenland's largest remaining ice tongues - Nioghalvfjerdsbræ (79 North Glacier, 79N), Ryder Glacier (RG), and Petermann Glacier (PG). Submarine melt rates under the ice tongues vary considerably, exceeding 50 m a-1 near the grounding zone and decaying rapidly downstream. Channels, likely originating from upstream subglacial channels, give rise to large melt variations across the ice tongues. We compare the total melt rates to the influx of ice to the ice tongue to assess their contribution to the current mass balance. At Petermann Glacier and Ryder Glacier, we find that the combined submarine and aerial melt approximately balances the ice flux from the grounded ice sheet. At Nioghalvfjerdsbræ the total melt flux (14.2 ± 0.96 km3 a-1 w.e., water equivalent) exceeds the inflow of ice (10.2 ± 0.59 km3 a-1 w.e.), indicating present thinning of the ice tongue.

Further research on melting activated and contaminated materials from the decommissioning of nuclear installations for the final storage

International Nuclear Information System (INIS)

Deipenau, H.; Seidler, M.

1990-07-01

The unconditional reuse of activated and contaminated materials by melting and the production of qualified casks (type A- and type B-containers) was proved. Investigations on nuclide distribution in the melting furnace, molten material, dust and slag were used as a basis for the erection of a new central melting facility. Melting contaminated carbon steel a mass of 2-5% of the contaminated material was generated as dust and slag. They must be handled and transported as radioactive waste. Melting non-ferrous material activity contents could be reached for unconditional reuse. Binding radioactive carbon in the metal matrix of cast iron is only possible by using crushed graphite. The investigations of this project showed that unconditional reuse of contaminated material is possible in industrial scale. Doses of the workers and of the people in the environment of the facility resulting from melting were far below the limits of the German radiation protection law. Up to 1990 a mass of 2000 Mg of contaminated material was melted in the Siempelkamp foundry. Mass inventories for the dismantling of a reference power plant SWR 900 MWe are calculated. (orig./HP) With 7 refs., 18 tabs., 12 figs [de

Simulation of flow in the unsaturated zone beneath Pagany Wash, Yucca Mountain

International Nuclear Information System (INIS)

Kwicklis, E.M.; Healy, R.W.; Flint, A.L.

1994-01-01

A one-dimensional numerical model was created to simulate water movement beneath Pagany Wash, Yucca Mountain, Nevada. Model stratigraphy and properties were based on data obtained from boreholes UE-25 UZ No. 4 and UE-25 UZ No. 5, which was drilled in the alluvial channel and bedrock sideslope of Pagany Wash. Although unable to account for multidimensional or preferential flowpaths beneath the wash, the model proved a useful conceptual tool with which to develop hypotheses and, in some cases, provide bounding calculations. The model indicated that liquid flux decreases with depth in the upper 120 m beneath the wash, with fluxes of several tens mm/yr in the nonwelded base of the Tiva Canyon Member and fluxes on the order of a tenth mm/yr in the upper Topopah Spring Member. Capillary barrier effects were indicated by the model to significantly delay the entry of large fluxes into the potential repository horizon during periods of increasing net infiltration, and to inhibit rapid drainage of water from the nonwelded and bedded intervals into the potential repository horizon during periods of moisture redistribution. Lateral moisture redistribution can be expected to be promoted by these effects

Melts of garnet lherzolite: experiments, models and comparison to melts of pyroxenite and carbonated lherzolite

Science.gov (United States)

Grove, Timothy L.; Holbig, Eva S.; Barr, Jay A.; Till, Christy B.; Krawczynski, Michael J.

2013-01-01

Phase equilibrium experiments on a compositionally modified olivine leucitite from the Tibetan plateau have been carried out from 2.2 to 2.8 GPa and 1,380–1,480 °C. The experiments-produced liquids multiply saturated with spinel and garnet lherzolite phase assemblages (olivine, orthopyroxene, clinopyroxene and spinel ± garnet) under nominally anhydrous conditions. These SiO2-undersaturated liquids and published experimental data are utilized to develop a predictive model for garnet lherzolite melting of compositionally variable mantle under anhydrous conditions over the pressure range of 1.9–6 GPa. The model estimates the major element compositions of garnet-saturated melts for a range of mantle lherzolite compositions and predicts the conditions of the spinel to garnet lherzolite phase transition for natural peridotite compositions at above-solidus temperatures and pressures. We compare our predicted garnet lherzolite melts to those of pyroxenite and carbonated lherzolite and develop criteria for distinguishing among melts of these different source types. We also use the model in conjunction with a published predictive model for plagioclase and spinel lherzolite to characterize the differences in major element composition for melts in the plagioclase, spinel and garnet facies and develop tests to distinguish between melts of these three lherzolite facies based on major elements. The model is applied to understand the source materials and conditions of melting for high-K lavas erupted in the Tibetan plateau, basanite–nephelinite lavas erupted early in the evolution of Kilauea volcano, Hawaii, as well as younger tholeiitic to alkali lavas from Kilauea.

A 9,000-year-old caribou hunting structure beneath Lake Huron.

Science.gov (United States)

O'Shea, John M; Lemke, Ashley K; Sonnenburg, Elizabeth P; Reynolds, Robert G; Abbott, Brian D

2014-05-13

Some of the most pivotal questions in human history necessitate the investigation of archaeological sites that are now under water. Nine thousand years ago, the Alpena-Amberley Ridge (AAR) beneath modern Lake Huron was a dry land corridor that connected northeast Michigan to southern Ontario. The newly discovered Drop 45 Drive Lane is the most complex hunting structure found to date beneath the Great Lakes. The site and its associated artifacts provide unprecedented insight into the social and seasonal organization of prehistoric caribou hunting. When combined with environmental and simulation studies, it is suggested that distinctly different seasonal strategies were used by early hunters on the AAR, with autumn hunting being carried out by small groups, and spring hunts being conducted by larger groups of cooperating hunters.

A comprehensive analysis of contaminant transport in the vadose zone beneath tank SX-109

International Nuclear Information System (INIS)

Ward, A.L.; Gee, G.W.; White, M.D.

1997-02-01

The Vadose Zone Characterization Project is currently investigating the subsurface distribution of gamma-emitting radionuclides in S and SX Waste Management Area (WMA-S-SX) located in the 200 West Area of the US Department of Energy's Hanford Site in southeastern Washington State. Spectral-gamma logging of boreholes has detected elevated 137 Cs concentrations as deep as 38 m, a depth considered excessive based on the assumed geochemistry of 137 Cs in Hanford sediments. Routine groundwater sampling under the Resource Conservation and Recovery Act (RCRA) have also detected elevated levels of site-specific contaminants downgradient of WMA-S-SX. The objective of this report is to explore the processes controlling the migration of 137 Cs, 99 Tc, and NO 3 through the vadose zone of WMA-S-SX, particularly beneath tank SX-109

Problem of corium melt coolability in passive protection systems against severe accidents in the containment

Directory of Open Access Journals (Sweden)

Ali Kalvand

2018-05-01

Full Text Available Paper is devoted to the development of the mathematical model and analysis of the problem of corium melt interaction with low-temperature melting blocks in the passive protection systems against severe accidents at the NPP, which is of high importance for substantiation of the nuclear power safety, for building and successful op-erating of passive protection systems. In the third-generation reactors passive protection systems against severe accidents at the NPP are mandatory, therefore this paper is of importance for the nuclear power safety. A few configurations for the cooling blocks’ distribution have been considered and an analysis of the blocks’ melting and corium’s cooling in the pool under reactor vessel have been done, which can serve more effective for further improvement of the safety current systems and for the development of new ones. The ways for solution of the problems and the methods for their successful elaboration were discussed. The developed mathematical models and the analysis performed in the paper might be helpful for the design of passive protection systems of the cori-um melt retention inside the containment after corium melt eruption from the broken reactor vessel.

Crustal thickness and Vp/Vs beneath the southeastern United States: Constraints from receiver function stacking

Science.gov (United States)

Yang, Q.; Gao, S. S.; Liu, K. H.

2017-12-01

To provide new constraints on crustal structure and evolution models beneath a collage of tectonic provinces in the southeastern United States, a total of 10,753 teleseismic receiver functions recorded by 125 USArray and other seismic stations are used to compute crustal thickness and Vp/Vs values. The resulting crustal thicknesses range from 25 km at the coast to 51 km beneath the peak of the southern Appalachians with an average of 36.2 km ± 5.5 km. The resulting crustal thicknesses correlate well with surface elevation and Bouguer gravity anomalies. Beneath the Atlantic Coastal Plain, the crustal thicknesses show a clear eastward thinning with a magnitude of 10 km, from about 40 km beneath the western margin to 30 km beneath the coast. The Vp/Vs values for the entire study area range from 1.71 to 1.90 with a mean value of 1.80 ± 0.04. The mean Vp/Vs value is 1.82±0.035 in the southern Appalachian Mountain. The slightly larger than normal crustal Vp/Vs for this area might be the result of significant erosion of the felsic upper crust over the past 300 million years. Alternatively, it could also suggest the existence of pervasive magmatic intrusion into the Appalachian crust. The Vp/Vs measurements in the Atlantic Coastal Plain increase toward the east, ranging from 1.75 to 1.82, probably indicating a gradual increase of mafic magmatic intrusion into thinner crust during the development of the passive continental margin.

Effects of nanoparticles on melting process with phase-change using the lattice Boltzmann method

Directory of Open Access Journals (Sweden)

Ahmed M. Ibrahem

Full Text Available In this work, the problem of nanoparticles dispersion effects on coupled heat transfer and solid-liquid phase change has been studied. The lattice Boltzmann method (LBM enthalpy-based is employed. The collision model of lattice Bhatnagar-Gross-Krook (LBGK is used to solve the problem of 1D melting by conduction. On the other hand, we use the model of multi-distribution functions (MDF to calculate the density, the velocity and the temperature for the problem of 2D melting by free convection, associated with different boundary conditions. In these simulations, the volume fractions of copper nanoparticles (0–2% added to water-base fluid and Rayleigh numbers of 103–105. We use the Chapman-Enskog expansion to derive the governing macroscopic quantities from the mesoscopic lattice Boltzmann equation. The results obtained by these models have been compared to an analytical solution or other numerical methods. The effects of nanoparticles on conduction and natural convection during the melting process have been investigated. Moreover, the influences of nanoparticles on moving of the phase change front, the thermal conductivity and the latent heat of fusion are also studied. Keywords: Lattice Boltzmann method, Nanofluids, Conduction melting, Convection melting, BGK collision model

Control and homogenization of oxygen distribution in Si crystals by the novel technique: electromagnetic Czochralski method (EMCZ)

Science.gov (United States)

Watanabe, Masahito; Eguchi, Minoru; Hibiya, Taketoshi

1999-07-01

A novel method for control and homogenization oxygen distribution in silicon crystals by using electromagnetic force (EMF) to rotate the melt without crucible rotation has been developed. We call it electromagnetic Czochralski method. An EMF in the azimuthal direction is generated in the melt by the interaction between an electric current through the melt in the radial direction and a vertical magnetic field. (B). The rotation rate (ωm) of the silicon melt is continuously changed from 0 to over 105 rpm under I equals 0 to 8 A and B equals 0 to 0.1 T. Thirty-mm-diameter silicon single crystals free of dislocations could be grown under several conditions. The oxygen concentration in the crystals was continuously changed from 1 X 1017 to 1 X 1018 atoms/cm3 with increase of melt rotation by electromagnetic force. The homogeneous oxygen distributions in the radial directions were achieved. The continuous change of oxygen concentration and the homogenization of oxygen distribution along the radial direction are attributed to the control of the diffusion-boundary-layer at both the melt/crucible and crystal/melt by forced flow due to the EMF. This new method would be useful for growth of the large-diameter silicon crystals with a homogeneous distribution of oxygen.

Fabrication of WCp/NiBSi metal matrix composite by electron beam melting

Energy Technology Data Exchange (ETDEWEB)

Peng, Hui, E-mail: penghui@buaa.edu.cn [School of Materials Science and Engineering, Beihang University (BUAA), No. 37 Xueyuan Road, Beijing 100191 (China); Beijing Key Laboratory for Advanced Functional Material and Thin Film Technology, Beihang University, No. 37 Xueyuan Road, Beijing 100191 (China); Key Laboratory of Aerospace Materials & Performance (Ministry of Education), Beihang University, No. 37 Xueyuan Road, Beijing 100191 (China); Liu, Chang [School of Materials Science and Engineering, Beihang University (BUAA), No. 37 Xueyuan Road, Beijing 100191 (China); Guo, Hongbo, E-mail: guo.hongbo@buaa.edu.cn [School of Materials Science and Engineering, Beihang University (BUAA), No. 37 Xueyuan Road, Beijing 100191 (China); Beijing Key Laboratory for Advanced Functional Material and Thin Film Technology, Beihang University, No. 37 Xueyuan Road, Beijing 100191 (China); Key Laboratory of Aerospace Materials & Performance (Ministry of Education), Beihang University, No. 37 Xueyuan Road, Beijing 100191 (China); Yuan, Yuan [Zhuzhou Seed Cemented Carbide Technology Co. Ltd, No. 1099 Xiangda Road, Zhuzhou, Hunan 412000 (China); Gong, Shengkai; Xu, Huibin [School of Materials Science and Engineering, Beihang University (BUAA), No. 37 Xueyuan Road, Beijing 100191 (China); Beijing Key Laboratory for Advanced Functional Material and Thin Film Technology, Beihang University, No. 37 Xueyuan Road, Beijing 100191 (China); Key Laboratory of Aerospace Materials & Performance (Ministry of Education), Beihang University, No. 37 Xueyuan Road, Beijing 100191 (China)

2016-06-01

A blend of NiBSi and WC powders was used as raw material for fabricating a metal matrix composite (MMC) by electron beam melting (EBM). Dense and crack-free microstructure was produced with evenly distributed WC reinforcements. Mechanical properties, including macro- and micro-hardness, flexural strength, impact toughness and compressive strength, were investigated.

Fabrication of WCp/NiBSi metal matrix composite by electron beam melting

International Nuclear Information System (INIS)

Peng, Hui; Liu, Chang; Guo, Hongbo; Yuan, Yuan; Gong, Shengkai; Xu, Huibin

2016-01-01

A blend of NiBSi and WC powders was used as raw material for fabricating a metal matrix composite (MMC) by electron beam melting (EBM). Dense and crack-free microstructure was produced with evenly distributed WC reinforcements. Mechanical properties, including macro- and micro-hardness, flexural strength, impact toughness and compressive strength, were investigated.

Level-Ice Melt Ponds in the Los Alamos Sea Ice Model, CICE

Science.gov (United States)

2012-12-06

terms obtained using the Bitz and Lips- comb (1999) thermodynamic model. The thickness distribution ( Thorndike et al., 1975) employs 5 ice thickness...D.L., 2004. A model of melt pond evolution on sea ice. J. Geophys. Res. 109, C12007. http://dx.doi.org/10.1029/2004JC002361. Thorndike , A.S., Rothrock

Material properties influence on steam explosion efficiency. Prototypic versus simulant melts, eutectic versus non-eutectic melts

International Nuclear Information System (INIS)

Leskovar, M.; Mavko, B.

2006-01-01

A steam explosion may occur during a severe nuclear reactor accident if the molten core comes into contact with the coolant water. A strong enough steam explosion in a nuclear power plant could jeopardize the containment integrity and so lead to a direct release of radioactive material to the environment. Details of processes taking place prior and during the steam explosion have been experimentally studied for a number of years with adjunct efforts in modelling these processes to address the scaling of these experiments. Steam explosion experiments have shown that there are important differences of behaviour between simulant and prototypical melts, and that also at prototypical melts the fuel coolant interactions depend on the composition of the corium. In experiments with prototypic materials no spontaneous steam explosions occurred (except with an eutectic composition), whereas with simulant materials the steam explosions were triggered spontaneously. The energy conversion ratio of steam explosions with prototypic melts is at least one order of magnitude lower than the energy conversion ratio of steam explosions with simulant melts. Although the different behaviour of prototypic and simulant melts has been known for a number of years, there is no reliable explanation for these differences. Consequently it is not possible to reliably estimate whether corium would behave so non-explosive also in reactor conditions, where the mass of poured melt is nearly three orders of magnitude larger than in experimental conditions. An even more fascinating material effect was observed recently at corium experiments with eutectic and non-eutectic compositions. It turned out that eutectic corium always exploded spontaneously, whereas non-eutectic corium never exploded spontaneously. In the paper, a possible explanation of both material effects (prototypic/simulant melts, eutectic/non-eutectic corium) on the steam explosion is provided. A model for the calculation of the

Melt processed high-temperature superconductors

CERN Document Server

1993-01-01

The achievement of large critical currents is critical to the applications of high-temperature superconductors. Recent developments have shown that melt processing is suitable for producing high J c oxide superconductors. Using magnetic forces between such high J c oxide superconductors and magnets, a person could be levitated.This book has grown largely out of research works on melt processing of high-temperature superconductors conducted at ISTEC Superconductivity Research Laboratory. The chapters build on melt processing, microstructural characterization, fundamentals of flux pinning, criti

Single-molecule study on polymer diffusion in a melt state: Effect of chain topology

KAUST Repository

Habuchi, Satoshi

2013-08-06

We report a new methodology for studying diffusion of individual polymer chains in a melt state, with special emphasis on the effect of chain topology. A perylene diimide fluorophore was incorporated into the linear and cyclic poly(THF)s, and real-time diffusion behavior of individual chains in a melt of linear poly(THF) was measured by means of a single-molecule fluorescence imaging technique. The combination of mean squared displacement (MSD) and cumulative distribution function (CDF) analysis demonstrated the broad distribution of diffusion coefficient of both the linear and cyclic polymer chains in the melt state. This indicates the presence of spatiotemporal heterogeneity of the polymer diffusion which occurs at much larger time and length scales than those expected from the current polymer physics theory. We further demonstrated that the cyclic chains showed marginally slower diffusion in comparison with the linear counterparts, to suggest the effective suppression of the translocation through the threading-entanglement with the linear matrix chains. This coincides with the higher activation energy for the diffusion of the cyclic chains than of the linear chains. These results suggest that the single-molecule imaging technique provides a powerful tool to analyze complicated polymer dynamics and contributes to the molecular level understanding of the chain interaction. © 2013 American Chemical Society.

Single-molecule study on polymer diffusion in a melt state: Effect of chain topology

KAUST Repository

Habuchi, Satoshi; Fujiwara, Susumu; Yamamoto, Takuya; Vá cha, Martin; Tezuka, Yasuyuki

2013-01-01

We report a new methodology for studying diffusion of individual polymer chains in a melt state, with special emphasis on the effect of chain topology. A perylene diimide fluorophore was incorporated into the linear and cyclic poly(THF)s, and real-time diffusion behavior of individual chains in a melt of linear poly(THF) was measured by means of a single-molecule fluorescence imaging technique. The combination of mean squared displacement (MSD) and cumulative distribution function (CDF) analysis demonstrated the broad distribution of diffusion coefficient of both the linear and cyclic polymer chains in the melt state. This indicates the presence of spatiotemporal heterogeneity of the polymer diffusion which occurs at much larger time and length scales than those expected from the current polymer physics theory. We further demonstrated that the cyclic chains showed marginally slower diffusion in comparison with the linear counterparts, to suggest the effective suppression of the translocation through the threading-entanglement with the linear matrix chains. This coincides with the higher activation energy for the diffusion of the cyclic chains than of the linear chains. These results suggest that the single-molecule imaging technique provides a powerful tool to analyze complicated polymer dynamics and contributes to the molecular level understanding of the chain interaction. © 2013 American Chemical Society.

Power law and exponential ejecta size distributions from the dynamic fragmentation of shock-loaded Cu and Sn metals under melt conditions

Energy Technology Data Exchange (ETDEWEB)

Durand, O.; Soulard, L. [CEA, DAM, DIF, F-91297 Arpajon (France)

2013-11-21

Large scale molecular dynamics (MD) simulations are performed to study and to model the ejecta production from the dynamic fragmentation of shock-loaded metals under melt conditions. A generic 3D crystal in contact with vacuum containing about 10{sup 8} atoms and with a sinusoidal free surface roughness is shock loaded so as to undergo a solid-liquid phase change on shock. The reflection of the shock wave at the interface metal/vacuum gives rise to the ejection of 2D jets/sheets of atoms (Richtmyer-Meshkov instabilities in the continuum limit), which develop and break up, forming ejecta (fragments) of different volumes (or mass). The fragmentation process is investigated by analyzing the evolution of the resulting volume distribution of the ejecta as a function of time. Two metals are studied (Cu and Sn) and the amplitude of the roughness is varied. The simulations show that the associated distributions exhibit a generic behavior with the sum of two distinct terms of varying weight, following the expansion rate of the jets: in the small size limit, the distribution obeys a power law dependence with an exponent equal to 1.15 ± 0.08; and in the large size limit, it obeys an exponential form. These two components are interpreted, with the help of additional simple simulations, as the signature of two different basic mechanisms of fragmentation. The power law dependence results from the fragmentation of a 2D network of ligaments arranged following a fractal (scale free) geometry and generated when the sheets of liquid metal expand and tear. The exponential distribution results from a 1D Poisson fragmentation process of the largest ligaments previously generated. Unlike the power law distribution, it is governed by a characteristic length scale, which may be provided by energy balance principle.

Power law and exponential ejecta size distributions from the dynamic fragmentation of shock-loaded Cu and Sn metals under melt conditions

International Nuclear Information System (INIS)

Durand, O.; Soulard, L.

2013-01-01

Large scale molecular dynamics (MD) simulations are performed to study and to model the ejecta production from the dynamic fragmentation of shock-loaded metals under melt conditions. A generic 3D crystal in contact with vacuum containing about 10 8 atoms and with a sinusoidal free surface roughness is shock loaded so as to undergo a solid-liquid phase change on shock. The reflection of the shock wave at the interface metal/vacuum gives rise to the ejection of 2D jets/sheets of atoms (Richtmyer-Meshkov instabilities in the continuum limit), which develop and break up, forming ejecta (fragments) of different volumes (or mass). The fragmentation process is investigated by analyzing the evolution of the resulting volume distribution of the ejecta as a function of time. Two metals are studied (Cu and Sn) and the amplitude of the roughness is varied. The simulations show that the associated distributions exhibit a generic behavior with the sum of two distinct terms of varying weight, following the expansion rate of the jets: in the small size limit, the distribution obeys a power law dependence with an exponent equal to 1.15 ± 0.08; and in the large size limit, it obeys an exponential form. These two components are interpreted, with the help of additional simple simulations, as the signature of two different basic mechanisms of fragmentation. The power law dependence results from the fragmentation of a 2D network of ligaments arranged following a fractal (scale free) geometry and generated when the sheets of liquid metal expand and tear. The exponential distribution results from a 1D Poisson fragmentation process of the largest ligaments previously generated. Unlike the power law distribution, it is governed by a characteristic length scale, which may be provided by energy balance principle

The structure of the crust and uppermost mantle beneath Madagascar

Science.gov (United States)

Andriampenomanana, Fenitra; Nyblade, Andrew A.; Wysession, Michael E.; Durrheim, Raymond J.; Tilmann, Frederik; Julià, Jordi; Pratt, Martin J.; Rambolamanana, Gérard; Aleqabi, Ghassan; Shore, Patrick J.; Rakotondraibe, Tsiriandrimanana

2017-09-01

The lithosphere of Madagascar was initially amalgamated during the Pan-African events in the Neoproterozoic. It has subsequently been reshaped by extensional processes associated with the separation from Africa and India in the Jurassic and Cretaceous, respectively, and been subjected to several magmatic events in the late Cretaceous and the Cenozoic. In this study, the crust and uppermost mantle have been investigated to gain insights into the present-day structure and tectonic evolution of Madagascar. We analysed receiver functions, computed from data recorded on 37 broad-band seismic stations, using the H-κ stacking method and a joint inversion with Rayleigh-wave phase-velocity measurements. The thickness of the Malagasy crust ranges between 18 and 46 km. It is generally thick beneath the spine of mountains in the centre part (up to 46 km thick) and decreases in thickness towards the edges of the island. The shallowest Moho is found beneath the western sedimentary basins (18 km thick), which formed during both the Permo-Triassic Karro rifting in Gondwana and the Jurassic rifting of Madagascar from eastern Africa. The crust below the sedimentary basin thickens towards the north and east, reflecting the progressive development of the basins. In contrast, in the east there was no major rifting episode. Instead, the slight thinning of the crust along the east coast (31-36 km thick) may have been caused by crustal uplift and erosion when Madagascar moved over the Marion hotspot and India broke away from it. The parameters describing the crustal structure of Archean and Proterozoic terranes, including average thickness (40 km versus 35 km), Poisson's ratio (0.25 versus 0.26), average shear-wave velocity (both 3.7 km s-1), and thickness of mafic lower crust (7 km versus 4 km), show weak evidence of secular variation. The uppermost mantle beneath Madagascar is generally characterized by shear-wave velocities typical of stable lithosphere (∼4.5 km s-1). However

The melting and solidification of nanowires

International Nuclear Information System (INIS)

Florio, B. J.; Myers, T. G.

2016-01-01

A mathematical model is developed to describe the melting of nanowires. The first section of the paper deals with a standard theoretical situation, where the wire melts due to a fixed boundary temperature. This analysis allows us to compare with existing results for the phase change of nanospheres. The equivalent solidification problem is also examined. This shows that solidification is a faster process than melting; this is because the energy transfer occurs primarily through the solid rather than the liquid which is a poorer conductor of heat. This effect competes with the energy required to create new solid surface which acts to slow down the process, but overall conduction dominates. In the second section, we consider a more physically realistic boundary condition, where the phase change occurs due to a heat flux from surrounding material. This removes the singularity in initial melt velocity predicted in previous models of nanoparticle melting. It is shown that even with the highest possible flux the melting time is significantly slower than with a fixed boundary temperature condition.

The melting and solidification of nanowires

Science.gov (United States)

Florio, B. J.; Myers, T. G.

2016-06-01

A mathematical model is developed to describe the melting of nanowires. The first section of the paper deals with a standard theoretical situation, where the wire melts due to a fixed boundary temperature. This analysis allows us to compare with existing results for the phase change of nanospheres. The equivalent solidification problem is also examined. This shows that solidification is a faster process than melting; this is because the energy transfer occurs primarily through the solid rather than the liquid which is a poorer conductor of heat. This effect competes with the energy required to create new solid surface which acts to slow down the process, but overall conduction dominates. In the second section, we consider a more physically realistic boundary condition, where the phase change occurs due to a heat flux from surrounding material. This removes the singularity in initial melt velocity predicted in previous models of nanoparticle melting. It is shown that even with the highest possible flux the melting time is significantly slower than with a fixed boundary temperature condition.

The melting and solidification of nanowires

Energy Technology Data Exchange (ETDEWEB)

Florio, B. J., E-mail: brendan.florio@ul.ie [University of Limerick, Mathematics Applications Consortium for Science and Industry (MACSI), Department of Mathematics and Statistics (Ireland); Myers, T. G., E-mail: tmyers@crm.cat [Centre de Recerca Matemàtica (Spain)

2016-06-15

A mathematical model is developed to describe the melting of nanowires. The first section of the paper deals with a standard theoretical situation, where the wire melts due to a fixed boundary temperature. This analysis allows us to compare with existing results for the phase change of nanospheres. The equivalent solidification problem is also examined. This shows that solidification is a faster process than melting; this is because the energy transfer occurs primarily through the solid rather than the liquid which is a poorer conductor of heat. This effect competes with the energy required to create new solid surface which acts to slow down the process, but overall conduction dominates. In the second section, we consider a more physically realistic boundary condition, where the phase change occurs due to a heat flux from surrounding material. This removes the singularity in initial melt velocity predicted in previous models of nanoparticle melting. It is shown that even with the highest possible flux the melting time is significantly slower than with a fixed boundary temperature condition.

Identification of squid species by melting temperature shifts on fluorescence melting curve analysis (FMCA) using single dual-labeled probe

Science.gov (United States)

Koh, Eunjung; Song, Ha Jeong; Kwon, Na Young; Kim, Gi Won; Lee, Kwang Ho; Jo, Soyeon; Park, Sujin; Park, Jihyun; Park, Eun Kyeong; Hwang, Seung Yong

2017-06-01

Real time PCR is a standard method for identification of species. One of limitations of the qPCR is that there would be false-positive result due to mismatched hybridization between target sequence and probe depending on the annealing temperature in the PCR condition. As an alternative, fluorescence melting curve analysis (FMCA) could be applied for species identification. FMCA is based on a dual-labeled probe. Even with subtle difference of target sequence, there are visible melting temperature (Tm) shift. One of FMCA applications is distinguishing organisms distributed and consumed globally as popular food ingredients. Their prices are set by species or country of origin. However, counterfeiting or distributing them without any verification procedure are becoming social problems and threatening food safety. Besides distinguishing them in naked eye is very difficult and almost impossible in any processed form. Therefore, it is necessary to identify species in molecular level. In this research three species of squids which have 1-2 base pair differences each are selected as samples since they have the same issue. We designed a probe which perfectly matches with one species and the others mismatches 2 and 1 base pair respectively and labeled with fluorophore and quencher. In an experiment with a single probe, we successfully distinguished them by Tm shift depending on the difference of base pair. By combining FMCA and qPCR chip, smaller-scale assay with higher sensitivity and resolution could be possible, andc furthermore, enabling results analysis with smart phone would realize point-of-care testing (POCT).

Methods for Melting Temperature Calculation

Science.gov (United States)

Hong, Qi-Jun

Melting temperature calculation has important applications in the theoretical study of phase diagrams and computational materials screenings. In this thesis, we present two new methods, i.e., the improved Widom's particle insertion method and the small-cell coexistence method, which we developed in order to capture melting temperatures both accurately and quickly. We propose a scheme that drastically improves the efficiency of Widom's particle insertion method by efficiently sampling cavities while calculating the integrals providing the chemical potentials of a physical system. This idea enables us to calculate chemical potentials of liquids directly from first-principles without the help of any reference system, which is necessary in the commonly used thermodynamic integration method. As an example, we apply our scheme, combined with the density functional formalism, to the calculation of the chemical potential of liquid copper. The calculated chemical potential is further used to locate the melting temperature. The calculated results closely agree with experiments. We propose the small-cell coexistence method based on the statistical analysis of small-size coexistence MD simulations. It eliminates the risk of a metastable superheated solid in the fast-heating method, while also significantly reducing the computer cost relative to the traditional large-scale coexistence method. Using empirical potentials, we validate the method and systematically study the finite-size effect on the calculated melting points. The method converges to the exact result in the limit of a large system size. An accuracy within 100 K in melting temperature is usually achieved when the simulation contains more than 100 atoms. DFT examples of Tantalum, high-pressure Sodium, and ionic material NaCl are shown to demonstrate the accuracy and flexibility of the method in its practical applications. The method serves as a promising approach for large-scale automated material screening in which

Recent Changes in the Arctic Melt Season

Science.gov (United States)

Stroeve, Julienne; Markus, Thorsten; Meier, Walter N.; Miller, Jeff

2007-01-01

Melt-season duration, melt-onset and freeze-up dates are derived from satellite passive microwave data and analyzed from 1979 to 2005 over Arctic sea ice. Results indicate a shift towards a longer melt season, particularly north of Alaska and Siberia, corresponding to large retreats of sea ice observed in these regions. Although there is large interannual and regional variability in the length of the melt season, the Arctic is experiencing an overall lengthening of the melt season at a rate of about 2 weeks decade(sup -1). In fact, all regions in the Arctic (except for the central Arctic) have statistically significant (at the 99% level or higher) longer melt seasons by greater than 1 week decade(sup -1). The central Arctic shows a statistically significant trend (at the 98% level) of 5.4 days decade(sup -1). In 2005 the Arctic experienced its longest melt season, corresponding with the least amount of sea ice since 1979 and the warmest temperatures since the 1880s. Overall, the length of the melt season is inversely correlated with the lack of sea ice seen in September north of Alaska and Siberia, with a mean correlation of -0.8.

Fundamental Aspects of Selective Melting Additive Manufacturing Processes

Energy Technology Data Exchange (ETDEWEB)

van Swol, Frank B. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Miller, James E. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)

2014-12-01

Certain details of the additive manufacturing process known as selective laser melting (SLM) affect the performance of the final metal part. To unleash the full potential of SLM it is crucial that the process engineer in the field receives guidance about how to select values for a multitude of process variables employed in the building process. These include, for example, the type of powder (e.g., size distribution, shape, type of alloy), orientation of the build axis, the beam scan rate, the beam power density, the scan pattern and scan rate. The science-based selection of these settings con- stitutes an intrinsically challenging multi-physics problem involving heating and melting a metal alloy, reactive, dynamic wetting followed by re-solidification. In addition, inherent to the process is its considerable variability that stems from the powder packing. Each time a limited number of powder particles are placed, the stacking is intrinsically different from the previous, possessing a different geometry, and having a different set of contact areas with the surrounding particles. As a result, even if all other process parameters (scan rate, etc) are exactly the same, the shape and contact geometry and area of the final melt pool will be unique to that particular configuration. This report identifies the most important issues facing SLM, discusses the fundamental physics associated with it and points out how modeling can support the additive manufacturing efforts.

Simulation of Wave-Plus-Current Scour beneath Submarine Pipelines

DEFF Research Database (Denmark)

Eltard-Larsen, Bjarke; Fuhrman, David R.; Sumer, B. Mutlu

2016-01-01

A fully coupled hydrodynamic and morphologic numerical model was utilized for the simulation of wave-plus-current scour beneath submarine pipelines. The model was based on incompressible Reynolds-averaged Navier–Stokes equations, coupled with k-ω turbulence closure, with additional bed and suspen......A fully coupled hydrodynamic and morphologic numerical model was utilized for the simulation of wave-plus-current scour beneath submarine pipelines. The model was based on incompressible Reynolds-averaged Navier–Stokes equations, coupled with k-ω turbulence closure, with additional bed...... and suspended load descriptions forming the basis for seabed morphology. The model was successfully validated against experimental measurements involving scour development and eventual equilibrium in pure-current flows over a range of Shields parameters characteristic of both clear-water and live-bed regimes....... This validation complements previously demonstrated accuracy for the same model in simulating pipeline scour processes in pure-wave environments. The model was subsequently utilized to simulate combined wave-plus-current scour over a wide range of combined Keulegan–Carpenter numbers and relative current strengths...

On melting of boron phosphide under pressure

OpenAIRE

Solozhenko, Vladimir; Mukhanov, V. A.

2015-01-01

Melting of cubic boron phosphide, BP, has been studied at pressures to 9 GPa using synchrotron X-ray diffraction and electrical resistivity measurements. It has been found that above 2.6 GPa BP melts congruently, and the melting curve exhibits negative slope (–60 ± 7 K/GPa), which is indicative of a higher density of the melt as compared to the solid phase.

Imaging of Upper-Mantle Upwelling Beneath the Salton Trough, Southern California, by Joint Inversion of Ambient Noise Dispersion Curves and Receiver Functions

Science.gov (United States)

Klemperer, S. L.; Barak, S.

2016-12-01

We present a new 2D shear-wave velocity model of the crust and upper-mantle across the Salton Trough, southern California, obtained by jointly inverting our new dataset of receiver functions and our previously published Rayleigh-wave group-velocity model (Barak et al., G-cubed, 2015), obtained from ambient-noise tomography. Our results show an upper-mantle low-velocity zone (LVZ) with Vs ≤4.2 km/s extending from the Elsinore Fault to the Sand Hills Fault, that together bracket the full width of major San Andreas dextral motion since its inception 6 Ma b.p., and underlying the full width of low topography of the Imperial Valley and Salton Trough. The lateral extent of the LVZ is coincident with the lateral extent of an upper-mantle anisotropic region interpreted as a zone of SAF-parallel melt pockets (Barak & Klemperer, Geology, 2016). The shallowest part of the LVZ is 40 km depth, coincident with S-receiver function images. The western part of the LVZ, between the Elsinore and San Jacinto faults (the region of greatest modern dextral slip), appears to continue to significantly greater depth; but a puzzling feature of our preliminary models is that the eastern part of the LVZ, from the San Jacinto Fault to the Sand Hills Fault, appears to be underlain by more-normalvelocity upper mantle (Vs ≥ 4.5 km/s) below 75 km depth. We compare our model to the current SCEC community models CVM-H and CVM-S, and to P-wave velocity models obtained by the active-source Salton Sea Imaging Project (SSIP). The hypothesized lower-crustal low-velocity zone beneath the Salton Trough in our previous model (Barak et al., G-cubed, 2015), there interpreted as a region of partial melt, is not supported by our new modeling. Melt may be largely absent from the lower crust of the Salton trough; but appears required in the upper mantle at depths as shallow as 40 km.

NMR investigations of the melting behaviour of mesogen compounds

International Nuclear Information System (INIS)

Limmer, S.; Grande, S.; Loesche, A.

1977-01-01

Proton NMR spectra of mesogen compounds in the solid phase are recorded. Between 20 and 40 K and 4 and 12 K below the melting point they exhibit a very narrow central line with a structure caused by the chemical shift, which is superimposed to the broad structureless line normally expected from polycrystalline solid phases. It is concluded that it originates from ''quasi-liquid'' molecules whose intensity grows drastically with increasing temperature and involves a maximum of about 2.5% of the whole intensity of the spectrum. In the region close to the melting point appears another lineshape, the so-called ''super-Lorentzian'' line, whose intensity increases still stronger than that of the narrow line. It can be shown that it is due to the existence of mesomorphic clusters the directors of which are statistically distributed in the sample. The impurity dependence of these effects is investigated and an attempt is made to explain them. (author)

Melting Can Hinder Impact-Induced Adhesion

Science.gov (United States)

Hassani-Gangaraj, Mostafa; Veysset, David; Nelson, Keith A.; Schuh, Christopher A.

2017-10-01

Melting has long been used to join metallic materials, from welding to selective laser melting in additive manufacturing. In the same school of thought, localized melting has been generally perceived as an advantage, if not the main mechanism, for the adhesion of metallic microparticles to substrates during a supersonic impact. Here, we conduct the first in situ supersonic impact observations of individual metallic microparticles aimed at the explicit study of melting effects. Counterintuitively, we find that under at least some conditions melting is disadvantageous and hinders impact-induced adhesion. In the parameter space explored, i.e., ˜10 μ m particle size and ˜1 km /s particle velocity, we argue that the solidification time is much longer than the residence time of the particle on the substrate, so that resolidification cannot be a significant factor in adhesion.

Property Investigation of Laser Cladded, Laser Melted and Electron Beam Melted Ti-Al6-V4

Science.gov (United States)

2006-05-01

UNCLASSIFIED/UNLIMITED UNCLASSIFIED/UNLIMITED Figure 3: Examples of electron beam melted net shape parts; powder bed [3]. 1.4 Laser Cladding ...description, www.arcam.com. [4] K.-H. Hermann, S. Orban, S. Nowotny, Laser Cladding of Titanium Alloy Ti6242 to Restore Damaged Blades, Proceedings...Property Investigation of Laser Cladded , Laser Melted and Electron Beam Melted Ti-Al6-V4 Johannes Vlcek EADS Deutschland GmbH Corporate Research

DETERMINATION OF HLW GLASS MELT RATE USING X-RAY COMPUTED TOMOGRAPHY

Energy Technology Data Exchange (ETDEWEB)

Choi, A.; Miller, D.; Immel, D.

2011-10-06

, a significant amount of glassy material interspersed among the gas bubbles will be excluded, thus underestimating the melt rate. Likewise, if they are drawn too high, many large voids will be counted as glass, thus overestimating the melt rate. As will be shown later in this report, there is also no guarantee that a given distribution of glass and gas bubbles along a particular sectioned plane will always be representative of the entire sample volume. Poor reproducibility seen in some LMR data may be related to these difficulties of the visual method. In addition, further improvement of the existing melt rate model requires that the overall impact of feed chemistry on melt rate be reflected on measured data at a greater quantitative resolution on a more consistent basis than the visual method can provide. An alternate method being pursued is X-ray computed tomography (CT). It involves X-ray scanning of glass samples, performing CT on the 2-D X-ray images to build 3-D volumetric data, and adaptive segmentation analysis of CT results to not only identify but quantify the distinct regions within each sample based on material density and morphologies. The main advantage of this new method is that it can determine the relative local density of the material remaining in the beaker after the heat treatment regardless of its morphological conditions by selectively excluding all the voids greater than a given volumetric pixel (voxel) size, thus eliminating much of the subjectivity involved in the visual method. As a result, the melt rate data obtained from CT scan will give quantitative descriptions not only on the fully-melted glass, but partially-melted and unmelted feed materials. Therefore, the CT data are presumed to be more reflective of the actual melt rate trends in continuously-fed melters than the visual data. In order to test the applicability of X-ray CT scan to the HLW glass melt rate study, several new series of HLW simulant/frit mixtures were melted in the

Estimation of Melt Pond Fractions on First Year Sea Ice Using Compact Polarization SAR

Science.gov (United States)

Li, Haiyan; Perrie, William; Li, Qun; Hou, Yijun

2017-10-01

Melt ponds are a common feature on Arctic sea ice. They are linked to the sea ice surface albedo and transmittance of energy to the ocean from the atmosphere and thus constitute an important process to parameterize in Arctic climate models and simulations. This paper presents a first attempt to retrieve the melt pond fraction from hybrid-polarized compact polarization (CP) SAR imagery, which has wider swath and shorter revisit time than the quad-polarization systems, e.g., from RADARSAT-2 (RS-2). The co-polarization (co-pol) ratio has been verified to provide estimates of melt pond fractions. However, it is a challenge to link CP parameters and the co-pol ratio. The theoretical possibility is presented, for making this linkage with the CP parameter C22/C11 (the ratio between the elements of the coherence matrix of CP SAR) for melt pond detection and monitoring with the tilted-Bragg scattering model for the ocean surface. The empirical transformed formulation, denoted as the "compact polarization and quad-pol" ("CPQP") model, is proposed, based on 2062 RS-2 quad-pol SAR images, collocated with in situ measurements. We compared the retrieved melt pond fraction with CP parameters simulated from quad-pol SAR data with results retrieved from the co-pol ratio from quad-pol SAR observations acquired during the Arctic-Ice (Arctic-Ice Covered Ecosystem in a Rapidly Changing Environment) field project. The results are shown to be comparable for observed melt pond measurements in spatial and temporal distributions. Thus, the utility of CP mode SAR for melt pond fraction estimation on first year level ice is presented.

Power-to-melt evaluation of fresh mixed-oxide fast reactor fuel. Technical improvements of the post-irradiation-experiment and the evaluation of the results for the power-to-melt test PTM-2 in 'JOYO'

International Nuclear Information System (INIS)

Yamamoto, Kazuya; Kushida, Naoya; Koizumi, Atsuhiro

1999-11-01

The second Power-To-Melt (PTM) test, PTM-2, was performed in the experimental fast reactor 'JOYO'. All of the twenty-four fuel pins of the irradiation vehicle, B5D-2, for the PTM-2 test, were provided for post-irradiation-experiment (PIE) to evaluate the PTM values. In this study, the PIE technique for PTM test was established and the PTM results were evaluated. The findings are as follows: The maximum fuel-melting ratio on the transverse section was 10.7%, and was within the limit of fuel-melting in this PTM test enough. Unexpected fuel-melting amount to a ratio of 11.8% was found at ∼24 mm below the peak power elevation in a test fuel pin. It is possible that this arose from secondary fuel-melting. Combination of metallographical observation with X-ray microanalysis of plutonium distribution was very effective for the identification of once-molten fuel zone. The PTM evaluation suggested that dependence of the PTM on the fuel pellet density was stronger than that of previous foreign PTM tests, while the dependence on the pellet-cladding gap and the oxygen-to-metal ratio was indistinctly. The dependence on the cladding temperature and the fill gas composition was not shown as well. (author)

Living and Working Beneath the Sea – Next Approach

Directory of Open Access Journals (Sweden)

Rowiński Lech

2017-04-01

Full Text Available The idea of living beneath the sea is very new if compared with millennia of shipping activity. In fact, ocean surface was considered mainly as medium suitable for transport of persons and goods as well as aggression and robbery. More practical attempts to live “on” the water surface are limited to well protected internal waters.

Evidence for large compositional ranges in coeval melts erupted from Kīlauea's summit reservoir: Chapter 7

Science.gov (United States)

Helz, Rosalind T.; Clague, David A.; Mastin, Larry G.; Rose, Timothy R.; Carey, Rebecca; Cayol, Valérie; Poland, Michael P.; Weis, Dominique

2015-01-01

Petrologic observations on Kīlauea's lavas include abundant microprobe analyses of glasses, which show the range of melts available in Kīlauea's summit reservoir over time. During the past two centuries, compositions of melts erupted within the caldera have been limited to MgO = 6.3–7.5 wt%. Extracaldera lavas of the 1959, 1971, and 1974 eruptions contain melts with up to 10.2, 8.9, and 9.2 wt% MgO, respectively, and the 1924 tephra contains juvenile Pele's tears with up to 9.1 wt% MgO. Melt compositions from explosive deposits at Kīlauea, including the Keanakāko‘i (A.D. 1500–1800), Kulanaokuaiki (A.D. 400–1000), and Pāhala (10–25 ka) tephra units, show large ranges of MgO contents. The range of melt MgO is 6.5–11.0 wt% for the Keanakāko‘i; the Kulanaokuaiki extends to 12.5% MgO and the Pāhala Ash includes rare shards with 13–14.5% MgO. The frequency distributions for MgO in the Keanakāko‘i and Kulanaokuaiki glasses are bimodal, suggesting preferential magma storage at two different depths. Kīlauea's summit reservoir contains melts ranging from 6.5 to at least 11.0 wt% MgO, and such melts were available for sampling near instantaneously and repeatedly over centuries. More magnesian melts are inferred to have risen directly from greater depth.

Modelling and parameterizing the influence of tides on ice-shelf melt rates

Science.gov (United States)

Jourdain, N.; Molines, J. M.; Le Sommer, J.; Mathiot, P.; de Lavergne, C.; Gurvan, M.; Durand, G.

2017-12-01

Significant Antarctic ice sheet thinning is observed in several sectors of Antarctica, in particular in the Amundsen Sea sector, where warm circumpolar deep waters affect basal melting. The later has the potential to trigger marine ice sheet instabilities, with an associated potential for rapid sea level rise. It is therefore crucial to simulate and understand the processes associated with ice-shelf melt rates. In particular, the absence of tides representation in ocean models remains a caveat of numerous ocean hindcasts and climate projections. In the Amundsen Sea, tides are relatively weak and the melt-induced circulation is stronger than the tidal circulation. Using a regional 1/12° ocean model of the Amundsen Sea, we nonetheless find that tides can increase melt rates by up to 36% in some ice-shelf cavities. Among the processes that can possibly affect melt rates, the most important is an increased exchange at the ice/ocean interface resulting from the presence of strong tidal currents along the ice drafts. Approximately a third of this effect is compensated by a decrease in thermal forcing along the ice draft, which is related to an enhanced vertical mixing in the ocean interior in presence of tides. Parameterizing the effect of tides is an alternative to the representation of explicit tides in an ocean model, and has the advantage not to require any filtering of ocean model outputs. We therefore explore different ways to parameterize the effects of tides on ice shelf melt. First, we compare several methods to impose tidal velocities along the ice draft. We show that getting a realistic spatial distribution of tidal velocities in important, and can be deduced from the barotropic velocities of a tide model. Then, we explore several aspects of parameterized tidal mixing to reproduce the tide-induced decrease in thermal forcing along the ice drafts.

Evidence for Slab Melt Contributions to the Mexican Volcanic Belt and Other Young Hot Slab Arcs from Lu-Hf Isotopes

Science.gov (United States)

Goldstein, S. L.; Cai, Y. M.; Langmuir, C. H.; Lagatta, A.; Straub, S. M.; Gomez-Tuena, A.; Martin Del Pozzo, A.

2007-12-01

substantial subducted slab melt contributions to these lavas. Preliminary data from the Colima region in western Mexico also indicate subducted ocean crust melt in stratovolcano lavas. The oceanic crust at the trench near Western and Central Mexico ranges in age from Pliocene to Miocene, thus represents subduction of a young hot slab. The southern Cascades are another case where a young hot slab is being subducted beneath a thick continental crust, and where both calcalkaline and high-Nb alkaline lavas are erupted. These suites show analogous trace element and isotopic relationships to Mexico that delineate contributions from melting of the subducted oceanic crust to the calcalkaline lavas. In contrast, the subducted ocean crust melt signature is absent from western Pacific arcs, where old cold slabs are being subducted, such as the Marianas, New Britain, and Kermedec. Thus the global data thus suggest that Lu- Hf isotopes represent an effective tracer for slab melting, and that young hot slabs melt and old cold slabs don't. We note that our Colima samples are from Jim Luhr, whose interest, enthusiastic support for MVB studies, and generosity are hereby acknowledged and greatly appreciated, and whose scientific counsel is greatly missed.

Saturation of cermets based on titanium carbide and diboride by metal melts

International Nuclear Information System (INIS)

Kitsaj, A.A.; Tsyganova, T.V.; Ordan'yan, S.S.

1985-01-01

Different sintered composites - TiC-Ni(Mo), TiC-Fe (Ni), TiB 2 -Fe (Mo) are studied for their interaction in contact with metal melts at the temperature of liquid phase existence in the cermet. Due to structural and physicochemical similarity of cermets the processes occuring with contact interaction are identical: additional quantity of liquid is imbibed into the cermet resulting in reconstruction of the solid phase frame and volumetric growth of the specimen. Elongation of the specimens permits concluding that the intensity of the solid phase (frame) reconstruction process in the cermet TiC-Fe (Ni) is lower than in TiC-Ni (Mo) and TiB 2 -Fe (Mo) systems. In the TiC-Fe (Ni) cermet it causes prevalence of the processes of diffusional levellng for compositions of the metal-binder and contacting metal over the process of laminar flow of the melt into the specimen. Choosing the composite components it is possible to control intensity of the cermet saturation by the additional quantity of the melt and distribution of the liquid phase in the article volume

Plasma arc melting of titanium-tantalum alloys

International Nuclear Information System (INIS)

Dunn, P.; Patterson, R.A.; Haun, R.

1994-01-01

Los Alamos has several applications for high temperature, oxidation and liquid-metal corrosion resistant materials. Further, materials property constraints are dictated by a requirement to maintain low density; e.g., less than the density of stainless steel. Liquid metal compatibility and density requirements have driven the research toward the Ti-Ta system with an upper bound of 60 wt% Ta-40 wt% Ti. Initial melting of these materials was performed in a small button arc melter with several hundred grams of material; however, ingot quantities were soon needed. But, refractory metal alloys whose constituents possess very dissimilar densities, melting temperatures and vapor pressures pose significant difficulty and require specialized melting practices. The Ti-Ta alloys fall into this category with the density of tantalum 16.5 g/cc and that of titanium 4.5 g/cc. Melting is further complicated by the high melting point of Ta(3020 C) and the relatively low boiling point of Ti(3287 C). Previous electron beam melting experience with these materials resulted, in extensive vaporization of the titanium and poor chemical homogeneity. Vacuum arc remelting(VAR) was considered as a melting candidate and discarded due to density and vapor pressure issues associated with electron beam. Plasma arc melting offered the ability to supply a cover gas to deal with vapor pressure issues as well as solidification control to help with macrosegregation in the melt and has successfully produced high quality ingots of the Ti-Ta alloys

Chemical decontamination and melt densification of chop-leach fuel hulls

International Nuclear Information System (INIS)

Dillon, R.L.; Griggs, B.; Kemper, R.S.; Nelson, R.G.

1976-01-01

This paper reports on decontamination and densification studies of chop-leach fuel hull residues designed to minimize the transuranic element (TRU) contaminated waste stream. Decontamination requirements have been established from studies of TRU element distribution in the fuel hull residues. Effective surface decontamination of Zircaloy requires removal of zirconium oxide corrosion products. Good decontamination factors have been achieved with aqueous solutions following high temperature HF conditioning of oxide films. Molten fluoride salt mixtures are effective decontaminants, but pose problems in metal loss and salt dragout. Molten metal decontamination methods are highly preliminary, but may be required to reduce TRU originating from tramp uranium in Zircaloy. Low melting (1300 0 C) alloy of Zircaloy, stainless steel, and Inconel have been prepared in induction heated graphite crucibles. High quality ingots of Zircaloy-2 have been prepared directly from short sections of descaled fuel clad tubing using the Inductoslag process. This material is readily capable of refabrication. Inductoslag melts have also been prepared from heavily oxidized Zircaloy tubing demonstrating melt densification without prior decontamination is technically feasible. Hydrogen absorption kinetics have been demonstrated with cast Zircaloy-2 and cast Zircaloy-stainless steel-Inconel alloys. Metallic fuel hull residues have been proposed as a storage medium for tritium released from fuel during reprocessing. (author)

The Effects of Ridge Axis Width on Mantle Melting at Mid-Ocean Ridges

Science.gov (United States)

Montesi, L.; Magni, V.; Gaina, C.

2017-12-01

Mantle upwelling in response to plate divergence produces melt at mid-ocean ridges. Melt starts when the solidus is crossed and stops when conductive cooling overcomes heat advection associated with the upwelling. Most mid-ocean ridge models assume that divergence takes place only in a narrow zone that defines the ridge axis, resulting in a single upwelling. However, more complex patterns of divergence are occasionally observed. The rift axis can be 20 km wide at ultraslow spreading center. Overlapping spreading center contain two parallel axes. Rifting in backarc basins is sometimes organized as a series of parallel spreading centers. Distributing plate divergence over several rifts reduces the intensity of upwelling and limits melting. Can this have a significant effect on the expected crustal thickness and on the mode of melt delivery at the seafloor? We address this question by modeling mantle flow and melting underneath two spreading centers separated by a rigid block. We adopt a non-linear rheology that includes dislocation creep, diffusion creep and yielding and include hydrothermal cooling by enhancing thermal conductivity where yielding takes place. The crustal thickness decreases if the rifts are separated by 30 km or more but only if the half spreading rate is between 1 and 2 cm/yr. At melting depth, a single upwelling remains the norm until the separation of the rifts exceeds a critical value ranging from 15 km in the fastest ridges to more than 50 km at ultraslow spreading centers. The stability of the central upwelling is due to hydrothermal cooling, which prevents hot mantle from reaching the surface at each spreading center. When hydrothermal cooling is suppressed, or the spreading centers are sufficiently separated, the rigid block becomes extremely cold and separates two distinct, highly asymmetric upwellings that may focus melt beyond the spreading center. In that case, melt delivery might drive further and further the divergence centers, whereas

Hydrogen study in melt inclusions trapped in quartz with nuclear microprobe

International Nuclear Information System (INIS)

Mosbah, M.; Tirira, J.; Gosset, J.; Massiot, P.

1990-01-01

Elastic recoil spectrometry induced by 3 MeV helium-4 microbeam has been used to determine hydrogen distribution within melt inclusions trapped in quartz. These minerals were selected from different geological environments: Guadeloupe (West Indies), Pantelleria Island (South Sicily - Italy) and San Pietro (South Sardinia - Italy). Bulk hydrogen contents are calculated (H assumed to be in H 2 O form). The knowledge of hydrogen distribution assists both in a better understanding and in the establishment of volcanic dynamism hypotheses. Finally, fluid hydrogen rich inclusions are evidenced and H concentration profile is simulated and reported for the first time in glass inclusion

Growth of binary solid solution single crystals and calculation of melt surface displacement velocity

International Nuclear Information System (INIS)

Agamaliyev, Z.A.; Tahirov, V.I.; Hasanov, Z.Y.; Quliyev, A.F.

2007-01-01

A binary solid solution single crystal growth method has been worked out. Cylinder feeding alloy with complex content distribution and truncated cone crucible are used. Second component distribution coefficient is more than unit. Content distribution along grown crystal is found by solving continuity equation. After reaching dynamic equilibrium state second component concentration in grown crystal is saturated the value of which is less than the average ona in the feeding alloy. Using the method Ge-Si perfect single crystals has been grown. Calculation method of melt surface displacement velocity has been offered as well

Efficiency of assisted hatching of the cryopreserved–melted embryos

Directory of Open Access Journals (Sweden)

V. A. Pitko

2018-04-01

Full Text Available Purpose. To measure outcomes of clinical research of efficiency of assisted hatching of cryopreserved embryos. Materials and methods. Patients who had un successful cycles IVF/ICSI with transfer of fresh embryos have been selected for participation in the research between 2014 and 2016 years. Patients were distributed in a random way for participation in the experiment and control groups. Results of embryos transfer of one or two cryopreserved and melted embryos were considered only. Embryos were cryopreserved at a stage of blastocyst, 5 days after extraction of oocytes by method of vitrification. Melting procedure was conducted in the morning of a day of embryos transfer following the instructions of the vitrification medium producer Cryotech (Japan. Assisted hatching was conducted with use of micropipettes of Holding Pipette Cook Medical (Australia and Assisted Hatching/Zona Drilling Pipette Cook Medical (Australia. The treated embryos were cultivated up to a repeated estimation of morphology of embryos before transfer. Transfer of embryos has been conducted by a standard method with the use of catheter for non-invasive transfer of embryo Sydney IVF Cook Medical (Australia. The quantity of the transferred embryos varied from one to two. Results. 100 cryopreserved embryos were transferred which have been distributed in a random way either to the group with the assisted hatching or to the control group (without assisted hatching. A number of parameters of patients from both groups was analyzed, i.e. age of the patient at the time of melting of embryos, duration of infertility, causes of infertility, quantity of previous unsuccessful cycles IVF/ICSI. Any essential differences between patients within two groups based on the aforementioned parameters were not revealed. Also, there were no essential differences in number of the melted embryos, survival rate of embryos, quantity of the embryos transferred to patients. However, at the same time

A Feasibility Study on UO2/ZrO2 Mixture Melting using Induction Skull Melting Method

International Nuclear Information System (INIS)

Hong, S. W.; Kim, J. H.; Kim, H. D.

1998-01-01

Using ISM(Induction Skull Melting) method, which is usually used for the crystallization of refractory materials, a feasibility study on melting of the UO 2 /ZrO 2 mixture(w/o 8:2) is carried out. Frequency, one of main design parameters for ISM, is determined from electrical resistance of UO 2 /ZrO 2 mixture. Heat loss from the crucible for UO 2 /ZrO 2 20kg melting is predicted by comparison with the existing experimental data for UO , ZrO 2 , and ThO 2 . The analysis shows that melting and superheating of the UO 2 /ZrO 2 mixture using induction skull melting method is possible. To attain the superheat of 300K for 20 kg of UO 2 /ZrO 2 , 100kHz, 100 kW power input for induction coil, and 570L/min coolant flow rate are found to be required. The results of this feasibility study will be adopted for designing UO 2 /ZrO 2 furnace using actual corium material at KAERI

Relationships between seismic wave-Speed, density, and electrical conductivity beneath Australia from seismology, mineralogy, and laboratory-based conductivity profiles

DEFF Research Database (Denmark)

Khan, A.; Koch, S.; Shankland, T. J.

2015-01-01

We present maps of the three-dimensional density (ρ), electrical conductivity (σ), and shear-wave speed (VS) structure of the mantle beneath Australia and surrounding ocean in the depth range of 100–800 km. These maps derived from stochastic inversion of seismic surface-wave dispersion data...... shear-wave speeds, low densities, and high conductivities. This trend appears to continue to depths well below 300 km. The slow-fast shear-wave speed distribution found here is also observed in independent seismic tomographic models of the Australian region, whereas the coupled slow-fast shear......-wave speed, low-high density, and high-low electrical conductivity distribution has not been observed previously. Toward the bottom of the upper mantle at 400 km depth marking the olivine ⃗ wadsleyite transformation (the “410–km” seismic discontinuity), the correlation between VS, ρ, and σ weakens...

Features of melting of indium monohalides

Energy Technology Data Exchange (ETDEWEB)

Dmitriev, V S; Smirniv, V A [AN SSSR, Chernogolovka. Inst. Fiziki Tverdogo Tela

1980-12-01

The character of InCl, InBr and InI melting is investigated by the methods of DTA, calorimetry, conductometry and chemical analysis. Partial decomposition of monohalogenides during melting according to the reactions of disproportionation is shown. The presence of disproportionation products (In/sup 0/ and In/sup 3 +/) is manifested in the properties of solid monohalogenides, prepared by the crystallization from melt, in their photosensitivity and electroconductivity.

Waveform modeling of the seismic response of a mid-ocean ridge axial melt sill

Science.gov (United States)

Xu, Min; Stephen, R. A.; Canales, J. Pablo

2017-12-01

Seismic reflections from axial magma lens (AML) are commonly observed along many mid-ocean ridges, and are thought to arise from the negative impedance contrast between a solid, high-speed lid and the underlying low-speed, molten or partially molten (mush) sill. The polarity of the AML reflection ( P AML P) at vertical incidence and the amplitude vs offset (AVO) behavior of the AML reflections (e.g., P AML P and S-converted P AML S waves) are often used as a diagnostic tool for the nature of the low-speed sill. Time-domain finite difference calculations for two-dimensional laterally homogeneous models show some scenarios make the interpretation of melt content from partial-offset stacks of P- and S-waves difficult. Laterally heterogeneous model calculations indicate diffractions from the edges of the finite-width AML reducing the amplitude of the AML reflections. Rough seafloor and/or a rough AML surface can also greatly reduce the amplitude of peg-leg multiples because of scattering and destructive interference. Mid-crustal seismic reflection events are observed in the three-dimensional multi-channel seismic dataset acquired over the RIDGE-2000 Integrated Study Site at East Pacific Rise (EPR, cruise MGL0812). Modeling indicates that the mid-crustal seismic reflection reflections are unlikely to arise from peg-leg multiples of the AML reflections, P-to- S converted phases, or scattering due to rough topography, but could probably arise from deeper multiple magma sills. Our results support the identification of Marjanović et al. (Nat Geosci 7(11):825-829, 2014) that a multi-level complex of melt lenses is present beneath the axis of the EPR.

Geothermal flux and basal melt rate in the Dome C region inferred from radar reflectivity and heat modelling

Science.gov (United States)

Passalacqua, Olivier; Ritz, Catherine; Parrenin, Frédéric; Urbini, Stefano; Frezzotti, Massimo

2017-09-01

Basal melt rate is the most important physical quantity to be evaluated when looking for an old-ice drilling site, and it depends to a great extent on the geothermal flux (GF), which is poorly known under the East Antarctic ice sheet. Given that wet bedrock has higher reflectivity than dry bedrock, the wetness of the ice-bed interface can be assessed using radar echoes from the bedrock. But, since basal conditions depend on heat transfer forced by climate but lagged by the thick ice, the basal ice may currently be frozen whereas in the past it was generally melting. For that reason, the risk of bias between present and past conditions has to be evaluated. The objective of this study is to assess which locations in the Dome C area could have been protected from basal melting at any time in the past, which requires evaluating GF. We used an inverse approach to retrieve GF from radar-inferred distribution of wet and dry beds. A 1-D heat model is run over the last 800 ka to constrain the value of GF by assessing a critical ice thickness, i.e. the minimum ice thickness that would allow the present local distribution of basal melting. A regional map of the GF was then inferred over a 80 km × 130 km area, with a N-S gradient and with values ranging from 48 to 60 mW m-2. The forward model was then emulated by a polynomial function to compute a time-averaged value of the spatially variable basal melt rate over the region. Three main subregions appear to be free of basal melting, two because of a thin overlying ice and one, north of Dome C, because of a low GF.

Melt Fragmentation Characteristics of Metal Fuel with Melt Injection Mass during Initiating Phase of SFR Severe Accidents

Energy Technology Data Exchange (ETDEWEB)

Heo, Hyo; Lee, Min Ho; Bang, In Cheol [Ulsan National Institute of Science and Technology, Ulsan (Korea, Republic of); Jerng, Dong Wook [Chung-Ang Univ., Seoul (Korea, Republic of)

2016-05-15

The PGSFR has adopted the metal fuel for its inherent safety under severe accident conditions. However, this fuel type is not demonstrated clearly yet under the such severe accident conditions. Additional experiments for examining these issues should be performed to support its licensing activities. Under initiating phase of hypothetic core disruptive accident (HCDA) conditions, the molten metal could be better dispersed and fragmented into the coolant channel than in the case of using oxide fuel. This safety strategy provides negative reactivity driven by a good dispersion of melt. If the coolant channel does not sufficient coolability, the severe recriticality would occur within the core region. Thus, it is important to examine the extent of melt fragmentation. The fragmentation behaviors of melt are closely related to a formation of debris shape. Once the debris shape is formed through the fragmentation process, its coolability is determined by the porosity or thermal conductivity of the melt. There were very limited studies for transient irradiation experiments of the metal fuel. These studies were performed by Transient Reactor Test Facility (TREAT) M series tests in U.S. The TREAT M series tests provided basic information of metal fuel performance under transient conditions. The effect of melt injection mass was evaluated in terms of the fragmentation behaviors of melt. These behaviors seemed to be similar between single-pin and multi-pins failure condition. However, the more melt was agglomerated in case of multi-pins failure.

Package of programs for calculating accidents involving melting of the materials in a fast-reactor vessel

International Nuclear Information System (INIS)

Vlasichev, G.N.

1994-01-01

Methods for calculating one-dimensional nonstationary temperature distribution in a system of physically coupled materials are described. Six computer programs developed for calculating accident processes for fast reactor core melt are described in the article. The methods and computer programs take into account melting, solidification, and, in some cases, vaporization of materials. The programs perform calculations for heterogeneous systems consisting of materials with arbitrary but constant composition and heat transfer conditions at material boundaries. Additional modules provide calculations of specific conditions of heat transfer between materials, the change in these conditions and configuration of the materials as a result of coolant boiling, melting and movement of the fuel and structural materials, temperature dependences of thermophysical properties of the materials, and heat release in the fuel. 11 refs., 3 figs

Electron beam melting of bearing materials

Energy Technology Data Exchange (ETDEWEB)

Goldschmied, G.; Schuler, A. (Technische Univ., Vienna (Austria). Inst. fuer Allgemeine Elektrotechnik); Elsinger, G.; Koroschetz, F. (MIBA Gleitlager AG, Laakirchen (Austria)); Tschegg, E.K. (Technische Univ., Vienna (Austria). Inst. fuer Angewandte und Technische Physik)

1990-06-01

This paper reports on a surface treatment method for the bearing materials AlSn6 which permits the use of this material without the overlay usually required. Microstructural refinement is achieved by means of a surface melting technique using an electron beam with successive rapid solidification. Extremely fine tin precipitates are formed in the melted surface layer which lead to significantly better tribological properties of the bearing material. Tests compared the tribological properties for AlSn6 bearings treated by the surface melting technique with those of untreated bearings. Whereas all untreated bearings failed by seizure after only 2 h of testing, 30% of the tested bearings which had been surface melted survived the entire testing program without damage.

Lower crustal relaxation beneath the Tibetan Plateau and Qaidam Basin following the 2001 Kokoxili earthquake

Science.gov (United States)

Ryder, I.; Burgmann, R.; Pollitz, F.

2011-01-01

In 2001 November a magnitude 7.8 earthquake ruptured a 400 km long portion of the Kunlun fault, northeastern Tibet. In this study, we analyse over five years of post-seismic geodetic data and interpret the observed surface deformation in terms of stress relaxation in the thick Tibetan lower crust. We model GPS time-series (first year) and InSAR line of sight measurements (years two to five) and infer that the most likely mechanism of post-seismic stress relaxation is time-dependent distributed creep of viscoelastic material in the lower crust. Since a single relaxation time is not sufficient to model the observed deformation, viscous flow is modelled by a lower crustal Burgers rheology, which has two material relaxation times. The optimum model has a transient viscosity 9 ?? 1017 Pa s, steady-state viscosity 1 ?? 1019 Pa s and a ratio of long term to Maxwell shear modulus of 2:3. This model gives a good fit to GPS stations south of the Kunlun Fault, while displacements at stations north of the fault are over-predicted. We attribute this asymmetry in the GPS residual to lateral heterogeneity in rheological structure across the southern margin of the Qaidam Basin, with thinner crust/higher viscosities beneath the basin than beneath the Tibetan Plateau. Deep afterslip localized in a shear zone beneath the fault rupture gives a reasonable match to the observed InSAR data, but the slip model does not fit the earlier GPS data well. We conclude that while some localized afterslip likely occurred during the early post-seismic phase, the bulk of the observed deformation signal is due to viscous flow in the lower crust. To investigate regional variability in rheological structure, we also analyse post-seismic displacements following the 1997 Manyi earthquake that occurred 250 km west of the Kokoxili rupture. We find that viscoelastic properties are the same as for the Kokoxili area except for the transient viscosity, which is 5 ?? 1017 Pa s. The viscosities estimated for the

Melt spreading code assessment, modifications, and application to the EPR core catcher design

International Nuclear Information System (INIS)

Farmer, M.T.

2009-01-01

The Evolutionary Power Reactor (EPR) is under consideration by various utilities in the United States to provide base load electrical production, and as a result the design is undergoing a certification review by the U.S. Nuclear Regulatory Commission (NRC). The severe accident design philosophy for this reactor is based upon the fact that the projected power rating results in a narrow margin for in-vessel melt retention by external cooling of the reactor vessel. As a result, the design addresses ex-vessel core melt stabilization using a mitigation strategy that includes: (1) an external core melt retention system to temporarily hold core melt released from the vessel; (2) a layer of 'sacrificial' material that is admixed with the melt while in the core melt retention system; (3) a melt plug in the lower part of the retention system that, when failed, provides a pathway for the mixture to spread to a large core spreading chamber; and finally, (4) cooling and stabilization of the spread melt by controlled top and bottom flooding. The overall concept is illustrated in Figure 1.1. The melt spreading process relies heavily on inertial flow of a low-viscosity admixed melt to a segmented spreading chamber, and assumes that the melt mass will be distributed to a uniform height in the chamber. The spreading phenomenon thus needs to be modeled properly in order to adequately assess the EPR design. The MELTSPREAD code, developed at Argonne National Laboratory, can model segmented, and both uniform and nonuniform spreading. The NRC is thus utilizing MELTSPREAD to evaluate melt spreading in the EPR design. MELTSPREAD was originally developed to support resolution of the Mark I containment shell vulnerability issue. Following closure of this issue, development of MELTSPREAD ceased in the early 1990's, at which time the melt spreading database upon which the code had been validated was rather limited. In particular, the database that was utilized for initial validation consisted

Nitrogen Control in VIM Melts

Science.gov (United States)

Jablonski, P. D.; Hawk, J. A.

NETL has developed a design and control philosophy for the addition of nitrogen to austenitic and ferritic steels. The design approach uses CALPHAD as the centerpiece to predict the level to which nitrogen is soluble in both the melt and the solid. Applications of this technique have revealed regions of "exclusion" in which the alloy, while within specification limits of prescribed, cannot be made by conventional melt processing. Furthermore, other investigations have found that substantial retrograde solubility of nitrogen exists, which can become problematic during subsequent melt processing and/or other finishing operations such as welding. Additionally, the CALPHAD method has been used to adjust primary melt conditions. To that end, nitrogen additions have been made using chrome nitride, silicon nitride, high-nitrogen ferrochrome as well as nitrogen gas. The advantages and disadvantages of each approach will be discussed and NETL experience in this area will be summarized with respect to steel structure.

Additive Manufacturing Processes: Selective Laser Melting, Electron Beam Melting and Binder Jetting-Selection Guidelines.

Science.gov (United States)

Gokuldoss, Prashanth Konda; Kolla, Sri; Eckert, Jürgen

2017-06-19

Additive manufacturing (AM), also known as 3D printing or rapid prototyping, is gaining increasing attention due to its ability to produce parts with added functionality and increased complexities in geometrical design, on top of the fact that it is theoretically possible to produce any shape without limitations. However, most of the research on additive manufacturing techniques are focused on the development of materials/process parameters/products design with different additive manufacturing processes such as selective laser melting, electron beam melting, or binder jetting. However, we do not have any guidelines that discuss the selection of the most suitable additive manufacturing process, depending on the material to be processed, the complexity of the parts to be produced, or the design considerations. Considering the very fact that no reports deal with this process selection, the present manuscript aims to discuss the different selection criteria that are to be considered, in order to select the best AM process (binder jetting/selective laser melting/electron beam melting) for fabricating a specific component with a defined set of material properties.

Additive Manufacturing Processes: Selective Laser Melting, Electron Beam Melting and Binder Jetting—Selection Guidelines

Science.gov (United States)

Konda Gokuldoss, Prashanth; Kolla, Sri; Eckert, Jürgen

2017-01-01

Additive manufacturing (AM), also known as 3D printing or rapid prototyping, is gaining increasing attention due to its ability to produce parts with added functionality and increased complexities in geometrical design, on top of the fact that it is theoretically possible to produce any shape without limitations. However, most of the research on additive manufacturing techniques are focused on the development of materials/process parameters/products design with different additive manufacturing processes such as selective laser melting, electron beam melting, or binder jetting. However, we do not have any guidelines that discuss the selection of the most suitable additive manufacturing process, depending on the material to be processed, the complexity of the parts to be produced, or the design considerations. Considering the very fact that no reports deal with this process selection, the present manuscript aims to discuss the different selection criteria that are to be considered, in order to select the best AM process (binder jetting/selective laser melting/electron beam melting) for fabricating a specific component with a defined set of material properties. PMID:28773031

Subsurface imaging reveals a confined aquifer beneath an ice-sealed Antarctic lake

DEFF Research Database (Denmark)

Dugan, H. A.; Doran, P. T.; Tulaczyk, S.

2015-01-01

Liquid water oases are rare under extreme cold desert conditions found in the Antarctic McMurdo Dry Valleys. Here we report geophysical results that indicate that Lake Vida, one of the largest lakes in the region, is nearly frozen and underlain by widespread cryoconcentrated brine. A ground...... this zone to be a confined aquifer situated in sediments with a porosity of 23-42%. Discovery of this aquifer suggests that subsurface liquid water may be more pervasive in regions of continuous permafrost than previously thought and may represent an extensive habitat for microbial populations. Key Points...... Geophysical survey finds low resistivities beneath a lake in Antarctic Dry Valleys Liquid brine abundant beneath Antarctic lake Aquifer provides microbial refugium in cold desert environment...

The Laser Damage Threshold for Materials and the Relation Between Solid-Melt and Melt-Vapor Interface Velocities

International Nuclear Information System (INIS)

Khalil, Osama Mostafa

2010-01-01

Numerous experiments have demonstrated and analytic theories have predicted that there is a threshold for pulsed laser ablation of a wide range of materials. Optical surface damage threshold is a very complex and important application of high-power lasers. Optical damage may also be considered to be the initial phase of laser ablation. In this work it was determined the time required and the threshold energy of a layer of thickness to heat up. We used the Finite Difference method to simulate the process of laser-target interaction in three cases. Namely, the case before melting begins using a continuous wave (c.w) laser source and a pulsed laser source, the case after the first change of state (from solid to melt), and the case after the second change of state (from melt to vapor). And also study the relation between the solid-melt and melt-vapor interface velocities to have a commonsense of the laser ablation process.

Melt-processing method for radioactive solid wastes

International Nuclear Information System (INIS)

Kobayashi, Hiroaki

1998-01-01

Radioactive solid wastes are charged into a water-cooled type cold crucible induction melting furnace disposed in high frequency coils, and high frequency currents are supplied to high frequency coils which surround the melting furnace to melt the solid wastes by induction-heating. In this case, heat plasmas are jetted from above the solid wastes to the solid wastes to conduct initial heating to melt a portion of the solid wastes. Then, high frequency currents are supplied to the high frequency coils to conduct induction heating. According to this method, even when waste components of various kinds of materials are mixed, a portion of the solid wastes in the induction melting furnace can be melted by the initial heating by jetting heat plasmas irrespective of the kinds and the electroconductivity of the materials of the solid wastes. With such procedures, entire solid wastes in the furnace can be formed into a molten state uniformly and rapidly. (T.M.)

High-Power Laser Cutting of Steel Plates: Heat Affected Zone Analysis

Directory of Open Access Journals (Sweden)

Imed Miraoui

2016-01-01

Full Text Available The thermal effect of CO2 high-power laser cutting on cut surface of steel plates is investigated. The effect of the input laser cutting parameters on the melted zone depth (MZ, the heat affected zone depth (HAZ, and the microhardness beneath the cut surface is analyzed. A mathematical model is developed to relate the output process parameters to the input laser cutting parameters. Three input process parameters such as laser beam diameter, cutting speed, and laser power are investigated. Mathematical models for the melted zone and the heat affected zone depth are developed by using design of experiment approach (DOE. The results indicate that the input laser cutting parameters have major effect on melted zone, heat affected zone, and microhardness beneath cut surface. The MZ depth, the HAZ depth, and the microhardness beneath cut surface increase as laser power increases, but they decrease with increasing cutting speed. Laser beam diameter has a negligible effect on HAZ depth but it has a remarkable effect on MZ depth and HAZ microhardness. The melted zone depth and the heat affected zone depth can be reduced by increasing laser cutting speed and decreasing laser power and laser beam diameter.

Characterization of melt-blended graphene – poly(ether ether ketone) nanocomposite

International Nuclear Information System (INIS)

Tewatia, Arya; Hendrix, Justin; Dong, Zhizhong; Taghon, Meredith; Tse, Stephen; Chiu, Gordon; Mayo, William E.; Kear, Bernard; Nosker, Thomas; Lynch, Jennifer

2017-01-01

Using a high shear melt-processing method, graphene-reinforced polymer matrix composites (G-PMCs) were produced with good distribution and particle–matrix interaction of bi/trilayer graphene at 2 wt. % and 5 wt. % in poly ether ether ketone (2Gn-PEEK and 5Gn-PEEK). The morphology, structure, thermal properties, and mechanical properties of PEEK, 2Gn-PEEK and 5 Gn-PEEK were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA), flexural mechanical testing, and dynamic mechanical analysis (DMA). Addition of graphene to PEEK induces surface crystallization, increased percent crystallinity, offers a composite that is thermally stable until 550 °C and enhances thermomechanical properties. Results show that graphene was successfully melt-blended within PEEK using this method.

Characterization of melt-blended graphene – poly(ether ether ketone) nanocomposite

Energy Technology Data Exchange (ETDEWEB)

Tewatia, Arya; Hendrix, Justin [Department of Materials Science and Engineering, Rutgers University, 607 Taylor Road, Piscataway, NJ, 08854 (United States); Dong, Zhizhong [Department of Mechanical Engineering, Rutgers University, 98 Brett Road, Piscataway, NJ 08854 (United States); Taghon, Meredith [Department of Materials Science and Engineering, Rutgers University, 607 Taylor Road, Piscataway, NJ, 08854 (United States); Tse, Stephen [Department of Mechanical Engineering, Rutgers University, 98 Brett Road, Piscataway, NJ 08854 (United States); Chiu, Gordon; Mayo, William E.; Kear, Bernard; Nosker, Thomas [Department of Materials Science and Engineering, Rutgers University, 607 Taylor Road, Piscataway, NJ, 08854 (United States); Lynch, Jennifer, E-mail: jklynch@rci.rutgers.edu [Department of Materials Science and Engineering, Rutgers University, 607 Taylor Road, Piscataway, NJ, 08854 (United States)

2017-02-15

Using a high shear melt-processing method, graphene-reinforced polymer matrix composites (G-PMCs) were produced with good distribution and particle–matrix interaction of bi/trilayer graphene at 2 wt. % and 5 wt. % in poly ether ether ketone (2Gn-PEEK and 5Gn-PEEK). The morphology, structure, thermal properties, and mechanical properties of PEEK, 2Gn-PEEK and 5 Gn-PEEK were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA), flexural mechanical testing, and dynamic mechanical analysis (DMA). Addition of graphene to PEEK induces surface crystallization, increased percent crystallinity, offers a composite that is thermally stable until 550 °C and enhances thermomechanical properties. Results show that graphene was successfully melt-blended within PEEK using this method.

Realization of Copper Melting Point for Thermocouple Calibrations

Directory of Open Access Journals (Sweden)

Y. A. ABDELAZIZ

2011-08-01

Full Text Available Although the temperature stability and uncertainty of the freezing plateau is better than that of the melting plateau in most of the thermometry fixed points, but realization of melting plateaus are easier than that of freezing plateaus for metal fixed points. It will be convenient if the melting points can be used instead of the freezing points in calibration of standard noble metal thermocouples because of easier realization and longer plateau duration of melting plateaus. In this work a comparison between the melting and freezing points of copper (Cu was carried out using standard noble metal thermocouples. Platinum - platinum 10 % rhodium (type S, platinum – 30 % rhodium / platinum 6 % rhodium (type B and platinum - palladium (Pt/Pd thermocouples are used in this study. Uncertainty budget analysis of the melting points and freezing points is presented. The experimental results show that it is possible to replace the freezing point with the melting point of copper cell in the calibration of standard noble metal thermocouples in secondary-level laboratories if the optimal methods of realization of melting points are used.

Partial enthalpies of Bi and Te in Bi-Te melts and of In and Te in In-Te melts

International Nuclear Information System (INIS)

Yassin, Abeer; Amzil, Abdelhamid; Castanet, Robert

2000-01-01

Full text.Calorimetric measurement are reported which allow the enthalpic behaviour of Bi-Te melts to be established. Further work is required, however, to supplement results obtained for In-Te melts. The partial enthalpies of bismuth and tellurium in the Bi-Te melts at 755K and those of indium and tellurium in the In-Te melts at 1010 and 987K were measured at high dilution by direct reaction calorimetry (drop method) with the help of a Tian-Calvet calorimeter. The limiting partial enthalpies of the components were deduced by extrapolation at infinite dilution: Δh f,∞ B i(755K)/KJ.mol -1 = -34.0 and Δh f,∞ Te(755K) /KJ·mol -1 = -24.1 in the Bi-Te melts Δh f,∞ In(1010K) /KJ·mol -1 = -75.9 and Δh f,∞ Te(1010K) /KJ·mol -1 = -47.8 in the In-Te melts Δh f,∞ In(987K) /KJ·mol -1 = -75.2 and Δh f,∞ Te(987K) /KJ·mol -1 = -48.0 in the In-Te melts

Theoretical work on melt-coolant interactions (steam explosions)

International Nuclear Information System (INIS)

Arnecke, G.; Jacobs, H.; Stehle, B.; Thurnay, K.; Vaeth, L.; Lummer, M.

1995-01-01

The code IVA3 is used for modelling the physical processes related to steam explosions, i.e. the premixing phase preceding the explosion as well as the explosion itself. This code has been replaced by the updated version IVA-KA in May 1994, which encompasses all model and code improvements performed till the beginning of 1994. The following further work on and with IVA-KA has been performed: 1. Inclusion of friction at inner and outer walls, improvement on the drag model, improvement of boundary conditions for outgoing flow, optional inclusion of improved water material data, improvement of the numerical procedure, correction of coding errors. 2. Three FARO-experiments (investigating the behaviour of molten material falling into water) were recalculated with IVA-KA. The time dependent pressure increase is reproduced very well for one experiment, but is not quite satisfactory for a second one. The third one cannot be simulated satisfactorily because of the presence of metallic zirconium in the melt, which is not being modelled by IVA-KA at present. 3. One PREMIX-experiment (similar to FARO, but at 1 bar ambient pressure and with smaller amounts of melt) is also being analyzed with IVA-KA. First results show a good representation of the material distribution during the penetration of the melt into the water. 4. One of the first two QUEOS-experiments performed at KfK has been simulated with IVA-KA. Some results are well reproduced by IVA-KA, but there may be a deficiency of the drag laws. (orig./HP)

A characterization of Greenland Ice Sheet surface melt and runoff in contemporary reanalyses and a regional climate model

Directory of Open Access Journals (Sweden)

Richard eCullather

2016-02-01

Full Text Available For the Greenland Ice Sheet (GrIS, large-scale melt area has increased in recent years and is detectable via remote sensing, but its relation to runoff is not known. Historical, modeled melt area and runoff from Modern-Era Retrospective Analysis for Research and Applications (MERRA-Replay, the Interim Re-Analysis of the European Centre for Medium Range Weather Forecasts (ERA-I, the Climate Forecast System Reanalysis (CFSR, the Modèle Atmosphérique Régional (MAR, and the Arctic System Reanalysis (ASR are examined. These sources compare favorably with satellite-derived estimates of surface melt area for the period 2000-2012. Spatially, the models markedly disagree on the number of melt days in the interior of the southern part of the ice sheet, and on the extent of persistent melt areas in the northeastern GrIS. Temporally, the models agree on the mean seasonality of daily surface melt and on the timing of large-scale melt events in 2012. In contrast, the models disagree on the amount, seasonality, spatial distribution, and temporal variability of runoff. As compared to global reanalyses, time series from MAR indicate a lower correlation between runoff and melt area (r2 = 0.805. Runoff in MAR is much larger in the second half of the melt season for all drainage basins, while the ASR indicates larger runoff in the first half of the year. This difference in seasonality for the MAR and to an extent for the ASR provide a hysteresis in the relation between runoff and melt area, which is not found in the other models. The comparison points to a need for reliable observations of surface runoff.

Isotopic discontinuities in ground water beneath Yucca Mountain, Nevada

International Nuclear Information System (INIS)

Stuckless, J.S.; Whelan, J.F.; Steinkampf, W.C.

1991-01-01

Analytical data for stable isotopes in ground water from beneath Yucca Mountain, when examined in map view, show areal patterns of heterogeneity that can be interpreted in terms of mixing of at least three end members. One end member must be isotopically heavy in terms of hydrogen and oxygen and have a young apparent 14 C age such as water found at the north end of Yucca Mountain beneath Fortymile Wash. A second end member must contain isotopically heavy carbon and have an old apparent 14 C age such as water from the Paleozoic aquifer. The third end member cannot be tightly defined. It must be isotopically lighter than the first with respect of hydrogen and oxygen and be intermediate to the first and second end members with respect to both apparent 14 C age and δ 13 C. The variable isotopic compositions of hydrogen and oxygen indicate that two of the end members are waters, but the variable carbon isotopic composition could represent either a third water end member or reaction of water with a carbon-bearing solids such as calcite. 15 refs., 4 figs., 1 tab

Shallow crustal radial anisotropy beneath the Tehran basin of Iran from seismic ambient noise tomography

Science.gov (United States)

Shirzad, Taghi; Shomali, Z. Hossein

2014-06-01

We studied the shear wave velocity structure and radial anisotropy beneath the Tehran basin by analyzing the Rayleigh wave and Love wave empirical Green's functions obtained from cross-correlation of seismic ambient noise. Approximately 199 inter-station Rayleigh and Love wave empirical Green's functions with sufficient signal-to-noise ratios extracted from 30 stations with various sensor types were used for phase velocity dispersion analysis of periods ranging from 1 to 7 s using an image transformation analysis technique. Dispersion curves extracted from the phase velocity maps were inverted based on non-linear damped least squares inversion method to obtain a quasi-3D model of crustal shear wave velocities. The data used in this study provide an unprecedented opportunity to resolve the spatial distribution of radial anisotropy within the uppermost crust beneath the Tehran basin. The quasi-3D shear wave velocity model obtained in this analysis delineates several distinct low- and high-velocity zones that are generally separated by geological boundaries. High-shear-velocity zones are located primarily around the mountain ranges and extend to depths of 2.0 km, while the low-shear-velocity zone is located near regions with sedimentary layers. In the shallow subsurface, our results indicate strong radial anisotropy with negative magnitude (VSV > VSH) primarily associated with thick sedimentary deposits, reflecting vertical alignment of cracks. With increasing depth, the magnitude of the radial anisotropy shifts from predominantly negative (less than -10%) to predominantly positive (greater than 5%). Our results show a distinct change in radial anisotropy between the uppermost sedimentary layer and the bedrock.

Origin and Distribution of Water Contents in Continental and Oceanic Lithospheric Mantle

Science.gov (United States)

Peslier, Anne H.

2013-01-01

The water content distribution of the upper mantle will be reviewed as based on the peridotite record. The amount of water in cratonic xenoliths appears controlled by metasomatism while that of the oceanic mantle retains in part the signature of melting events. In both cases, the water distribution is heterogeneous both with depth and laterally, depending on localized water re-enrichments next to melt/fluid channels. The consequence of the water distribution on the rheology of the upper mantle and the location of the lithosphere-asthenosphere boundary will also be discussed.

Ferric iron partitioning between pyroxene and melt during partial melting of the Earth's upper mantle

Science.gov (United States)

Rudra, A.; Hirschmann, M. M.

2017-12-01

The oxidation state of the Earth's mantle influences melt production, volatile behavior, partitioning of key trace elements and possible saturation of alloy at depth. Average Fe3+/FeT ratios in MORBs indicate oxygen fugacitiy of the source regions is close to QFM, in contrast to a 3 log unit variation of fO2 recorded by abyssal peridotites. Quantification of the relationship between basalt and source Fe3+/FeT, oxygen fugacity, and melting requires constraints on Fe3+ partitioning between melt and mantle minerals and in particular the principal Fe3+ host, pyroxene. McCanta et al. (2004) investigated valence dependent partitioning of Fe between Martian ferroan pigeonites and melt, but behavior in terrestrial pyroxene compositions relevant to MORB petrogenesis has not been investigated. We are conducting 1 atm controlled fO2 experiments over 4 log unit variation of fO2 between ΔQFM = 2.5 to -1.5 to grow pyroxenes of variable tetrahedral and octahedral cationic population from andesitic melts of varying Mg#, alumina and alkali content. Dynamic crystallization technique facilitates growth of pyroxene crystals (100-200 um) that EPMA analyses show to be compositionally homogeneous and in equilibrium with the melt. Fe3+/FeT ratio of the synthetic pyroxenes have been analyzed by XAFS spectroscopy at the APS (GSECARS) synchrotron. To quantify the x-ray anisotropy in pyroxenes, we collected Fe K-edge XAFS spectra of oriented natural single crystals for a wide range compositions whose Fe3+/FeT ratios we determined by Mossbauer spectroscopy. We have collected both XANES and EXAFS spectral regions spanning from 7020-7220 eV to explore predictive capabilities of different spectral regions about ferric iron concentration and site occupancy. Our results will document the Fe3+ compatibility in pyroxenes of different compositions under a variety of fO2 conditions, which in turn will better constrain the interrelationship between mantle redox and melting.

Plasma arc melting of zirconium

International Nuclear Information System (INIS)

Tubesing, P.K.; Korzekwa, D.R.; Dunn, P.S.

1997-01-01

Zirconium, like some other refractory metals, has an undesirable sensitivity to interstitials such as oxygen. Traditionally, zirconium is processed by electron beam melting to maintain minimum interstitial contamination. Electron beam melted zirconium, however, does not respond positively to mechanical processing due to its large grain size. The authors undertook a study to determine if plasma arc melting (PAM) technology could be utilized to maintain low interstitial concentrations and improve the response of zirconium to subsequent mechanical processing. The PAM process enabled them to control and maintain low interstitial levels of oxygen and carbon, produce a more favorable grain structure, and with supplementary off-gassing, improve the response to mechanical forming

In situ observations of bubble growth in basaltic, andesitic and rhyodacitic melts

Science.gov (United States)

Masotta, M.; Ni, H.; Keppler, H.

2014-02-01

Bubble growth strongly affects the physical properties of degassing magmas and their eruption dynamics. Natural samples and products from quench experiments provide only a snapshot of the final state of volatile exsolution, leaving the processes occurring during its early stages unconstrained. In order to fill this gap, we present in situ high-temperature observations of bubble growth in magmas of different compositions (basalt, andesite and rhyodacite) at 1,100 to 1,240 °C and 0.1 MPa (1 bar), obtained using a moissanite cell apparatus. The data show that nucleation occurs at very small degrees of supersaturaturation (bubbles occurring simultaneously with the nucleation of crystals. During the early stages of exsolution, melt degassing is the driving mechanism of bubble growth, with coalescence becoming increasingly important as exsolution progresses. Ostwald ripening occurs only at the end of the process and only in basaltic melt. The average bubble growth rate ( G R) ranges from 3.4 × 10-6 to 5.2 × 10-7 mm/s, with basalt and andesite showing faster growth rates than rhyodacite. The bubble number density ( N B) at nucleation ranges from 7.9 × 104 mm-3 to 1.8 × 105 mm-3 and decreases exponentially over time. While the rhyodacite melt maintained a well-sorted bubble size distribution (BSD) through time, the BSDs of basalt and andesite are much more inhomogeneous. Our experimental observations demonstrate that bubble growth cannot be ascribed to a single mechanism but is rather a combination of many processes, which depend on the physical properties of the melt. Depending on coalescence rate, annealing of bubbles following a single nucleation event can produce complex bubble size distributions. In natural samples, such BSDs may be misinterpreted as resulting from several separate nucleation events. Incipient crystallization upon cooling of a magma may allow bubble nucleation already at very small degrees of supersaturation and could therefore be an important

Effects of surface shape on the geometry and surface topography of the melt pool in low-power density laser melting

KAUST Repository

Kim, Youngdeuk; Kim, Wooseung

2011-01-01

The quantitative correlations between workpiece volume and melt pool geometry, as well as the flow and thermal features of the melt pool are established. Thermocapillary convections in melt pool with a deformable free surface are investigated

Melting technique for vanadium containing steels

Energy Technology Data Exchange (ETDEWEB)

Grishanov, M P; Gutovskij, I B; Vakhrushev, A S

1980-04-28

To descrease cost price of high-quality vanadium steels a method of their melting in open-hearth furnaces with acid lining using slag-metal fraction of vanadium, which is loaded in the content of 2.1-4.7% of melting mass, is suggested. Introduction of slag-metal fraction of vanadium ensures the formation of slag with composition that guarantees the necessary content of vanadium in steel and does not require introduction of expensive vanadium-containing ferroalloys into the melt.

Coaxial monitoring of temperature field in selective pulsed laser melting

Science.gov (United States)

Liu, Che; Chen, Zhongyun; Cao, Hongzhong; Zhou, Jianhong

2017-10-01

Selective Laser Melting is a rapid manufacturing technology which produces complex parts layer by layer. The presence of thermal stress and thermal strain in the forming process often leads to defects in the formed parts. In order to detect fabricate errors and avoid failure which caused by thermal gradient in time. An infrared thermal imager and a high speed CCD camera were applied to build a coaxial optical system for real-time monitoring the temperature distribution and changing trend of laser affected zone in SLM forming process. Molten tracks were fabricated by SLM under different laser parameters such as frequency, pulse width. And the relationship between the laser parameters and the temperature distribution were all obtained and analyzed.

Direct observations of evolving subglacial drainage beneath the Greenland Ice Sheet.

Science.gov (United States)

Andrews, Lauren C; Catania, Ginny A; Hoffman, Matthew J; Gulley, Jason D; Lüthi, Martin P; Ryser, Claudia; Hawley, Robert L; Neumann, Thomas A

2014-10-02

Seasonal acceleration of the Greenland Ice Sheet is influenced by the dynamic response of the subglacial hydrologic system to variability in meltwater delivery to the bed via crevasses and moulins (vertical conduits connecting supraglacial water to the bed of the ice sheet). As the melt season progresses, the subglacial hydrologic system drains supraglacial meltwater more efficiently, decreasing basal water pressure and moderating the ice velocity response to surface melting. However, limited direct observations of subglacial water pressure mean that the spatiotemporal evolution of the subglacial hydrologic system remains poorly understood. Here we show that ice velocity is well correlated with moulin hydraulic head but is out of phase with that of nearby (0.3-2 kilometres away) boreholes, indicating that moulins connect to an efficient, channelized component of the subglacial hydrologic system, which exerts the primary control on diurnal and multi-day changes in ice velocity. Our simultaneous measurements of moulin and borehole hydraulic head and ice velocity in the Paakitsoq region of western Greenland show that decreasing trends in ice velocity during the latter part of the melt season cannot be explained by changes in the ability of moulin-connected channels to convey supraglacial melt. Instead, these observations suggest that decreasing late-season ice velocity may be caused by changes in connectivity in unchannelized regions of the subglacial hydrologic system. Understanding this spatiotemporal variability in subglacial pressures is increasingly important because melt-season dynamics affect ice velocity beyond the conclusion of the melt season.

The Impacts of Soil Fertility and Salinity on Soil Nitrogen Dynamics Mediated by the Soil Microbial Community Beneath the Halophytic Shrub Tamarisk.

Science.gov (United States)

Iwaoka, Chikae; Imada, Shogo; Taniguchi, Takeshi; Du, Sheng; Yamanaka, Norikazu; Tateno, Ryunosuke

2018-05-01

Nitrogen (N) is one of the most common limiting nutrients for primary production in terrestrial ecosystems. Soil microbes transform organic N into inorganic N, which is available to plants, but soil microbe activity in drylands is sometimes critically suppressed by environmental factors, such as low soil substrate availability or high salinity. Tamarisk (Tamarix spp.) is a halophytic shrub species that is widely distributed in the drylands of China; it produces litter enriched in nutrients and salts that are thought to increase soil fertility and salinity under its crown. To elucidate the effects of tamarisks on the soil microbial community, and thus N dynamics, by creating "islands of fertility" and "islands of salinity," we collected soil samples from under tamarisk crowns and adjacent barren areas at three habitats in the summer and fall. We analyzed soil physicochemical properties, inorganic N dynamics, and prokaryotic community abundance and composition. In soils sampled beneath tamarisks, the N mineralization rate was significantly higher, and the prokaryotic community structure was significantly different, from soils sampled in barren areas, irrespective of site and season. Tamarisks provided suitable nutrient conditions for one of the important decomposers in the area, Verrucomicrobia, by creating "islands of fertility," but provided unsuitable salinity conditions for other important decomposers, Flavobacteria, Gammaproteobacteria, and Deltaproteobacteria, by mitigating salt accumulation. However, the quantity of these decomposers tended to be higher beneath tamarisks, because they were relatively unaffected by the small salinity gradient created by the tamarisks, which may explain the higher N mineralization rate beneath tamarisks.

New Pn and Sn tomographic images of the uppermost mantle beneath the Mediterranean region

Science.gov (United States)

Gil, A.; Díaz, J.; Gallart, J.

2012-04-01

We present here new images of the seismic velocity and anisotropy variations in the uppermost mantle beneath the Mediterranean region, compiled from inversion of Pn and Sn phases. The method of Hearn (1996) has been applied to Pn and Sn lectures from the catalogs of the International Seismological Center and the Spanish Instituto Geografico Nacional. A total of 1,172,293 Pn arrivals coming from 16,527 earthquakes recorded at 1,657 stations with epicentral distances between 220 km and 1400 km have been retained (331,567 arrivals from 15,487events at 961 stations for Sn). Our results, grossly consistent with available 3D tomography images, show significant features well correlated with surface geology. The Pn velocities are high (>8.2 km/s) beneath major sedimentary basins (western Alboran Sea, Valencia Trough, Adriatic Sea, Aquitaine, Guadalquivir, Rharb, Aquitaine and Po basins), and low (Islands, probably related to a thermal anomaly associated to the westward displacement of the Alboran block along the Emile Baudot escarpment 16 Ma ago. The Pn anisotropic image shows consistent orientations sub-parallel to major orogenic structures, such as Betics, Apennines, Calabrian Arc and Alps. The station delays beneath Betic and Rif ranges are strongly negative, suggesting the presence of crustal thickening all along the Gibraltar Arc. However, only the Betics have a very strong low-velocity anomaly and a pronounced anisotropy pattern. The Sn tomographic image correlates well with the Pn image, even if some relevant differences can be observed beneath particular regions.

Influence of gas-generation on melt/concrete interaction

International Nuclear Information System (INIS)

Powers, D.A.

1979-01-01

Gases formed during the interaction of a high-temperature melt with concrete are shown to stem from the thermal dehydration and decarboxylation of the concrete. The kinetics of these decomposition reactions are described. Gases within the melt cause an apparent swelling of the melt. The observed swelling is not easily correlated to the rate of gas evolution. Metallic melts cause CO 2 /CO and H 2 O liberated from the melt to be reduced to CO and hydrogen. When these gases escape from the melt they assist in aerosol formation. As the gases cool they react along a pathway whose oxygen fugacity is apparently buffered by the iron-Wuestite equilibrium. Methane is a product of the gas-phase reaction. (orig./HP) [de

Rhenium corrosion in chloride melts

International Nuclear Information System (INIS)

Stepanov, A.D.; Shkol'nikov, S.N.; Vetyukov, M.M.

1989-01-01

The results investigating rhenium corrosion in chloride melts containing sodium, potassium and chromium ions by a gravimetry potentials in argon atmosphere in a sealing quarth cell are described. Rhenium corrosion is shown to be rather considerable in melts containing CrCl 2 . The value of corrosion rate depending on temperature is determined

UNCONSTRAINED MELTING AND SOLIDIFICATION INSIDE ...

African Journals Online (AJOL)

2015-09-01

Sep 1, 2015 ... There is a large number of experimental and numerical works on melting and solidification of PCM[6-10], and also its usage as thermal management in building [11-14], electronic devices [15-16] and solar energy. [17-20].Most investigated geometries in melting and freezing process are sphere (spherical.

Tidal influences on a future evolution of the Filchner-Ronne Ice Shelf cavity in the Weddell Sea, Antarctica

Science.gov (United States)

Mueller, Rachael D.; Hattermann, Tore; Howard, Susan L.; Padman, Laurie

2018-02-01

Recent modeling studies of ocean circulation in the southern Weddell Sea, Antarctica, project an increase over this century of ocean heat into the cavity beneath Filchner-Ronne Ice Shelf (FRIS). This increase in ocean heat would lead to more basal melting and a modification of the FRIS ice draft. The corresponding change in cavity shape will affect advective pathways and the spatial distribution of tidal currents, which play important roles in basal melting under FRIS. These feedbacks between heat flux, basal melting, and tides will affect the evolution of FRIS under the influence of a changing climate. We explore these feedbacks with a three-dimensional ocean model of the southern Weddell Sea that is forced by thermodynamic exchange beneath the ice shelf and tides along the open boundaries. Our results show regionally dependent feedbacks that, in some areas, substantially modify the melt rates near the grounding lines of buttressed ice streams that flow into FRIS. These feedbacks are introduced by variations in meltwater production as well as the circulation of this meltwater within the FRIS cavity; they are influenced locally by sensitivity of tidal currents to water column thickness (wct) and non-locally by changes in circulation pathways that transport an integrated history of mixing and meltwater entrainment along flow paths. Our results highlight the importance of including explicit tidal forcing in models of future mass loss from FRIS and from the adjacent grounded ice sheet as individual ice-stream grounding zones experience different responses to warming of the ocean inflow.

Shape evolution of a melting nonspherical particle

Science.gov (United States)

Kintea, Daniel M.; Hauk, Tobias; Roisman, Ilia V.; Tropea, Cameron

2015-09-01

In this study melting of irregular ice crystals was observed in an acoustic levitator. The evolution of the particle shape is captured using a high-speed video system. Several typical phenomena have been discovered: change of the particle shape, appearance of a capillary flow of the melted liquid on the particle surface leading to liquid collection at the particle midsection (where the interface curvature is smallest), and appearance of sharp cusps at the particle tips. No such phenomena can be observed during melting of spherical particles. An approximate theoretical model is developed which accounts for the main physical phenomena associated with melting of an irregular particle. The agreement between the theoretical predictions for the melting time, for the evolution of the particle shape, and the corresponding experimental data is rather good.

Melt-quenched glasses of metal-organic frameworks

DEFF Research Database (Denmark)

Bennett, T.D.; Yue, Yuanzheng; Li, P.

2016-01-01

Crystalline solids dominate the field of metal−organic frameworks (MOFs), with access to the liquid and glass states of matter usually prohibited by relatively low temperatures of thermal decomposition. In this work, we give due consideration to framework chemistry and topology to expand...... of other MOFs. The glasses formed upon vitrification are chemically and structurally distinct from the three other existing categories of melt-quenched glasses (inorganic nonmetallic, organic, and metallic), and retain the basic metal−ligand connectivity of crystalline MOFs, which connects their mechanical...... the phenomenon of the melting of 3D MOFs, linking crystal chemistry to framework melting temperature and kinetic fragility of the glass-forming liquids. Here we show that melting temperatures can be lowered by altering the chemistry of the crystalline MOF state, which provides a route to facilitate the melting...

Melt inclusion: methods, applications and problem: Silica-rich melts in quartz xenoliths from Vulcano islands and their bearing on processes of crustal melting and crust-magma interaction in the Aeolian Arc, Italy

NARCIS (Netherlands)

Frezzotti, M.L.; Zavon, V.; Peccerillo, A.; Nikogosian, I.

2002-01-01

Silica-rich melts in quartz xenoliths from Vulcano islands and their bearing on processes of crustal melting and crust-magma interaction in the Aeolian Arc, Italy Proceedings of workshop Melt inclusion: methods, applications and problem. Napoli, Italy, September 2002, p. 71-73

To the calculation technique and interpretation of atom radial distribution curves in ternary alloy systems

International Nuclear Information System (INIS)

Dutchak, Ya.I.; Frenchko, V.S.; Voznyak, O.M.

1975-01-01

Certain models of the structure of three-component melts are considered: the ''quasi-eutectic'' one, the model of statistical distribution of atoms and the ''polystructural'' model. The analytical expressions are given for the area under the first maximum of the curve describing the radial distribution of atoms for certain versions of the ''polystructural'' model. On the example of In-Ga-Ga and Bi-Cd-Sn eutectic melts the possibility of estimating the nature of atomic ordering in three-component melts through checking the models under consideration has been demonstrated

Study on superheat of TiAl melt during cold crucible levitation melting. TiAl no cold crucible levitation yokai ni okeru yoto kanetsudo no kenkyu

Energy Technology Data Exchange (ETDEWEB)

Miwa, K.; Kobayashi, K.; Ninomiya, M. (Government Industrial Research Institute, Nagoya, Nagoya (Japan))

1992-06-20

Investigations were given on effects of test sample weights and sample positions in cold crucibles on superheat of melts when the intermetallic compound TiAl is melted using cold crucible levitation melting process, one of noncontaminated melting processes. The cold crucibles used in the experiment are a water-cooled copper crucible with an inner diameter of 42 mm and a length of 140 mm, into which a column-like ingot sample with an outer diameter of 32 mm (Al containing Ti at 33.5% by mass) was put and melted using the levitation melting. Comparisons and discussions were given on the relationship between sample weights and melt temperatures, the relationship between positions of the inserted samples and melt temperatures, and the state of contamination at melting of casts obtained from the melts resulted from the levitation melting and high-frequency melting poured into respective ceramic dies. Elevating the superheat temperature of the melts requires optimizing the sample weights and positions. Melt temperatures were measured using a radiation thermometer and a thermocouple, and the respective measured values were compared. 7 refs., 4 figs., 1 tab.

Multiple-frequency tomography of the upper mantle beneath the African/Iberian collision zone

Science.gov (United States)

Bonnin, Mickaël; Nolet, Guust; Villaseñor, Antonio; Gallart, Josep; Thomas, Christine

2014-09-01

During the Cenozoic, the geodynamics of the western Mediterranean domain has been characterized by a complex history of subduction of Mesozoic oceanic lithosphere. The final stage of these processes is proposed to have led to the development of the Calabria and Gibraltar arcs, whose formation is still under debate. In this study, we take advantage of the dense broad-band station networks now available in the Alborán Sea region, to develop a high-resolution 3-D tomographic P velocity model of the upper mantle beneath the African/Iberian collision zone that will better constraint the past dynamics of this zone. The model is based on 13200 teleseismic arrival times recorded between 2008 and 2012 at 279 stations for which cross-correlation delays are measured with a new technique in different frequency bands centred between 0.03 and 1.0 Hz, and for the first time interpreted using multiple frequency tomography. Our model shows, beneath the Alborán Sea, a strong (4 per cent) fast vertically dipping anomaly observed to at least 650 km depth. The arched shape of this anomaly, and its extent at depth, are coherent with a lithospheric slab, thus favouring the hypothesis of a westward consumption of the Ligurian ocean slab by roll-back during Cenozoic. In addition to this fast anomaly in the deep upper mantle, high intensity slow anomalies are widespread in the lithosphere and asthenosphere beneath Morocco and southern Spain. These anomalies are correlated at the surface with the position of the Rif and Atlas orogens and with Cenozoic volcanic fields. We thus confirm the presence, beneath Morocco, of an anomalous (hot?) upper mantle, but without clear indication for a lateral spreading of the Canary plume to the east.

A detailed map of the 660-kilometer discontinuity beneath the izu-bonin subduction zone.

Science.gov (United States)

Wicks, C W; Richards, M A

1993-09-10

Dynamical processes in the Earth's mantle, such as cold downwelling at subduction zones, cause deformations of the solid-state phase change that produces a seismic discontinuity near a depth of 660 kilometers. Observations of short-period, shear-to-compressional wave conversions produced at the discontinuity yield a detailed map of deformation beneath the Izu-Bonin subduction zone. The discontinuity is depressed by about 60 kilometers beneath the coldest part of the subducted slab, with a deformation profile consistent with the expected thermal signature of the slab, the experimentally determined Clapeyron slope of the phase transition, and the regional tectonic history.

Alakit and Daldyn kimberlite fields, Siberia, Russia: Two types of mantle sub-terranes beneath central Yakutia?

Directory of Open Access Journals (Sweden)

I.V. Ashchepkov

2017-07-01

Full Text Available Mineral data from Yakutian kimberlites allow reconstruction of the history of lithospheric mantle. Differences occur in compositions of mantle pyropes and clinopyroxenes from large kimberlite pipes in the Alakit and Daldyn fields. In the Alakit field, Cr-diopsides are alkaline, and Stykanskaya and some other pipes contain more sub-calcic pyropes and dunitic-type diamond inclusions, while in the Daldyn field harzburgitic pyropes are frequent. The eclogitic diamond inclusions in the Alakit field are sharply divided in types and conditions, while in the Daldyn field they show varying compositions and often continuous Pressure–Temperature (P–T ranges with increasing Fe# with decreasing pressures. In Alakit, Cr-pargasites to richterites were found in all pipes, while in Daldyn, pargasites are rare Dalnyaya and Zarnitsa pipes. Cr-diopsides from the Alakit region show higher levels of light Rare Earth Elements (LREE and stronger REE-slopes, and enrichment in light Rare Earth Elements (LREE, sometimes Th-U, and small troughs in Nb-Ta-Zr. In the Daldyn field, the High Field Strength Elements HFSE troughs are more common in clinopyroxenes with low REE abundances, while those from sheared and refertilized peridotites have smooth patterns. Garnets from Alakit show HREE minima, but those from Daldyn often have a trough at Y and high U and Pb. PTXfO2 diagrams from both regions show similarities, suggesting similar layering and structures. The degree of metasomatism is often higher for pipes which show dispersion in P–Fe# trends for garnets. In the mantle beneath Udachnaya and Aykhal, pipes show 6–7 linear arrays of P–Fe# in the lower part of the mantle section at 7.5–3.0 GPa, probably reflecting primary subduction horizons. Beneath the Sytykanskaya pipe, there are several horizons with opposite inclinations which reflect metasomatic processes. The high dispersion of the P–Fe# trend indicating widespread metasomatism is associated with decreased

Simulation of melt spreading in consideration of phase transitions

Energy Technology Data Exchange (ETDEWEB)

Spengler, C. [Gesellschaft fuer Anlagen- und Reaktorsicherheit (GRS) mbH, Koeln (Germany)

2002-07-01

The analysis of melt spreading and relocation phenomena in the containment of LWR power plants in case of hypothetical severe accidents leading to core melting is an important issue for reactor safety investigations. For the simulation of melt spreading the code LAVA has been developed on the basis of a method from the related subject of volcanology by adding more detailed models for heat transfer phenomena and flow rheology. The development is supported by basic analysis of the spreading of gravity currents as well as experimental investigations of the rheology of solidifying melts. These exhibit strong non-Newtonian effects in case of a high content of solids in the freezing melt. The basic model assumption in LAVA is the ideal Bingham plastic approach to the non-Newtonian, shear-thinning characteristic of solidifying melts. For the recalculation of melt spreading experiments, the temperature-dependent material properties for solidifying melt mixtures have been calculated using correlations from the literature. With the parameters and correlations for the rheological material properties approached by results from literature, it was possible to recalculate successfully recent spreading experiments with simulant materials and prototypic reactor core materials. An application to the behaviour of core melt in the reactor cavity assumed a borderline case for the issue of spreading. This limit is represented by melt conditions (large solid fraction, low volume flux), under which the melt is hardly spreadable. Due to the persistent volume flux the reactor cavity is completely, but inhomogeneously filled with melt. The degree of inhomogeneity is rather small, so it is concluded, that for the long-term coolability of a melt pool in narrow cavities the spreading of melt will probably have only negligible influence. (orig.)

Geothermal flux and basal melt rate in the Dome C region inferred from radar reflectivity and heat modelling

Directory of Open Access Journals (Sweden)

O. Passalacqua

2017-09-01

Full Text Available Basal melt rate is the most important physical quantity to be evaluated when looking for an old-ice drilling site, and it depends to a great extent on the geothermal flux (GF, which is poorly known under the East Antarctic ice sheet. Given that wet bedrock has higher reflectivity than dry bedrock, the wetness of the ice–bed interface can be assessed using radar echoes from the bedrock. But, since basal conditions depend on heat transfer forced by climate but lagged by the thick ice, the basal ice may currently be frozen whereas in the past it was generally melting. For that reason, the risk of bias between present and past conditions has to be evaluated. The objective of this study is to assess which locations in the Dome C area could have been protected from basal melting at any time in the past, which requires evaluating GF. We used an inverse approach to retrieve GF from radar-inferred distribution of wet and dry beds. A 1-D heat model is run over the last 800 ka to constrain the value of GF by assessing a critical ice thickness, i.e. the minimum ice thickness that would allow the present local distribution of basal melting. A regional map of the GF was then inferred over a 80 km  ×  130 km area, with a N–S gradient and with values ranging from 48 to 60 mW m−2. The forward model was then emulated by a polynomial function to compute a time-averaged value of the spatially variable basal melt rate over the region. Three main subregions appear to be free of basal melting, two because of a thin overlying ice and one, north of Dome C, because of a low GF.

Evidence for early hunters beneath the Great Lakes

OpenAIRE

O'Shea, John M.; Meadows, Guy A.

2009-01-01

Scholars have hypothesized that the poorly understood and rarely encountered archaeological sites from the terminal Paleoindian and Archaic periods associated with the Lake Stanley low water stage (10,000–7,500 BP) are lost beneath the modern Great Lakes. Acoustic and video survey on the Alpena-Amberley ridge, a feature that would have been a dry land corridor crossing the Lake Huron basin during this time period, reveals the presence of a series of stone features that match, in form and loca...

Deep groundwater and potential subsurface habitats beneath an Antarctic dry valley

DEFF Research Database (Denmark)

Mikucki, J. A.; Auken, E.; Tulaczyk, S.

2015-01-01

The occurrence of groundwater in Antarctica, particularly in the ice-free regions and along the coastal margins is poorly understood. Here we use an airborne transient electromagnetic (AEM) sensor to produce extensive imagery of resistivity beneath Taylor Valley. Regional-scale zones of low subsu...

Magnetic susceptibility of semiconductor melts

International Nuclear Information System (INIS)

Kutvitskij, V.A.; Shurygin, P.M.

1975-01-01

The temperature dependences chi of various alloys confirm the existence of cluster formations in molten semiconductors, the stability of these formations in melts being considerably affected by the anion nature. The concentrational dependences of the magnetic susceptibility for all the investigated systems exhibit the diamagnetism maxima corresponding to the compound compositions. Heating the melt causes ''smearing'' the maxima, which is related with the cluster structure dissociation. The existence of the maxima concentrational dependence chi corresponding to BiTe and BiSe is found in the isotherms. The non-linear dependence of chi on the composition shows the absence of a single-valued relation between the phase diagram and the chi-diagram for melts

Vacancies and a generalised melting curve of metals

International Nuclear Information System (INIS)

Gorecki, T.

1979-01-01

The vacancy mechanism of the melting process is used as a starting point for deriving an expression for the pressure dependence of the melting temperature of metals. The results obtained for the initial slope of the melting curve are compared with experimental data for 45 metals and in most cases the agreement is very good. The nonlinearity of the melting curve and the appearance of a maximum on the melting curve at a pressure approximately equal to the bulk modules is also predicted, with qualitative agreement with experimental data. A relation between bonding energy, atomic volume, and bulk modulus of metals is established. On the basis of this relation and the proposed vacancy mechanism, a generalised equation for the pressure dependence of the melting temperature of metals is derived. (author)

Dating Howardite Melt Clasts: Evidence for an Extended Vestan Bombardment?

Science.gov (United States)

Cartwright, J. A.; Hodges, K. V.; Wadhwa, M.; Mittlefehldt, D. W.

2016-01-01

Howardites are polymict breccias that, together with eucrites and diogenites (HED), likely originate from the vestan surface (regolith/ megaregolith), and display a heterogeneous distribution of eucritic and diogenitic material. Melt clasts are also present alongside other regolithic features within howardites, and are noteworthy for their compositional variability and appearance. Melt clasts formed by impact events provide a snapshot of the timings and conditions of surface gardening and bombardment on the vestan surface. By dating such clasts, we aim to better constrain the timings of impact events on Vesta, and to establish whether the impact flux in the asteroid belt was similar to that on the Moon. As the Moon is used as the basis for characterising impact models of the inner solar system, it is necessary to verify that apparent wide-scale events are seen in other planetary bodies. In particular, the observed clustering of Apollo melt clast ages between 3.8-4.0 Ga has led to two hypotheses: 1) The Moon was subjected to a sudden event - 'Lunar Cataclysm' or period of 'Late Heavy Bombardment' (LHB), 2) The age cluster represents the end of an epoch of declining bombardment or 'Heavy Bombardment. No consensus has emerged regarding one or other hypothesis. We are testing these hypotheses by seeking evidence for such events in materials other than those derived from the Moon.

Relationship of Powder Feedstock Variability to Microstructure and Defects in Selective Laser Melted Alloy 718

Science.gov (United States)

Smith, T. M.; Kloesel, M. F.; Sudbrack, C. K.

2017-01-01

Powder-bed additive manufacturing processes use fine powders to build parts layer by layer. For selective laser melted (SLM) Alloy 718, the powders that are available off-the-shelf are in the 10-45 or 15-45 micron size range. A comprehensive investigation of sixteen powders from these typical ranges and two off-nominal-sized powders is underway to gain insight into the impact of feedstock on processing, durability and performance of 718 SLM space-flight hardware. This talk emphasizes an aspect of this work: the impact of powder variability on the microstructure and defects observed in the as-fabricated and full heated material, where lab-scale components were built using vendor recommended parameters. These typical powders exhibit variation in composition, percentage of fines, roughness, morphology and particle size distribution. How these differences relate to the melt-pool size, porosity, grain structure, precipitate distributions, and inclusion content will be presented and discussed in context of build quality and powder acceptance.

Review: Recharge rates and chemistry beneath playas of the High Plains aquifer, USA

Science.gov (United States)

Gurdak, Jason J.; Roe, Cassia D.

2010-12-01

Playas are ephemeral, closed-basin wetlands that are hypothesized as an important source of recharge to the High Plains aquifer in central USA. The ephemeral nature of playas, low regional recharge rates, and a strong reliance on groundwater from the High Plains aquifer has prompted many questions regarding the contribution and quality of recharge from playas to the High Plains aquifer. As a result, there has been considerable scientific debate about the potential for water to infiltrate the relatively impermeable playa floors, travel through the unsaturated zone sediments that are tens of meters thick, and subsequently recharge the High Plains aquifer. This critical review examines previously published studies on the processes that control recharge rates and chemistry beneath playas. Reported recharge rates beneath playas range from less than 1.0 to more than 500 mm/yr and are generally 1-2 orders of magnitude higher than recharge rates beneath interplaya settings. Most studies support the conceptual model that playas are important zones of recharge to the High Plains aquifer and are not strictly evaporative pans. The major findings of this review provide science-based implications for management of playas and groundwater resources of the High Plains aquifer and directions for future research.

Isothermal crystallization and melting behavior of polypropylene/layered double hydroxide nanocomposites

International Nuclear Information System (INIS)

Lonkar, Sunil P.; Singh, R.P.

2009-01-01

The effect of layered double hydroxide (LDH) nanolayers on the crystallization behavior of polypropylene (PP) was studied based on the preparation of nanocomposites by a melt intercalation method. The isothermal crystallization kinetics and subsequent melting behavior of PP/LDH hybrids were studied with differential scanning calorimetry (DSC), polarized optical microscopy (POM), and wide-angle X-ray diffraction (WAXD). Studies revealed that the LDH promoted heterogeneous nucleation, accelerating the crystallization of PP. The Avrami equation successfully describes the isothermal crystallization kinetics of PP/LDH hybrids and signifies heterogeneous nucleation in crystal growth of PP. The varying values of Avrami exponent (n) and half crystallization time (t 1/2 ) of PP and PP/LDH hybrids describes overall crystallization behavior. The crystallite size (D hkl ) and distribution of different crystallites in PP varied in presence of LDH. A significant increase in melting temperature is observed for PP/LDH hybrids. The POM showed that smaller and less perfect crystals were formed in nanocomposites because of molecular interaction between PP chains and LDH. The value of fold surface free energy (σ e ) of PP chains decreased with increasing LDH content. Finally, the overall results signify that LDH at nanometer level acted as nucleating agent and accelerate the overall crystallization process of PP.

Lessons learnt from FARO/TERMOS corium melt quenching experiments