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1

Core-melt source reduction system  

DOEpatents

A core-melt source reduction system for ending the progression of a molten core during a core-melt accident and resulting in a stable solid cool matrix. The system includes alternating layers of a core debris absorbing material and a barrier material. The core debris absorbing material serves to react with and absorb the molten core such that containment overpressurization and/or failure does not occur. The barrier material slows the progression of the molten core debris through the system such that the molten core has sufficient time to react with the core absorbing material. The system includes a provision for cooling the glass/molten core mass after the reaction such that a stable solid cool matrix results. 4 figs.

Forsberg, C.W.; Beahm, E.C.; Parker, G.W.

1995-04-25

2

Core-melt source reduction system  

DOEpatents

A core-melt source reduction system for ending the progression of a molten core during a core-melt accident and resulting in a stable solid cool matrix. The system includes alternating layers of a core debris absorbing material and a barrier material. The core debris absorbing material serves to react with and absorb the molten core such that containment overpressurization and/or failure does not occur. The barrier material slows the progression of the molten core debris through the system such that the molten core has sufficient time to react with the core absorbing material. The system includes a provision for cooling the glass/molten core mass after the reaction such that a stable solid cool matrix results.

Forsberg, Charles W. (Oak Ridge, TN); Beahm, Edward C. (Oak Ridge, TN); Parker, George W. (Concord, TN)

1995-01-01

3

Melting of the Earth's inner core.  

PubMed

The Earth's magnetic field is generated by a dynamo in the liquid iron core, which convects in response to cooling of the overlying rocky mantle. The core freezes from the innermost surface outward, growing the solid inner core and releasing light elements that drive compositional convection. Mantle convection extracts heat from the core at a rate that has enormous lateral variations. Here we use geodynamo simulations to show that these variations are transferred to the inner-core boundary and can be large enough to cause heat to flow into the inner core. If this were to occur in the Earth, it would cause localized melting. Melting releases heavy liquid that could form the variable-composition layer suggested by an anomaly in seismic velocity in the 150 kilometres immediately above the inner-core boundary. This provides a very simple explanation of the existence of this layer, which otherwise requires additional assumptions such as locking of the inner core to the mantle, translation from its geopotential centre or convection with temperature equal to the solidus but with composition varying from the outer to the inner core. The predominantly narrow downwellings associated with freezing and broad upwellings associated with melting mean that the area of melting could be quite large despite the average dominance of freezing necessary to keep the dynamo going. Localized melting and freezing also provides a strong mechanism for creating seismic anomalies in the inner core itself, much stronger than the effects of variations in heat flow so far considered. PMID:21593868

Gubbins, David; Sreenivasan, Binod; Mound, Jon; Rost, Sebastian

2011-05-19

4

Impact of the proposed core melt policy  

SciTech Connect

Recent encounters with FEMA/NRC and New Jersey have focused our attention on the proposed severe core melt policy. Currently, these federal agencies make the supposition that an automatic evacuation out to 5 miles upon a General Emergency declaration would provide greater protection to the public than an independent grounded assessment which would include the option to shelter. This policy appears to be contrary to EPA-400 and supportable decision making. This talk discusses the policy.

Tosch, K. [Bureau of Nuclear Engineering, Trenton, NJ (United States)

1995-12-31

5

The Core Melt Stabilization Concept of the EPR and its Experimental Validation  

Microsoft Academic Search

The strategy of the European Pressurized Water Reactor (EPR) to avoid severe accident conditions is based on the improved defense-in-depth approaches of the French 'N4' and the German 'Konvoi' plants. In addition, the EPR takes measures, at the design stage, to drastically limit the consequences of a postulated core-melt accident. The latter requires a strengthening of the confinement function and

Manfred

2006-01-01

6

Fe Melting at the Conditions of the Earth's Core  

Microsoft Academic Search

Since iron is the primary constituent of the Earth's core, understanding its properties at high pressures and temperatures is of great geophysical importance. In particular, its melting temperature, along with those of its alloys, constrains the composition and temperature at the inner-core, outer-core boundary. We present findings on the melting behavior of Fe from molecular dynamics (MD) simulations. Our description

S. Akber-Knutson; A. van Duin; P. D. Asimow; T. J. Ahrens; W. A. Goddard

2005-01-01

7

Measurements of natural circulation flow in a scale model PWR reactor system during postulated degraded core accidents using laser anemometry  

NASA Technical Reports Server (NTRS)

The natural circulation of a single-phase fluid in a scale-model pressurized water reactor system was studied during a postulated degraded core accident. A half section of a one-seventh scale model with a plexiglass adiabatic window was employed. Water and SF6 were used as the fluid. LDA was used to perform velocity measurements along the center plane of the model at five elevations. It was found that the recirculation flow patterns are nearly symmetric except near the hot legs and in the upper head and that the fluid in the upper plenum is well mixed.

Kadambi, J. R.; Schneider, S. J.; Stewart, W. A.

1987-01-01

8

The Core Melt Stabilization Concept of the EPR and its Experimental Validation  

SciTech Connect

The strategy of the European Pressurized Water Reactor (EPR) to avoid severe accident conditions is based on the improved defense-in-depth approaches of the French 'N4' and the German 'Konvoi' plants. In addition, the EPR takes measures, at the design stage, to drastically limit the consequences of a postulated core-melt accident. The latter requires a strengthening of the confinement function and a significant reduction of the risk of short- and long-term containment failure. Scenarios with potentially high mechanical loads and large early releases like: high-pressure RPV failure, global hydrogen detonation, and energetic steam explosion must be prevented. The remaining low-pressure sequences are mitigated by dedicated measures that include hydrogen recombination, sustained heat removal out of the containment, and the stabilization of the molten core in an ex-vessel core catcher located in a compartment lateral to the pit. The spatial separation protects the core catcher from loads during RPV failure and, vice versa, eliminates concerns related with its unintended flooding during power operation. To make the relocation of the melt into the core catcher scenario-independent and robust against the uncertainties associated with in-vessel molten pool formation and RPV failure, the corium is temporarily retained, accumulated and conditioned in the pit during interaction with a sacrificial concrete layer. Spreading of the accumulated molten pool is initiated by penetrating a concrete plug in the bottom. The increase in surface-to-volume ratio achieved by the spreading process strongly enhances quenching and cool-down of the melt after flooding. The required water is passively drained from the IRWST. After availability of the containment heat removal system the steam from the boiling pool is re-condensed by sprays. The CHRS can also optionally cool the core catcher directly, which, in consequence, establishes a sub-cooled pool near-atmospheric pressure levels in the containment. The described concept rests on a large experimental knowledge base which covers all main phenomena involved, including melt interaction with structural material, melt spreading, melt and quenching, as well as the efficacy of the core catcher cooling. Besides giving an overview of the EPR core melt mitigation concept, the paper summarizes its R and D bases and describes which conclusions have been drawn from the various experimental projects and how these conclusions are used in the validation of the EPR concept. (author)

Fischer, Manfred [AREVA ANP GmbH (Germany)

2006-07-01

9

The severe accident mitigation concept and the design measures for core melt retention of the European Pressurized Reactor (EPR)  

Microsoft Academic Search

For the mitigation of severe accidents, the European Pressurized Water Reactor (EPR) has adopted and improved the defense-in-depth approaches of its predecessors, the French “N4” and the German “Konvoi” plants. Beyond the corresponding evolutionary changes, the EPR includes a new, 4th level of defense-in-depth that is aimed at limiting the consequences of a postulated severe accident with core melting. It

Manfred Fischer

2004-01-01

10

Melting of subducted basalt at the core-mantle boundary.  

PubMed

The geological materials in Earth's lowermost mantle control the characteristics and interpretation of seismic ultra-low velocity zones at the base of the core-mantle boundary. Partial melting of the bulk lower mantle is often advocated as the cause, but this does not explain the nonubiquitous character of these regional seismic features. We explored the melting properties of mid-oceanic ridge basalt (MORB), which can reach the lowermost mantle after subduction of oceanic crust. At a pressure representative of the core-mantle boundary (135 gigapascals), the onset of melting occurs at ~3800 kelvin, which is ~350 kelvin below the mantle solidus. The SiO2-rich liquid generated either remains trapped in the MORB material or solidifies after reacting with the surrounding MgO-rich mantle, remixing subducted MORB with the lowermost mantle. PMID:24855266

Andrault, Denis; Pesce, Giacomo; Bouhifd, Mohamed Ali; Bolfan-Casanova, Nathalie; Hénot, Jean-Marc; Mezouar, Mohamed

2014-05-23

11

Quantifying signal dispersion in a hybrid ice core melting system.  

PubMed

We describe a microcontroller-based ice core melting and data logging system allowing simultaneous depth coregistration of a continuous flow analysis (CFA) system (for microparticle and conductivity measurement) and a discrete sample analysis system (for geochemistry and microparticles), both supplied from the same melted ice core section. This hybrid melting system employs an ice parcel tracking algorithm which calculates real-time sample transport through all portions of the meltwater handling system, enabling accurate (1 mm) depth coregistration of all measurements. Signal dispersion is analyzed using residence time theory, experimental results of tracer injection tests and antiparallel melting of replicate cores to rigorously quantify the signal dispersion in our system. Our dispersion-limited resolution is 1.0 cm in ice and ~2 cm in firn. We experimentally observe the peak lead phenomenon, where signal dispersion causes the measured CFA peak associated with a given event to be depth assigned ~1 cm shallower than the true event depth. Dispersion effects on resolution and signal depth assignment are discussed in detail. Our results have implications for comparisons of chemistry and physical properties data recorded using multiple instruments and for deconvolution methods of enhancing CFA depth resolution. PMID:23050603

Breton, Daniel J; Koffman, Bess G; Kurbatov, Andrei V; Kreutz, Karl J; Hamilton, Gordon S

2012-11-01

12

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

SciTech Connect

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.

Forsberg, C.W.; Parker, G.W.; Rudolph, J.C.; Osborne-Lee, I.W. [Oak Ridge National Lab., TN (United States); Kenton, M.A. [Dames and Moore, Westmont, IL (United States)

1996-09-01

13

The adiabatic gradient and the melting point gradient in the core of the earth  

Microsoft Academic Search

The melting gradient and the adiabatic gradient throughout the core of the earth are compared. The temperature of melting of iron at pressures equivalent to the inner core-outer core boundary is estimated to be circa 4250øC with a melting point gradient of approximately 500 ø through the outer core. The adiabatic gradient through the outer core is estimated to be

G. Higgins; G. C. Kennedy

1971-01-01

14

Water isotopic ratios from a continuously melted ice core sample  

NASA Astrophysics Data System (ADS)

A new technique for on-line high resolution isotopic analysis of liquid water, tailored for ice core studies is presented. We built an interface between a Wavelength Scanned Cavity Ring Down Spectrometer (WS-CRDS) purchased from Picarro Inc. and a Continuous Flow Analysis (CFA) system. The system offers the possibility to perform simultaneuous water isotopic analysis of ?18O and ?D on a continuous stream of liquid water as generated from a continuously melted ice rod. Injection of sub ?l amounts of liquid water is achieved by pumping sample through a fused silica capillary and instantaneously vaporizing it with 100% efficiency in a~home made oven at a temperature of 170 °C. A calibration procedure allows for proper reporting of the data on the VSMOW-SLAP scale. We apply the necessary corrections based on the assessed performance of the system regarding instrumental drifts and dependance on the water concentration in the optical cavity. The melt rates are monitored in order to assign a depth scale to the measured isotopic profiles. Application of spectral methods yields the combined uncertainty of the system at below 0.1‰ and 0.5‰ for ?18O and ?D, respectively. This performance is comparable to that achieved with mass spectrometry. Dispersion of the sample in the transfer lines limits the temporal resolution of the technique. In this work we investigate and assess these dispersion effects. By using an optimal filtering method we show how the measured profiles can be corrected for the smoothing effects resulting from the sample dispersion. Considering the significant advantages the technique offers, i.e. simultaneuous measurement of ?18O and ?D, potentially in combination with chemical components that are traditionally measured on CFA systems, notable reduction on analysis time and power consumption, we consider it as an alternative to traditional isotope ratio mass spectrometry with the possibility to be deployed for field ice core studies. We present data acquired in the field during the 2010 season as part of the NEEM deep ice core drilling project in North Greenland.

Gkinis, V.; Popp, T. J.; Blunier, T.; Bigler, M.; Schüpbach, S.; Kettner, E.; Johnsen, S. J.

2011-11-01

15

Temperatures in the earth's core from melting-point measurements of iron at high static pressures  

Microsoft Academic Search

The most reliable method for determining the temperature gradient at the earth's core is the estimation of Fe and Fe-rich compounds' melting temperature at the pressure of the inner core boundary. Attention is presently given to melting-point measurements on Fe and Fe-O compounds at up to 2 Mbar. An extrapolation of these results to 3.3 Mbar yields an inner core

R. Boehler

1993-01-01

16

Modeling of melt retention in EU-APR1400 ex-vessel core catcher  

SciTech Connect

A core catcher is adopted in the EU-APR1400 reactor design for management and mitigation of severe accidents with reactor core melting. The core catcher concept incorporates a number of engineering solutions used in the catcher designs of European EPR and Russian WER-1000 reactors, such as thin-layer corium spreading for better cooling, retention of the melt in a water-cooled steel vessel, and use of sacrificial material (SM) to control the melt properties. SM is one of the key elements of the catcher design and its performance is critical for melt retention efficiency. This SM consists of oxide components, but the core catcher also includes sacrificial steel which reacts with the metal melt of the molten corium to reduce its temperature. The paper describes the required properties of SM. The melt retention capability of the core catcher can be confirmed by modeling the heat fluxes to the catcher vessel to show that it will not fail. The fulfillment of this requirement is demonstrated on the example of LBLOCA severe accident. Thermal and physicochemical interactions between the oxide and metal melts, interactions of the melts with SM, sacrificial steel and vessel, core catcher external cooling by water and release of non-condensable gases are modeled. (authors)

Granovsky, V. S.; Sulatsky, A. A.; Khabensky, V. B.; Sulatskaya, M. B. [Alexandrov Research Inst. of Technology NITI, Sosnovy Bor (Russian Federation); Gusarov, V. V.; Almyashev, V. I.; Komlev, A. A. [Saint Petersburg State Technological Univ. SPbSTU, St.Petersburg (Russian Federation); Bechta, S. [KTH, Stockholm (Sweden); Kim, Y. S. [KHNP, 1312 Gil 70, Yuseongdaero, Yuseong-gu, Daejeon (Korea, Republic of); Park, R. J.; Kim, H. Y.; Song, J. H. [KAERI, 989 Gil 111, Daedeokdaero, Yuseong-gu, Daejeon (Korea, Republic of)

2012-07-01

17

Melt in the impact breccias from the Eyreville drill cores, Chesapeake Bay impact structure, USA  

NASA Astrophysics Data System (ADS)

The center of the 35.3 Ma Chesapeake Bay impact structure (85 km diameter) was drilled during 2005/2006 in an ICDP-0USGS drilling project. The Eyreville drill cores include polymict impact breccias and associated rocks (1397-01551 m depth). Tens of melt particles from these impactites were studied by optical and electron microscopy, electron microprobe, and microRaman spectroscopy, and classified into six groups: m1—clear or brownish melt, m2—brownish melt altered to phyllosilicates, m3—colorless silica melt, m4—melt with pyroxene and plagioclase crystallites, m5—dark brown melt, and m6—melt with globular texture. These melt types have partly overlapping major element abundances, and large compositional variations due to the presence of schlieren, poorly mixed melt phases, partly digested clasts, and variable crystallization and alteration. The different melt types also vary in their abundance with depth in the drill core. Based on the chemical data, mixing calculations were performed to determine possible precursors of these melt particles. The calculations suggest that most melt types formed mainly from the thick sedimentary section of the target sequence (mainly the Potomac Formation), but an additional crystalline basement (schist/gneiss) precursor is likely for the most abundant melt types m2 and m5. Sedimentary rocks with compositions similar to those of the melt particles are present among the Eyreville core samples. Therefore, sedimentary target rocks were the main precursor of the Eyreville melt particles. However, the composition of the melt particles is not only the result of the precursor composition but also the result of changes during melting and solidification, as well as postimpact alteration, which must also be considered. The variability of the melt particle compositions reflects the variety of target rocks and indicates that there was no uniform melt source. Original heterogeneities, resulting from melting of different target rocks, may be preserved in impactites of some large impact structures that formed in volatile-rich targets, because no large melt body exists, in which homogenization would have taken place.

Bartosova, Katerina; Hecht, Lutz; Koeberl, Christian; Libowitzky, Eugen; Reimold, Wolf Uwe

2011-03-01

18

Examination of offsite radiological emergency protective measures for nuclear reactor accidents involving core melt  

E-print Network

Evacuation, sheltering followed by population relocation, and iodine prophylaxis are evaluated as offsite public protective measures in response to nuclear reactor accidents involving core-melt. Evaluations were conducted ...

Aldrich, David C.

1979-01-01

19

Redistribution of Core-forming Melt During Shear Deformation of Partially Molten Peridotite  

NASA Technical Reports Server (NTRS)

To investigate the role of deformation on the distribution of core-forming melt in a partially molten peridotite, samples of olivine-basalt-iron sulfide were sheared to large strains. Dramatic redistribution of sulfide and silicate melts occur during deformation. Additional information is contained in the original extended abstract.

Hustoft, J. W.; Kohlstedt, D. L.

2002-01-01

20

Convection at the melting point: A thermal history of the earth's core  

Microsoft Academic Search

Higgins and Kennedy (1971) concluded that the Earth's fluid core has a stable stratification if it is at its melting point. Busse (1972) and Elsasser suggested as an alternative that a hydrostatic-isentropic distribution of particulate solid can produce neutral stability in a partially molten core. Here this suggestion is quantified and a determination is made of the efficiency of the

Willem V. R. Malkus

1972-01-01

21

Melt eruptions during molten corium concrete interactions  

NASA Astrophysics Data System (ADS)

The melt eruption phenomenon could occur during severe accidents at existing light water nuclear reactors. A postulated beyond-design basis accident includes the melting and relocation of the reactor core onto the concrete basemat of containment. The continually heated melt can reach high temperatures and thermally attack the underlying concrete, MCCI. As the melt cools, a crust forms on the upper surface of the melt pool. Melt eruptions occur when gases from the decomposing concrete passes through channels in the crust ejecting melt onto the upper surface of the crust. The impact of melt eruptions on the coolability of the melt is important when estimating the probability and timing of containment failure. This work focuses on understanding and modeling the melt eruption phenomenon. A model has been developed to predict the amount of melt ejected during melt eruptions. This entrainment model has been verified against an experimental database developed as part of this work. Several phenomena have been identified and modeled which may predict the creation and closure of eruptions sites. The models have been integrated into a MCCI systems code. The new melt eruption model predicted reasonable rates of melt ejection and the number and diameter of eruption sites for a sample simulation of a postulated reactor scale MCCI. Results from the new melt eruption model suggest an ex-vessel core melt under flooded conditions could readily quench.

Robb, Kevin Richard

22

Chemical Convention in the Lunar Core from Melting Experiments on the Ironsulfur System  

SciTech Connect

By reanalyzing Apollo lunar seismograms using array-processing methods, a recent study suggests that the Moon has a solid inner core and a fluid outer core, much like the Earth. The volume fraction of the lunar inner core is 38%, compared with 4% for the Earth. The pressure at the Moon's core-mantle boundary is 4.8 GPa, and that at the ICB is 5.2 GPa. The partially molten state of the lunar core provides constraints on the thermal and chemical states of the Moon: The temperature at the inner core boundary (ICB) corresponds to the liquidus of the outer core composition, and the mass fraction of the solid core allows us to infer the bulk composition of the core from an estimated thermal profile. Moreover, knowledge on the extent of core solidification can be used to evaluate the role of chemical convection in the origin of early lunar core dynamo. Sulfur is considered an antifreeze component in the lunar core. Here we investigate the melting behavior of the Fe-S system at the pressure conditions of the lunar core, using the multi-anvil apparatus and synchrotron and laboratory-based analytical methods. Our goal is to understand compositionally driven convection in the lunar core and assess its role in generating an internal magnetic field in the early history of the Moon.

Li, J.; Liu, J.; Chen, B.; Li, Z.; Wang, Y. (Michigan); (UC)

2012-03-26

23

A unified approach for calculating core melt frequency caused by internal and external initiating events  

Microsoft Academic Search

A unified approach for calculating the core melt frequency of a specific reactor caused by both internal and external accident initiators is demonstrated. Two classes of internal initiators are examined: transients, of which turbine trip is the chosen example; and loss-of-coolant events of various sizes. The concepts of hazard and fragility analysis first proposed for seismic risk analysis are linked

Carolyn D. Heising; Virgilio Lopes Oliveira

1995-01-01

24

Possible reasons of shock melt deficiency in the Bosumtwi drill cores  

Microsoft Academic Search

Pre-drilling numerical modeling of the Bosumtwi impact event predicted a 200 m thick coherent melt layer, as well as abundant highly shocked target material within the central part of the crater structure. However, these predictions are in disagreement with data from drill core obtained in 2004-2005. Here I provide a brief overview of previous results and discuss possible reasons behind

N. Artemieva

2007-01-01

25

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

SciTech Connect

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 of: (1) comparison to an analytical solution for the dam break problem, (2) water spreading tests in a 1/10 linear scale model of the Mark I containment by Theofanous et al., and (3) steel spreading tests by Suzuki et al. that were also conducted in a geometry similar to the Mark I. The objective of this work was to utilize the MELTSPREAD code to check the assumption of uniform melt spreading in the EPR core catcher design. As a starting point for the project, the code was validated against the worldwide melt spreading database that emerged after the code was originally written in the very early 1990's. As part of this exercise, the code was extensively modified and upgraded to incorporate findings from these various analytical and experiment programs. In terms of expanding the ability of the code to analyze various melt simulant experiments, the options to input user-specified melt and/or substrate material properties was added. The ability to perform invisicid and/or adiabatic spreading analysis was also added so that comparisons with analytical solutions and isothermal spreading tests could be carried out. In terms of refining the capability to carry out reactor material melt spreading analyses, the code was upgraded with a new melt viscosity model; the capability was added to treat situations in which solid fraction buildup between the liquidus-solidus is non-linear; and finally, the ability to treat an interfacial heat transfer resistance between the melt and substrate was incorporated. This last set of changes substantially improved the predictive capability of the code in terms of addressing reactor material melt spreading tests. Aside from improvements and upgrades, a method was developed to fit the model to the various melt spreading tests in a manner that allowed uncertainties in the model predictions to be statistically characterized. With these results, a sensitivity study was performed to investigate the assumption of uniform spreading in the EPR core catcher that addressed parametric variations in: (1) melt pour mass, (2) melt composition, (3) me

Farmer, M. T .; Nuclear Engineering Division

2009-03-30

26

Effect of Hydrogen and Carbon on the Melting Temperature of the Core  

NASA Astrophysics Data System (ADS)

The temperature of the Earth's outer core has been discussed based on the melting temperature of Fe- O-S alloys (e.g., Boehler, 1996). Although hydrogen and carbon are the possible candidates of the core component, their effects on the melting temperature of iron at high-pressures are unclear. Using a Kawai-type multi-anvil apparatus at SPring-8 synchrotron, we carried out a series of melting experiments on FeH and Fe3C up to 20 and 28 GPa, respectively. In the experiments on FeH, Fe sponge mixed with MgO was packed into a NaCl container with a hydrogen source, LiAlH4 (e.g., Fukai et al., 1989). During heating under high-pressures, hydrogenation of iron was observed by volume change. The phase boundary between ?'-phase (low-temperature phase) and ?-phase (high-temperature phase) of iron-hydride was determined using both cooling and heating experiments. Hydrogen concentrations in the ?-FeHx and ?'-FeHx were calculated based on the excess volume data from that of pure iron. It is found that ?-FeHx and ?'-FeHx synthesized in our experiments at pressures between 10 and 20 GPa are nearly stoichiometric FeH. Melting temperature of the ?-FeH was determined by the abrupt change in the X-ray diffraction patterns (crystalline to amorphous). The melting temperatures were determined to be 1473, 1473, 1493, 1573 and 1593 K at 10, 11.5, 15, 18 and 20 GPa, respectively. In the experiments using Fe3C, the synthesized Fe3C powder was encapsulated in a MgO container. In the diffraction sequences during heating, the peaks of Fe3C disappeared, and the new peaks identified as those of Fe7C3 were observed with halo caused by liquid. Finally, the Fe7C3 peaks disappeared, and only the halo pattern was observed. Based on these observations, the incongruent melting of Fe3C to Fe7C3 and liquid is estimated to occur at 1823 and 1923 K at 19.7 and 27.0 GPa, respectively. The liquidus temperatures of the Fe3C composition are found to be at 2098 and 2198 K at 19.5 and 26.8 GPa, respectively. The melting temperatures of Fe3C determined by our experiments are >700 K lower than that of the previous estimation based on thermodynamic calculation (Wood, 1993). Our experimental results show a possibility that the hydrogen and carbon lower the melting temperature of iron (outer core) dramatically. The melting temperatures of ?-FeH and Fe3C at 20 GPa are already 500 K lower than that of pure iron estimated by Anderson and Isaak (2000). Extrapolating our experimental melting curves for FeH and Fe3C to core pressures using Lindemann's melting law, we obtained the melting temperatures to be ~2600 and ~2900 K at the core-mantle boundary (CMB), respectively. In the presence of both hydrogen and carbon, melting temperature of the Earth's outer core could be >1500 K lower than that of the previous estimates, implying that the temperature gap at CMB could be much smaller than the current estimates.

Nakajima, Y.; Sakamaki, K.; Takahashi, E.; Fukai, Y.; Suzuki, T.; Funakoshi, K.

2007-12-01

27

Is Core-Formation Enhanced by Deformation? Olivine-FeS Melt Experiments With the Deformation-DIA  

NASA Astrophysics Data System (ADS)

Contrary to most common silicate melt phases, a high dihedral angle (>60°) between metallic melt and silicate minerals leads to an early breakdown of the grain-scale melt network before complete melt extraction by porous flow can be achieved. This inefficient segregation from a solid matrix provides important support for the magma ocean model of core formation, which allows molten metal droplets to segregate from silicate melt by gravitational settling. However, some authors have demonstrated that deformation can dynamically enhance melt connectivity so that extensive melting of the silicate proto-earth may not have been necessary. In this study, deformation experiments with FeS melt in a matrix of synthetic olivine (Fo90) were performed to investigate a potentially enhanced dynamic melt segregation as a function of strain rate and melt fraction. The experiments were performed with a deformation-DIA, a cubic multi-anvil device, at a confining pressure of 3 GPa and at a temperature of 1400°C using a wide range of melt fractions (1-15 vol. %) and strain rates (10-2-10-6 s-1). The samples were quenched rapidly to preserve the dynamic melt geometry. Our results show that despite local wetting of grain boundaries, especially during high strain rate experiments, no interconnected melt networks were present at melt fractions below ~3 vol. %. Thus, melt migration by continuous porous flow should be inhibited. However, deformation has a significant effect on melt distribution. Compared to statically annealed samples, the amount of melt in large melt pockets (> 200 mm2) decreases, while the amount of melt in smaller pockets increases, i.e. deformation disperses melt more evenly throughout the grain matrix. At the same time, the overall melt fraction decreases to an apparently stable value of ~1.5 vol. %. Segregated melt can often be observed at the side of the capsule. Although no continuous melt pathways were observed in the low melt-fraction experiments, individual melt patches must have still been mobilized during deformation. Thus, although deformation can aid melt segregation to a certain extent, a decrease of melt-fraction below ~1.5 vol.% did not occur in our experiments so that deformation could not have been the sole mechanism for an efficient core formation.

Walte, N. P.; Frost, D. J.; Rubie, D. C.

2005-12-01

28

The structure of melting mushy zones, with implications for Earth's inner core (Invited)  

NASA Astrophysics Data System (ADS)

Seismologists have inferred hemispherical differences in the isotropic wavespeed, the elastic anisotropy, the attenuation, and the attenuation anisotropy of Earth's inner core. One hypothesis for these hemispherical differences involves an east-west translation of the inner core, with enhanced solidification on one side and melting on the other. Another hypothesis is that long term mantle control over outer core convection can lead to hemispherical variations in solidification that could even result in melting in some regions of the inner core boundary. It has also been hypothesized that the inner core is growing dendritically, resulting in an inner core that has the structure of a mushy zone (albeit one with a high solid fraction). It would therefore be helpful to understand how the structure of a melting mushy zone might look in comparison with one that is solidifying, in an effort to help interpret the seismic inferences. We have carried out experiments on the solidification of ammonium chloride from an aqueous solution, yielding a mushy zone. The experiments run in a centrifuge, in order to reach a more realistic ratio of convective velocity to phase change rate, expected to be very large at the boundary of the inner core. Hypergravity thus increases the experimental solid fraction of the mush. So far the maximum gravity we have achieved is 200 g. A Peltier cell provides cooling at one end of the cell, and after the mushy zone has grown we turn on a heater at the other end. Probes monitor the temperature along the height of the cell. As ammonium chloride in the mushy zone melts it produces more dense fluid, which results in convection in the mushy zone, a greater ammonium chloride concentration deeper in the mushy zone, and hence enhanced solidification there. This thus changes the solid fraction profile from that during solidification, which may be observable in the lab experiments using ultrasonic transducers and post-mortem under a microscope. The melting may also change the propagation of chimney convection. It remains unclear whether these changes will be observable seismically.

Bergman, M. I.; Huguet, L.; Alboussiere, T.

2013-12-01

29

Anomalous Melting Scenario of the Two-Dimensional Core-Softened System  

NASA Astrophysics Data System (ADS)

We present a computer simulation study of the phase behavior of two-dimensional (2D) classical particles repelling each other through an isotropic core-softened potential. As in the analogous three-dimensional (3D) case, a reentrant-melting transition occurs upon compression for not too high pressures, along with a spectrum of waterlike anomalies in the fluid phase. However, in two dimensions in the low density part of the phase diagram melting is a continuous two-stage transition, with an intermediate hexatic phase. All available evidence supports the Kosterlitz-Thouless-Halperin-Nelson-Young scenario for this melting transition. On the other hand, at the high density part of the phase diagram one first-order transition takes place.

Dudalov, D. E.; Fomin, Yu. D.; Tsiok, E. N.; Ryzhov, V. N.

2014-04-01

30

Hot-melt extruded ethylcellulose cylinders containing a HPMC–Gelucire® core for sustained drug delivery  

Microsoft Academic Search

The objective of the study was to develop a sustained release system consisting of a hot-melt extruded ethylcellulose pipe surrounding a drug-containing hydroxypropyl methylcellulose (HPMC)–Gelucire® 44\\/14 core, yielding a monolithic matrix system applicable in the domain of sustained drug release. The influence of HPMC substitution type and viscosity grade was investigated through dissolution testing and erosion studies. All sustained release

E Mehuys; C Vervaet; J. P Remon

2004-01-01

31

An Interconnected Network of Core-Forming Melts Produced by Shear Deformation  

NASA Technical Reports Server (NTRS)

The formation mechanism of terrestrial planetary is still poorly understood, and has been the subject of numerous experimental studies. Several mechanisms have been proposed by which metal-mainly iron with some nickel-could have been extracted from a silicate mantle to form the core. Most recent models involve gravitational sinking of molten metal or metal sulphide through a partially or fully molten mantle that is often referred to as a'magma ocean. Alternative models invoke percolation of molten metal along an interconnected network (that is, porous flow) through a solid silicate matrix. But experimental studies performed at high pressures have shown that, under hydrostatic conditions, these melts do not form an interconnected network, leading to the widespread assumption that formation of metallic cores requires a magma ocean. In contrast, here we present experiments which demonstrate that shear deformation to large strains can interconnect a significant fraction of initially isolated pockets of metal and metal sulphide melts in a solid matrix of polycrystalline olivine. Therefore, in a dynamic (nonhydrostatic) environment, percolation remains a viable mechanism for the segregation and migration of core-forming melts in a solid silicate mantle.

Bruhn, D.; Groebner, N.; Kohlstedt, D. L.

2000-01-01

32

Potassium Solubility in Fe-S Melts and Implications for the Earth's Core  

NASA Astrophysics Data System (ADS)

Potassium as a radiogenic heat source in the Earth's core has been suggested over 30 years ago but several attempts at experimental confirmation have only yielded ambiguous results. This may have been in part due to severe experimental difficulties caused by volatility of K at high temperature and the ubiquitous solubility of K not only in water but also in "water-free" hydrocarbon oils used in polishing and other organic solvents. We report here on experiments performed under conditions in which the above difficulties have been overcome by using a double capsule technique to contain the sample and by new methods of polishing without the use of liquids. We have taken a two-level approach in our experiments - first to establish that K is in fact soluble in sulfide melts at low pressure and temperature and then to determine the effect of pressure and temperature on solubility of K in systems similar to Bulk Silicate Earth. In synthetic systems composed of K-silicate, Fe-metal, and FeS, potassium is readily soluble in the Fe-S melts at 2 GPa and magmatic temperatures at fO2 close to IW. The sulfide-silicate distribution coefficient DK is 0.03 at 1200° C but increases by a factor of 7 to 0.2 at 1600° C showing a perfect correlation in a plot of ln DK vs. 1/T. These experiments indicate a significant temperature-dependent solubility of K in Fe-S melts and provide clues to the formation of K-bearing sulfide minerals in some meteorites. If the Earth's core formed by segregation of metallic liquids in the Fe-FeS system, even the level of solubility observed at these low temperatures suggests that a significant amount of potassium will be present in the core and will serve as a radiogenic heat source in the core. For example, using the DK at 1600° C, we calculate that the present heat production due to K in the core to be ~3x1012 W for a Chondritic Earth Model and 1x1012 W for a potassium poor Bulk Earth Model. The estimate for the present day heat flux from the CMB of 3-12 x1012 W shows that the radiogenic heat due to 40 K in the core can be a significant fraction of the CMB heat flux. The presence of radiogenic heat in the core has important implications for the time of formation of the inner core, convection in the outer core, the geomagnetic field and the lower mantle geochemistry and dynamics.

van Westrenen, W.; Murthy, V.; Fei, Y.

2002-05-01

33

Comparison of the effect of hazard and response/fragility uncertainties on core melt probability uncertainty  

SciTech Connect

This report proposes a method for comparing the effects of the uncertainty in probabilistic risk analysis (PRA) input parameters on the uncertainty in the predicted risks. The proposed method is applied to compare the effect of uncertainties in the descriptions of (1) the seismic hazard at a nuclear power plant site and (2) random variations in plant subsystem responses and component fragility on the uncertainty in the predicted probability of core melt. The PRA used is that developed by the Seismic Safety Margins Research Program.

Mensing, R.W.

1985-01-01

34

Partitioning of potassium between silicates and sulphide melts - Experiments relevant to the earth's core.  

NASA Technical Reports Server (NTRS)

The partitioning of potassium between roedderite, K2Mg5Si12O30 and an Fe-FeS melt was investigated at temperatures about 40 C above the Fe-FeS eutectic. Roedderite was considered a prime candidate for one of the potassium-bearing phases in the primitive earth because roedderite and merrihueite are the only two silicates containing essential potassium which have been identified in stony meteorites. Application of the results to a primitive chondritic earth is discussed, and it is concluded that extraction of most of the earth's potassium into the Fe-FeS core would occur under the conditions in the early earth.-

Goettel, K. A.

1972-01-01

35

Diverse melting modes and structural collapse of hollow bimetallic core-shell nanoparticles: a perspective from molecular dynamics simulations.  

PubMed

Introducing hollow structures into metallic nanoparticles has become a promising route to improve their catalytic performances. A fundamental understanding of thermal stability of these novel nanostructures is of significance for their syntheses and applications. In this article, molecular dynamics simulations have been employed to offer insights into the thermodynamic evolution of hollow bimetallic core-shell nanoparticles. Our investigation reveals that for hollow Pt-core/Au-shell nanoparticle, premelting originates at the exterior surface, and a typical two-stage melting behavior is exhibited, similar to the solid ones. However, since the interior surface provides facilitation for the premelting initiating at the core, the two-stage melting is also observed in hollow Au-core/Pt-shell nanoparticle, remarkably different from the solid one. Furthermore, the collapse of hollow structure is accompanied with the overall melting of the hollow Pt-core/Au-shell nanoparticle while it occurs prior to that of the hollow Au-core/Pt-shell nanoparticle and leads to the formation of a liquid-core/solid-shell structure, although both of them finally transform into a mixing alloy with Au-dominated surface. Additionally, the existence of stacking faults in the hollow Pt-core/Au-shell nanoparticle distinctly lowers its melting point. This study could be of great importance to the design and development of novel nanocatalysts with both high activity and excellent stability. PMID:25394424

Huang, Rao; Shao, Gui-Fang; Zeng, Xiang-Ming; Wen, Yu-Hua

2014-01-01

36

Nickel and helium evidence for melt above the core-mantle boundary.  

PubMed

High (3)He/(4)He ratios in some basalts have generally been interpreted as originating in an incompletely degassed lower-mantle source. This helium source may have been isolated at the core-mantle boundary region since Earth's accretion. Alternatively, it may have taken part in whole-mantle convection and crust production over the age of the Earth; if so, it is now either a primitive refugium at the core-mantle boundary or is distributed throughout the lower mantle. Here we constrain the problem using lavas from Baffin Island, West Greenland, the Ontong Java Plateau, Isla Gorgona and Fernandina (Galapagos). Olivine phenocryst compositions show that these lavas originated from a peridotite source that was about 20 per cent higher in nickel content than in the modern mid-ocean-ridge basalt source. Where data are available, these lavas also have high (3)He/(4)He. We propose that a less-degassed nickel-rich source formed by core-mantle interaction during the crystallization of a melt-rich layer or basal magma ocean, and that this source continues to be sampled by mantle plumes. The spatial distribution of this source may be constrained by nickel partitioning experiments at the pressures of the core-mantle boundary. PMID:23302797

Herzberg, Claude; Asimow, Paul D; Ionov, Dmitri A; Vidito, Chris; Jackson, Matthew G; Geist, Dennis

2013-01-17

37

Partitioning of Moderately Siderophile Elements Among Olivine, Silicate Melt, and Sulfide Melt: Constraints on Core Formation in the Earth and Mars  

NASA Technical Reports Server (NTRS)

This study investigates the effects of Variations in the fugacities of oxygen and sulfur on the partitioning of first series transition metals (V, Cr, Mn, Fe, Co, Ni. and Cu) and W among coexisting sulfide melt, silicate melt, and olivine. Experiments were performed at 1 atm pressure, 1350 C, with the fugacities of oxygen and sulfur controlled by mixing CO2, CO, and SO2 gases. Starting compositions consisted of a CaO-MgO-Al2O3-SiO2-FeO-Na2O analog for a barred olivine chondrule from an ordinary chondrite and a synthetic komatiite. The f(sub O2)/f(sub S2), conditions ranged from log of f(sub O2) = -7.9 to - 10.6, with log of f(sub S2) values ranging from - 1.0 to -2.5. Our experimental results demonstrate that the f(sub O2)/f(sub S2) dependencies of sulfide melt/silicate melt partition coefficients for the first series transition metals arc proportional to their valence states. The f(sub O2)/f(sub S2) dependencies for the partitioning of Fe, Co, Ni, and Cu are weaker than predicted on the basis of their valence states. Variations in conditions have no significant effect on olivine/melt partitioning other than those resulting from f(sub O2)-induced changes in the valence state of a given element. The strong f(sub O2)/f(sub S2) dependence for the olivine/silicate melt partitioning of V is attributable to a change of valence state, from 4+ to 3+, with decreasing f(sub O2). Our experimentally determined partition coefficients are used to develop models for the segregation of sulfide and metal from the silicate portion of the early Earth and the Shergottite parent body (Mars). We find that the influence of S is not sufficient to explain the overabundance of siderophile and chalcophile elements that remained in the mantle of the Earth following core formation. Important constraints on core formation in Mars are provided by our experimental determination of the partitioning of Cu between silicate and sulfide melts. When combined with existing estimates for siderophile element abundances in the Martian mantle and a mass balance constraint from Fe, the experiments allow a determination of the mass of the Martian core (approx. 17 to 22 wt% of the planet) and its S content (approx.0.4 wt%). These modeling results indicate that Mars is depleted in S, and that its core is solid.

Gaetani, Glenn A.; Grove, Timothy L.

1997-01-01

38

Hard-Core Bosons on the Kagome Lattice: Valence-Bond Solids and Their Quantum Melting  

NASA Astrophysics Data System (ADS)

Using large scale quantum Monte Carlo simulations and dual vortex theory, we analyze the ground state phase diagram of hard-core bosons on the kagome lattice with nearest-neighbor repulsion. In contrast with the case of a triangular lattice, no supersolid emerges for strong interactions. While a uniform superfluid prevails at half filling, two novel solid phases emerge at densities ?=1/3 and ?=2/3. These solids exhibit an only partial ordering of the bosonic density, allowing for local resonances on a subset of hexagons of the kagome lattice. We provide evidence for a weakly first-order phase transition at the quantum melting point between these solid phases and the superfluid.

Isakov, S. V.; Wessel, S.; Melko, R. G.; Sengupta, K.; Kim, Yong Baek

2006-10-01

39

Dynamic loads from reactor pressure vessel core melt-through under high primary systems pressure  

SciTech Connect

Estimates are presented of the thermal-hydraulic load acting on a pressurized water reactor pressure vessel and its support girder after lower head failure at high pressure (227 MPa). The estimates are based on one-dimensional calculations performed with the RELAP5/MOD3 transient analysis thermal-hydraulics code. The information obtained provides a force-function input for structural dynamic calculations of an increased containment. On the assumption of a global circumferential rupture of the vessel lower head, the computations show a load peak of 340 MN and a continuing load of 160 MN acting on the vessel support ring. The analysis is related to the containment concept of Eibl, Kessler, and Hennies, which is aimed at developing passive mechanisms that can safely confine core-melt consequences.

Jacobs, G. [Forschungszentrum Karlsruhe (Germany)

1995-09-01

40

Partitioning of potassium between silicates and sulphide melts: Experiements relevant to the earth's core  

NASA Technical Reports Server (NTRS)

The partitioning of potassium between roedderite, K2Mg5Si12O30 and an Fe-FeS melt was investigaged at temperatures about 40 C above the Fe-FeS eutectic. Roedderite was considered a prime candidate for one of the potassium-bearing phases in the primitive earth because roedderite and merrihueite are the only two silicates containing essential potassium which have been identified in stony meteorites. A mean K2S/FeS weight ratio of (3.340 + or - 0.015) x 0.001 was determined in these experiments; a K2S/FeS weight ratio of about 0.01 would be sufficient to extract all potassium in a chondritic earth into the core. Application of these results to a primitive chondritic earth is discussed and it is concluded that extraction of most of the earth's potassium into the Fe-FeS core would occur under the conditions in the early earth.

Goettel, K. A.

1972-01-01

41

Melting Scenario of the Two-Dimensional Core-Softened System: First-Order or Continuous Transition?  

NASA Astrophysics Data System (ADS)

We present a computer simulation study of the phase behavior of two-dimensional classical particles repelling each other through an isotropic core-softened potential. As in the analogous three dimensional case, a reentrant-melting transition occurs upon compression for not too high pressures. However, in two dimensions in the low density part of the phase diagram melting is a continuous two-stage transition, with an intermediate hexatic phase. All available evidence supports the Kosterlitz-Thouless-Halperin-Nelson-Young (KTHNY) scenario for this melting transition. On the other hand, at high density part of the phase diagram one first-order transition takes place. We expect that such a phenomenology can be checked in confined monolayers of charge-stabilized colloids with a softened core and water confined between two hydrophobic plates.

Dudalov, D. E.; Fomin, Yu D.; Tsiok, E. N.; Ryzhov, V. N.

2014-05-01

42

MELT Bibliography. Materials Correlated with the Core Curriculum Competencies of the Mainstream English Language Training Project, Office of Refugee Resettlement.  

ERIC Educational Resources Information Center

This bibliography is intended to assist teachers and administrators involved in competency-based, English as a second language (ESL) instruction. The materials included in the bibliography have been correlated with the core curriculum competencies of the Mainstream English Language Training (MELT) Project. The guide is divided into three parts.…

Brod, Shirley, Comp.; Sample, Barbara J.

43

Melting phase relation of FeH x up to 20 GPa: Implication for the temperature of the Earth's core  

NASA Astrophysics Data System (ADS)

High-pressure and high-temperature X-ray diffraction experiments on FeH x up to 20 GPa and 1598 K were performed using a Kawai-type multi-anvil apparatus, SPEED-MkII, installed at BL04B1 beam line of SPring-8 synchrotron facility. Iron powder was packed in a container made of NaCl, a very efficient sealing material for hydrogen under high pressure, together with a hydrogen source, LiAlH 4. The temperature of hydrogenation, transition of iron hydride phases, and melting of ?-FeH x were all determined in situ in the pressure range between 10 and 20 GPa. Hydrogen concentration in both ?'- and ?-FeH x phases reached x = 1.0 above 10 GPa. Melting temperatures of ?-FeH were determined to be 1473, 1448 ± 25, 1538 ± 15, 1548 ± 25 and 1585 ± 13 K at 10, 11.5, 15, 18 and 20 GPa, respectively. These temperatures are nearly 700 K lower than that of pure iron under the corresponding pressures. The Clapeyron-slope (d T/d P slope) of the melting curve of ?-FeH is 13 K/GPa, which is significantly smaller than those of other possible core constituents (Fe, FeO, FeS). By extrapolating the ?'-? phase boundary linearly and the melting curve of ?-FeH based on Lindemann's melting law, the triple point of ?'- and ?-FeH and iron hydride melt is located at P = 60 GPa and T = 2000 K. Beyond the triple point, an attempt to construct a melting curve of ?'-FeH by the Lindemann's law using estimated thermal equation of state of ?'-FeH was unsuccessful. Therefore, we decided, instead, to extrapolate the melting curve of ?-FeH beyond the triple point to 135 GPa yielding the melting temperature of FeH ˜ 2600 K at core mantle boundary (CMB). Based on these results, we propose that the temperature of the Earth's outer core could be much lower than current estimates, if the Earth's outer core incorporated significant amounts of hydrogen.

Sakamaki, K.; Takahashi, E.; Nakajima, Y.; Nishihara, Y.; Funakoshi, K.; Suzuki, T.; Fukai, Y.

2009-05-01

44

Natural convection model of molten pool penetration into a melting miscible substrate  

Microsoft Academic Search

Studies of postulated severe accidents in nuclear reactors have involved consideration of the extent of core-debris-melt penetration into the lighter and miscible concrete substrate below the reactor vessel. It is suggested in this paper that the melting of concrete by an overlying pool of oxidic core material\\/concrete mixture is partially driven by classical liquid-turbulent natural convection, with plumes of molten

Epstein

1993-01-01

45

Uranium partitioning between liquid iron and silicate melt at high pressures: implications for uranium solubility in planetary cores  

E-print Network

We have investigated the partitioning of U between silicate melt and Fe liquid at pressures of 3.0 to14.5 GPa and temperatures of 1660 to 2500 oC. The solubility of U in liquid Fe is in the range of 0.6 to 800 ppm and increases with temperature (T) and pressure (P). When P = or > 7 GPa and T > Tmelt of the silicate phase (olivine), the U concentration in Fe is 3 to 5 times greater than for run products where T Tmelt of the silicate phase), then > 2.4 ppb U could have entered the core. Alternatively, if a core with same composition formed by percolation (T Uranium; partition coefficients; high pressure; dynamos; planetary cores; heat sources, LA-ICP-MS.

Xuezhao Bao; Richard A. Secco; Joel E. Gagnon; Brian J. Fryer

2006-06-29

46

Rapid, dynamic segregation of core forming melts: Results from in-situ High Pressure- High Temperature X-ray Tomography  

NASA Astrophysics Data System (ADS)

The timing and mechanisms of core formation in the Earth, as well as in Earth-forming planetesimals is a problem of significant importance in our understanding of the early evolution of terrestrial planets . W-Hf isotopic signatures in meteorites indicate that core formation in small pre-differentiated planetesimals was relatively rapid, and occurred over the span of a few million years. This time scale is difficult to achieve by percolative flow of the metallic phase through a silicate matrix in textural equilibrium. It has been suggested that during this active time in the early solar system, dynamic processes such as impacts may have caused significant deformation in the differentiating planetesimals, which could lead to much higher permeability of the core forming melts. Here, we have measured the change in permeability of core forming melts in a silicate matrix due to deformation. Mixtures of San Carlos olivine and FeS close to the equilibrium percolation threshold (~5 vol%FeS) were pre-synthesized to achieve an equilibrium microstructure, and then loaded into the rotational Drickamer apparatus at GSE-CARS, sector 13-BMD, at the Advanced Photon Source (Argonne National Laboratory). The samples were subsequently pressed to ~2GPa, and heated to 1100°C. Alternating cycles of rotation to collect X-ray tomography images, and twisting to deform the sample were conducted until the sample had been twisted by 1080°. Qualitative and quantitative analyses were performed on the resulting 3-dimensional x-ray tomographic images to evaluate the effect of shear deformation on permeability and migration velocity. Lattice-Boltzmann simulations were conducted, and show a marked increase in the permeability with increasing deformation, which would allow for much more rapid core formation in planetesimals.

Watson, H. C.; Yu, T.; Wang, Y.

2011-12-01

47

Bayes' postulate for trinomial trials  

NASA Astrophysics Data System (ADS)

In this paper, we discuss Bayes' postulate and its interpretation. We extend the binomial trial method proposed by de Finetti [1] to trinomial trials, for which we argue that the consideration of equiprobability a priori for the possible outcomes of the trinomial trials implies that the parameter vector has Dirichlet(1,1) as prior. Based on this result, we agree with Stigler [2] in that the notion in Bayes' postulate stating "absolutely know nothing" is related to the possible outcomes of an experiment and not to "non-information" about the parameter.

Diniz, M. A.; Polpo, A.

2012-10-01

48

Rapid Detection of KIT Mutations in Core-Binding Factor Acute Myeloid Leukemia Using High-Resolution Melting Analysis  

PubMed Central

The most frequent KIT mutations reported in core-binding factor acute myeloid leukemia are point mutations and insertions/deletions in exons 17 and 8. The vast majority of KIT mutation detection procedures are time-consuming, costly, or with a high lower limit of detection. High-resolution melting (HRM) is a gene scanning method that combines simplicity and rapid identification of genetic variants. We describe an HRM method for the simultaneous screening of exons 8 and 17 KIT mutations and report the results obtained in 69 core-binding factor acute myeloid leukemia patients. Mutation detection was compared with sequencing as the gold standard. The HRM method used high-resolution melting master reagents (Roche) and the LightCycler 480 (Roche) platform. HRM was reproducible, showed a lower limit of detection of 1%, and discriminated all patients with mutated KIT from controls without false positive or false negative results. Additionally, most of the mutations were differentiated from the other mutations. KIT mutations were present in 15.9% of patients, showing a higher incidence in inv(16) (25.8%) than in t(8;21) (7.9%). The presence of a KIT mutation was associated with a high white blood cell count, and adult patients with an exon 17 mutation had a higher incidence of relapse. These findings verify that HRM is a reliable, rapid, and sensitive method for KIT mutation screening. Furthermore, our study corroborates the unfavorable prognosis associated with exon 17 KIT mutations. PMID:19644024

Fuster, Óscar; Barragán, Eva; Bolufer, Pascual; Cervera, José; Larráyoz, Maria José; Jiménez-Velasco, Antonio; Martínez-López, Joaquín; Valencia, Ana; Moscardó, Federico; Sanz, Miguel Ángel

2009-01-01

49

Evidence for Past Melting at the Base of the GISP2 Ice Core from Uranium-Thorium Disequilibrium Measurements  

NASA Astrophysics Data System (ADS)

We measured 238U-234U-230Th disequilibria by mass spectrometric methods for silty ice samples from the base of the GISP2 Greenland ice core, at a depth of 3040-3052 m. The expected age of these samples is >150 kyr based on counting ice layers. We separated the samples into several fractions by filtration and analyzed the <50 nm (truly dissolved + particulate) and >200 nm (particulate) filtered fractions. In the <50 nm fractions, low Th/U mass ratios of 0.51-0.65 indicate that a large portion (86-89%) of U is truly dissolved and not associated with particles. In addition, 230Th/234U activity ratios are quite low (0.18-0.24), suggesting either recent 230Th loss and/or 234U addition to the samples. This Th/U fractionation is not consistent with an age >150 kyr. Since liquid water is characterized by 230Th/234U activity ratios <<1, these results suggest that recent melting/freezing event(s) have occurred at the base of the GISP2 core. The particulate (>200 nm) fraction is characterized by Th/U ratios of ~4.4-4.9, 234U/238U activity ratios of 1.049-1.056, and 230Th/234U activity ratios of 1.12-1.23. The U-Th disequilibrium in the particles is consistent with recent (<350 kyr) fractionation of U-Th in these ice samples. We have modeled these results using a two component mass balance calculation, with dissolved and particulate pools for each radionuclide. The main assumption is that all of the 232Th in the <50 nm fraction is due to particles, due to the low aqueous solubility of 232Th. By mass balance, 230Th/234U activity ratios for the truly dissolved fraction are 0.031-0.062, and dates for when the samples were last frozen are 3.5-6.9 kyr. These results are consistent with the notion of ice melting at the base of large continental ice sheets, with recent evidence of large sub-glacial lakes in Antarctica and active melting at the base of the nearby N-GRIP Greenland ice core. There also appears to be a significant difference in age for the deepest ice sample (3.5 kyr; 3052 m) and the other samples (5.2-6.9 kyr; 3040-3048 m), suggesting that the deepest part of the ice core adjacent to bedrock at 3053.3 m depth may have existed as liquid water for at least several hundred - few thousand years.

Goldstein, S. J.; Lee, V. E.; Nishiizumi, K.; Murrell, M. T.; Amato, R. S.; Nunn, A. J.

2011-12-01

50

Evidence for Recent Melting at the Base of the GISP2 Ice Core From Uranium-Thorium Disequilibrium Measurements  

NASA Astrophysics Data System (ADS)

We measured 238U-234U-230Th disequilibria by mass spectrometric methods for a set of dusty ice samples from the base of the GISP2 Greenland ice core, at a depth of 3040-3052 m. The goal of this work was to further test the Fireman (1986) recoil-based model for producing uranium-series disequilibria in dusty ice on samples thought to be > 150 ka in age based on layer counting. However, the base of the GISP2 core is greatly disturbed in chemistry and dustiness relative to upper portions of the core. Samples consisted of 11 cm sections of ice core with sample weights of 340-430 g. We separated the samples into several fractions by filtration and analyzed the < 0.05 um fraction. This fraction had exceedingly high U and Th concentrations (2.5- 5 ppb U; 1.4-2.7 ppb Th). These U and Th concentrations are a factor of 1000 higher than measured for ice at Allan Hills, Antarctica. Low Th/U ratios of 0.51-0.65 indicate that a large portion of the uranium present in the samples is dissolved and not associated with particles, which are expected to have Th/U ratios around 3. However, 234U/238U activity ratios range from 0.972-0.992 (+/- 0.001), indicating a depletion of 234U relative to secular equilibrium of 1-3%. In addition, 230Th/234U activity ratios are quite low (0.18-0.24), suggesting either recent Th loss and/or U addition to the samples. This recent Th/U fractionation is not consistent with an age > 150 ka. Since liquid water would be characterized by 230Th/234U activity ratios ?1, the low 230Th/234U activity ratios likely indicate that recent melting/freezing event(s) have occurred at the base of the GISP2 core. We can model these results with a two component mass balance calculation, with dissolved and particulate pools for each radionuclide. Although several assumptions are required to calculate ages, preliminary results of these calculations suggest that the melting events may be as young as <10 ka.

Goldstein, S. J.; Murrell, M. T.; Nunn, A. J.; Nishiizumi, K.

2007-12-01

51

Detailed Analysis of a Late-Phase Core-Melt Progression for the Evaluation of In-vessel Corium Retention  

SciTech Connect

Detailed analyses of a late-phase melt progression in the advanced power reactor (APR)1400 were completed to identify the melt and the thermal-hydraulic states of the in-vessel materials in the reactor vessel lower plenum at the time of reactor vessel failure to evaluate the candidate strategies for an in-vessel corium retention (IVR). Initiating events considered included high-pressure transients of a total loss of feed water (LOFW) and a station blackout (SBO) and low-pressure transients of a 0.0009-m2 small, 0.0093-m2 medium, and 0.0465-m2 large-break loss-of-coolant accident (LOCA) without safety injection. Best-estimate simulations for these low-probability events with conservative accident progression assumptions that lead to reactor vessel failure were performed by using the SCDAP/RELAP5/MOD3.3 computer code. The SCDAP/RELAP5/MOD3.3 results have shown that the pressurizer surge line failed before the reactor vessel failure, which results in a rapid decrease of the in-vessel pressure and a delay of the reactor vessel failure time of ~40 min in the high-pressure sequences of the total LOFW and the SBO transients. In all the sequences, ~80 to 90% of the core material was melted and relocated to the lower plenum of the reactor vessel at the time of reactor vessel failure. The maximum value of the volumetric heat source in the corium pool was estimated as 1.9 to 3.7 MW/m3. The corium temperature was ~2800 to 3400 K at the time of reactor vessel failure. The highest volumetric heat source sequence is predicted for the 0.0465-m2 large-break LOCA without safety injection in the APR1400, because this sequence leads to an early reactor vessel failure.

J. L. Rempe; R. J. Park; S. B. Kim; K. Y. Suh; F. B.Cheung

2006-12-01

52

LWR source terms for loss-of-coolant and core melt accidents  

SciTech Connect

Fission product source terms for loss-of-coolant and core meltdown accidents in light water reactors are reviewed. The results presented in the Reactor Safety Study are summarized, and modifications of these results, due to more recent experimental studies, are described.

Malinauskas, A.P.; Lorenz, R.A.; Albrecht, H.; Wild, H.

1980-01-01

53

Hard-Core Bosons on the Kagome Lattice: Valence-Bond Solids and Their Quantum Melting  

Microsoft Academic Search

Using large scale quantum Monte Carlo simulations and dual vortex theory, we analyze the ground state phase diagram of hard-core bosons on the kagome lattice with nearest-neighbor repulsion. In contrast with the case of a triangular lattice, no supersolid emerges for strong interactions. While a uniform superfluid prevails at half filling, two novel solid phases emerge at densities rho=1\\/3 and

S. V. Isakov; S. Wessel; R. G. Melko; K. Sengupta; Yong Baek Kim

2006-01-01

54

Valence Bond Solids and Their Quantum Melting in Hard-Core Bosons on the Kagome Lattice  

Microsoft Academic Search

Using large scale quantum Monte Carlo simulations and dual vortex theory we\\u000aanalyze the ground state phase diagram of hard-core bosons on the kagome\\u000alattice with nearest neighbor repulsion. In contrast to the case of a\\u000atriangular lattice, no supersolid emerges for strong interactions. While a\\u000auniform superfluid prevails at half-filling, two novel solid phases emerge at\\u000adensities $\\\\rho=1\\/3$ and

S. V. Isakov; S. Wessel; R. G. Melko; K. Sengupta; Yong Baek Kim

2006-01-01

55

Melting relationships of the Fe-S-Si system up to 60 GPa: Implications for the thermal structure of the Earth's core  

NASA Astrophysics Data System (ADS)

The Earth's core is mainly composed of iron alloy, however the lighter elements are required in the core to account for the core density deficit (Birch, 1964). The potential light elements have been considered to be S, Si, O, C, and H (Poirier, 1994). Alloying light elements significantly affects the physical properties of iron and depresses its melting temperature(e.g., Boehler, 1996b). Sulfur and silicon are considered as major light element components based on cosmochemical study (McDonough, 2003) and high pressure partitioning experiments (e.g., Sakai et al., 2006), therefore the melting relationship of the Fe-S-Si system is the key information to clarify the thermal and compositional structure of the Earth's core. Many melting experiments of Fe-light elements alloys have been performed under high pressure corresponding Earth's core using diamond anvil cell. However in the case of the Fe-S-Si ternary system, there are no experimental data at high pressure and the phase and melting relations have not been clarified in detail under core conditions. In this study, the phase relationships and the solidus temperature of the Fe-S-Si system were determined up to 60 GPa using a laser-heated diamond anvil cell combined with in situ X-ray diffraction technique. The sample composition used for this study were Fe80.1S12.7Si7.2(Fe-8wt.%S-4wt.%Si) and Fe74.4S18.5Si7.1(Fe-12wt.%S-4wt.%Si), which are in the range of the amounts of the light elements to explain the density deficit in the Earth's core (Chen et al., 2007). In situ X-ray diffraction experiments were conducted at the BL10XU beamline at the SPring-8 facility (Ohishi et al., 2008). On the basis of diffraction patterns, Fe(hcp/fcc) which contains silicon and Fe3S are stable phases under subsolidus conditions. First Fe3S phase melts at the solidus temperature, and Fe-Si alloy coexists with partial melts above the eutectic temperature in this system. This melting sequence is consistent with the study of the Fe-Fe3S system observed earlier by Kamada et al. (2010). The solidus temperature is significantly lower than the melting temperature of pure Fe (Ma et al., 2004) and close to the eutectic point of the Fe-Fe3S system (Morard et al., 2008), suggesting that the effect of 7.2 at.% silicon on the eutectic temperature in the Fe-Fe3S system is minor. In order to draw the solidus curve as a function of pressure, we fitted the present results using the Simon's law. The obtained fitting parameters are a=104(16) and c=0.88(1). Based on our results of the melting relationship, the temperature at the core-mantle boundary should be greater than 2900(200) K and the temperature at the boundary of the inner and outer cores is estimated to be 5680(350) K, assuming that sulfur and silicon are the light elements in the Earth's core. The results in this study provide important constraints on the thermal structure of the Earth's core.

Sakairi, T.; Ohtani, E.; Sakai, T.; Kamada, S.; Miyahara, M.; Hirao, N.; Ohishi, Y.

2012-12-01

56

Melting of Fe and Fe0.9375Si0.0625 at Earth's core pressures studied using ab initio molecular dynamics  

NASA Astrophysics Data System (ADS)

The issue of melting of pure iron and iron alloyed with lighter elements at high pressure is critical to the physics of the Earth. The iron melting curve in the relevant pressure range between 3 and 4 Mbar is reasonably well established from the theoretical point of view. However, so far no one attempted a direct atomistic simulation of iron alloyed with light elements. We investigate here the impact of alloying the body-centered cubic (bcc) Fe with Si. We simulate melting of the bcc Fe and Fe0.9375Si0.0625 alloy by ab initio molecular dynamics. The addition of light elements to the hexagonal-close-packed (hcp) iron is known to depress its melting temperature (Tm) . We obtain, in marked contrast, that alloying of bcc Fe with Si does not lead to Tm depression; on the contrary, the Tm slightly increases. This suggests that if Si is a typical impurity in the Earth’s inner core, then the stable phase in the core is bcc rather than hcp.

Belonoshko, Anatoly B.; Rosengren, Anders; Burakovsky, Leonid; Preston, Dean L.; Johansson, Börje

2009-06-01

57

Informational approach to the quantum symmetrization postulate  

NASA Astrophysics Data System (ADS)

A remarkable feature of quantum theory is that particles with identical intrinsic properties must be treated as indistinguishable if the theory is to give valid predictions in all cases. In the quantum formalism, indistinguishability is expressed via the symmetrization postulate (Dirac P 1926 Proc. R. Soc. A 112 661, Heisenberg W 1926 Z. Phys. 38 411), which restricts a system of identical particles to the set of symmetric states (‘bosons’) or the set of antisymmetric states (‘fermions’). However, the physical basis and range of validity of the symmetrization postulate has not been established. A well-known topological derivation of the postulate implies that its validity depends on the dimensionality of the space in which the particles move (Laidlaw M and DeWitt C 1971 Phys. Rev. D 3 1375–8, Leinaas J M and Myrheim J 1977 Il Nuovo Cimento B 37 1–23). Here we show that the symmetrization postulate can be derived by strictly adhering to the informational requirement that particles which cannot be experimentally distinguished from one another are not labelled. Our key novel postulate is the operational indistinguishability postulate, which posits that the amplitude of a process involving several indistinguishable particles is determined by the amplitudes of all possible transitions of these particles when treated as distinguishable. The symmetrization postulate follows by requiring consistency with the rest of the quantum formalism. The derivation implies that the symmetrization postulate admits no natural variants. In particular, the possibility that identical particles generically exhibit anyonic behavior in two dimensions is excluded.

Goyal, Philip

2015-01-01

58

A MELCOR Application to Two Light Water Reactor Nuclear Power Plant Core Melt Scenarios with Assumed Cavity Flooding Action  

Microsoft Academic Search

The MELCOR 1.8.4 code Bottom Head package has been applied to simulate two reactor cavity flooding scenarios for when the corium material relocates to the lower-plenum region in postulated severe accidents. The applications were preceded by a review of two main physical models, which highly impacted the results. A model comparison to available bibliography models was done, which allowed some

Francisco Martin-Fuertes; Juan Manuel Martin-Valdepenas; Jose Mira; Maria Jesus Sanchez

2003-01-01

59

Overview of Special Relativity Einstein's Two Postulates  

E-print Network

Overview of Special Relativity Einstein's Two Postulates Relativistic mechanics modify Newton transformations Relativistic equations for mechanics Principle of relativity: the laws of physics apply in all vectors: antisymmetric tensor (4-d) 3 #12;Galilean versus Special Relativity Galilean Relativity Special

Hart, Gus

60

Thermal behavior of core-shell and three-shell layered clusters: Melting of Cu1Au54 and Cu12Au43  

NASA Astrophysics Data System (ADS)

The meltinglike transition of the Cu1Au54 and Cu12Au43 clusters is investigated by canonical Monte Carlo simulations, based on the second-moment approximation of the tight-binding potentials. The structures of both the Cu1Au54 and Cu12Au43 clusters, shown to be icosahedral, are obtained from the so-called semi-grand-canonical ensemble Monte Carlo simulation at 100K . A core-shell structure is found in Cu1Au54 , with a single Cu atom in the center and 54 Au atoms on the surface and in interior shells of the cluster. On the other hand, Cu12Au43 possesses a three-shell onionlike structure, with a single Au atom located in the center, 12 Cu atoms in the middle shell, and 42 Au atoms occupying the surface shell of the cluster. Melting characteristics are observed by the changes in the caloric curve, heat capacity, root-mean-square bond-length fluctuation, and deformation parameter. It is found that doping of Au55 with a single Cu atom can sharply raise the melting point of the cluster. In addition, the three-shell onionlike structure can be transformed into the core-shell structure at the higher temperatures after melting. It is also found that surface segregation of Au atoms in Cu1Au54 and Cu12Au43 occurs in the liquid phase. In addition, the simulation results show that the melting point increases with the concentration of Cu in the 55-atom Cu-Au bimetallic cluster.

Cheng, Daojian; Huang, Shiping; Wang, Wenchuan

2006-08-01

61

Hot-melt co-extrusion for the production of fixed-dose combination products with a controlled release ethylcellulose matrix core.  

PubMed

In this study, hot-melt co-extrusion was evaluated as a technique for the production of fixed-dose combination products, using ethylcellulose as a core matrix former to control the release of metoprolol tartrate and a polyethylene oxide-based coat formulation to obtain immediate release of hydrochlorothiazide. By lowering the concentration of the hydrophilic additive polyethylene oxide in the plasticized ethylcellulose matrix or by lowering the drug load, the in vitro metoprolol tartrate release from the core was substantially sustained. The in vitro release of hydrochlorothiazide from the polyethylene oxide/polyethylene glycol coat was completed within 45 min for all formulations. Tensile testing of the core/coat mini-matrices revealed an adequate adhesion between the two layers. Raman mapping showed no migration of active substances. Solid state characterization indicated that the crystalline state of metoprolol tartrate was not affected by thermal processing via hot-melt extrusion, while hydrochlorothiazide was amorphous in the coat. These solid state characteristics were confirmed during the stability study. Considering the bioavailability of metoprolol tartrate after oral administration to dogs, the different co-extruded formulations offered a range of sustained release characteristics. Moreover, high metoprolol tartrate plasma concentrations were reached in dogs allowing the administered dose to be halved. PMID:24486558

Vynckier, A-K; Dierickx, L; Saerens, L; Voorspoels, J; Gonnissen, Y; De Beer, T; Vervaet, C; Remon, J P

2014-04-10

62

Radiological Impact Assessment (RIA) following a postulated accident in PHWRS  

SciTech Connect

Radiological Impact Assessment (RIA) following postulated accident i.e Loss of Coolant Accident (LOCA) with failed Emergency Core Cooling System (ECCS), performed as part of the reactor safety analysis of a typical 700 MWe Indian Pressurized Heavy Water Reactor(PHWR). The rationale behind the assessment is that the public needs to be protected in the event that the postulated accident results in radionuclide release outside containment. Radionuclides deliver dose to the human body through various pathways namely, plume submersion, exposure due to ground deposition, inhalation and ingestion. The total exposure dose measured in terms of total effective dose equivalent (TEDE) is the sum of doses to a hypothetical adult human at exclusion zone boundary by all the exposure pathways. The analysis provides the important inputs to decide upon the type of emergency counter measures to be adopted during the postulated accident. The importance of the various pathways in terms of contribution to the total effective dose equivalent(TEDE) is also assessed with respect to time of exposure. Inhalation and plume gamma dose are the major contributors towards TEDE during initial period of accident whereas ingestion and ground shine dose start dominating in TEDE in the extended period of exposure. Moreover, TEDE is initially dominated by I-131, Kr-88, Te-132, I-133 and Sr-89, whereas, as time progresses, Xe-133,I-131 and Te-132 become the main contributors. (authors)

Soni, N.; Kansal, M.; Rammohan, H. P.; Malhotra, P. K. [Reactor Safety and Analysis, Nuclear Power Corporation of India Ltd., Nabhkiya Urja Bhavan, Anushakti Nagar, Mumbai Maharashtra 400094 (India)

2012-07-01

63

Koch's Postulates, Carnivorous Cows, and Tuberculosis Today  

PubMed Central

With Koch's announcement in 1882 of his work with the tubercle bacillus, his famous postulates launched the rational world of infectious disease and an abrupt social change—strict patient isolation. The postulates, so successful at their inception, soon began to show some problems, particularly with cholera, which clearly violated some of Koch's requirements. Subsequent studies of other diseases and the discovery of entirely new ones have so altered and expanded the original postulates that they now are little but a precious touch of history. The present additions and replacements of the original concepts are skillful changes that several authors have devised to introduce new order into understanding complex viral and prion diseases. In 1988, this knowledge, with the totally rational response of the British population and its cattle industry, was critical in promptly blocking the threatened epidemic of human prion disease. In contrast, the recent upsurge of tuberculosis (TB) in the worldwide AIDS epidemic in developing countries, and the sudden increase in metabolic syndrome in wealthy ones, suggests the need for focused sociobiologic research seeking ways to affect the damaging lifestyle behavior of many less educated populations in both settings. The world awaits an equivalent of Koch's Postulates in sociobiology to explain and possibly avert large self-destructive behaviors. PMID:21886302

2011-01-01

64

Equivalence Postulate and Quantum Origin of Gravitation  

Microsoft Academic Search

We suggest that quantum mechanics and gravity are intimately related. In particular, we investigate the quantum Hamilton-Jacobi equation in the case of two free particles and show that the quantum potential, which is attractive, may generate the gravitational potential. The investigation, related to the formulation of quantum mechanics based on the equivalence postulate, is based on the analysis of the

Marco Matone; G. Galilei

2000-01-01

65

Thirty-seven year mass balance of Devon Ice Cap, Nunavut, Canada, determined by shallow ice coring and melt modeling  

Microsoft Academic Search

In April–May 2000, eight boreholes were drilled to ?15–20 m depth on the Devon Ice Cap. 137Cs ? activity profiles of each borehole showed a peak count rate at depth that is associated with fallout from atmospheric thermonuclear weapons testing in 1963. Snow, firn, and ice densities were measured at each core site and were used to estimate the average

Douglas Mair; David Burgess; Martin Sharp

2005-01-01

66

Ringwoodite rim around olivine core in shock-induced melt veins of Antarctic chondrite : Mechanisms of transformation and Fe-Mg diffusion  

NASA Astrophysics Data System (ADS)

Introduction: High-pressure minerals, produced by shock metamorphism, are common in and around melt veins in highly shocked chondrites. The shock duration can be constrained by using transformation kinetics, such as the crystallization rate of the melt-vein matrix[1-2], or growth rate of the high-pressure minerals [3-4], or using elements diffusion rate between two minerals [5]. Using transformation kinetics to constrain shock duration de-pend on the details of the transformation mechanism. For example, growth of topotaxial ringwoodite in olivine with coherent interfaces is slower than growth of inclusions with incoherent interfaces [4-5]. Similarly, diffusion-controlled growth, where rates are determined by long-range diffusion, is generally much slower than interface-controlled growth, which is only dependent on diffusion across the interface [6-8]. The occurrences of the high-pressure mineral rims were recently reported in shock-induced melt veins in several heavily shocked (S6) chondrites, ALH78003, Peace River and GRV052049 [9-11]. Here we report EMAP and Raman results of the ringwoodite rims around olivine cores in shock veins of the Antarctic chondrites GRV 022321, and to elucidate the mechanisms of transformation and Mg-Fe diffusion of the olivine to ringwoodite. Results: GRV022321 has a network of black veins which enclose abundant host-rock fragments. The enclosed fragments have sizes ranging from 5 µm to 30 µm, with a brighter rim up to several µm wide and a dark core in reflected light and BSE image. The Raman data reveal that the rim mineral is ringwoodite signature, and the core minerals are dominated by olivine and mixed minor ringwoodite. EMAP data confirm that the ringwoodite in rim is richer in faylite (Fa) than the olivine core. The Fa values range from 50 to 10 with the outer rim having highest Fa value, and the inside darker area with a lower value. Discussion: The occurrence of the rounded shape grains with smooth edges embedded in the fine matrix in shock-induced melt veins suggest that they are enclosed host-rock fragments and that the ringwoodite in the rim was transformed by solid-state transformation from previous olivine. The variable extent of transformation is likely a result of temperature variations during shock, with the hottest outer olivine forming the ringwoodite rim. The outer hotter ringwoodite attract more Fe than inside cooler olivine, and Mg-Fe diffusion occurs in rapid transformation at high pressure and temperature over up to 10 µm distance. The sample is unique because we can test and double check different shock duration constraints in future work. References: [1] Langenhorst and Poirier (2000) EPSL 184, 37-55. [2] Xie, Z. et al. (2006) GCA, 70. 504-515. [3] Ohtani et al. (2004) EPSL 227(3-4), 505-515. [4] Xie and Sharp (2007), EPLS, 433-445. [5] Beck, et al. (2005) Nature 435, 1071-1074. [6] Kerschhofer et al. (1996) Science 274 (5284), 79-81. [7] Kerschhofer et al. (2000) PEPI 121, 59-76. [8] Sharp and DeCarli (2006) MESS II, 653-677. [9] Ohtani et al. (2006), Shock Waves, 16:45-52. [10] Miyahara et al. (2008) Proceedings. of NAS 105,8542-8547. [11] Feng et al. (2007), MAPS 42, A45.

Xie, Z.; Li, X.; Sharp, T. G.; de Carli, P. S.

2009-12-01

67

Testing the ureilite projectile hypothesis for the El'gygytgyn impact: Determination of siderophile element abundances and Os isotope ratios in ICDP drill core samples and melt rocks  

NASA Astrophysics Data System (ADS)

The geochemical nature of the impactites from International Continental Scientific Drilling Project—El'gygytgyn lake drill core 1C is compared with that of impact melt rock fragments collected near the western rim of the structure and literature data. Concentrations of major and trace elements, with special focus on siderophile metals Cr, Co, Ni, and the platinum group elements, and isotope ratios of osmium (Os), were determined to test the hypothesis of an ureilite impactor at El'gygytgyn. Least squares mixing calculations suggest that the upper volcanic succession of rhyolites, dacites, and andesites were the main contributors to the polymict impact breccias. Additions of 2-13.5 vol% of basaltic inclusions recovered from drill core intervals between 391.6 and 423.0 mblf can almost entirely account for the compositional differences observed for the bottom of a reworked fallout deposit at 318.9 mblf, a polymict impact breccia at 471.4 mblf, and three impact melt rock fragments. However, the measured Os isotope ratios and slightly elevated PGE content (up to 0.262 ng g-1 Ir) of certain impactite samples, for which the CI-normalized logarithmic PGE signature displays a relatively flat (i.e., chondritic) pattern, can only be explained by the incorporation of a small meteoritic contribution. This component is also required to explain the exceptionally high siderophile element contents and corresponding Ni/Cr, Ni/Co, and Cr/Co ratios of impact glass spherules and spherule fragments that were recovered from the reworked fallout deposits and from terrace outcrops of the Enmyvaam River approximately 10 km southeast of the crater center. Mixing calculations support the presence of approximately 0.05 wt% and 0.50-18 wt% of ordinary chondrite (possibly type-LL) in several impactites and in the glassy spherules, respectively. The heterogeneous distribution of the meteoritic component provides clues for emplacement mechanisms of the various impactite units.

Goderis, S.; Wittmann, A.; Zaiss, J.; Elburg, M.; Ravizza, G.; Vanhaecke, F.; Deutsch, A.; Claeys, P.

2013-07-01

68

A MELCOR Application to Two Light Water Reactor Nuclear Power Plant Core Melt Scenarios with Assumed Cavity Flooding Action  

SciTech Connect

The MELCOR 1.8.4 code Bottom Head package has been applied to simulate two reactor cavity flooding scenarios for when the corium material relocates to the lower-plenum region in postulated severe accidents. The applications were preceded by a review of two main physical models, which highly impacted the results. A model comparison to available bibliography models was done, which allowed some code modifications on selected default assumptions to be undertaken. First, the corium convective heat transfer to the wall when it becomes liquid was modified, and second, the default nucleate boiling regime curve in a submerged hemisphere was replaced by a new curve (and, to a much lesser extent, the critical heat flux curve was slightly varied).The applications were devoted to two prototypical light water reactor nuclear power plants, a 2700-MW(thermal) pressurized water reactor (PWR) and a 1381-MW(thermal) boiling water reactor (BWR). The main conclusions of the cavity flooding simulations were that the PWR lower-head survivability is extended although it is clearly not guaranteed, while in the BWR sequence the corium seems to be successfully arrested in the lower plenum.Three applications of the CFX 4.4 computational fluid dynamics code were carried out in the context of the BWR scenario to support the first modification of the aforementioned two scenarios for MELCOR.Finally, in the same BWR context, a statistic predictor of selected output parameters as a function of input parameters is presented, which provides reasonable results when compared to MELCOR full calculations in much shorter CPU processing times.

Martin-Fuertes, Francisco; Martin-Valdepenas, Juan Manuel; Mira, Jose; Sanchez, Maria Jesus [Universidad Politecnica de Madrid (Spain)

2003-10-15

69

Nonlinear damage analysis: Postulate and evaluation  

NASA Technical Reports Server (NTRS)

The objective of this program is to assess the viability of a damage postulate which asserts that the fatigue resistance curve of a metal is history dependent due to inelastic action. The study focusses on OFE copper because this simple model material accentuates the inelastic action central to the damage postulate. Data relevant to damage evolution and crack initiation are developed via a study of surface topography. The effects of surface layer residual stresses are explored via comparative testing as were the effects in initial prestraining. The results of the study very clearly show the deformation history dependence of the fatigue resistance of OFE copper. Furthermore the concept of deformation history dependence is shown to qualitatively explain the fatigue resistance of all histories considered. Likewise quantitative predictions for block cycle histories are found to accurately track the observed results. In this respect the assertion that damage per cycle for a given level of the damage parameter is deformation history dependent appears to be physically justified.

Leis, B. N.; Forte, T. P.

1983-01-01

70

Examination of melted fuel rods and released core material from the first Phebus-FP reactor accident experiment  

NASA Astrophysics Data System (ADS)

In the first Phebus test, 20, one meter long, lightly irradiated UO 2 fuel rods and a central Ag-In-Cd control rod were heated by fission power to an estimated 3000°C. In this paper results are reported for the composition of the molten corium pool in the lower part of the test assembly and deposits of released core material in the vertical line. The examination techniques used comprised optical microscopy, scanning electron microscopy, X-ray microbeam analysis, inductively coupled plasma mass spectroscopy, X-ray diffraction and ?-spectroscopy. The matrix of the corium pool was a single phase of composition (U 0.50Zr 0.47Fe 0.02Y 0.01)O 2 ± x. Inclusions in the solidified pool were ReIr alloys, W with minor concentrations of Fe and Ni and spinels of Cr, Fe and Ni. The main constituents of the deposit in the vertical line were Re, Ag, In and Sn. Tin formed a thin layer on the steel surface. Droplets of the corium matrix phase were embedded in the deposit. Traces of 137Cs were mainly responsible for the ?-activity of the deposit.

Bottomley, P. D. W.; Stalios, A. D.; Glatz, J.-P.; Sätmark, B.; Walker, C. T.

2000-02-01

71

Experimental study of platinum solubility in silicate melt to 14 GPa and 2273 K: Implications for accretion and core formation in Earth  

NASA Astrophysics Data System (ADS)

We determined the solubility limit of Pt in molten haplo-basalt (1 atm anorthite-diopside eutectic composition) in piston-cylinder and multi-anvil experiments at pressures between 0.5 and 14 GPa and temperatures from 1698 to 2223 K. Experiments were internally buffered at ˜IW + 1. Pt concentrations in quenched-glass samples were measured by laser-ablation inductively coupled-plasma mass spectrometry (LA-ICPMS). This technique allows detection of small-scale heterogeneities in the run products while supplying three-dimensional information about the distribution of Pt in the glass samples. Analytical variations in 195Pt indicate that all experiments contain Pt nanonuggets after quenching. Averages of multiple, time-integrated spot analyses (corresponding to bulk analyses) typically have large standard deviations, and calculated Pt solubilities in silicate melt exhibit no statistically significant covariance with temperature or pressure. In contrast, averages of minimum 195Pt signal levels show less inter-spot variation, and solubility shows significant covariance with pressure and temperature. We interpret these results to mean that nanonuggets are not quench particles, that is, they were not dissolved in the silicate melt, but were part of the equilibrium metal assemblage at run conditions. We assume that the average of minimum measured Pt abundances in multiple probe spots is representative of the actual solubility. The metal/silicate partition coefficients ( Dmet/sil) is the inverse of solubility, and we parameterize Dmet/sil in the data set by multivariate regression. The statistically robust regression shows that increasing both pressure and temperature causes Dmet/silto decrease, that is, Pt becomes more soluble in silicate melt. Dmet/sil decreases by less than an order of magnitude at constant temperature from 1 to 14 GPa, whereas isobaric increase in temperature produces a more dramatic effect, with Dmet/sil decreasing by more than one order of magnitude between 1623 and 2223 K. The Pt abundance in the Earth's mantle requires that Dmet/sil is ˜1000 assuming core-mantle equilibration. Geochemical models for core formation in Earth based on moderately and slightly siderophile elements are generally consistent with equilibrium metal segregation at conditions generally in the range of 20-60 GPa and 2000-4000 K. Model extrapolations to these conditions show that the Pt abundance of the mantle can only be matched if oxygen fugacity is high (˜IW) and if Pt mixes ideally in molten iron, both very unlikely conditions. For more realistic values of oxygen fugacity (˜IW - 2) and experimentally-based constraints on non-ideal mixing, models show that Dmet/sil would be several orders of magnitude too high even at the most favorable conditions of pressure and temperature. These results suggest that the mantle Pt budget, and by implication other highly siderophile elements, was added by late addition of a 'late veneer' phase to the accreting proto-Earth.

Ertel, Werner; Walter, Michael J.; Drake, Michael J.; Sylvester, Paul J.

2006-05-01

72

Model for T-Antigen-Dependent Melting of the Simian Virus 40 Core Origin Based on Studies of the Interaction of the Beta-Hairpin with DNA?  

PubMed Central

The interaction of simian virus 40 (SV40) T antigen (T-ag) with the viral origin has served as a model for studies of site-specific recognition of a eukaryotic replication origin and the mechanism of DNA unwinding. These studies have revealed that a motif termed the “beta-hairpin” is necessary for assembly of T-ag on the SV40 origin. Herein it is demonstrated that residues at the tip of the “beta-hairpin” are needed to melt the origin-flanking regions and that the T-ag helicase domain selectively assembles around one of the newly generated single strands in a manner that accounts for its 3?-to-5? helicase activity. Furthermore, T-ags mutated at the tip of the “beta-hairpin” are defective for oligomerization on duplex DNA; however, they can assemble on hybrid duplex DNA or single-stranded DNA (ssDNA) substrates provided the strand containing the 3? extension is present. Collectively, these experiments indicate that residues at the tip of the beta-hairpin generate ssDNA in the core origin and that the ssDNA is essential for subsequent oligomerization events. PMID:17287270

Kumar, Anuradha; Meinke, Gretchen; Reese, Danielle K.; Moine, Stephanie; Phelan, Paul J.; Fradet-Turcotte, Amélie; Archambault, Jacques; Bohm, Andrew; Bullock, Peter A.

2007-01-01

73

Chameleonic equivalence postulate and wave function collapse  

E-print Network

A chameleonic solution to the cosmological constant problem and the non-equivalence of different conformal frames at the quantum level have been recently suggested [Phys. Rev. D82 (2010) 044006]. In this article we further discuss the theoretical grounds of that model and we are led to a chameleonic equivalence postulate (CEP). Whenever a theory satisfies our CEP (and some other additional conditions), a density-dependence of the mass of matter fields is naturally present. Let us summarize the main results of this paper. 1) The CEP can be considered the microscopic counterpart of the Einstein's Equivalence Principle and, hence, a chameleonic description of quantum gravity is obtained: in our model, (quantum) gravitation is equivalent to a conformal anomaly. 2) To illustrate one of the possible applications of the CEP, we point out a connection between chameleon fields and quantum-mechanical wave function collapse. The collapse is induced by the chameleonic nature of the theory. We discuss the collapse for a Stern-Gerlach experiment and for a diffraction experiment with electrons. More research efforts are necessary to verify whether these ideas are compatible with phenomenological constraints.

Andrea Zanzi

2014-04-03

74

Melting Snowflakes  

Microsoft Academic Search

Many snowflakes in various melting stages were directly sampled at the, ground in almost the same way as described by Knight. From these observations the degrees of melting of snowflakes are classified into five stages. Breakup behavior of melting snowflakes is also discussed.

Yasushi Fujiyoshi

1986-01-01

75

Melting Ice  

NSDL National Science Digital Library

Monitor the temperature of a melting ice cube and use temperature probes to electronically plot the data on graphs. Investigate what temperature the ice is as it melts in addition to monitoring the temperature of liquid the ice is submerged in.

2012-07-19

76

Melting relationships in the system Fe-Feo at high pressures: Implications for the composition and formation of the earth's core  

Microsoft Academic Search

A reconnaissance investigation has been carried out on melting relationships in the system Fe-FeO at pressures up to 25 GPa\\u000a and temperatures up to 2200 C using an MA-8 apparatus. Limited studies were also made of the Co-CoO and Ni-NiO systems. In\\u000a the system FeFeO, the rapid exsolution of FeO from liquids during quenching causes some difficulties in interpretation of

Takumi Kato; A. E. Ringwood

1989-01-01

77

Glacier Melt  

NSDL National Science Digital Library

This short video shows an example of melting alpine glaciers in the Austrian Alps (Goldberg Glacier). Disappearing alpine glaciers have social and environmental impacts, including the decline of fresh water supplies and contributing to sea level rise.

Geographic, National

78

I. High pressure melting of [gamma]-iron and the thermal profile in the Earth's core. II. High pressure, high temperature equation of state of fayalite (Fe2SiO4)  

NASA Astrophysics Data System (ADS)

The melting curve of [...]-iron in the pressure range of 100 to 300 GPa has been derived by computing Gibbs free energies at high pressures and high temperatures from thermodynamic and equations of state (EOS) data for the [...], [...] and liquid-phases. Our calculations indicate the melting curve of iron is very sensitive to the EOS of both the solid [...] and melt phase. Our best estimate of the EOS parameters for [...]-iron are: p0 = 8.775 ± 0.012 Mg/m3, [...] = 205 ± 4 GPa, [...] = 4.80 ± 0.01 (referenced to 12 GPa and 300 K). The calculation favors the melting curve of Boehler [1993] or Saxena et al. [1993]. Shock-wave experiments on pure iron preheated to 1573 K were conducted in 17-73 GPa range. The shock-wave equation of state of [gamma]-iron at 1573 K initial temperature can be fit with [...] = 4.102(0.015) km/s + 1.610(0.014)[...] with [...] = 7.413 ± 0.012 Mg/m3. [Gamma]-iron's bulk modulus and its pressure derivative are 124.7±1.1 GPa and 5.44±0.06 respectively.We present new data for sound velocities in the [gamma]- and liquid-phases. In the [gamma]-phase, to a first approximation, the longitudinal sound velocity is linear with respect to density: Vp = -3.13(0.72) + 1.119(0.084) [...] (units for Vp and [...] are km/s and Mg/m3 respectively). Melting was observed in the highest pressure (about 70-73 GPa) experiments at a calculated shock temperature of about 2775 ± 160 K. This result is consistent with our calculated [...]-iron melting curve which is close to those measured by Boehler [1993] and Saxena et al. [1993]. The liquid iron sound velocity data yield a Gruneisen parameter value for liquid iron of 1.63±0.28 at 9.37±0.02 Mg/m3 at 71.6 GPa. The quantity [...] from our data is 15.2±2.6 Mg/m3, which is within the bounds of Brown and McQueen [1986] (13.3-19.6 Mg/m3). Based on upward pressure and temperature extrapolation of our melting curve of [gamma]-iron, the estimated inner core-outer core boundary temperature is 5500±400 K, the temperature at the core-mantle boundary on the outer core side is about 3930±630 K, and the thermal boundary layer at the core-mantle boundary has a temperature difference between 400 and 1400 K.The shock-wave equation of state of initially solid (300 K) and molten (1573 K) fayalite (Fe2SiO4, Fa) are reported in the ranges 23 to 212 GPa and 5 to 47 GPa, respectively. The 300 K data appear to undergo a phase change in the 35-55 GPa range. The density of the high pressure phase (HPP) is consistent with a dense oxide mixture. Although the initially 300 K fayalite may melt along its Hugoniot, this is not explicitly detected. Fitting the HPP Hugoniot data in the shock velocity ([...])-particle velocity ([...]) plane yields:[...] = 4.375(0.027) Mg/m3, (1)[...] = 4.07(0.22) km/s + 1.43(0.06) [...], (2)where [...] is the initial density. The isentropic bulk modulus [...] = 72.4 ± 8.0 GPa, and its pressure derivative [...] = 4.72±0.24. The 1573 K data set yields: [...] = 3.750(0.018) Mg/m3, (3) [...] = 2.63(0.02) km/s + 1.59(0.01) [...], (4)and [...] = 25.9 ± 0.4 GPa, [...] = 5.36 ± 0.04. The bulk modulus compares favorably with Agee [1992a]'s result (24.4 GPa), but the pressure derivative is quite different (10.1 from Agee [1992a]).Above 50 GPa, the high pressure regime of the Hugoniot of the solid fayalite can be fit with oxide mixture models using stishovite and FeO (either LPP or HPP). The fayalitic liquid compression data above 40 GPa are well fit with ideal mixing of partial molar volumes of stishovite and FeO (LPP or HPP), in support of the hypothesis of Rigden et al. [1989].A model basalt incorporating the liquid fayalite data shows the neutral buoyancy zone of basic silicate melts of plausible terrestrial compositions is at about 250-400 km depth based on the PREM Earth model.

Chen, George (Guangqing)

79

One Hair Postulate for Hawking Radiation as Tunneling Process  

E-print Network

For Hawking radiation, treated as a tunneling process, the no-hair theorem of black hole together with the law of energy conservation is utilized to postulate that the tunneling rate only depends on the external qualities (e.g., the mass for the Schwarzschild black hole) and the energy of the radiated particle. This postulate is justified by the WKB approximation for calculating the tunneling probability. Based on this postulate, a general formula for the tunneling probability is derived without referring to the concrete form of black hole metric. This formula implies an intrinsic correlation between the successive processes of the black hole radiation of two or more particles. It also suggests a kind of entropy conservation and thus resolves the puzzle of black hole information loss in some sense.

H. Dong; Qing-yu Cai; X. F. Liu; C. P. Sun

2009-07-13

80

Melting in super-earths.  

PubMed

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. PMID:24664915

Stixrude, Lars

2014-04-28

81

Melting at High Pressures  

NASA Astrophysics Data System (ADS)

At high pressures, melts tend to become more similar to the crystalline solid phases. In general, the change in volume with melting, ? V, becomes small and the entropy of melting, ? S, becomes constant leading to a melting curve that bends over and approaches a constant. [1] Solids near melting also show approaching dynamical instabilities near melting, such as enhanced diffusivities in a premelting region. [2] Some materials display different behavior. Na, for example, shows a melting curve with a maximum followed by a negative pressure slope down to low temperatures. [3] Raty et al. proposed that the electronic structure of liquid and solid sodium are different, due to opening of a pseudogap in liquid Na, leading to increased density of the liquid and a negative melting slope. [4] We have performed first-principles molecular dynamics simulations for solid and liquid sodium as a function of P and T, and find no evidence of a pseudogap or electronic transition in Na. Rather we find that liquid Na is denser due to closer first neighbors with icosohedral packing due to softening of the potential such as occurs in a Gaussian core potential. We are also performing first-principles MD for Mg2SiO4 liquid to understand diffusivity and dynamical properties of the melt using the QBOX code. Initial results show D=(14, 3.2, 16) 10-6 m2/s for (Mg,Si,O) at P=0 and 6000K and D=(5.7, 1.9, 9.2) 10-6 m2/s at 5000K. Lower temperature and higher pressure simulations are in progress. [1] R. E. Cohen, and Z. Gong, Phys. Rev. B 50, 12301 (1994). [2] R. E. Cohen, and J. Weitz, in Properties of Earth and Planetary Materials at High Pressure and Temperature, edited by M. H. Manghnani, and T. Yagi (AGU, Washington, D.C., 1998), pp. 185. [3] E. Gregoryanz et al., Phys. Rev. Lett. 94, 185502 (2005). [4] J.-Y. Raty, E. Schwegler, and S. A. Bonev, Nature 449, 448 (2007). [5] F. H. Stillinger, and P. G. Debenedetti, Biophysical Chemistry 105, 211 (2003).

Cohen, R. E.; Vorberger, J.; Militzer, B.; Caracas, R.; Gygi, F.

2008-12-01

82

Crustal structure of a rifted oceanic core complex and its conjugate side at the MAR at 5S: Implications for melt  

E-print Network

, Dynamics and mechanics of faulting, Kinematics of crustal and mantle deformation, Atlantic Ocean. 1 the magmatic evolution of the core complex from the analysis of seismic layer 3 and crustal thickness of detachment faulting. Hence, the footwall rifting at 5°S may be a generic mechanism of detachment termination

Tilmann, Frederik

83

Fission product transport and behavior during two postulated loss of flow transients in the air  

SciTech Connect

This document discusses fission product behavior during two postulated loss-of-flow accidents (leading to high- and low-pressure core degradation, respectively) in the Advanced Test Reactor (ATR). These transients are designated ATR Transient LCPI5 (high-pressure) and LPP9 (low-pressure). Normally, transients of this nature would be easily mitigated using existing safety systems and procedures. In these analyses, failure of these safety systems was assumed so that core degradation and fission product release could be analyzed. A probabilistic risk assessment indicated that the probability of occurrence for these two transients is of the order of 10{sup {minus}5 }and 10{sup {minus}7} per reactor year for LCP15 and LPP9, respectively.

Adams, J.P.; Carboneau, M.L.

1991-12-31

84

Fission product transport and behavior during two postulated loss of flow transients in the air  

SciTech Connect

This document discusses fission product behavior during two postulated loss-of-flow accidents (leading to high- and low-pressure core degradation, respectively) in the Advanced Test Reactor (ATR). These transients are designated ATR Transient LCPI5 (high-pressure) and LPP9 (low-pressure). Normally, transients of this nature would be easily mitigated using existing safety systems and procedures. In these analyses, failure of these safety systems was assumed so that core degradation and fission product release could be analyzed. A probabilistic risk assessment indicated that the probability of occurrence for these two transients is of the order of 10{sup {minus}5 }and 10{sup {minus}7} per reactor year for LCP15 and LPP9, respectively.

Adams, J.P.; Carboneau, M.L.

1991-01-01

85

Equivalence Postulate and the Quantum Potential of Two Free Particles  

Microsoft Academic Search

Commutativity of the diagram of the maps connecting three one--particle\\u000astate, implied by the Equivalence Postulate (EP), gives a cocycle condition\\u000awhich unequivocally leads to the quantum Hamilton--Jacobi equation. Energy\\u000aquantization is a direct consequences of the local homeomorphicity of the\\u000atrivializing map. We review the EP and show that the quantum potential for two\\u000afree particles, which depends on

Marco Matone; G. Galilei

2002-01-01

86

Melting Glaciers  

NSDL National Science Digital Library

Due to the potential disastrous consequences to the environment and to numerous societies, scientists, governments, and civilians are concerned with the growing trend of glacial melt. This topic-in-depth explores various geographic regions where this phenomenon has recently been observed. Providing background into the study of glaciology, this report begins with a Web site (1) discussing the unique features of glaciers. The US Army Corps of Engineers offers visitors an insight to glacial properties including their locations, movements, and influences; along with a series educational images. The second site (2) explains the exceptionality of the two hundred sixty six glaciers at Glacier National Park. Through a collection of images, animations, and pictures provided by the National Park Service, users can learn about ice dams, climatic impacts, and the erosive powers of ice and water. The rest of the topic-in-depth discusses findings of glacial melting from around the world. NASA (3) addresses the Artic warming's affects on glacier formations. This Web site provides a few animations displaying ice sheet extent and the cracking of icebergs. On a positive note, visitors can learn how the decrease in glaciers has opened up new habitat for some Artic species. The next Web site (4), also by NASA, discusses the findings of a twenty-five year study of Patagonia's glaciers. Educators and students can discover how NASA utilized the Space Shuttle Endeavor to study the entire 17,200 square kilometer region. The site also discusses potential causes of the melting in this region, which has contributed to almost ten percent of the global sea-level change from mountain glaciers. As reported by the BBC (5), Dr. Harrison at the University of Oxford has determined that the glaciers in parts of Kazakhstan have been decreasing annually by almost two cubic kilometers between 1955 and 2000. Visitors can learn how the melting of these four hundred sixteen glaciers will adversely affect the region's rivers and its water supply. The Taipei Times (6) reports that the Swiss Alpine glacial melting has probably intensified due to this summer's record-breaking heat wave. This Web site provides short, intriguing descriptions of consequences of the "rush of melt water streaming from the ice wall." Users can learn about predictions in the 1990s that the glaciers would shrink to ten percent of their 1850 size by the end of the twenty first century. In the next Web site (7), the BBC provides a captivating illustration of the effects the Peruvian glacial melts may have on tourism, the country's water supply, and more. Students and educators can learn about NASA studies showing cracks in the ice, which could lead to the flooding of large cities. Visitors can also find out how the recent glacier recessions have affected some ancient spiritual traditions. The last site, by the USGS, (8) features excerpts from Myrna Hall and Daniel Fagre's 2003 research paper in BioScience. Visitors can discover the melt rate and spatial distributions of glaciers for two possible future climate situations. Providing an amazing animation, users will be amazed by the changes predicted by the model.

Enright, Rachel

87

Melt Production in Oblique Impacts  

NASA Astrophysics Data System (ADS)

Hydrocode modeling is a fundamental tool for the study of melt production in planetary impact events. Until recently, however, numerical modeling of impacts for melt production studies has been limited to vertical impacts. We present the first results of the investigation of melt production in oblique impacts. Simulations were carried out using Sandia's three-dimensional hydrocode CTH, coupled to the SESAME equation of state. While keeping other impact parameters constant, the calculations span impact angles (measured from the surface) from 90° (vertical impact) to 15°. The results show that impact angle affects the strength and distribution of the shock wave generated in the impact. As a result, both the isobaric core and the regions of melting in the target appear asymmetric and concentrated in the downrange, shallower portion of the target. The use of a pressure-decay power law (which describes pressure as function of linear distance from the impact point) to reconstruct the region of melting and vaporization is therefore complicated by the asymmetry of the shock wave. As an analog to the pressure decay versus distance from the impact point, we used a "volumetric pressure decay," where the pressure decay is modeled as a function of volume of target material shocked at or above the given shock pressure. We find that the volumetric pressure decay exponent is almost constant for impact angles from 90° to 30°, dropping by about a factor of two for a 15° impact. In the range of shock pressures at which most materials of geologic interest melt or begin to vaporize, we find that the volume of impact melt decreases by at most 20% for impacts from 90° down to 45°. Below 45°, however, the amount of melt in the target decreases rapidly with impact angle. Compared to the vertical case, the reduction in volume of melt is about 50% for impacts at 30° and more than 90% for a 15° impact. These estimates do not include possible melting due to shear heating, which can contribute to the amount of melt production especially in very oblique impacts. Studies of melt production in vertical impacts suggest an energy scaling law in agreement with the point source limit. An energy scaling law, however, does not seem to hold for oblique impacts, even when the impact velocity is substituted by its vertical component. However, we find that for impact angles between about 30° and 90° (a range that includes 75% of impact events on planetary surfaces) the volume of melt is directly proportional to the volume of the transient crater generated by the impact.

Pierazzo, E.; Melosh, H. J.

2000-05-01

88

Causation and disease: the Henle-Koch postulates revisited.  

PubMed

The Henle-Koch postulates are reviewed in terms of their full validity in Koch's day and in light of subsequent developments. The changing guidelines developed for viral diseases, for viruses in relation to cancer and to chronic central nervous system infection, and for causative agents in chronic diseases are discussed chronologically. A set of guidelines for both acute infectious and chronic diseases is presented. The need for recognizing the role of the host and the spectrum of host responses, for sound biologic sense in evaluating causal roles of agents in disease, and for flexibility in adapting our guidelines to new knowledge are emphasized. PMID:782050

Evans, A S

1976-05-01

89

The necessity of the second postulate in special relativity  

E-print Network

Many authors noted that the principle of relativity together with space-time homogeneity and isotropy restrict the form of the coordinate transformations from one inertial frame to another to being Lorentz-like. The equations contain a free parameter, $k$ (equal to $c^{-2}$ in special relativity), which value is claimed to be merely an empirical matter, so that special relativity does not need the postulate of constancy of the speed of light. I analyze this claim and argue that the distinction between the cases $k = 0$ and $k \

Alon Drory

2014-08-15

90

Permafrost melting and dissolution of the landscape of Mars  

NASA Astrophysics Data System (ADS)

It is supposed that during or after the updoming of the Noctis Labyrinthus-/Valles Marineris dome, postulated permafrost either completely or partly melted. The result was probably a slow sliding of the overlying volcanic rocks to the east, southeast and south, according to the inclination of the areas surface.

Jones, H. P.

1982-10-01

91

Analysis of hydrodynamic phenomena in simulant experiments investigating cavity interactions following postulated vessel meltthrough  

SciTech Connect

An analysis of hydrodynamic phenomena in simulant experiments examining aspects of ex-vessel material interactions in a PWR reactor cavity following postulated core meltdown and localized breaching of the reactor vessel has been carried out. While previous analyses of the tests examined thresholds for the onset of sweepout of fluid from the cavity, the present analysis considers the progression of specific hydrodynamic phenomena involved in the dispersal process: crater formation due to gas jet impingement, radial wave motion and growth, entrainment and transport of liquid droplets, liquid layer formation due to droplet recombination, fluidization of liquid remaining in the cavity, removal of fluidized liquid droplets from the cavity, and the ultimate removal of the remaining liquid layer within the tunnel passageway. Phenomenological models which may be used to predict the phenomena are presented.

Sienicki, J.J.; Spencer, B.W.

1984-01-01

92

Skylab M551 metals melting experiment  

NASA Technical Reports Server (NTRS)

The objectives of the M551 Metals Melting Experiment were to: (1) study behavior of molten metal, (2) characterize metals melted and solidified in the low gravity space environment compared to one-gravity of earth, and (3) determine feasibility of joining metals in space. The experiment used the electron beam (EB) and chamber of the M512 apparatus to make a dwell puddle and a melt in a rotating disc of varying thickness. Hence, the EB performed cut-through, full and partial penetration melts, in addition to a resolidified button. The three disc materials were aluminum 2219-T87, 304 stainless steel, and pure tantalum to provide a wide range of density and melting conditions. Observations to date include the proof that EB welding, cutting, and melting can be done successfully in low gravity. Earlier, some welding authorities had postulated that without gravity the EB would force the molten puddle out of contact. However, the experiment proved that surface tension forces predominate. From the viewpoint of cast-solidification, small, equiaxed grains in Skylab specimens compared to large, elongated grains in ground based specimens were observed. The former are thought to be associated with constitutional supercooling and nucleation where the latter are associated with dendritic solidification. In further support of the more equiaxed grain growth in Skylab, symmetric subgrain patterns were frequently observed where there was much less symmetry in ground based specimens.

Poorman, R. M.

1975-01-01

93

A random spatial network model based on elementary postulates  

USGS Publications Warehouse

In contrast to the random topology model, this model ascribes a unique spatial specification to generated drainage networks, a distinguishing property of some network growth models. The simplicity of the postulates creates an opportunity for potential analytic investigations of the probabilistic structure of the drainage networks, while the spatial specification enables analyses of spatially dependent network properties. In the random topology model all drainage networks, conditioned on magnitude (number of first-order streams), are equally likely, whereas in this model all spanning trees of a grid, conditioned on area and drainage density, are equally likely. As a result, link lengths in the generated networks are not independent, as usually assumed in the random topology model. -from Authors

Karlinger, M.R.; Troutman, B.M.

1989-01-01

94

Causation and Disease: The Henle-Koch Postulates Revisited 1  

PubMed Central

The Henle-Koch postulates are reviewed in terms of their full validity in Koch's day and in light of subsequent developments. The changing guidelines developed for viral diseases, for viruses in relation to cancer and to chronic central nervous system infection, and for causative agents in chronic diseases are discussed chronologically. A set of guidelines for both acute infectious and chronic diseases is presented. The need for recognizing the role of the host and the spectrum of host responses, for sound biologic sense in evaluating causal roles of agents in disease, and for flexibility in adapting our guidelines to new knowledge are emphasized. ImagesFIG. 1FIG. 2FIG. 3FIG. 4FIG. 5FIG. 6FIG. 7FIG. 8 PMID:782050

Evans, Alfred S.

1976-01-01

95

Pb Partitioning Between Sulfide Melt and Silicate Melt  

NASA Astrophysics Data System (ADS)

The geochemical behavior of Pb in the earth is replete with enigmas and paradoxes. There is no satisfactory "balanced budget" for Pb amongst the various terrestrial reservoirs, and consequently, no consensus understanding of the U-Th-Pb isotope tracer system, or the behavior of Pb during melting processes. Most oceanic mantle melts have Pb isotopic compositions that are more radiogenic than Earth's Geochron (First Pb paradox), and all have high and relatively constant Ce/Pb or Nd/Pb ratios compared to "bulk silicate earth" (Third Pb paradox). Yet experimental silicate mineral/melt partition coefficients for Ce (or Nd) and Pb differ significantly, so that significant fractionations in Ce/Pb should abound among various mantle reservoirs and various melting regimes. New insights into the mantle geochemistry of Pb can be achieved by noting that, due to its chalcophilic nature, Pb will be strongly controlled by sulfide phases during melting and differentiation processes, as well as possible large scale sequestering of sulfide into the deep mantle or core during plate recycling. Here we report results from new experiments on the partitioning of Pb between coexisting sulfide and silicate melts at upper mantle conditions, providing a quantitative basis for evaluating the role of sulfide in controlling the geochemical behavior of Pb. Experiments were carried out on a 10:1 mix of natural MORB and FeS, doped with Pb, in a solid-medium piston-cylinder device. Starting materials were placed in a San Carlos olivine-lined Ni capsule, with a solid magnetite-wüstite buffer, that was pressure sealed. Run products are homogeneous basalt glass and spherical sulfide blebs up to 250?m in diameter. Pb was analyzed by laser ablation ICP-MS (100x100?m area rastered with a 40?m spot), using 57Fe as an internal standard. Standards were NIST 611 glass and synthetic FeS doped with 1065 ppm Pb. Matrix effects on Pb/Fe ion production in the silicate and sulfide standards were small (<8%). Major elements were determined by electron microprobe. The sulfide melt-silicate melt partition coefficient determined for Pb at 1 GPa and 1300°C is 37.7 ± 2.8 (±1 se, all known uncertainties propagated). Assuming a bulk earth peridotite S content of 250 ppm, and corresponding modal sulfide abundance of 0.069 wt.%, nearly 90% of the Pb budget will be contained in the sulfide. We used a non-modal fractional aggregated melting model to assess the behavior of the canonical ratios Ce/Pb and Nd/Pb during melting of a "bulk earth" peridotite (0-4% garnet facies melt, followed by 4- 10% spinel facies melt; S saturation in the melt was increased from 1000 ppm at start of melting to 1400 ppm at 10% melt. Resulting modal sulfide abundance decreases from 0.069% at start of melting to 0.036% at 10% melt). With our 1 GPa partition coefficient, the Nd/Pb ratio of the melt is constant within 10% over the whole range of melting. More generally, there is always a combination of partition coefficient and initial S values that produces a virtually constant melt Nd/Pb ratio, thus satisfying the Hofmann et al. (1986) observation of constant Ce/Pb in all OIB and MORB. Even significant variations in initial S (200-300 ppm) or partition coefficient (30-50) produce less scatter in Nd/Pb (± 20%) than is observed in the oceanic basalt data set. On the other hand, invariant Nd/Pb ratios during melting still accurately reflect the initial source ratio, so that the "Third Pb Paradox" is alive and well! This implies that the mantle sources of OIB and MORB are characterized by significant depletions in Pb, likely due to long-term sequestering of Pb-bearing sulfide into the deep mantle or core. This process provides an explanation for the "First Pb Paradox" as well.

Hart, S.; Gaetani, G.

2006-12-01

96

A Reevaluation of Impact Melt Production  

NASA Astrophysics Data System (ADS)

The production of melt and vapor is an important process in impact cratering events. Because significant melting and vaporization do not occur in impacts at velocities currently achievable in the laboratory, a detailed study of the production of melt and vapor in planetary impact events is carried out with hydrocode simulations. Sandia's two-dimensional axisymmetric hydrocode CSQ was used to estimate the amount of melt and vapor produced for widely varying initial conditions: 10 to 80 km/sec for impact velocity, 0.2 to 10 km for the projectile radius. Runs with different materials demonstrate the material dependency of the final result. These results should apply to any size projectile (for given impact velocity and material), since the results can be dynamically scaled so long as gravity is unimportant in affecting the early-time flow. In contrast with the assumptions of previous analytical models, a clear difference in shape, impact-size dependence, and depth of burial has been found between the melt regions and the isobaric core. In particular, the depth of the isobaric core is not a good representation of the depth of the melt regions, which form deeper in the target. While near-surface effects cause the computed melt region shapes to look like "squashed spheres" the spherical shape is still a good analytical analog. One of the goals of melt production studies is to find proper scaling laws to infer melt production for any impact event of interest. We tested the point source limit scaling law for melt volumes (? = 0.55-0.6) proposed by M. D. Bjorkman and K. A. Holsapple (1987, Int. J. Impact Eng.5, 155-163). Our results indicate that the point source limit concept does not apply to melt and vapor production. Rather, melt and vapor production follows an energy scaling law (? = 0.67), in good agreement with previous results of T. J. Ahrens and J. D. O'Keefe [1977, in Impact and Explosion Cratering(D. J. Roddy, R. O. Pepin, and R. B. Merrill, Eds.), pp. 639-656, Pergamon Press, Elmsford, NY]. Finally we tested the accuracy of our melt production calculation against a terrestrial dataset compiled by R. A. F. Grieve and M. J. Cintala (1992, Meteorities27, 526-538). The hydrocode melt volumes are in good agreement with the estimated volumes of that set of terrestrial craters on crystalline basements. At present there is no good model for melt production from impact craters on sedimentary targets.

Pierazzo, E.; Vickery, A. M.; Melosh, H. J.

1997-06-01

97

Melting of peridotite to 140 gigapascals.  

PubMed

Interrogating physical processes that occur within the lowermost mantle is a key to understanding Earth's evolution and present-day inner composition. Among such processes, partial melting has been proposed to explain mantle regions with ultralow seismic velocities near the core-mantle boundary, but experimental validation at the appropriate temperature and pressure regimes remains challenging. Using laser-heated diamond anvil cells, we constructed the solidus curve of a natural fertile peridotite between 36 and 140 gigapascals. Melting at core-mantle boundary pressures occurs at 4180 ± 150 kelvin, which is a value that matches estimated mantle geotherms. Molten regions may therefore exist at the base of the present-day mantle. Melting phase relations and element partitioning data also show that these liquids could host many incompatible elements at the base of the mantle. PMID:20847269

Fiquet, G; Auzende, A L; Siebert, J; Corgne, A; Bureau, H; Ozawa, H; Garbarino, G

2010-09-17

98

Reevaluation of superheat conditions postulated in NRC Information Notice 84-90  

Microsoft Academic Search

Information Notice 84-90, ''Main Steam Line Break Effect on Environmental Qualification of Equipment,'' describes a potential problem regarding existing plant analyses and Equipment Qualification (EQ) related to a postulated Main Steam Line Break (MSLB) with releases of superheated stream. This notice states that certain methodologies for computing mass and energy releases for a postulated MSLB did not account for heat

A. Alsammarae; D. Kruger; D. Beutel; M. Spisak

1994-01-01

99

Reevaluation of superheat conditions postulated in NRC Information Notice 84-90 [nuclear plant  

Microsoft Academic Search

Information Notice 84-90, “Main Steam Line Break Effect on Environmental Qualification of Equipment”, describes a potential problem regarding existing plant analyses and equipment qualification (EQ) related to a postulated main steam line break (MSLB) with releases of superheated steam. This notice states that certain methodologies for computing mass and energy releases for a postulated MSLB did not account for heat

A. Alsammarae; D. Kruger; D. Beutel; M. Spisak

1994-01-01

100

6.2. Pure death processes 6.2.1. Postulates of pure death processes.  

E-print Network

45 6.2. Pure death processes 6.2.1. Postulates of pure death processes. {X(t) : t [0, )} is called a pure death process with parameters µ0 = 0, µ1, ..., µN , and state space {0, 1, ..., N are equivalent, but Postulate 2 is incomplete and cannot be considered as a definition for pure death process. 6

Chen, Kani

101

Melting of Colloidal Crystals  

NASA Astrophysics Data System (ADS)

We experimentally studied the melting and freezing behaviors of colloidal crystals composed of diameter tunable poly-N-isopropylacrylamide (NIPA or pNIPAM) microgel spheres by bright-field and confocal video microscopies. The melting behaviors of three-dimensional (3D), two-dimensional (2D) and multilayer thin films of both single crystals and polycrystals were systematically studied with single-particle dynamics. Thick films (>4 layers) melt heterogeneously, while thin films (<5 layers) melt homogeneously even in polycrystals. A novel heterogeneous melting at dislocation is discovered in 5- to 12-layer films. The equilibrium phase behaviors are different in three thickness regimes: thick films have a liquid-solid coexistence regime which decreases with the film thickness and vanishes at 4 layers, thin films melt into the liquid phase in one step, while monolayers melt in two steps with an intermediate hexatic phase. These results provide new challenges in theory.

Peng, Yi; Wang, Ziren; Alsayed, Ahmed; Yodh, Arjun; Han, Yilong

2012-02-01

102

Melting in the Fe-Ni system  

NASA Astrophysics Data System (ADS)

The melting temperature of the Fe-rich core alloy at the inner core boundary (ICB) condition of 330 GPa is a key geophysical parameter because it represents an anchor point on the geotherm. An accurate knowledge of the melting curves of candidate alloys is therefore highly desirable. In spite of this, there is still considerable uncertainty in the melting point even of pure Fe at these conditions; estimates range from as low as 4850K based on one laser heated diamond anvil cell (LHDAC) study [1] to as high as 6900K based on recent quantum Monte Carlo calculations [2]. In reality we expect that the bulk core alloy may contain 5-10 wt% Ni (based on cosmochemical and meteoritic arguments) and up to 10 wt% of an as yet undetermined mix of light elements (with Si, S, C and O being the most likely candidates). While some recent studies have looked at the effects of light elements on the melting curve of Fe [e.g.: 3,4] with some of these studies including a small amount of Ni in their starting material, to date there has been no systematic study of melting temperatures in the Fe-Ni system. To address this issue, we have embarked upon just such a study. Using the LHDAC we have determined the melting curve of the pure Ni end-member to 180 GPa, and that of pure Fe to 50 GPa, using perturbations in the power vs. temperature function as the melting criterion [5]. Ar or NaCl were employed as pressure media while temperature was measured using standard spectroradiometric techniques [6]. In the case of Ni, perturbations were observed for both the sample and the Ar medium, allowing us to determine the melting curve of Ar and Ni simultaneously. Our results thus far for Ni and Ar agree closely with all of the available data, while extending the melting curves by a factor of two in pressure. In the case of Fe, our current dataset is also in good agreement with previous studies [2,7]. The agreement of all three melting curves with the literature data as well as other materials previously tested [see 5] gives us confidence in the accuracy of our techniques. In the case of Ni, we observe no change in slope, strongly suggesting that Ni remains in the fcc structure to inner core conditions, as opposed to Fe, which converts to the hcp structure at 60-100 GPa. Below this pressure, the Fe and Ni melting curves are nearly indistinguishable, but above it the Fe melting curve becomes much steeper, such that by 330 GPa, the difference between the two is 1500-3600K depending on which iron melting curve is chosen from the literature [1,2]. The addition of Ni to Fe expands the fcc field and pushes the fcc-hcp-liquid triple point to higher pressures [e.g.: 8] delaying the point at which the melting curve begins to steepen, which could lead to a significant melting point depression at the ICB. We hope to present additional data at the meeting to test this hypothesis, including further data on pure Fe, as well as one or more intermediate alloy compositions (up to 200 GPa). [1] Boehler, R. (1993). Nature 363, 534-536 [2] Alfè, D. & Sola, E. (2009). PRL 103, 078501 [3] Morard, G. et al. (2011). PCM 38, 767-776. [4] Asanuma, H. et al. (2010). PCM 37, 353-359. [5] Lord, O. T. et al. (2010). JGR 115, B06208. [6] Walter, M. J. & Koga, K. T. (2004). PEPI. 143-144, 541-558. [7] Shen, G. et al. (1998). GRL 25, 373-376. [8] Kuwayama, Y. et al. (2008). EPSL, 273, 379-385.

Lord, O. T.; Walter, M. J.; Vocadlo, L.; Wood, I. G.; Dobson, D. P.

2012-12-01

103

Permeability and 3-Dimensional Melt Distribution in Partially Molten Rocks  

NASA Astrophysics Data System (ADS)

Quantitative knowledge of the distribution of small amounts of silicate melt in peridotite and of its influence on permeability are critical to our understanding of melt migration and segregation processes in the upper mantle, as well as interpretations of the geochemical and geophysical observations at ocean ridges. For a system containing a single solid phase of isotropic interfacial energy, chemical and mechanical equilibrium requires a constant mean curvature of solid-melt interfaces and a single dihedral angle. Under these conditions, a simple power-law relationship between permeability, grain size and melt fraction, has been derived [e.g., von Bargen and Waff, 1986]. However, microstructural observations on texturally equilibrated, partially molten rocks reveal that the melt distribution is more complex than predicted by the isotropic model. Several factors, such as non-hydrostatic stress, anisotropic interfacial energy, or the presence of a second solid phase, will alter the power-law relationship. Better estimates for the permeability of partially molten rock require an accurate assessment of 3-dimensional melt distribution at the grain-scale. Existing studies of melt distribution, carried out on 2-D slices through experimental charges, have produced divergent models for melt distribution at small melt fractions. While some studies conclude that small amounts of melt are distributed primarily along 3-grain junctions [e.g., Wark et al., 2003], others predict an important role for melt distribution along grain boundaries at low melt fractions [e.g., Faul 1997]. Using X-ray synchrotron microtomography, we have carried out the first high quality non-destructive imaging of 3-dimensional melt distribution in experimentally equilibrated olivine-basalt aggregates [Zhu et al., 2009]. Microtomographic images of melt distribution were obtained on 1 mm cylindrical cores with melt fractions of 0.2, 0.1, and 0.02, at a spatial resolution of 0.7 microns. Textual information such as melt channel size and channel connectivity was determined using AVIZO and MATLAB. Our data indicate that as melt fraction decreases from 0.2 to 0.02, grain size increases slightly whereas melt interconnectivity decreases. Network modeling and the Lattice Boltzmann method provide a quantitative link between the macroscale transport properties and microscale melt distribtution. Incorporating our quantitative 3-D melt distribution data into these models allow us to simulate melt transport and, thereby, calculate the permeability and electrical conductivity of partially molten peridotite, especially at low melt fractions.

Zhu, Wen-Lu; Gaetani, Glenn; Fusseis, Florian

2010-05-01

104

Experimental melting curve of iron revisited  

NASA Astrophysics Data System (ADS)

With new experimental data presented in the last 2 years, it becomes possible to resolve conflicts in the data sets used in constructing the melting curve of iron, Tm(P). On the basis of these new data, several data sets have been dropped: the Williams et al. [1987] melting curve up to 100 GPa and the Bass et al [1987] and Yoo et al. [1993] shock-wave-derived Tm(P) in the 200-300 GPa range based on light emissivity measurements. The Boehler [1993] Tm(P) curve to 200 GPa and the Brown and McQueen [1986] shock-wave-determined Tm(240) remain, leaving a gap between 240 and 330 GPa. We fill this gap using the Lindemann law of melting. The Lindemann law and the temperature values along the Brown and McQueen [1986] Hugoniot require the value of the Grüneisen ratio, ?; thus ? connects Tm at 330 GPa with Tm found for values of the Hugoniot. It is further shown that the heat of crystallization, ?Hm, is dependent on ?. Thus, through 7, a connection is made between the melting curve and the power generated within the inner core. The effect of all these connections of physical properties through ? leads us to recommend 5600-6500 K as the Tm of iron at inner-outer core boundary conditions. Though argument continues concerning the amount and nature of alloying elements, there remains little ground for doubting that both inner and outer cores consist mainly of iron.

Anderson, Orson L.; Duba, Al

1997-10-01

105

Melt containment member  

DOEpatents

A tubular melt containment member for transient containment of molten metals and alloys, especially reactive metals and alloys, includes a melt-contacting layer or region that comprises an oxygen-deficient rare earth oxide material that is less reactive as compared to the counterpart stoichiometric rare earth oxide. The oxygen-deficient (sub-stoichiometric) rare earth oxide can comprise oxygen-deficient yttria represented by Y.sub.2O.sub.3-x wherein x is from 0.01 to 0.1. Use of the oxygen-deficient rare earth oxide as the melt-contacting layer or region material reduces reaction with the melt for a given melt temperature and melt contact time.

Rieken, Joel R.; Heidloff, Andrew J.

2014-09-09

106

The Relationship between Lattice Enthalpy and Melting Point in Magnesium and Aluminium Oxides. Science Notes  

ERIC Educational Resources Information Center

This "Science Note" presents a study by Christopher Talbot and Lydia Yap, who teach IB Chemistry at Anglo-Chinese School (Independent), Republic of Singapore, to pre-university students. Pre-university students may postulate the correlation between the magnitude of the lattice enthalpy compound and its melting point, since both…

Talbot, Christopher; Yap, Lydia

2013-01-01

107

Fragility of sugar melts.  

PubMed

Continuous viscosity of the sugar melt ranged from the superheated to the supercooled, was measured with a rotating viscometer. The thermal properties of sugars have been investigated by differential scanning calorimetric and thermogravimetry. The melt fragility and the fragility of the supercooled liquid have been calculated. This study indicated that, for the whole sugar system, the melt fragility and the fragility of the supercooled liquid separately show negative linear relations with the glass-forming ability and can be used as indicators of this property. In an individual sugar system, the fragility of the supercooled liquid has a direct proportion to melt fragility, which depends on the different inherent characteristic temperatures. PMID:22328122

Liu, Jiantong; Ren, Zhenfeng; Lin, Lejia; Li, Hui; Jia, Ran

2012-02-01

108

Ash melting treatment by rotating type surface melting furnace  

Microsoft Academic Search

Results of melting treatment of fly ash from municipal solid waste incinerators are described, and safety and an effective use of slag discharged from the melting treatment are studied. The fly ash has an average particle size of 22 ?m and a melting fluidity point of 1280–1330°C and was able to be melted by using a Kubota melting furnace without

Sei-ichi Abe; Fumiaki Kambayashi; Masaharu Okada

1996-01-01

109

Hundred years of Koch's Postulates and the history of etiology in plant virus research  

Microsoft Academic Search

The centenary of Koch's Postulates in plant pathology is a moment to look back at the history of etiology in the study of plant virus diseases and at the development of our knowledge of plant viruses.

L. Bos

1981-01-01

110

Melting of compressed iron by monitoring atomic dynamics  

NASA Astrophysics Data System (ADS)

We present a novel method for detecting the solid-liquid phase boundary of compressed iron at high temperatures using synchrotron Mössbauer spectroscopy (SMS). Our approach is unique because the dynamics of the iron atoms are monitored. This process is described by the Lamb-Mössbauer factor, which is related to the mean-square displacement of the iron atoms. Focused synchrotron radiation with 1 meV bandwidth passes through a laser-heated 57Fe sample inside a diamond-anvil cell, and the characteristic SMS time signature vanishes when melting occurs. At our highest compression measurement and considering thermal pressure, we find the melting point of iron to be TM=3025±115 K at P=82±5 GPa. When compared with previously reported melting points for iron using static compression methods with different criteria for melting, our melting trend defines a steeper positive slope as a function of pressure. The obtained melting temperatures represent a significant step toward a reliable melting curve of iron at Earth's core conditions. For other terrestrial planets possessing cores with liquid portions rich in metallic iron, such as Mercury and Mars, the higher melting temperatures for compressed iron may imply warmer internal temperatures.

Jackson, Jennifer M.; Sturhahn, Wolfgang; Lerche, Michael; Zhao, Jiyong; Toellner, Thomas S.; Alp, E. Ercan; Sinogeikin, Stanislav V.; Bass, Jay D.; Murphy, Caitlin A.; Wicks, June K.

2013-01-01

111

Superconducting tin core fiber  

NASA Astrophysics Data System (ADS)

In this study, we demonstrated superconductivity in a fiber with a tin core and fused silica cladding. The fibers were fabricated via a modified melt-draw technique and maintained core diameters ranging from 50-300 microns and overall diameters of 125-800 microns. Superconductivity of this fiber design was validated via the traditional four-probe test method in a bath of liquid helium at temperatures on the order of 3.8 K. The synthesis route and fiber design are perquisites to ongoing research dedicated all-fiber optoelectronics and the relationships between superconductivity and the material structures, as well as corresponding fabrication techniques.

Homa, Daniel; Liang, Yongxuan; Hill, Cary; Kaur, Gurbinder; Pickrell, Gary

2015-01-01

112

Development of a fuel-rod simulator and small-diameter thermocouples for high-temperature, high-heat-flux tests in the Gas-Cooled Fast Reactor Core Flow Test Loop  

SciTech Connect

The Core Flow Test Loop was constructed to perform many of the safety, core design, and mechanical interaction tests in support of the Gas-Cooled Fast Reactor (GCFR) using electrically heated fuel rod simulators (FRSs). Operation includes many off-normal or postulated accident sequences including transient, high-power, and high-temperature operation. The FRS was developed to survive: (1) hundreds of hours of operation at 200 W/cm/sup 2/, 1000/sup 0/C cladding temperature, and (2) 40 h at 40 W/cm/sup 2/, 1200/sup 0/C cladding temperature. Six 0.5-mm type K sheathed thermocouples were placed inside the FRS cladding to measure steady-state and transient temperatures through clad melting at 1370/sup 0/C.

McCulloch, R.W.; MacPherson, R.E.

1983-03-01

113

Radiological consequences of a postulated drop of a maximally Lloaded FFTF fuel cask  

SciTech Connect

Onsite and site boundary radiological consequences were estimated for a postulated accidental drop of an Interim Storage Cask (ISC) loaded 7 assemblies at the maximum available burnup. The postulated cask drop was assumed to occur from the maximum physically attainable height during crane movement of the cask. The resulting onsite and site boundary doses of 45 mSv and 0.04 mSv are far below the corresponding 1 Sv and 250 mSv risk guidelines for highly unlikely accidents

Scott, P.A.

1995-09-22

114

The train/embankment thought experiment, Einstein's second postulate of special relativity and relativity of simultaneity  

E-print Network

The relativistic time dilatation effect and Einstein's second postulate of special relativity are used to analyse train/embankment thought expriments, both Einstein's original one, and an extension where observers on two trains moving at different speeds, as well as on the embankment, are considered. Whereas the relativistic analysis of Einstein's experiment shows, in contradiction to Einstein's interpretation, no `relativity of simultaneity' effect, the latter is apparent for certain events in the two-train experiment. The importance of relativistic kinematics --embodied for photons in Einstein's second postulate-- for the correct interpretation of the experiments is pointed out and demonstrated by detailed calculation of a related example.

J. H. Field

2009-01-09

115

Degraded core modeling in MELCOR  

SciTech Connect

A package of phenomenological models has been developed for the MELCOR code system to calculate the thermal response of structures in the core and lower plenum of an LWR during a severe accident. This package treats all important modes of heat transfer within the core, as well as oxidation, debris formation, and relocation of core and structural materials during melting, candling, and slumping. Comparison of MELCOR and MARCON calculations for the Browns Ferry BWR primary system shows many areas of agreement during the early stages of core heatup and oxidation, but very large differences at later times. Many of these differences are attributed to the effects of candling predicted by MELCOR and the lack of any mechanistic candling or debris relocation models in MARCON. The melting and slumping behavior calculated by MELCOR is in qualitative agreement with our current understanding of the processes involved.

Summers, R.M.

1986-01-01

116

Viscosity of the earth's core.  

NASA Technical Reports Server (NTRS)

Calculation of the viscosity of the core at the boundary of the inner and outer core. It is assumed that this boundary is a melting transition and the viscosity limits of the Andrade (1934,1952) hypothesis (3.7 to 18.5 cp) are adopted. The corresponding kinematic viscosities are such that the precessional system explored by Malkus (1968) would be unstable. Whether it would be sufficiently unstable to overcome a severely subadiabatic temperature gradient cannot be determined.

Gans, R. F.

1972-01-01

117

INTRODUCTION Cryptomonad algae are postulated to be a chimaera of two  

E-print Network

INTRODUCTION Cryptomonad algae are postulated to be a chimaera of two different eukaryotic cells incorporating cryptomonad endosymbiont gene sequences ally them loosely with red algae (Douglas et al., 1991a that the endosymbiont was an early evolutionary intermediate that pre-dates the red algae (Cavalier-Smith, 1992

McFadden, Geoff

118

Higher-order interference and single-system postulates characterizing quantum theory  

NASA Astrophysics Data System (ADS)

We present a new characterization of quantum theory in terms of simple physical principles that is different from previous ones in two important respects: first, it only refers to properties of single systems without any assumptions on the composition of many systems; and second, it is closer to experiment by having absence of higher-order interference as a postulate, which is currently the subject of experimental investigation. We give three postulates—no higher-order interference, classical decomposability of states, and strong symmetry—and prove that the only non-classical operational probabilistic theories satisfying them are real, complex, and quaternionic quantum theory, together with three-level octonionic quantum theory and ball state spaces of arbitrary dimension. Then we show that adding observability of energy as a fourth postulate yields complex quantum theory as the unique solution, relating the emergence of the complex numbers to the possibility of Hamiltonian dynamics. We also show that there may be interesting non-quantum theories satisfying only the first two of our postulates, which would allow for higher-order interference in experiments while still respecting the contextuality analogue of the local orthogonality principle.

Barnum, Howard; Müller, Markus P.; Ududec, Cozmin

2014-12-01

119

Mining MEDLINE: Postulating a Beneficial Role for Curcumin Longa in Retinal Diseases  

E-print Network

Mining MEDLINE: Postulating a Beneficial Role for Curcumin Longa in Retinal Diseases Padmini supporting the suggested connection between curcumin and retinal diseases. In particular, curcumin influ, the evidence suggests that curcumin may have a beneficial and therapeutic role in the context of these dis

Srinivasan, Padmini

120

Sequence-based identification of microbial pathogens: a reconsideration of Koch's postulates.  

PubMed Central

Over 100 years ago, Robert Koch introduced his ideas about how to prove a causal relationship between a microorganism and a disease. Koch's postulates created a scientific standard for causal evidence that established the credibility of microbes as pathogens and led to the development of modern microbiology. In more recent times, Koch's postulates have evolved to accommodate a broader understanding of the host-parasite relationship as well as experimental advances. Techniques such as in situ hybridization, PCR, and representational difference analysis reveal previously uncharacterized, fastidious or uncultivated, microbial pathogens that resist the application of Koch's original postulates, but they also provide new approaches for proving disease causation. In particular, the increasing reliance on sequence-based methods for microbial identification requires a reassessment of the original postulates and the rationale that guided Koch and later revisionists. Recent investigations of Whipple's disease, human ehrlichiosis, hepatitis C, hantavirus pulmonary syndrome, and Kaposi's sarcoma illustrate some of these issues. A set of molecular guidelines for establishing disease causation with sequence-based technology is proposed, and the importance of the scientific concordance of evidence in supporting causal associations is emphasized. PMID:8665474

Fredericks, D N; Relman, D A

1996-01-01

121

Fun Microbiology: Using a Plant Pathogenic Fungus To Demonstrate Koch's Postulates.  

ERIC Educational Resources Information Center

Describes an experiment using a plant pathogenic fungus in which students learn to follow aseptic techniques, grow and produce spores of a fungus, use a hemacytometer for enumerating spores, prepare serial dilutions, grow and inoculate plants, isolate a pure culture using agar streak plates, and demonstrate the four steps of Koch's postulates.…

Mitchell, James K.; Orsted, Kathy M.; Warnes, Carl E.

1997-01-01

122

Higher-order interference and single-system postulates characterizing quantum theory  

E-print Network

We present a new characterization of quantum theory in terms of simple physical principles that is different from previous ones in two important respects: first, it only refers to properties of single systems without any assumptions on the composition of many systems; and second, it is closer to experiment by having absence of higher-order interference as a postulate, which is currently the subject of experimental investigation. We give three postulates -- no higher-order interference, classical decomposability of states, and strong symmetry -- and prove that the only non-classical operational probabilistic theories satisfying them are real, complex, and quaternionic quantum theory, together with 3-level octonionic quantum theory and ball state spaces of arbitrary dimension. Then we show that adding observability of energy as a fourth postulate yields complex quantum theory as the unique solution, relating the emergence of the complex numbers to the possibility of Hamiltonian dynamics. We also show that there may be interesting non-quantum theories satisfying only the first two of our postulates, which would allow for higher-order interference in experiments while still respecting the contextuality analogue of the local orthogonality principle.

Howard Barnum; Markus P. Mueller; Cozmin Ududec

2015-01-03

123

Thermal response of a can handling unit (CHU) to a postulated plutonium hydride burn  

Microsoft Academic Search

A series of analyses were performed to support the design of the Can Handling Unit (CHU). The subject analyses focused on determining the time to repressurize a subatmospheric storage can containing plutonium metal versus the initial hole size and the transient thermal response to a postulated chemical reaction of 150 grams of plutonium hydride. Limiting the amount of gaseous reactants

1998-01-01

124

Free Radical Halogenation, Selectivity, and Thermodynamics: The Polanyi Principle and Hammond's Postulate  

ERIC Educational Resources Information Center

The underlying ideas of the Polanyi principle and Hammond's postulate in relation to the simple free halogenation reactions and their selectivity and thermodynamics is presented. The results indicate that the chlorine atom exhibits a slightly less selectivity in the liquid phase as compared to in the gas phase.

Scala, Alfred A.

2004-01-01

125

An Inexpensive and Safe Experiment to Demonstrate Koch's Postulates Using Citrus Fruit  

ERIC Educational Resources Information Center

Citrus fruit (oranges, tangerines, grapefruit or lemons) purchased in a grocery store can be experimentally infected with readily-available sources of "Penicillium digitatum" to demonstrate the four basic steps of Koch's postulates, also known as proof of pathogenicity. The mould is isolated from naturally-infected citrus fruit into pure culture…

Jakobi, Steven

2010-01-01

126

The melting curve of iron to 250 gigapascals - A constraint on the temperature at earth's center  

NASA Technical Reports Server (NTRS)

The melting curve of iron, the primary constituent of earth's core, has been measured to pressures of 250 gigapascals with a combination of static and dynamic techniques. The melting temperature of iron at the pressure of the core-mantle boundary (136 GPa) is 4800 + or - 200 K, whereas at the inner core-outer core boundary (330 GPa), it is 7600 + or - 500 K. A melting temperature for iron-rich alloy of 6600 K at the inner core-outer core boundary and a maximum temperature of 6900 K at earth's center are inferred. This latter value is the first experimental upper bound on the temperature at earth's center, and these results imply that the temperature of the lower mantle is significantly less than that of the outer core.

Williams, Quentin; Jeanloz, Raymond; Bass, Jay; Svendsen, Bob; Ahrens, Thomas J.

1987-01-01

127

High-pressure partial melting and melt loss in felsic granulites in the Kutná Hora complex, Bohemian Massif (Czech Republic)  

NASA Astrophysics Data System (ADS)

Felsic granulites from the Kutná Hora complex in the Moldanubian zone of central Europe preserve mineral assemblage that records transition from early eclogite to granulite facies conditions, and exhibits leucocratic banding, which is interpreted as an evidence for melt loss during the decompression path. The granulites are layered and consist of variable proportions of quartz, ternary feldspar, garnet, biotite, kyanite, and rutile. In the mesocratic layers, garnet grains show relatively high Ca contents corresponding to 28-41 mol% grossular end member. They have remarkably flat compositional profiles in their cores but their rims exhibit an increase in pyrope and a decrease in grossular and almandine components. In contrast, garnets from the leucocratic layers have relatively low Ca contents (15-26 mol% grossular) that further decrease towards the rims. In addition to modeling of pressure-temperature pseudosections, compositions of garnet core composition, garnet rim-ternary feldspar-kyanite-quartz equilibrium, ternary feldspar composition, and the garnet-biotite equilibrium provide five constraints that were used to reconstruct the pressure-temperature path from eclogite through the granulite and amphibolite facies. In both layers, garnet cores grew during omphacite breakdown and phengite dehydration melting at 940 °C and 2.6 GPa. Subsequent decompression heating to 1020 °C and 2.1 GPa produced Ca- and Fe-poor garnet rims due to the formation of Ca-bearing ternary feldspar and partial melt. In both the mesocratic and leucocratic layer, the maximum melt productivity was 26 and 18 vol.%, respectively, at peak temperature constrained by the maximum whole-rock H2O budget, ~ 1.05-0.75 wt.%, prior to the melting. The preservation of prograde garnet-rich assemblages required nearly complete melt loss (15-25 vol.%), interpreted to have occurred at 1000-1020 °C and 2.2-2.4 GPa by garnet mode isopleths, followed by crystallization of small amounts of residual melt at 760 °C and 1.0 GPa. Phase formation and melt productivity were independently determined by experiments in the piston-cylinder apparatus at 850-1100 °C and 1.7-2.1 GPa. Both the thermodynamic calculations and phase equilibrium experiments suggest that the partial melt was produced by the dehydration melting: muscovite + quartz = melt + K-feldspar + kyanite. The presence of partial melt facilitated attainment of mineral equilibria at peak temperature thus eliminating any potential relics of early high-pressure phases such as phengite or omphacite. By contrast, adjacent mafic granulites and eclogites, which apparently share the same metamorphic path but have not undergone partial melting commonly preserve relics or inclusions of eclogite-facies mineral assemblages.

Nahodilová, Radmila; Faryad, Shah Wali; Dolejš, David; Tropper, Peter; Konzett, Jürgen

2011-07-01

128

Concord Consortium: Melting Ice  

NSDL National Science Digital Library

This activity combines a hands-on lab with a computer simulation, as students investigate and graph the changing temperature of a melting ice cube. In the first step, learners use a sensor to monitor temperature as ice melts in a cup of water. In the second step, the ice cube is melted in a cup of salt water. Interactive graphs allow easy plotting of Temperature vs. Time. The activity concludes with a simulation of the atomic structure of a hot liquid and a cold liquid. Click "Withdraw the Barrier" and watch the changing kinetic energy of the cold liquid particles as they mix with the hot liquid. This item is part of the Concord Consortium, a nonprofit research and development organization dedicated to transforming education through technology.

129

The extreme melt across the Greenland ice sheet in 2012  

NASA Astrophysics Data System (ADS)

The discovery of the 2012 extreme melt event across almost the entire surface of the Greenland ice sheet is presented. Data from three different satellite sensors - including the Oceansat-2 scatterometer, the Moderate-resolution Imaging Spectroradiometer, and the Special Sensor Microwave Imager/Sounder - are combined to obtain composite melt maps, representing the most complete melt conditions detectable across the ice sheet. Satellite observations reveal that melt occurred at or near the surface of the Greenland ice sheet across 98.6% of its entire extent on 12 July 2012, including the usually cold polar areas at high altitudes like Summit in the dry snow facies of the ice sheet. This melt event coincided with an anomalous ridge of warm air that became stagnant over Greenland. As seen in melt occurrences from multiple ice core records at Summit reported in the published literature, such a melt event is rare with the last significant one occurring in 1889 and the next previous one around seven centuries earlier in the Medieval Warm Period. Given its rarity, the 2012 extreme melt across Greenland provides an exceptional opportunity for new studies in broad interdisciplinary geophysical research.

Nghiem, S. V.; Hall, D. K.; Mote, T. L.; Tedesco, M.; Albert, M. R.; Keegan, K.; Shuman, C. A.; DiGirolamo, N. E.; Neumann, G.

2012-10-01

130

Viscosity Measurement for Tellurium Melt  

NASA Technical Reports Server (NTRS)

The viscosity of high temperature Te melt was measured using a new technique in which a rotating magnetic field was applied to the melt sealed in a suspended ampoule, and the torque exerted by rotating melt flow on the ampoule wall was measured. Governing equations for the coupled melt flow and ampoule torsional oscillation were solved, and the viscosity was extracted from the experimental data by numerical fitting. The computational result showed good agreement with experimental data. The melt velocity transient initiated by the rotating magnetic field reached a stable condition quickly, allowing the viscosity and electrical conductivity of the melt to be determined in a short period.

Lin, Bochuan; Li, Chao; Ban, Heng; Scripa, Rosalia N.; Su, Ching-Hua; Lehoczky, Sandor L.

2006-01-01

131

Freezing and Melting  

NSDL National Science Digital Library

This article tells how the freezing point of a substance is also its melting point. The energy of the substance's molecules changes with temperature, thus with changes in state. Also described is how freezing points can be lowered, or depressed, by adding a substance.

2010-01-01

132

Feeder apparatus for melting furnaces, particularly for plasma melting furnaces  

Microsoft Academic Search

The invention comprises a charging apparatus for melting furnaces, especially for plasma melting furnaces, for the continuous melting of preferably prepared aluminum scrap material. With the help of the proposed solution a controlled and regulated supply of the scrap material along with the prevention of a direct application of the plasma arc or other energy sources directly to the material

K. Primke; P. Papsdorf; G. Pohle; K. P. Trautmann

1984-01-01

133

Partial-melt electrical conductivity: Influence of melt composition  

SciTech Connect

The electrical conductivity of a partial melt is influenced by many factors, including melt conductivity, crystalline conductivity, and melt fraction, each of which is influenced by temperature. We have performed measurements of bulk conductivity as a function of temperature of an Fo{sub 80}-basalt partial melt between 684{degree} and 1244{degree}C at controlled oxygen fugacity. Melt fraction and composition variations with temperature calculated using MELTS [Ghiorso and Sack, 1995] indicate that the effect on melt conductivity of changing melt composition is balanced by changes in temperature (T). Thus bulk conductivity as a function of T or melt fraction in this system can be calculated assuming a constant melt conductivity. The bulk conductivity is well modeled by simple parallel calculations, by the Hashin-Shtrikman upper bound, or by Archie{close_quote}s law ({sigma}{sub partial melt}/{sigma}{sub melt}=C{sub 1}X{sub m}{sup n}). We estimate apparent values of the Archie{close_quote}s law parameters between 1150{degree} and 1244 {degree}C as C{sub 1}=0.73{plus_minus}0.02 and n=0.98{plus_minus}0.01. Estimates of the permeability of the system are obtained by using an electrical conductivity-critical scale length relationship and range from {approximately}10{sup {minus}14} to 10{sup {minus}18} m{sup 2}, comparing favorably with previously published values. {copyright} 1999 American Geophysical Union

Roberts, J.J. [Lawrence Livermore National Laboratory, Livermore, California (United States)] [Lawrence Livermore National Laboratory, Livermore, California (United States); Tyburczy, J.A. [Department of Geology, Arizona State University, Tempe (United States)] [Department of Geology, Arizona State University, Tempe (United States)

1999-04-01

134

Evolution of the CPT Invariance into a Basic Postulate in Physics  

E-print Network

Einstein-Podolsky-Rosen's paper in 1935 is discussed in parallel with an EPR experiment on $K^0\\bar{K}^0$ system in 1998, yielding a strong hint of distinction in both wave-function and operators between particle and antiparticle at the level of quantum mechanics (QM). Then it is proposed that the CPT invariance in particle physics leads naturally to a basic postulate that the (newly defined) space-time inversion (${\\bf x}\\to -{\\bf x},t\\to -t$) is equivalent to the transformation between particle and its antiparticle. The evolution of this postulate from nonrelativistic QM via relativistic QM till the quantum field theory is discussed in some detail. The Klein paradox for both Klein-Gordon equation and Dirac equation is also discussed. Keywords: CPT invariance, Antiparticle, Quantum mechanics, Quantum field theory

Guang-jiong Ni; Suqing Chen; Jianjun Xu

2012-07-23

135

Four-photon interference: a realizable experiment to demonstrate violation of EPR postulates for perfect correlations  

NASA Astrophysics Data System (ADS)

Bell's theorem reveals contradictions between the predictions of quantum mechanics and the EPR postulates for a pair of particles only in situations involving imperfect statistical correlations. However, with three or more particles, contradictions emerge even for perfect correlations. We describe an experiment which can be realized in the laboratory, using four-photon entangled states generated by parametric down-conversion, to demonstrate this contradiction at the level of perfect correlations. Keywords: Bell's theorem, perfect correlations, GHZ, EPR

Hariharan, P.; Samuel, J.; Sinha, Supurna

1999-04-01

136

Four-photon interference: a realizable experiment to demonstrate violation of EPR postulates for perfect correlations  

NASA Astrophysics Data System (ADS)

Bell's theorem reveals contradictions between the predictions of quantum mechanics and the EPR postulates for a pair of particles only in situations involving imperfect statistical correlations. However, with three or more particles, contradictions emerge even for perfect correlations. We describe an experiment which can be realized in the laboratory, using four-photon entangled states generated by parametric down-conversion, to demonstrate this contradiction at the level of perfect correlations.

Hariharan, P.; Samuel, J.; Sinha, Supurna

1999-04-01

137

Supplemental Analysis to Support Postulated Events in Process Hazards Analysis for the HEAF  

Microsoft Academic Search

The purpose of this report is to conduct a limit scope risk assessment by generating event trees for the accident scenarios described in table 4-2 of the HEAF SAR, ref 1. Table 4-2 lists the postulated event\\/scenario descriptions for non-industrial hazards for HEAF. The event tree analysis decomposes accident scenarios into basic causes that appear as branches on the event

H Lambert; G Johnson

2001-01-01

138

SAS4A: A computer model for the analysis of hypothetical core disruptive accidents in liquid metal reactors  

SciTech Connect

To ensure that the public health and safety are protected under any accident conditions in a Liquid Metal Fast Breeder Reactor (LMFBR), many accidents are analyzed for their potential consequences. The SAS4A code system, described in this paper, provides such an analysis capability, including the ability to analyze low probability events such as the Hypothetical Core Disruptive Accidents (HCDAs). The SAS4A code system has been designed to simulate all the events that occur in a LMFBR core during the initiating phase of a Hypothetical Core Disruptive Accident. During such postulated accident scenarios as the Loss-of-Flow and Transient Overpower events, a large number of interrelated physical phenomena occur during a relatively short time. These phenomena include transient heat transfer and hydrodynamic events, coolant boiling and fuel and cladding melting and relocation. During to the strong neutronic feedback present in a nuclear reactor, these events can significantly influence the reactor power. The SAS4A code system is used in the safety analysis of nuclear reactors, in order to estimate the energetic potential of very low probability accidents. The results of SAS4A simulations are also used by reactor designers in order to build safer reactors and eliminate the possibility of any accident which could endanger the public safety.

Tentner, A.M.; Birgersson, G.; Cahalan, J.E.; Dunn, F.E.; Kalimullah; Miles, K.J.

1987-01-01

139

The Light-Velocity Postulate: The Essential Difference between the Theories of Lorentz-Poincare and Einstein  

ERIC Educational Resources Information Center

Einstein, who had already developed the light-quantum theory, knew the inadequacy of Maxwell's theory in the microscopic sphere. Therefore, in writing his paper on special relativity, he had to set up the light-velocity postulate independently of the relativity postulate in order to make the electromagnetic foundation of physics compatible with…

Abiko, Seiya

2005-01-01

140

Thermodynamics of Oligonucleotide Duplex Melting  

ERIC Educational Resources Information Center

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…

Schreiber-Gosche, Sherrie; Edwards, Robert A.

2009-01-01

141

Dynamics and evolution of the deep mantle resulting from thermal, chemical, phase and melting effects  

E-print Network

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2.3. Thermal conductivityDynamics and evolution of the deep mantle resulting from thermal, chemical, phase and melting the silicate mantle and liquid iron alloy outer core ­ is the most important boundary inside our planet

Tackley, Paul J.

142

The melting curve of Ni to 1 Mbar  

NASA Astrophysics Data System (ADS)

The melting curve of Ni has been determined to 125 GPa using laser-heated diamond anvil cell (LH-DAC) experiments in which two melting criteria were used: firstly, the appearance of liquid diffuse scattering (LDS) during in situ X-ray diffraction (XRD) and secondly, plateaux in temperature vs. laser power functions in both in situ and off-line experiments. Our new melting curve, defined by a Simon-Glatzel fit to the data where TM (K) =[ (PM/18.78±10.20 + 1) ] 1 / 2.42 ± 0.66 × 1726, is in good agreement with the majority of the theoretical studies on Ni melting and matches closely the available shock wave melting data. It is however dramatically steeper than the previous off-line LH-DAC studies in which determination of melting was based on the visual observation of motion aided by the laser speckle method. We estimate the melting point (TM) of Ni at the inner-core boundary (ICB) pressure of 330 GPa to be TM = 5800 ± 700 K (2 ?), within error of the value for Fe of TM = 6230 ± 500 K determined in a recent in situ LH-DAC study by similar methods to those employed here. This similarity suggests that the alloying of 5-10 wt.% Ni with the Fe-rich core alloy is unlikely to have any significant effect on the temperature of the ICB, though this is dependent on the details of the topology of the Fe-Ni binary phase diagram at core pressures. Our melting temperature for Ni at 330 GPa is ?2500 K higher than that found in previous experimental studies employing the laser speckle method. We find that those earlier melting curves coincide with the onset of rapid sub-solidus recrystallization, suggesting that visual observations of motion may have misinterpreted dynamic recrystallization as convective motion of a melt. This finding has significant implications for our understanding of the high-pressure melting behaviour of a number of other transition metals.

Lord, Oliver T.; Wood, Ian G.; Dobson, David P.; Vo?adlo, Lidunka; Wang, Weiwei; Thomson, Andrew R.; Wann, Elizabeth T. H.; Morard, Guillaume; Mezouar, Mohamed; Walter, Michael J.

2014-12-01

143

Quantum melting of the vortex lattice in high-Tc superconductors  

Microsoft Academic Search

In the new high-Tc superconductors both thermal as well as quantum fluctuations are large. The latter smear the vortex cores over a distance of the order of the coherence length and thereby strongly affect the melting transition. Taking account of quantum fluctuations, the shape of the melting line is given by a universal function which is different from a simple

Gianni Blatter; Boris Ivlev

1993-01-01

144

Near-total surface melt detected on the Greenland Ice Sheet  

NASA Astrophysics Data System (ADS)

On 12 July 2012, 98.6% of the surface of the Greenland Ice Sheet melted, an event so expansive that a similar episode had not previously been seen in the satellite era. Ice core records indicate that the most recent melting event of this scale was 123 years ago. The one before that occurred another 7 centuries prior, during the Medieval Warm Period. Just 2 weeks following the near-total melt of the surface of the Greenland Ice Sheet, after the surface ice had refrozen to seasonal levels, a second episode pushed the melt area back up to 79.2%. Compiling measurements from three different satellite systems and from in-the-field observations, Nghiem et al. describe the extent of the melt. The authors suggest that warm air ridges stagnating over Greenland, coincident with the melt episodes, may have underlain the extensive melting.

Schultz, Colin

2013-01-01

145

Fluctuations during melting  

SciTech Connect

Repetitive melting and recrystallization, of crystals in a solid-liquid mixture in quasi-equilibrium, is reported. The experiments were performed at constant volume and ambient temperature inside a diamond anvil cell. The results, which the authors believed are the first to show the importance of fluctuations during a first order phase transition, can be partially understood on the basis of a recent generalized theory of Ostwald ripening.

Grimsditch, M. [Argonne National Lab., IL (United States). Materials Science Div.; Karpov, V. [State Technical Univ., St. Petersburg (Russian Federation)

1995-10-01

146

Melt spinning study  

NASA Technical Reports Server (NTRS)

Containerless processing of materials provides an excellent opportunity to study nucleation phenomena and produce unique materials, primarily through the formation of metastable phases and deep undercoolings. Deep undercoolings can be readily achieved in falling drops of molten material. Extended solute solubilities and greatly refined microstructures can also be obtained in containerless processing experiments. The Drop Tube Facility at Marshall Space Flight Center has played an important role in enhancing that area of research. Previous experiments performed in the Drop Tube with refractory metals has shown very interesting microstructural changes associated with deep undercoolings. It is apparent also that the microstructure of the deep undercooled species may be changing due to the release of the latent heat of fusion during recalescence. For scientific purposes, it is important to be able to differentiate between the microstructures of the two types of metallic species. A review of the literature shows that although significant advances have been made with respect to the engineering aspects of rapid solidification phenomena, there is still much to be learned in terms of understanding the basic phenomena. The two major ways in which rapid solidification processing provides improved structures and hence improved properties are: (1) production of refined structures such as fine dendrites and eutectics, and (2) production of new alloy compositions, microstructures, and phases through extended solid solubility, new phase reaction sequences, and the formation of metallic-glass microstructures. The objective of this work has been to determine the optimal methodology required to extract this excess energy without affecting the thermo-physical parameters of the under-cooled melt. In normal containerless processing experiments recalescence occurs as the melt returns toward the melting point in order to solidify. A new type of experiment is sought in which the resultant microstructure of the undercooled species is frozen in without going through the melting point regime and subsequent near equilibrium solidification of the remaining liquid. This experimental approach entails the design of an appropriate melt spinning system which is compatible with Drop Tube operations and processing constraints. That work is the goal of this study.

Workman, Gary L.; Rathz, Thomas

1993-01-01

147

Carbonatitic melts in diamond inclusions  

NASA Astrophysics Data System (ADS)

Fluid inclusions in diamonds are commonly smaller than a micrometer and form clouds or concentric zones carrying many millions of inclusions. Fluid composition varies between four end-members: Hydrous melts rich in silica and alkalis, carbonatitic melts rich in magnesium and calcium, brines rich in chlorine and potassium and sulfide melts rich in iron and nickel. Carbonatitic melts were found together with all the other fluids. No mixing or mutual occurrence was detected between the other three end-members. The carbonatitic melts in most diamonds are rich in magnesium, calcium and iron and carry variable amounts of alkalies and barium. Carbonate and water absorption in the IR spectrum along with EPMA detection of variable amounts of chlorine, silica and phosphorus indicate that the micro-inclusions trapped carbonatitic melts. A clear continuous array extends from the carbonatitic melt composition towards the hydrous, silicic end member. Another array connects the carbonatitic melt with the brines. The occurrence of carbonatitic melts in conjunction with all other fluids indicates their important role in the evolution of all fluids and in diamond growth. This is also supported by experimental diamond growth from carbonate-rich melts at pressures and temperatures recorded by natural diamonds. Carbon for diamond growth may originate from reduction of the carbonate in the melt, dissolved elemental carbon or contemporaneous resorption of other diamonds. Metasomatic interaction with melts or fluids is evident in many diamond-inclusions and xenocrysts. The carbonatitic melts as well as the other melts and brines can account for many such enrichment or resetting events. The entrapment of these fluids in diamond micro-inclusions provides a unique opportunity for a direct study of their composition and evolution.

Izraeli, E. S.; Klein-Bendavid, O.; Navon, O.

2003-04-01

148

Silicate melt inclusions in clinopyroxene phenocrysts from mafic dikes in the eastern North China Craton: Constraints on melt evolution  

NASA Astrophysics Data System (ADS)

Silicate melt inclusions (SMIs) in magmatic minerals provide key information on the chemical and mineralogical evolution of source magmas. The widespread Cretaceous mafic dikes in the Jiaojia region of the eastern North China Craton contain abundant SMIs within clinopyroxene phenocrysts. The daughter minerals in these SMIs include amphibole, plagioclase, pyrite and ilmenite, together with CO2 + CH4 and CH4 as the major volatile phase. The total homogenization temperatures of the SMIs range between 1280 and 1300 °C. The host clinopyroxene phenocrysts in these dolerite dikes are dominantly augite with minor diopside. From LA-ICPMS analyses of the SMIs, we identify two compositional groups: (1) low-MgO (6.0-7.6 wt.%) SMIs and (2) high-MgO (11.2-13.9 wt.%) SMIs. The Low-MgO group exhibits higher concentrations of TiO2, Al2O3, Na2O, P2O5 and lower CaO and CaO/Al2O3 ratio as compared to the high-MgO SMIs. The trace element patterns of the two types of SMIs are similar to those of the host mafic dikes. However, the low-MgO SMIs and host mafic dikes are clearly more enriched in all the trace elements as compared to the high-MgO type, especially with regard to the highly incompatible elements. The estimated capture temperatures and pressures are 1351-1400 °C and 1.6-2.1 GPa for the high-MgO SMIs and 1177-1215 °C and 0.6-1.1GPa for the low-MgO type. The high-MgO and low-MgO SMIs were trapped at depths of ?51-68 km and ?20-35 km, respectively. Computations show that the parental melt is mafic with SiO2 content 49.6 wt% and Mg# 80.0 with relatively low total alkali contents (1.35 wt% Na2O + K2O) and high CaO (15.2 wt%). Exploratory runs with the program MELTS and pMELTS show that the low-MgO and high-MgO SMIs were derived from the same parental melt through different degrees of crystallization. Clinopyroxene and a small amount of olivine were the fractionating phases during the evolution from parental melts to high MgO melts, while the low MgO melts experienced significant fractional crystallization of olivine and clinopyroxene. We postulate the newly accreted lithospheric clinopyroxenite as the major source for the Jiaojia dolerite dikes, with melting of the source at a depth of ?68-80 km.

Cai, Ya-Chun; Fan, Hong-Rui; Santosh, M.; Hu, Fang-Fang; Yang, Kui-Feng; Liu, Xuan; Liu, Yongsheng

2015-01-01

149

Modeling and analyses of postulated UF{sub 6} release accidents in gaseous diffusion plant  

SciTech Connect

Computer models have been developed to simulate the transient behavior of aerosols and vapors as a result of a postulated accident involving the release of uranium hexafluoride (UF{sub 6}) into the process building of a gaseous diffusion plant. UF{sub 6} undergoes an exothermic chemical reaction with moisture (H{sub 2}O) in the air to form hydrogen fluoride (HF) and radioactive uranyl fluoride (UO{sub 2}F{sub 2}). As part of a facility-wide safety evaluation, this study evaluated source terms consisting of UO{sub 2}F{sub 2} as well as HF during a postulated UF{sub 6} release accident in a process building. In the postulated accident scenario, {approximately}7900 kg (17,500 lb) of hot UF{sub 6} vapor is released over a 5 min period from the process piping into the atmosphere of a large process building. UO{sub 2}F{sub 2} mainly remains as airborne-solid particles (aerosols), and HF is in a vapor form. Some UO{sub 2}F{sub 2} aerosols are removed from the air flow due to gravitational settling. The HF and the remaining UO{sub 2}F{sub 2} are mixed with air and exhausted through the building ventilation system. The MELCOR computer code was selected for simulating aerosols and vapor transport in the process building. MELCOR model was first used to develop a single volume representation of a process building and its results were compared with those from past lumped parameter models specifically developed for studying UF{sub 6} release accidents. Preliminary results indicate that MELCOR predicted results (using a lumped formulation) are comparable with those from previously developed models.

Kim, S.H.; Taleyarkhan, R.P.; Keith, K.D.; Schmidt, R.W. [Oak Ridge National Lab., TN (United States); Carter, J.C. [J.C. Carter Associates, Inc., Oak Ridge, TN (United States); Dyer, R.H. [Dyer Enterprises, Oak Ridge, TN (United States)

1995-10-01

150

Thermal response of a can handling unit (CHU) to a postulated plutonium hydride burn  

SciTech Connect

A series of analyses were performed to support the design of the Can Handling Unit (CHU). The subject analyses focused on determining the time to repressurize a subatmospheric storage can containing plutonium metal versus the initial hole size and the transient thermal response to a postulated chemical reaction of 150 grams of plutonium hydride. Limiting the amount of gaseous reactants either by inerting the CHU or using a very small hole size for the initial opening appears to be a viable method of controlling the rate of the exothermic chemical reactions and system temperatures.

Crea, B.A.

1998-05-21

151

Ground motion estimation in Delhi from postulated regional and local earthquakes  

NASA Astrophysics Data System (ADS)

Ground motions are estimated at 55 sites in Delhi, the capital of India from four postulated earthquakes (three regional M w = 7.5, 8.0, and 8.5 and one local). The procedure consists of (1) synthesis of ground motion at a hard reference site (NDI) and (2) estimation of ground motion at other sites in the city via known transfer functions and application of the random vibration theory. This work provides a more extensive coverage than earlier studies (e.g., Singh et al., Bull Seism Soc Am 92:555-569, 2002; Bansal et al., J Seismol 13:89-105, 2009). The Indian code response spectra corresponding to Delhi (zone IV) are found to be conservative at hard soil sites for all postulated earthquakes but found to be deficient for M w = 8.0 and 8.5 earthquakes at soft soil sites. Spectral acceleration maps at four different natural periods are strongly influenced by the shallow geological and soil conditions. Three pockets of high acceleration values are seen. These pockets seem to coincide with the contacts of (a) Aravalli quartzite and recent Yamuna alluvium (towards the East), (b) Aravalli quartzite and older quaternary alluvium (towards the South), and (c) older quaternary alluvium and recent Yamuna alluvium (towards the North).

Mittal, Himanshu; Kumar, Ashok; Kamal

2013-04-01

152

Analysis of radiation doses from operation of postulated commercial spent fuel transportation systems: Main report  

SciTech Connect

This report contains a system study of estimated radiation doses to the public and workers resulting from the transport of spent fuel from commercial nuclear power reactors to a geologic repository. The report contains a detailed breakdown of activities and a description of time/distance/dose-rate estimates for each activity within the system. Collective doses are estimated for each of the major activities at the reactor site, in transit, and at the repository receiving facility. Annual individual doses to the maximally exposed individuals or groups of individuals are also estimated. A total of 17 alternatives and subalternatives to the postulated reference transportation system are identified, conceptualized, and their dose-reduction potentials and costs estimated. Resulting ratios of ..delta..cost/..delta..collective system dose for each alternative relative to the postulated reference transportation system are given. Most of the alternatives evaluated are estimated to provide both cost and dose reductions. Major reductions in transportation system dose and cost are estimated to result from using higher-capacity rail and truck casks, and particularly when replacing legalweight truck casks with ''advanced design'' overweight truck casks. The greatest annual dose reduction to the highest exposed individual workers (i.e., at the repository) is estimated to be achieved by using remote handling equipment for the cask handling operations at the repository. Additional shielding is also effective in reducing doses to both radiation workers at the reactor and repository and to transport workers. 69 refs., 36 figs., 156 tabs.

Schneider, K.J.; Hostick, C.J.; Ross, W.A.; Peterson, R.W.; Smith, R.I.; Stiles, D.L.; Daling, P.M.; Weakley, S.A.; Grinde, R.B.; Young, J.R.

1987-11-01

153

Attempt at clarification of Einstein's postulate of constancy of light velocity  

E-print Network

We have realized that under Lorentz transformations the tick number of a moving common clock remains unchanged, that is, the hand of the clock never runs slow, but the time interval between its two consecutive ticks contracts, so the relative time has to be recorded by using the tau-clocks required by the transformations, instead of unreal slowing clocks. Thus it is argued that using rest common clocks or the equivalent the measured velocity of light emitted by a moving source, which is quasi-velocity of foreign light, is dependent of the source velocity. Nevertheless, the velocity of foreign light that should be measured by using tau-clocks is independent of the source velocity. The velocity of native light emitted by a rest source obeys the postulate of relativity in accordance with both Maxwell equations and the result of Michelson-Morley experiment. On the other hand, the velocity of foreign light obeys both Ritz's emission theory except the Lorentz factor and the postulate of constancy of light velocity if measured by using tau-clocks. Thus the emission theory does not conflict with special relativity. The present argument leads to a logical consequence that the so-called positive conclusions from experiments testing constancy of the velocity of light emitted by moving sources if using common clocks or the equivalent, instead of tau-clocks, exactly contradicts Lorentz transformations.

Wang Guowen

2005-12-05

154

Chicxulub Impact Melts: Geochemical Signatures of Target Lithology Mixing and Post-Impact Hydrothermal Fluid Processes  

NASA Technical Reports Server (NTRS)

Impact melts within complex impact craters are generally homogeneous, unless they differentiated, contain immiscible melt components, or were hydrothermally altered while cooling. The details of these processes, however, and their chemical consequences, are poorly understood. The best opportunity to unravel them may lie with the Chicxulub impact structure, because it is the world s most pristine (albeit buried) large impact crater. The Chicxulub Scientific Drilling Project recovered approx. 100 meters of impactites in a continuous core from the Yaxcopoil-1 (YAX-1) borehole. This dramatically increased the amount of melt available for analyses, which was previously limited to two small samples N17 and N19) recovered from the Yucatan-6 (Y-6) borehole and one sample (N10) recovered from the Chicxulub-1 (C-1) borehole. In this study, we describe the chemical compositions of six melt samples over an approx. 40 m section of the core and compare them to previous melt samples from the Y-6 and C-1 boreholes.

Kring, David A.; Zurcher, Lukas; Horz, Freidrich; Mertzmann, Stanley A.

2004-01-01

155

Melting of Ice under Pressure  

SciTech Connect

The melting of ice under pressure is investigated with a series of first principles molecular dynamics simulations. In particular, a two-phase approach is used to determine the melting temperature of the ice-VII phase in the range of 10 to 50 GPa. Our computed melting temperatures are consistent with existing diamond anvil cell experiments. We find that for pressures between 10 to 40 GPa, ice melts as a molecular solid. For pressures above {approx}45 GPa there is a sharp increase in the slope of the melting curve due to the presence of molecular dissociation and proton diffusion in the solid, prior to melting. The onset of significant proton diffusion in ice-VII as a function of increasing temperature is found to be gradual and bears many similarities to that of a type-II superionic solid.

Schwegler, E; Sharma, M; Gygi, F; Galli, G

2008-07-31

156

Melting of ice under pressure  

PubMed Central

The melting of ice under pressure is investigated with a series of first-principles molecular dynamics simulations. In particular, a two-phase approach is used to determine the melting temperature of the ice-VII phase in the range of 10–50 GPa. Our computed melting temperatures are consistent with existing diamond anvil cell experiments. We find that for pressures between 10 and 40 GPa, ice melts as a molecular solid. For pressures above ?45 Gpa, there is a sharp increase in the slope of the melting curve because of the presence of molecular dissociation and proton diffusion in the solid before melting. The onset of significant proton diffusion in ice-VII as a function of increasing temperature is found to be gradual and bears many similarities to that of a type-II superionic solid. PMID:18809909

Schwegler, Eric; Sharma, Manu; Gygi, François; Galli, Giulia

2008-01-01

157

Melting in Martian Snowbanks  

NASA Technical Reports Server (NTRS)

Precipitation as snow is an emerging paradigm for understanding water flow on Mars, which gracefully resolves many outstanding uncertainties in climatic and geomorphic interpretation. Snowfall does not require a powerful global greenhouse to effect global precipitation. It has long been assumed that global average temperatures greater than 273K are required to sustain liquid water at the surface via rainfall and runoff. Unfortunately, the best greenhouse models to date predict global mean surface temperatures early in Mars' history that differ little from today's, unless exceptional conditions are invoked. Snowfall however, can occur at temperatures less than 273K; all that is required is saturation of the atmosphere. At global temperatures lower than 273K, H2O would have been injected into the atmosphere by impacts and volcanic eruptions during the Noachian, and by obliquity-driven climate oscillations more recently. Snow cover can accumulate for a considerable period, and be available for melting during local spring and summer, unless sublimation rates are sufficient to remove the entire snowpack. We decided to explore the physics that controls the melting of snow in the high-latitude regions of Mars to understand the frequency and drainage of snowmelt in the high martian latitudes.

Zent, A. P.; Sutter, B.

2005-01-01

158

B Alloy Melt  

NASA Astrophysics Data System (ADS)

The solidification of undercooled Ni-4.5 wt pct B alloy melt was investigated by using the glass fluxing technique. The alloy melt was undercooled up to ? T p ~ 245 K (245 °C), where a mixture of ?-Ni dendrite, Ni3B dendrite, rod eutectic, and precipitates was obtained. If ? T p < 175 K ± 10 K (175 °C ± 10 °C), the solidification pathway was found as primary transformation and eutectic transformation (L ? Ni3B and L ? Ni/Ni3B); if ? T p ? 175 K ± 10 K (175 °C ± 10 °C), the pathway was found as metastable eutectic transformation, metastable phase decomposition, and residual liquid solidification (L ? Ni/Ni23B6, Ni23B6 ? Ni/Ni3B, and Lr ? Ni/Ni3B). A high-speed video system was adopted to observe the solidification front of each transformation. It showed that for residual liquid solidification, the solidification front velocity is the same magnitude as that for eutectic transformation, but is an order of magnitude larger than for metastable eutectic transformation, which confirms the reaction as Lr ? Ni/Ni3B; it also showed that this velocity decreases with increasing ? T r, which can be explained by reduction of the residual liquid fraction and decrease of Ni23B6 decomposition rate.

Liu, Feng; Xu, Junfeng; Zhang, Di; Jian, Zengyun

2014-10-01

159

Holographic Meson Melting  

E-print Network

The plasma phase at high temperatures of a strongly coupled gauge theory can be holographically modelled by an AdS black hole. Matter in the fundamental representation and in the quenched approximation is introduced through embedding D7-branes in the AdS-Schwarzschild background. Low spin mesons correspond to the fluctuations of the D7-brane world volume. As is well known by now, there are two different kinds of embeddings, either reaching down to the black hole horizon or staying outside of it. In the latter case the fluctuations of the D7-brane world volume represent stable low spin mesons. In the plasma phase we do not expect mesons to be stable but to melt at sufficiently high temperature. We model this meson melting by the quasinormal modes of D7-brane fluctuations for the embeddings that do reach down to the horizon. The inverse of the imaginary part of the quasinormal frequency gives the lifetime of the meson in the hot plasma. We briefly comment on the possible application of our model to quarkonium s...

Hoyos, C; Montero, S; Hoyos, Carlos; Landsteiner, Karl; Montero, Sergio

2007-01-01

160

Holographic Meson Melting  

E-print Network

The plasma phase at high temperatures of a strongly coupled gauge theory can be holographically modelled by an AdS black hole. Matter in the fundamental representation and in the quenched approximation is introduced through embedding D7-branes in the AdS-Schwarzschild background. Low spin mesons correspond to the fluctuations of the D7-brane world volume. As is well known by now, there are two different kinds of embeddings, either reaching down to the black hole horizon or staying outside of it. In the latter case the fluctuations of the D7-brane world volume represent stable low spin mesons. In the plasma phase we do not expect mesons to be stable but to melt at sufficiently high temperature. We model the late stages of this meson melting by the quasinormal modes of D7-brane fluctuations for the embeddings that do reach down to the horizon. The inverse of the imaginary part of the quasinormal frequency gives the typical relaxation time back to equilibrium of the meson perturbation in the hot plasma. We briefly comment on the possible application of our model to quarkonium suppression.

Carlos Hoyos; Karl Landsteiner; Sergio Montero

2006-12-18

161

Melting and spheroidization of hexagonal boron nitride in a microwave-powered, atmospheric pressure nitrogen plasma `  

SciTech Connect

We have developed a method for producing spherically-shaped, hexagonal phase boron nitride (hBN) particles of controlled diameter in the 10-100 micron size range. Specifically, platelet-shaped hBN particles are passed as an aerosol through a microwave-generated, atmospheric pressure, nitrogen plasma. In the plasma, agglomerates formed by collisions between input hBN particles, melt and forms spheres. We postulate that this unprecedented process takes place in the unique environment of a plasma containing a high N-atom concentration, because in such an environment the decomposition temperature can be raised above the melting temperature. Indeed, given the following relationship [1]: BN{sub (condensed)} {leftrightarrow} B{sub (gas)} + N{sub (gas)}. Standard equilibrium thermodynamics indicate that the decomposition temperature of hBN is increased in the presence of high concentrations of N atoms. We postulate that in our plasma system the N atom concentration is high enough to raise the decomposition temperature above the (undetermined) melting temperature. Keywords Microwave plasma, boron nitride, melting, spherical, thermodynamics, integrated circuit package.

Gleiman, S. S. (Seth S.); Phillips, J. (Jonathan)

2001-01-01

162

Melting processes under microgravity conditions  

NASA Astrophysics Data System (ADS)

The Rensselaer Isothermal Dendritic Growth Experiment (RIDGE) uses the large data archive amassed through a series of three NASA-supported microgravity experiments (IDGE/USMP-2, -3, and -4), all of which flew aboard the space shuttle Columbia. The IDGE instruments aboard USMP-2 and -3 provided in-flight CCD images, and 35-mm films (postflight). USMP-4 also allowed streaming of near-real-time video. Using 30 fps video data, it became possible for the first time to study both freezing and melting sequences for high-purity pivalic acid (PVA). We report on the melting process observed for PVA crystal fragments, observed under nearly ideal convection-free conditions. Conduction-limited melting processes are of importance in orbital melting of materials, meteoritic genesis, mushy-zone evolution, and in fusion weld pools where length scales for thermal buoyancy are restricted. Microgravity video show clearly that PVA dendrites melt into fragments that shrink at accelerating rates to extinction. The melting paths of individual fragments follow characteristic time dependences derived from theory. The theoretical melting kinetics against which the experimental observations are carefully compared is based on conduction-limited quasi-static melting under shape-preserving conditions. Good agreement between theory and experiment is found for the stable melting of needle-shaped prolate spheroidal PVA crystal fragments with aspect ratios near C /A = 12.

Glicksman, M.; Lupulescu, A.; Koss, M.

163

Lunar highland melt rocks - Chemistry, petrology and silicate mineralogy  

NASA Technical Reports Server (NTRS)

A selected suite containing several of the largest samples of lunar highland melt rocks includes impact melt specimens (anorthositic gabbro, low-K Fra Mauro) and volcanic specimens (intermediate-K Fra Mauro). Although previous assumptions of LKFM volcanism have fallen into disfavor, no fatal arguments against this hypothesis have been presented, and the evidence of a possibly 'inherited igneous' olivine-plagioclase cosaturation provides cause for keeping a volcanic LKFM hypothesis viable. Comparisons of silicate mineralogy with melt rock compositions provide information on the specimen's composition and cooling history. Plagioclase-rock compositions can be matched to the experimentally determined equilibria for appropriate samples to identify melt rocks with refractory anorthitic clasts. Olivine-rock compositions indicate that melt rock vitrophyres precipitate anomalously Fe-rich olivine; the cause of this anomaly is not immediately evident. The Al-Ti and Ca-Fe-Mg zonation in pyroxene provide information on relative cooling rates of highland melt rocks, but Cr- and Al-content (where Al-rich low-Ca pyroxene cores are preserved in rapidly cooled samples) can be correlated with composition of the host rock.

Vaniman, D. T.; Papike, J. J.

1980-01-01

164

Molecular dynamics simulations of the melting of KCl nanoparticles  

NASA Astrophysics Data System (ADS)

Molecular dynamics (MD) simulations are used to investigate the thermodynamic properties and structural changes of KCl spherical nanoparticles at various sizes (1064, 1736, 2800, 3648, 4224 and 5832 ions) upon heating. The melting temperature is dependent on both the size and shape of KCl models, and the behaviour of the first order phase transition is also found in the present work. The surface melting found here is different from the melting phenomena of KCl models or other alkali halides studied in the past. In the premelting stage, a mixed phase containing liquid and solid ions covers the surface of nanoparticles. The only peak of heat capacity spreads out a significant segment of temperature, probably exhibiting both heterogeneous melting on the surface and homogeneous melting in the core. The coexistence of two melting mechanisms, homogeneous and heterogeneous ones, in our model is unlike those considered previously. We also found that the critical Lindemann ratio of the KCl nanoparticle becomes much more stable when the size of the nanoparticle is of the order of thousands of ions. A picture of the structural evolution upon heating is studied in more detail via the radial distribution function (RDF) and coordination numbers. Our results are in a good agreement with previous MD simulations and experimental observations.

Van Sang, Le; Thi Thuy Huong, Ta; Nguyen Tue Minh, Le

2014-10-01

165

Melt pool dynamics during selective electron beam melting  

NASA Astrophysics Data System (ADS)

Electron beam melting is a promising additive manufacturing technique for metal parts. Nevertheless, the process is still poorly understood making further investigations indispensable to allow a prediction of the part's quality. To improve the understanding of the process especially the beam powder interaction, process observation at the relevant time scale is necessary. Due to the difficult accessibility of the building area, the high temperatures, radiation and the very high scanning speeds during the melting process the observation requires an augmented effort in the observation equipment. A high speed camera in combination with an illumination laser, band pass filter and mirror system is suitable for the observation of the electron beam melting process. The equipment allows to observe the melting process with a high spatial and temporal resolution. In this paper the adjustment of the equipment and results of the lifetime and the oscillation frequencies of the melt pool for a simple geometry are presented.

Scharowsky, T.; Osmanlic, F.; Singer, R. F.; Körner, C.

2014-03-01

166

Current knowledge on core degradation phenomena, a review  

NASA Astrophysics Data System (ADS)

Degraded core processes are a key factor in the progression of a severe accident; they provide the initial conditions for in- and ex-vessel phenomena, lead to threats to the containment and determine the fission product and hydrogen source term. The knowledge of in-vessel melt relocation processes is also important with respect to cooling recovery actions (flooding of the core) and reactor pressure vessel (RPV) failure analysis. The core-melt progression is a non-coherent stepwise process which results in melting and liquefaction of core materials at different temperatures; oxidized Zircaloy cladding shells may significantly delay or prevent relocation of molten (U, Zr, O) mixtures contained within them. The various melts solidify on cooldown at different temperatures, i.e. at different axial locations, with ceramic crusts overlying metallic ones. These crusts may support melt pools; if the accident is unrecovered, the crusts may fail leading to massive relocation of molten material and debris into the lower plenum. Reflooding of an overheated core can result in a renewed temperature rise with localized melt formation, additional release of fission products, and in an increased hydrogen production; this increases the threat to the integrity of the reactor pressure vessel and to the containment as well as potentially misleading the operators regarding their recovery actions. There are principal remaining technical uncertainties in predicting late-phase core degradation after the initial intact rod geometry has been lost and regarding the effects of irradiated fuel which still have to be examined.

Hofmann, P.

167

In Brief: Melting glaciers  

NASA Astrophysics Data System (ADS)

Glaciers in Patagonia and Alaska have been losing their mass, and for longer than glaciers elsewhere in the world, according to a 7 December report compiled by the United Nations Environment Programme (UNEP). “Climate change is causing significant mass loss of glaciers in high mountains worldwide,” notes the report, which calls for accelerated research, monitoring, and modeling of glaciers and snow and their role in water supplies. The report “also highlights the vulnerability and exposure of people dependent upon [glacier-fed] rivers to floods, droughts and eventually shortages as a result of changes in the melting and freezing cycles linked with climate change and other pollution impacts,” according to UNEP executive director Achim Steiner. For more information, visit http://www.grida.no/publications/high­mountain-glaciers/.

Showstack, Randy; Tretkoff, Ernie

2010-12-01

168

Is Greenland Melting?  

NSDL National Science Digital Library

In this chapter, using My World GIS, users explore data that characterize the dynamic Greenland Ice Sheet. By examining photographs, map views, and tabular data, users gain an understanding of how and why scientists are monitoring the ice sheet and what they are finding. Users explore map layers that represent ice sheet thickness, weather station locations, and annual melt extents of the ice sheet. They learn about the working conditions that Arctic scientists must endure to collect their data, and how sensors on satellites are used to gather information from an area as large as Greenland. Finally, users learn about scientists' methods for measuring ice flowing downhill from Greenland, and examine that data to learn how fast the ice is moving.

169

Geometric calculus-based postulates for the derivation and extension of the Maxwell equations  

NASA Astrophysics Data System (ADS)

Clifford analysis, particularly application of the geometric algebra of three-dimensional physical space and its associated geometric calculus, enables a compact formulation of Maxwell's electromagnetic (EM) equations from a set of physically relevant and mathematically pleasing postulates. This formulation results in a natural extension of the Maxwell equations yielding wave solutions in addition to the usual EM waves. These additional solutions do not contradict experiment and have three properties in common with the apparent properties of dark energy. These three properties are that the wave solutions 1) propagate at the speed of light, 2) do not interact with ordinary electric charges or currents, and 3) possess retrograde momentum. By retrograde momentum, we mean that the momentum carried by such a wave is directed oppositely to the direction of energy transport. A "gas" of such waves generates negative pressure.

McClellan, Gene E.

2012-09-01

170

Fritz Zwicky's Postulate of Freedom from Prejudice Considered from the Standpoint of the Theory of Knowledge  

NASA Astrophysics Data System (ADS)

What can we say about unprejudiced thinking as postulated by Ritz Zwicky? Freedom from prejudice in opposition to stamped by theory. How does knowledge come about? Through sense perception and thought. The phenomenon is always mediated by organs, respectively by technical instruments. Which conclusion can we draw from this fact? Is the organ of knowledge by which we know nature a part of nature? Can the dialectic materialism explain the processes of human consciousness? What is the fundamental difference between think and perceive? Has human consciousness only a share in nature or also in the spiritual world? The role of the observer in the Copenhagen interpretation. Is the quantum theory applicable to psychic phenomena?

Lutz, Markus

171

Existence of an information unit as a postulate of quantum theory  

E-print Network

Does information play a significant role in the foundations of physics? Information is the abstraction that allows us to refer to the states of systems when we choose to ignore the systems themselves. This is only possible in very particular frameworks, like in classical or quantum theory, or more generally, whenever there exists an information unit such that the state of any system can be reversibly encoded in a sufficient number of such units. In this work we show how the abstract formalism of quantum theory can be deduced solely from the existence of an information unit with suitable properties, together with two further natural assumptions: the continuity and reversibility of dynamics, and the possibility of characterizing the state of a composite system by local measurements. This constitutes a new set of postulates for quantum theory with a simple and direct physical meaning, like the ones of special relativity or thermodynamics, and it articulates a strong connection between physics and information.

Lluis Masanes; Markus P. Mueller; Remigiusz Augusiak; David Perez-Garcia

2012-08-02

172

Existence of an information unit as a postulate of quantum theory.  

PubMed

Does information play a significant role in the foundations of physics? Information is the abstraction that allows us to refer to the states of systems when we choose to ignore the systems themselves. This is only possible in very particular frameworks, like in classical or quantum theory, or more generally, whenever there exists an information unit such that the state of any system can be reversibly encoded in a sufficient number of such units. In this work, we show how the abstract formalism of quantum theory can be deduced solely from the existence of an information unit with suitable properties, together with two further natural assumptions: the continuity and reversibility of dynamics, and the possibility of characterizing the state of a composite system by local measurements. This constitutes a set of postulates for quantum theory with a simple and direct physical meaning, like the ones of special relativity or thermodynamics, and it articulates a strong connection between physics and information. PMID:24062431

Masanes, Lluís; Müller, Markus P; Augusiak, Remigiusz; Pérez-García, David

2013-10-01

173

Solubility limits of silicate melts  

Microsoft Academic Search

A statistical mechanical model of silica melt is presented in which metal oxides are incorporated into the bonding network. In this approach a Flory-type lattice model for binary silicate melts is coupled with a set of chemical reactions that determine the extent of metal oxide incorporation into the silica network and regulate the distribution of nonbridging oxygens around a central

L. Rene Corrales; Keith D. Keefer

1997-01-01

174

Liquid entrainment by an expanding core disruptive accident bubble—a Kelvin\\/Helmholtz phenomenon  

Microsoft Academic Search

The final stage of a postulated energetic core disruptive accident (CDA) in a liquid metal fast breeder reactor is believed to involve the expansion of a high-pressure core-material bubble against the overlying pool of sodium. Some of the sodium will be entrained by the CDA bubble which may influence the mechanical energy available for damage to the reactor vessel. The

Michael Epstein; Hans K. Fauske; Shigenobu Kubo; Toshio Nakamura; Kazuya Koyama

2001-01-01

175

The melting curve of MgSiO3 perovskite from ab initio molecular dynamics using the coexistience method  

Microsoft Academic Search

Despite its importance in understanding such things as the crystallisation of the Earth's mantle from a magma ocean or the existence of melt in the current mantle, the melting temperature of the lower mantle phase MgSiO3 perovskite is poorly know. Estimates of its melting temperature at the core-mantle-boundary range from 5400 K to over 8000 K. We have used, therefore,

John Brodholt

2008-01-01

176

Crystallization and Melting of Diopside - Anorthite  

NSDL National Science Digital Library

This short exercise introduces students to phase diagrams that have a eutectic and a peritectic. After learning about such phase diagrams, students answer questions about melt composition, temperature, cooling and melting, crystalization, and melt:crystal ratios.

Perkins, Dexter

177

Generation, mobilization and crystallization of impact-induced alkali-rich melts in granitic target rocks: Evidence from the Araguainha impact structure, central Brazil  

NASA Astrophysics Data System (ADS)

This paper provides important insights into the generation, extraction and crystallization of clast-laden impact melt rocks from the Araguainha impact structure, central Brazil. Despite the mixed nature of the Araguainha target rocks (comprising a 2 km thick sequence of sedimentary rocks and underlying granitic basement), the exposed melt bodies are characterised by an alkali-rich granitic matrix embedding mineral and rock fragments derived only from the target granite. The melt rocks occur in the form of a massive impact melt sheet overlying the eroded central uplift structure, and as melt veins in the granite of the core of the central uplift. Bulk-rock major and trace element data (including platinum group elements) indicate that the precursor melts were generated locally, principally by partial melting of the target granite, without any contribution from the sedimentary sequence or the projectile. The dense network of melt veins was formed in isolation, by selective melting of plagioclase and alkali feldspar within the granite target. Plagioclase and alkali feldspar melted discretely and congruently, producing domains in the matrix of the melt veins, which closely match the stoichiometry of these minerals. The compositionally discrete initial melt phases migrated through a dense network of microfractures before being assembled into larger melt veins. Freezing of the melt veins was substantially fast, and the melt components were quenched in the form of alkali-feldspar and plagioclase schlieren in the matrix of the melt veins. The overlying impact melt rock is, in contrast, characterised by a granophyric matrix consisting of albite, sanidine, quartz, biotite and chlorite. In this case, melt components appear to have been more mobile and to have mixed completely to form a granitic parental melt. We relate the melting of the minerals to post-shock temperatures that exceeded the melting point of feldspars.

Machado, R.; Lana, C.; Stevens, G.; Filho, C. R. S.; Reimold, W. U.; McDonald, Iain

2009-12-01

178

DUBLIN CORE  

EPA Science Inventory

The Dublin Core is a metadata element set intended to facilitate discovery of electronic resources. It was originally conceived for author-generated descriptions of Web resources, and the Dublin Core has attracted broad ranging international and interdisciplinary support. The cha...

179

International Conference on Microwave and High Frequency Heating, AMPERE-2013 Nottingham, UK, September 2013 Basalt Melting by Localized-Microwave  

E-print Network

, September 2013 255 Basalt Melting by Localized-Microwave Thermal-Runaway Instability E. Jerby*, Y. Meir, M an experimental and theoretical study of the thermal-runaway instability induced by localized microwaves in basalt stones. This effect leads to the inner melting of the basalt core, and further to its eruption similarly

Jerby, Eli

180

Commercial Zone Melting Ingots  

NASA Astrophysics Data System (ADS)

Bismuth telluride-based compounds have been extensively utilized for commercial application. However, thermoelectric materials must suffer numerous mechanical vibrations and thermal stresses while in service, making it equally important to discuss the mechanical properties, especially at high temperature. In this study, the compressive and bending strengths of Bi0.5Sb1.5Te3 commercial zone melting (ZM) ingots were investigated at 25, 100, and 200 °C, respectively. Due to the obvious anisotropy of materials prepared by ZM method, the effect of anisotropy on the strengths was also explored. Two-parameter Weibull distribution was employed to fit a series of values acquired by a universal testing machine. And digital speckle photography was applied to record the strain field evolution, providing visual observation of surface strain. The compressive and bending strengths along ZM direction were approximately three times as large as those perpendicular to the ZM direction independent of the temperature, indicating a weak van der Waals bond along the c axis.

Zheng, Yun; Xie, Hongyao; Shu, Shengcheng; Yan, Yonggao; Li, Han; Tang, Xinfeng

2014-06-01

181

Polar basal melting on Mars  

NASA Astrophysics Data System (ADS)

The potential importance of basal melting on Mars is illustrated through the discussion of four examples: (1) the origin of the major polar reentrants, (2) the removal and storage of an ancient Martian ice sheet, (3) the mass balance of the polar terrains, and (4) the possibility of basal melting at temperate latitudes. This analysis suggests that the process of basal melting may play a key role in understanding the evolution of the Martian polar terrains and the long-term climatic behavior of water on Mars.

Clifford, S. M.

1987-08-01

182

Lithium diffusion in silicate melts  

NASA Astrophysics Data System (ADS)

The diffusion properties of Li in an andesitic and pitchstone melt have been determined over the temperature range 1300-1400°C. The diffusion data have been fitted to an Arrhenius relationship between log D0 and 1/ T, and give relatively small activation energies of diffusion: 21.4±5.8 kcal mol -1 in the andesite and 20.1±2.8 kcal mol -1 in the pitchstone. Li +, unlike several other cations, shows similar diffusivities in these melt compositions to that in a basaltic melt. Despite the similar ionic radius of Li + to that of Co 2+, the diffusion properties of the two ions are very different from each other.

Cunningham, G. J.; Henderson, P.; Lowry, R. K.; Nolan, J.; Reed, S. J. B.; Long, J. V. P.

1983-10-01

183

Electrical Conductivity of Cryolite Melts  

NASA Astrophysics Data System (ADS)

This paper proposes an equation for the electrical conductivity of multicomponent cryolite-based mixtures. The equation is based on a physical model which assumes that the conductivity is proportional to the number density of the effective electric charges in the melt. The various authors in the available literature show a great discrepancy in conductivity data of cryolite-based melts. The equation based on the physical model enables determination of which set of data is preferable. Special consideration in this respect is given to the influence of magnesium flouride and lithium flouride additions to the melt.

Fellner, P.; Grjotheim, K.; Kvande, H.

1985-11-01

184

Nuclear reactor melt-retention structure to mitigate direct containment heating  

DOEpatents

A light water nuclear reactor melt-retention structure to mitigate the extent of direct containment heating of the reactor containment building. The structure includes a retention chamber for retaining molten core material away from the upper regions of the reactor containment building when a severe accident causes the bottom of the pressure vessel of the reactor to fail and discharge such molten material under high pressure through the reactor cavity into the retention chamber. In combination with the melt-retention chamber there is provided a passageway that includes molten core droplet deflector vanes and has gas vent means in its upper surface, which means are operable to deflect molten core droplets into the retention chamber while allowing high pressure steam and gases to be vented into the upper regions of the containment building. A plurality of platforms are mounted within the passageway and the melt-retention structure to direct the flow of molten core material and help retain it within the melt-retention chamber. In addition, ribs are mounted at spaced positions on the floor of the melt-retention chamber, and grid means are positioned at the entrance side of the retention chamber. The grid means develop gas back pressure that helps separate the molten core droplets from discharged high pressure steam and gases, thereby forcing the steam and gases to vent into the upper regions of the reactor containment building.

Tutu, Narinder K. (Manorville, NY); Ginsberg, Theodore (East Setauket, NY); Klages, John R. (Mattituck, NY)

1991-01-01

185

Melting granites to make granites  

NASA Astrophysics Data System (ADS)

Large-scale partial melting in the continental crust is widely attributed to fluid-absent incongruent breakdown of hydrous minerals in the case of pelites, greywackes and meta-mafic rocks. Granite is a far more common rock in the continental crust, but fluid-absent hydrate-breakdown melting is unlikely to result in significant melting in granites because of their low modal abundance of mica or amphibole. Experiments show that fluid-present melting can produce ~30% melt at low temperatures (690°C). Thus, granites and leucogranites can be very fertile if H2O-present melting occurs via reactions such as plagioclase + quartz + K-feldspar + H2O = melt, because of their high modal proportions of the reactant phases. Our study investigates the Kinawa Migmatite in the São Francisco Craton, southeastern Brazil. This migmatite is derived from an Archaean TTG sequence and can be divided into; 1) pink diatexites, 2) leucosomes, 3) grey gneisses and 4) amphibolites. The migmatite records upper-amphibolite to beginning of granulite facies metamorphism in a P-T range from 5.1-6.6 kbar and ~650-780°C. Pink diatexites are the most abundant rocks, and their appearance varies depending on the amount of melt they contained. Three types are recognised: residual diatexites (low melt fraction (Mf)), schlieren diatexites (moderate Mf) and homogeneous diatexites (high Mf). They are very closely related spatially in the field, with mostly transitional contacts. There is a sequence with progressive loss of ferromagnesian minerals, schollen and schlieren through the sequence to the most melt-rich parts of the diatexites as magmatic flow became more intense. There are fewer ferromagnesian minerals, thus the melt becomes cleaner (more leucocratic) and, because the schlieren have disaggregated the aspect is more homogeneous. These parts are texturally similar to leucogranites in which the biotite is randomly distributed and pre-melting structures are completely destroyed. The likely protolith for the migmatites was a leucocratic granodiorite (with modal K-feldspar up to 30% and biotite up to 5%), and from geochemical modelling the degree of partial melting ranged from 0.21 to 0.25. Furthermore, the residual diatexites show a complementary low modal proportion, or even absence, of K-feldspar, but an increase in modal plagioclase, quartz (up to 56 and 37% respectively) and biotite (5-16%). This suggests that the melting reaction did not involve biotite and that plagioclase and quartz were in excess. As result the melt generated is fairly leucocratic, and most of the mafic phases in it are inherited. Anatectic melts in the Kinawa Migmatite were mildly metaluminous and distinctly leucocratic (A/CNK from 0.97 to 1.01; SiO2 from 72.8 to 75.65%; (FeOT+MgO+TiO2) from 0.49 to 2.3%). Since most granites have a higher (FeOT+MgO+TiO2), additional processes must add the "mafic component" to these melts before they form plutons.

Carvalho, Bruna B.; Sawyer, Edward W.; Janasi, Valdecir de A.

2014-05-01

186

The NiSi melting curve to 70 GPa  

NASA Astrophysics Data System (ADS)

The melting curve of NiSi has been determined to 70 GPa on the basis of laser-heated diamond anvil cell (LH-DAC) experiments in which changes in the gradient of temperature vs. laser power functions were used as the melting criterion. The melting curve was corroborated with in situ X-ray diffraction experiments in both the LH-DAC and multi-anvil press in which the appearance of liquid diffuse scattering in the diffraction patterns was used as the melting criterion. At all pressures, the NiSi melting curve is lower than that of FeSi, with the difference in melting temperature reaching a maximum of 900 K at 14 GPa. The location of the B31 + B20 + L triple point has been constrained to 12 ± 2 GPa and 1550 ± 100 K and the B20 + B2 + L triple point to 28.5 ± 1.5 GPa and 2165 ± 60 K. On the basis of the in situ LH-DAC experiments the Clapeyron slope of the B20 ? B2 transition is estimated at -67 MPa K-1. Extrapolation of the B2-NiSi liquidus to core-mantle boundary (CMB) conditions (135 GPa) suggests the melting point of NiSi (3700 ± 400 K) will be only marginally lower than that of isostructural FeSi (4000 ± 200 K). Thus any (Fe,Ni)Si solid solution present within the D? layer is expected to remain solid, with the possible exception of the very hottest region adjacent to the CMB.

Lord, Oliver T.; Wann, Elizabeth T. H.; Hunt, Simon A.; Walker, Andrew M.; Santangeli, James; Walter, Michael J.; Dobson, David P.; Wood, Ian G.; Vo?adlo, Lidunka; Morard, Guillaume; Mezouar, Mohamed

2014-08-01

187

Postcumulus Processes in Oceanic-Type Olivine-Rich Cumulates: the Role of Melt Entrapment vs. Melt-Rock Interaction  

NASA Astrophysics Data System (ADS)

Evaluation of postcumulus processes in cumulate rocks can provide insights on the mechanisms and scales of melt migration and interaction within the crust, thus contributing to define crustal accretion models. Here we present a microstructural-geochemical study on MORB-type primitive olivine-rich cumulates intruded in the Erro-Tobbio (ET) mantle peridotites (Voltri Massif, Ligurian Alps, Italy), an on-land analogue of (ultra-) slow spreading settings. Postcumulus crystallization is indicated by the occurrence of accessory interstitial minerals (Ti- pargasite, opx , Fe-Ti oxides), and by chemical zoning in intercumulus clinopyroxene related to its textural occurence, i.e. marked REE, Ti, Zr enrichment at almost constant Mg-numbers (88-90) and LREE depletion, from core to rim of coarse anhedral clinopyroxene, to thin vermicular cpx grains. Interstitial pargasites have high Nb, Zr, REE contents although preserving "primitive" major element compositions (Mgvalue = 0.86-0.89) and LREE depletion. Significant trace element enrichment at almost constant LREE fractionation in interstitial clinopyroxenes and Ti-rich pargasites argue against the infiltration of exotic evolved melts and indicate that interstitial minerals were mainly related to close-system trapped melt crystallization. Geochemical modeling shows that crystallization of less than 5% trapped melt is sufficient to produce the REE enrichments observed in cpx. The progressive increase in (REE-Zr-Ti) abundances from core to rim of large clinopyroxene grains is accounted by an "in-situ" fractional crystallization process. Anomalous Zr enrichment is observed in thin (< 400 µm) interstitial and vermicular clinopyroxenes and pargasitic amphiboles, representing the very last melt fraction (reasonably < 2%). At this final crystallization stage, the low residual porosity likely inhibited large-scale melt migration. AFC modeling indicates that the high Zr/Nd ratios in cpx could be related to small-scale migration and interaction between residual, evolved, low melt fractions and the olivine cumulus matrix, consistent with textural evidence of lobate contacts between vermicular clinopyroxenes and cumulus olivine, indicative of partial olivine resorption. Our study points that small amount of melt trapped in an olivine-rich matrix can induce significant trace element enrichment in minerals. Such an evidence argue against large-scale residual melt migration, this latter being controlled by porosity and permeability of the crystal mush, and indicates that compaction was very efficient. This could have been favoured by the interplay of different factors, i.e. slow cooling rates and low thermal gradients, and synkinematic deformation (Natland and Dick, 2001, J. V. G. Res, 110, 191-233). The ET cumulates could thus represent the base of a stack of cumulates (3-5 Kb intrusion depth) from which differentiated melts migrated upwards and crystallized at shallower lithospheric environments. Overall, this indicates that different melt transport and interaction processes may act during crust accretion at very slow spreading settings, e.g. low melt fraction entrapment of indigenous melts in compaction-dominated deep-seated gabbroic intrusions vs. migration of exotic evolved melts through uppermost crustal levels.

Borghini, G.; Rampone, E.

2008-12-01

188

Postulated Feedbacks of Deciduous Forest Phenology on Seasonal Climate Patterns in the Western Canadian Interior.  

NASA Astrophysics Data System (ADS)

A large portion of the western Canadian interior exhibits a distinctive seasonal pattern in long-term mean surface temperatures characterized by anomalously warmer conditions in spring and autumn than would be expected from a sinusoidal model. The anomaly is greatest over the southern boreal forest of western Canada, where trembling aspen (Populus tremuloides Michx.)-a deciduous, broad-leaved species-is an important component. In this region, mean temperatures are 2°-3°C warmer in April and October but nearly 2°C cooler in June and July, relative to a best-fitting sinusoidal function. Another feature of the climate in this region is that average precipitation is low (15-30 mm month1) from October to April but increases sharply during the summer growing season (50-100 mm month1 from June to August). Eddy correlation and sap flow measurements in a boreal aspen forest indicate profound seasonal changes in transpiration and energy partitioning associated with the deciduous nature of the forest canopy. Latent heat (water vapor) flux reaches a maximum during the summer period when leaves are present, while sensible heat flux is highest in early spring when the forest is leafless. Thus, it is postulated that feedbacks of leaf phenology of aspen forests, which occupy a large area of the western Canadian interior, may contribute significantly to the distinctive seasonal patterns of mean temperature and precipitation that occur in this region.

Hogg, E. H.; Price, D. T.; Black, T. A.

2000-12-01

189

Analysis of a Schnute postulate-based unified growth mode for model selection in evolutionary computations  

PubMed Central

In order to evaluate the feasibility of a combined evolutionary algorithm-information theoretic approach to select the best model from a set of candidate invasive species models in ecology, and/or to evolve the most parsimonious model from a suite of competing models by comparing their relative performance, it is prudent to use a unified model that covers a myriad of situations. Using Schnute’s postulates as a starting point, we present a single, unified model for growth that can be successfully utilized for model selection in evolutionary computations. Depending on the parameter settings, the unified equation can describe several growth mechanisms. Such a generalized model mechanism, which encompasses a suite of competing models, can be successfully implemented in evolutionary computational algorithms to evolve the most parsimonious model that best fits ground truth data. We have done exactly this by testing the effectiveness of our reaction-diffusion-advection (RDA) model in an evolutionary computation model selection algorithm. The algorithm was validated (with success) against field data sets of the Zebra mussel invasion of Lake Champlain in the United States. PMID:17197072

Bentil, D.E.; Osei, B.M.; Ellingwood, C.D.; Hoffmann, J.P.

2007-01-01

190

Analysis of a Schnute postulate-based unified growth model for model selection in evolutionary computations.  

PubMed

In order to evaluate the feasibility of a combined evolutionary algorithm-information theoretic approach to select the best model from a set of candidate invasive species models in ecology, and/or to evolve the most parsimonious model from a suite of competing models by comparing their relative performance, it is prudent to use a unified model that covers a myriad of situations. Using Schnute's postulates as a starting point [Schnute, J., 1981. A versatile growth model with statistically stable parameters, Can. J. Fish Aquat. Sci. 38, 1128-1140], we present a single, unified model for growth that can be successfully utilized for model selection in evolutionary computations. Depending on the parameter settings, the unified equation can describe several growth mechanisms. Such a generalized model mechanism, which encompasses a suite of competing models, can be successfully implemented in evolutionary computational algorithms to evolve the most parsimonious model that best fits ground truth data. We have done exactly this by testing the effectiveness of our reaction-diffusion-advection (RDA) model in an evolutionary computation model selection algorithm. The algorithm was validated (with success) against field data sets of the Zebra mussel invasion of Lake Champlain in the United States. PMID:17197072

Bentil, D E; Osei, B M; Ellingwood, C D; Hoffmann, J P

2007-01-01

191

Serum-derived bovine immunoglobulin/protein isolate: postulated mechanism of action for management of enteropathy  

PubMed Central

The health and performance of the gastrointestinal tract is influenced by the interaction of a variety of factors, including diet, nutritional status, genetics, environment, stress, the intestinal microbiota, immune status, and gut barrier. Disruptions in one or more of these factors can lead to enteropathy or intestinal disorders that are known to occur in concert with certain disease states or conditions such as irritable bowel syndrome or human immunodeficiency virus (HIV) infection. Nutritional support in the form of a medical food along with current therapies could help manage the adverse effects of enteropathy, which include effects on nutrient digestion, absorption, and metabolism, as well as utilization of nutrients from foodstuffs. Numerous studies have demonstrated that oral administration of plasma- or serum-derived protein concentrates containing high levels of immunoglobulins can improve weight management, normalize gut barrier function, and reduce the severity of enteropathy in animals. Recent trials in humans provide preliminary evidence that a serum-derived bovine immunoglobulin/protein isolate is safe and improves symptoms, nutritional status, and various biomarkers associated with enteropathy in patients with HIV infection or diarrhea-predominant irritable bowel syndrome. This review summarizes data from preclinical and clinical studies with immunoglobulin-containing plasma/serum protein concentrates, with a focus on the postulated mode of action of serum-derived bovine immunoglobulin/protein isolate for patients with enteropathy. PMID:24904221

Petschow, Bryon W; Burnett, Bruce; Shaw, Audrey L; Weaver, Eric M; Klein, Gerald L

2014-01-01

192

Melting of metals during rapid bulk heating  

NASA Astrophysics Data System (ADS)

The melting of metals is studied during electric-current pulse heating at high rates (106-109 K/s). This process is found to be nonequilibrium: it proceeds with the overheating of the onset and end of melting and is nonisothermal. The experimentally measured enthalpies of nonequilibrium melting are used to calculate the nonisothermicity of nonequilibrium melting ? T and nonisothermicity factor ? T/ T m , where ? T reflects the increase or decrease in the temperature of the end of nonequilibrium melting with respect to equilibrium melting temperature T m . For many metals with a melting temperature of 500-3695 K, melting factor of nonisothermic melting ? T/ T m ranges from 0.8-4.6% to -(0.2-5.1)% and depends on the relation between homogeneous and heterogeneous nucleation. The nonisothermicity of melting is confirmed by direct temperature measurements during melting of hafnium and zirconium. The contribution of the energy consumed for heating of a two-phase solid metal-melt system during nonisothermal melting in the course of pulsed heating to the melting heat is estimated. The relaxation times of equilibrium melting of some metals are estimated using nonequilibrium pulsed measurements. The role of the melting nonisothermicity factor in increasing the melting temperature of a graphite sample placed in a closed volume and heated with an electric current pulse at a rate of 5 × 109 K/s is determined.

Chekhovskoi, V. Ya.; Tarasov, V. D.

2009-08-01

193

Pressure melting and ice skating  

NASA Astrophysics Data System (ADS)

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 ?m 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 ?m thick because of the high pressures.

Colbeck, S. C.

1995-10-01

194

Scaleable Clean Aluminum Melting Systems  

SciTech Connect

The project entitled 'Scaleable Clean Aluminum Melting Systems' was a Cooperative Research and Development Agreements (CRADAs) between Oak Ridge National Laboratory (ORNL) and Secat Inc. The three-year project was initially funded for the first year and was then canceled due to funding cuts at the DOE headquarters. The limited funds allowed the research team to visit industrial sites and investigate the status of using immersion heaters for aluminum melting applications. Primary concepts were proposed on the design of furnaces using immersion heaters for melting. The proposed project can continue if the funding agency resumes the funds to this research. The objective of this project was to develop and demonstrate integrated, retrofitable technologies for clean melting systems for aluminum in both the Metal Casting and integrated aluminum processing industries. The scope focused on immersion heating coupled with metal circulation systems that provide significant opportunity for energy savings as well as reduction of melt loss in the form of dross. The project aimed at the development and integration of technologies that would enable significant reduction in the energy consumption and environmental impacts of melting aluminum through substitution of immersion heating for the conventional radiant burner methods used in reverberatory furnaces. Specifically, the program would couple heater improvements with furnace modeling that would enable cost-effective retrofits to a range of existing furnace sizes, reducing the economic barrier to application.

Han, Q.; Das, S.K. (Secat, Inc.)

2008-02-15

195

Quantitative characterization of 3-dimensional melt distribution in partially molten olivine-basalt aggregates using X-ray synchrotron microtomography  

NASA Astrophysics Data System (ADS)

Quantitative knowledge of the distribution of small amounts of silicate melt in peridotite and of its influence on permeability are critical to our understanding of melt migration and segregation processes in the upper mantle. Estimates for the permeability of partially molten rock require 3D melt distribution at the grain-scale. Existing studies of melt distribution, carried out on 2D slices through experimental charges, have produced divergent models for melt distribution at small melt fractions. While some studies conclude that small amounts of melt are distributed primarily along triple junctions [e.g., Wark et al., 2003], others predict an important role for melt distribution along grain boundaries at low melt fractions [e.g., Faul 1997]. Using X-ray synchrotron microtomography, we have obtained the first high quality non-destructive imaging of 3D melt distribution in olivine-basalt aggregates. Textually equilibrated partially molten samples consisting of magnesian olivine plus 2, 5, 10, or 20% primitive basalt were synthesized at 1.5 GPa and 1350°C in experiments lasting 264-336 hours. Microtomographic images of melt distribution were obtained on cylindrical cores, 1 mm in diameter, at a spatial resolution of 1 micron. Textual information such as melt channel size, dihedral angle and channel connectivity was then quantified using AVIZO and MATLAB. Our results indicate that as melt fraction decreases, melt becomes increasingly distributed along 3 grain junctions, in agreement with theoretical predictions. We do not find significant amounts of melt along grain boundaries at low melt fractions. We found that the true dihedral angle ranges from 50 to 70°, in agreements with results using 2D microcopy. Comparison between the samples provides a quantitative characterization of how melt fraction affects melt distribution including connectivity. The geometrical data have been incorporated into our network model to obtain macroscale transport properties for partially molten dunite. Results from this tomographic study thus provide constraints on rates of melt migration and melt extraction within the partially molten regions beneath ocean ridges. Fig 1. Melt channels in an olivine-basalt sample with 10 vol% melt.

Zhu, W.; Gaetani, G. A.; Fusseis, F.

2009-12-01

196

Implications of dairy systems on enteric methane and postulated effects on total greenhouse gas emission.  

PubMed

The effects of feeding total mixed ration (TMR) or pasture forage from a perennial sward under a management intensive grazing (MIG) regimen on grain intake and enteric methane (EM) emission were measured using chambers. Chamber measurement of EM was compared with that of SF6 employed both within chamber and when cows grazed in the field. The impacts of the diet on farm gate greenhouse gas (GHG) emission were also postulated using the results of existing life cycle assessments. Emission of EM was measured in gas collection chambers in Spring and Fall. In Spring, pasture forage fiber quality was higher than that of the silage used in the TMR (47.5% v. 56.3% NDF; 24.3% v. 37.9% ADF). Higher forage quality from MIG subsequently resulted in 25% less grain use relative to TMR (0.24 v. 0.32 kg dry matter/kg milk) for MIG compared with TMR. The Fall forage fiber quality was still better, but the higher quality of MIG pasture was not as pronounced as that in Spring. Neither yield of fat-corrected milk (FCM) which averaged 28.3 kg/day, nor EM emission which averaged 18.9 g/kg dry matter intake (DMI) were significantly affected by diet in Spring. However, in the Fall, FCM from MIG (21.3 kg/day) was significantly lower than that from TMR (23.4 kg/day). Despite the differences in FCM yield, in terms of EM emission that averaged 21.9 g/kg DMI was not significantly different between the diets. In this study, grain requirement, but not EM, was a distinguishing feature of pasture and confinement systems. Considering the increased predicted GHG emissions arising from the production and use of grain needed to boost milk yield in confinement systems, EM intensity alone is a poor predictor of the potential impact of a dairy system on climate forcing. PMID:23896042

Fredeen, A; Juurlink, S; Main, M; Astatkie, T; Martin, R C

2013-11-01

197

A TEST OF HEBB'S POSTULATE AT IDENTIFIED SYNAPSES WHICH MEDIATE CLASSICAL CONDITIONING IN APLYSZ-A1  

Microsoft Academic Search

In 1949, D. 0. Hebb proposed a novel mechanism for producing changes in the strength of synapses that could account for associative learning. According to Hebb, the strength of a synapse might increase when the use of that synapse contributes to the generation of action potentials in a postsynaptic neuron. Thus, an essential feature of this postulate is that action

THOMAS J. CAREW; ROBERT D. HAWKINS; THOMAS W. ABRAMS; ERIC R. KANDEL

198

Noble gas, iodine, and cesium transport in a postulated loss of decay heat removal accident at Browns Ferry  

Microsoft Academic Search

This report presents an analysis of the movement of noble gas, iodine, and cesium fission products within the Mark-I containment BWR reactor system represented by Browns Ferry Unit 1 during a postulated accident sequence initiated by a loss of decay heat removal capability following a scram. The event analysis showed that this accident could be brought under control by various

R. P. Wichner; S. A. Hodge; C. F. Weber; E. C. Beahm; A. L. Wright

1984-01-01

199

Evolutions of lamellar structure during melting and solidification of Fe9577 nanoparticle from molecular dynamics simulations  

NASA Astrophysics Data System (ADS)

A structural evolution during solidification and melting processes of nanoparticle Fe9577 was investigated from MD simulations. A perfect lamellar structure, consisting alternately of fcc and hcp layers, was obtained from solidification process. A structural heredity of early embryo is proposed to explain the structural preference of solidification. Defects were found inside the solid core and play the same role as surface premelting on melting. hcp was found more stable than fcc in high temperature. The difference between melting and solidification points can be deduced coming fully from the overcoming of thermodynamic energy barrier, instead of kinetic delay of structural relaxation.

Wu, Yongquan; Shen, Tong; Lu, Xionggang

2013-03-01

200

Experimental determination of the solubility of iridium in silicate melts: Preliminary results  

NASA Technical Reports Server (NTRS)

Little is known of the geochemical behavior of iridium. Normally this element is taken to be chalcophile and/or siderophile so that during planetary differentiation processes, e.g., core formation, iridium is extracted from silicate phases into metallic phases. Experimental determination of the metal/silicate partition coefficient of iridium is difficult simply because it is so large. Also there are no data on the solubility behavior of iridium in silicate melts. With information on the solubility of iridium in silicate melts it is possible, in combination with experimental data for Fe-Ir alloys, to calculate the partition coefficient between a metallic phase and a silicate melt.

Borisov, Alexander; Dingwell, Donald B.; Oneill, Hugh ST.C.; Palme, Herbert

1992-01-01

201

Climate change and forest fires synergistically drive widespread melt events of the Greenland Ice Sheet  

PubMed Central

In July 2012, over 97% of the Greenland Ice Sheet experienced surface melt, the first widespread melt during the era of satellite remote sensing. Analysis of six Greenland shallow firn cores from the dry snow region confirms that the most recent prior widespread melt occurred in 1889. A firn core from the center of the ice sheet demonstrated that exceptionally warm temperatures combined with black carbon sediments from Northern Hemisphere forest fires reduced albedo below a critical threshold in the dry snow region, and caused the melting events in both 1889 and 2012. We use these data to project the frequency of widespread melt into the year 2100. Since Arctic temperatures and the frequency of forest fires are both expected to rise with climate change, our results suggest that widespread melt events on the Greenland Ice Sheet may begin to occur almost annually by the end of century. These events are likely to alter the surface mass balance of the ice sheet, leaving the surface susceptible to further melting. PMID:24843158

Keegan, Kaitlin M.; Albert, Mary R.; McConnell, Joseph R.; Baker, Ian

2014-01-01

202

Climate change and forest fires synergistically drive widespread melt events of the Greenland Ice Sheet.  

PubMed

In July 2012, over 97% of the Greenland Ice Sheet experienced surface melt, the first widespread melt during the era of satellite remote sensing. Analysis of six Greenland shallow firn cores from the dry snow region confirms that the most recent prior widespread melt occurred in 1889. A firn core from the center of the ice sheet demonstrated that exceptionally warm temperatures combined with black carbon sediments from Northern Hemisphere forest fires reduced albedo below a critical threshold in the dry snow region, and caused the melting events in both 1889 and 2012. We use these data to project the frequency of widespread melt into the year 2100. Since Arctic temperatures and the frequency of forest fires are both expected to rise with climate change, our results suggest that widespread melt events on the Greenland Ice Sheet may begin to occur almost annually by the end of century. These events are likely to alter the surface mass balance of the ice sheet, leaving the surface susceptible to further melting. PMID:24843158

Keegan, Kaitlin M; Albert, Mary R; McConnell, Joseph R; Baker, Ian

2014-06-01

203

Fundamentals of Melt-Water Interfacial Transport Phenomena: Improved Understanding for Innovative Safety Technologies in ALWRs  

SciTech Connect

The interaction and mixing of high-temperature melt and water is the important technical issue in the safety assessment of water-cooled reactors to achieve ultimate core coolability. For specific advanced light water reactor (ALWR) designs, deliberate mixing of the core-melt and water is being considered as a mitigative measure, to assure ex-vessel core coolability. The goal of this work is to provide the fundamental understanding needed for melt-water interfacial transport phenomena, thus enabling the development of innovative safety technologies for advanced LWRs that will assure ex-vessel core coolability. The work considers the ex-vessel coolability phenomena in two stages. The first stage is the melt quenching process and is being addressed by Argonne National Lab and University of Wisconsin in modified test facilities. Given a quenched melt in the form of solidified debris, the second stage is to characterize the long-term debris cooling process and is being addressed by Korean Maritime University in via test and analyses. We then address the appropriate scaling and design methodologies for reactor applications.

M. Anderson; M. Corradini; K.Y. Bank; R. Bonazza; D. Cho

2005-04-26

204

Cracks preserve kimberlite melt composition  

NASA Astrophysics Data System (ADS)

The chemical composition of kimberlite melts has previously been estimated by measuring aphanitic intrusive rocks (deposit composition) or by partial melting experiments on carbonated lherzolites (source composition). Pervasively altered, degassed and contaminated material preclude the determination of the primitive melt composition. Here we present data on melt compositions trapped in unaltered olivine cracks that have been healed and overgrown prior to shallow level emplacement. During the ascent of kimberlite magma the prograding crack tip samples mantle peridotite xenoliths. Xenoliths rapidly disaggregate over the first few kilometers of transport producing a population of olivine xenocrysts that are released to the fluid-rich melt. Rapid ascent of the kimberlite magma causes depressurization and creates internal elastic stresses in the olivine crystals that can only be alleviated by volumetric expansion or brittle failure. On the time scales operative during kimberlite ascent volume expansion is negligible and brittle failure occurs. Small wetting angles between the fluid-rich melt and olivine allow infiltration of the melt into the crack. These very thin cracks (<5 µm) heal rapidly and preserve primary kimberlitic material en route to the surface. We use the electron microprobe with a focused beam (interaction volume less than 2 µm) to analyze the small volumes of material found in the healed cracks of the olivine. We analyzed for 18 elements including oxygen, which we obtained by utilizing a non-linear time dependent intensity acquisition and empirically determined mass absorption coefficients. By accurately knowing the amount of oxygen in a sample, we assign oxygen molecules to all other analyzed elements (e.g. MgO, Al2O3) and the remaining oxygen is assigned to hydrogen and carbon. The analysis total is used as a constraint on the proportion of each species. Mg/Ca ratios of the cracks vary from 0.6-5 indicating a compositional continuum between alkali-poor, carbonate-rich melt and Mg-rich silicate melt. OH/CO2 ratios (0-7) and other volatiles (S, F, Cl) are variable and do not correlate with any of the other major elements, consistent with a variably degassed fluid phase. Element associations indicated that Ca, Ni, Ba and Sr co-vary and are inversely related to Mg, Si, Fe, (and several other minor elements). In summary, crack-filling material is Ca and Mg-rich (up to 55 wt.% CaO+MgO), silica-poor (11-32 wt.% SiO2) and are volatile rich ( up to 28 wt.%).

Brett, R. C.; Vigouroux-Caillibot, N.; Donovan, J. J.; Russell, K.

2009-12-01

205

Potassium in the Earth's core?  

NASA Astrophysics Data System (ADS)

The partitioning of K and Na between liquid Fe-S-O alloys and silicate melt has been determined over the pressure and temperature range 2.5-24 GPa and 1500-1900°C. In experiments with S-free Fe alloys, the alkali elements show completely lithophile behaviour. When S is added, however, K and Na begin to enter the Fe-liquid phase and their distribution coefficients DI (=[I] metal/[I] silicate) correlate strongly with O content (and FeO activity) of the Fe-S-O liquid and with the composition of the silicate melt. For potassium, DK is ˜1.0 for Fe-sulphide liquid containing 30% S and 8% O. Increasing temperature leads to increasing O solubility in the Fe-sulphide liquid and correspondingly higher values of DK. Increasing pressure on the other hand slightly reduces DK values. Given a planetary core containing 10 wt% S and 4-8 wt% O, then several hundred ppm K would be present in the Fe-sulphide liquid if it segregated at low pressures, e.g. in a small planetary body such as Mars. If, as has recently been suggested, the Earth's core separated at the base of a deep magma ocean, then its highest possible K content is about 250 ppm. The latter would generate approximately 20% of the total heat production of the core. K can only be present in the core, however, if, at some time during its formation, a discrete O-rich FeS liquid separated from the silicate mantle. Finally, the sulphide compositions produced in our experiments imply that a combination of S and O could contribute significantly to the light element content of the Earth's core.

Gessmann, C. K.; Wood, B. J.

2002-06-01

206

Does partial melting explain geophysical anomalies?  

NASA Astrophysics Data System (ADS)

The existence of partial melt is frequently invoked to explain geophysical anomalies such as low seismic wave velocity and high electrical conductivity. I review various experimental and theoretical studies to evaluate the plausibility of this explanation. In order for a partial melt model to work, not only the presence of melt, but also the presence of appropriate amount of melt needs to be explained. Using the mineral physics observations on the influence of melt on physical properties and the physics and chemistry of melt generation and transport, I conclude that partial melt model for the asthenosphere with homogeneous melt distribution does not work. One needs to invoke inhomogeneous distribution of melt if one wishes to explain observed geophysical anomalies by partial melting. However, most of models with inhomogeneous melt distribution are either inconsistent with some geophysical observations or the assumed structures are geodynamically unstable and/or implausible. Therefore partial melt models for the geophysical anomalies of the asthenosphere are unlikely to be valid, and some solid-state mechanisms must be invoked. The situation is different in the deep upper mantle where melt could completely wet grain-boundaries and continuous production of melt is likely by “dehydration melting” at around 410-km. In the ultralow velocity zone in the D? layer, where continuous production of melt is unlikely, easy separation of melt from solid precludes the partial melt model for low velocities and high electrical conductivity unless the melt density is extremely close to the density of co-existing solid minerals or if there is a strong convective current to support the topography of the ULVZ region. Compositional variation such as Fe-enrichment is an alternative cause for the anomalies in the D? layer.

Karato, Shun-ichiro

2014-03-01

207

Accident progression event tree analysis for postulated severe accidents at N Reactor  

SciTech Connect

A Level II/III probabilistic risk assessment (PRA) has been performed for N Reactor, a Department of Energy (DOE) production reactor located on the Hanford reservation in Washington. The accident progression analysis documented in this report determines how core damage accidents identified in the Level I PRA progress from fuel damage to confinement response and potential releases the environment. The objectives of the study are to generate accident progression data for the Level II/III PRA source term model and to identify changes that could improve plant response under accident conditions. The scope of the analysis is comprehensive, excluding only sabotage and operator errors of commission. State-of-the-art methodology is employed based largely on the methods developed by Sandia for the US Nuclear Regulatory Commission in support of the NUREG-1150 study. The accident progression model allows complex interactions and dependencies between systems to be explicitly considered. Latin Hypecube sampling was used to assess the phenomenological and systemic uncertainties associated with the primary and confinement system responses to the core damage accident. The results of the analysis show that the N Reactor confinement concept provides significant radiological protection for most of the accident progression pathways studied.

Wyss, G.D.; Camp, A.L.; Miller, L.A.; Dingman, S.E.; Kunsman, D.M. (Sandia National Labs., Albuquerque, NM (USA)); Medford, G.T. (Science Applications International Corp., Albuquerque, NM (USA))

1990-06-01

208

Molecular dynamics simulation study of the melting of Pd-Pt nanoclusters  

NASA Astrophysics Data System (ADS)

Bimetallic nanoclusters are of interest because of their utility in catalysis and sensors. The thermal characteristics of bimetallic Pt-Pd nanoclusters of different sizes and compositions were investigated through molecular dynamics simulations using quantum Sutton-Chen (QSC) many-body potentials. Monte Carlo simulations employing the bond order simulation model were used to generate minimum energy configurations, which were utilized as the starting point for molecular dynamics simulations. The calculated initial configurations of the Pt-Pd system consisted of surface segregated Pd atoms and a Pt-rich core. Melting characteristics were studied by following the changes in potential energy and heat capacity as functions of temperature. Structural changes accompanying the thermal evolution were studied by the bond order parameter method. The Pt-Pd clusters exhibited a two-stage melting: surface melting of the external Pd atoms followed by homogeneous melting of the Pt core. These transitions were found to depend on the composition and size of the nanocluster. Melting temperatures of the nanoclusters were found to be much lower than those of bulk Pt and Pd. Bulk melting temperatures of Pd and Pt simulated using periodic boundary conditions compare well with experimental values, thus providing justification for the use of QSC potentials in these simulations. Deformation parameters were calculated to characterize the structural evolution resulting from diffusion of Pd and Pt atoms. The results indicate that in Pd-Pt clusters, Pd atoms prefer to remain at the surface even after melting. In addition, Pt also tends to diffuse to the surface after melting due to reduction of its surface energy with temperature. This mixing pattern is different from those reported in some of the earlier studies on melting of bimetallics.

Sankaranarayanan, Subramanian K. R. S.; Bhethanabotla, Venkat R.; Joseph, Babu

2005-05-01

209

Why does salt melt ice?  

NSDL National Science Digital Library

This tutorial on the chemical interaction between salt and ice explains how molecules on the surface of the ice escape into the water (melting), and how molecules of water are captured on the surface of the ice (freezing). It was created by the Chemistry Department at Frostburg State University (no, really).

Senese, Fred

210

Development of Zone Melting Furnace  

Microsoft Academic Search

A mirror furnace (Image Furnace (IMF)) for the First Material Processing Test (FMPT) project had been successfully developed in 1986. The IMF will be launched by the space shuttle 'Endeavor' on September, 1992. Based on the experience of the IMF development, an improved mirror furnace (Zone Melting Furnace (ZMF)) is now being developed as experimental equipment for the Japanese Experiment

Shinichi Yoda; Kiwao Shibukawa; Keishi Murakami; Kazumori Hama; Kiyoshi Tanaka; Takao Yokota; Hiroshi Nishimura; Seiichi Takasu

1992-01-01

211

Plama Torches Melt the Rock  

USGS Multimedia Gallery

Plasma torches at Zybek Advanced Products blaze at over 37,000 degrees Fahrenheit, melting the rock mixture. __________ The USGS has created man-made moon dirt, or regolith, to help NASA prepare for upcoming moon explorations. Four tons of the simulant is expected to be made by this summer of 2009...

2009-05-26

212

Water solubility in trachytic melts  

Microsoft Academic Search

New data on water solubility in trachytic melts at pressures from 20 to 200 MPa and 850 °C are reported. Three trachytes, which differ mainly in Na\\/K ratio, were studied. The glasses obtained from water saturated experiments were analysed using both infrared spectroscopy (FTIR) and Karl Fischer Titration (KFT). The independent KFT data on total water contents were used to

V. Di Matteo; M. R. Carroll; H. Behrens; F. Vetere; R. A. Brooker

2004-01-01

213

Batch calcination studies: melt formation  

Microsoft Academic Search

It is shown that the formation of a meltable calcine by batch calcination of an acidic waste solution containing primary sodium, iron, and aluminum sulfate and nitrate can be predicted. Calcine melting at temperatures less than 900°C can be correlated with the sodium to metal ion ratio and the sulfate to salt nitrate ratio. The minor constituents present in the

Shefcik

1961-01-01

214

Water storage and early hydrous melting of the Martian mantle  

NASA Astrophysics Data System (ADS)

We report an experimental investigation of the near-solidus phase equilibria of a water-saturated analog of the Martian mantle. Experiments were performed at low temperatures (700-920 °C) and high pressure (4-7 GPa) using multi-anvil apparatus and piston cylinder device (4 GPa). The results of this study are used to explore the role of water during early melting and chemical differentiation of Mars, and to further our understanding of the near-solidus behavior in planetary mantle compositions at high pressure. Water has a significant effect on the temperature of melting and, therefore, on accretion and subsequent differentiation processes. Experiments locate the wet solidus at ?800 °C, and is isothermal between 4 GPa and 7 GPa. The Martian primitive mantle can store significant amounts of water in hydrous minerals stable near the solidus. Humite-group minerals and phase E represent the most abundant hydrous minerals stable in the 4-7 GPa pressure range. The amount of water that can be stored in the mantle and mobilized during melting ranges from 1 to up to 4 wt% near the wet solidus. We discuss thermal models of Mars accretion where the planet formed very rapidly and early on in solar system history. We incorporate the time constraint of Dauphas and Pourmand (2011) that Mars had accreted to 50% of its present mass in 1.8 Myr and include the effects of 26Al radioactive decay and heat supplied by rapid accretion. When accretion has reached 30% of Mars current mass (?70% of its present size), melting starts, and extends from 100 to 720 km depth. Below this melt layer, water can still be bound in crystalline solids. The critical stage is at 50% accretion (?80% of its size), where Mars is above the wet and dry solidi with most of its interior melted. This is earlier in the accretion process than what would be predicted from dry melting. We suggest that water may have promoted early core formation on Mars and rapidly extended melting over a large portion of Mars interior.

Pommier, A.; Grove, T. L.; Charlier, B.

2012-06-01

215

Who Done It? Or what's that brown fuzzy stuff on my plum? (Koch's Postulates for Proof of Pathogenicity)  

NSDL National Science Digital Library

This resource demonstrates how plant pathologists and microbiologists determine what pathogens cause disease in plants or animals. In this lab students will learn about Kochs Postulates, the critical steps used to prove that a particular microbe is the cause of a specific disease in a host organism (plant or animal). This lesson is suitable for grades 7-12 and does not require the purchase or maintenance of special cultures. A simplified exercise, without cultures, to demonstrate the Germ Theory also is described.

Claudia A. Jasalavich (Nashua, NH; )

2001-11-28

216

A Postulated Planetary Collision, the Terrestrial Planets, the Moon and Smaller Solar-System Bodies  

NASA Astrophysics Data System (ADS)

In a scenario produced by the Capture Theory of planetary formation, a collision between erstwhile solar-system giant planets, of masses 798.75 and 598.37 M ?, is simulated using smoothed-particle hydrodynamics. Due to grain-surface chemistry that takes place in star-forming clouds, molecular species containing hydrogen, with a high D/H ratio taken as 0.01, form a layer around each planetary core. Temperatures generated by the collision initiate D-D reactions in these layers that, in their turn, trigger a reaction chain involving heavier elements. The nuclear explosion shatters and disperses both planets, leaving iron-plus-silicate stable residues identified as a proto-Venus and proto-Earth. A satellite of one of the colliding planets, captured or retained by the proto-Earth core, gave the Moon; two massive satellites released into heliocentric orbits became Mercury and Mars. For the Moon and Mars, abrasion of their surfaces exposed to collision debris results in hemispherical asymmetry. Mercury, having lost a large part of its mantle due to massive abrasion, reformed to give the present high-density body. Debris from the collision gave rise to asteroids and comets, much of the latter forming an inner reservoir stretching outwards from the inner Kuiper Belt that replenishes the Oort Cloud when it is depleted by a severe perturbation. Other features resulting from the outcome of the planetary collision are the relationship of Pluto and Triton to Neptune, the presence of dwarf planets and light-atom isotopic anomalies in meteorites.

Woolfson, M. M.

2013-11-01

217

Ethics CORE  

NSDL National Science Digital Library

The Ethics CORE Digital Library, funded by the National Science Foundation, "brings together information on best practices in research, ethics instruction and responding to ethical problems that arise in research and professional life." It's a remarkable site where visitors can make their way through ethics resources for dozens of different professions and activities. The Resources by Discipline area is a great place to start. Here you will find materials related to the biological sciences, business, computer & information science, along with 14 additional disciplines. The Current News area is a great place to learn about the latest updates from the field. Of note, these pieces can easily be used in the classroom or shared with colleagues. The dynamism of the site can be found at the Interact with Ethics CORE area. Active learning exercises can be found here, along with instructional materials and visitors' own lessons learned.

218

Assessment of the Environmental Impact of Tritium Release from Wolsong Tritium Removal Facility at the Postulated Accident  

SciTech Connect

In Korea, Wolsong Tritium Removal Facility (WTRF) is scheduled to begin operation in 2005 to reduce the amount of tritium generated in the moderator and coolant. The objective of this study is to evaluate the environmental impact of tritium released from WTRF in the postulated accident. In order to achieve this, a computer code was developed at KAIST (Korea Advanced Institute of Science and Technology). This code can be used to evaluate the individual and public dose with the source term. This source term can represent not only the concentration of tritium that will be stored at the long term tritium storage vault located in the underground of WTRF building but also may be released to the environment from the WTRF online system by variously postulated accidents. To validate this code, calculated results were compared with the previous reference under the same assumption. Even if the most severe postulated accident that the tritium may be released through the fracture of the storage vault was occurred, the result of individual dose at the exclusion area boundary is turned out to be within the radiation dose limit.

Yook, Daesik [Korea Advanced Institute of Science and Technology (Korea, Republic of); Lee, KunJai [Korea Advanced Institute of Science and Technology (Korea, Republic of); Chung, Hongsuk [Korea Atomic Energy Research Institute (Korea, Republic of)

2005-07-15

219

Volatilization of Fission Products from Metallic Melts in the Melt-Dilute Treatment Technology Development for Al-Based DOE Spent Nuclear Fuels  

SciTech Connect

The melt-dilute treatment technology is being developed to facilitate the ultimate disposition of highly enriched Al-Base DOE spent nuclear fuels in a geologic repository such as that proposed for Yucca Mountain. Currently, approximately 28 MTHM is expected to be returned to the Savannah River Site from domestic and foreign research reactors. The melt-dilute treatment technology will melt the fuel assemblies to reduce their volume and alloys them with depleted uranium to isotopically dilute the 235U concentration. The resulting alloy is cast into a form for long term geologic repository storage. Benefits accrued from the melt-dilute process include the potential for significant volume reduction; reduced criticality potential, and proliferation concerns. A critical technology element in the development of the melt-dilute process is the development of offgas system requirements. The volatilization of radioactive species during the melting stage of the process primarily constitutes the offgas in this process. Several of the species present following irradiation of a fuel assembly have been shown to be volatile or semi-volatile under reactor core melt-down conditions. Some of the key species that have previously been studied are krypton, iodine, and cesium. All of these species have been shown to volatilize during melting experiments however, the degree to which they are released is highly dependent upon atmosphere, fuel burnup, temperature, and fuel composition. With this in mind an analytical and experimental program has been undertaken to assess the volatility and capture of species under the melt-dilute operating conditions.

Adams, T.

1999-11-18

220

EXPERIMENTAL AND COMPUTATIONAL INVESTIGATION OF SNOW MELTING  

E-print Network

EXPERIMENTAL AND COMPUTATIONAL INVESTIGATION OF SNOW MELTING ON HEATED HORIZONTAL SURFACES By SEAN INVESTIGATION OF SNOW MELTING ON HEATED HORIZONTAL SURFACES Thesis Approved: Dean of the Graduate College Thesis..............................................................................................................5 2.3 Snow/Ice Physical Properties

221

Confirmation of a meteoritic component in impact-melt rocks of the Chesapeake Bay impact structure, Virginia, USA - Evidence from osmium isotopic and PGE systematics  

Microsoft Academic Search

The osmium isotope ratios and platinum-group element (PGE) concentrations of impact-melt rocks in the Chesapeake Bay impact structure were determined. The impact-melt rocks come from the cored part of a lower-crater section of suevitic crystalline-clast breccia in an 823 m scientific test hole over the central uplift at Cape Charles, Virginia. The 187Os\\/188Os ratios of impact-melt rocks range from 0.151

Seung Ryeol Lee; J. Wright Horton; Richard J. Walker

2006-01-01

222

Water Storage and Early Hydrous Melting of the Martian Mantle  

NASA Astrophysics Data System (ADS)

We present an experimental investigation of a water-saturated analogue of the Martian mantle at low temperature (700-920°C) and high pressure (4-7GPa) using a multi-anvil apparatus. The results of this study are used to explore the role of water in the early chemical differentiation of the planet, and to further our understanding of the near-solidus behavior in planetary mantle compositions at high pressure. Water has a significant effect on the temperature of melting and therefore, on accretion and subsequent differentiation processes. Results show that the wet solidus reaction, located at ~800°C, remains at that temperature between 4GPa and 7GPa. The Martian primitive mantle can store significant amounts of water in hydrous minerals stable near the solidus. Humite minerals and phase E represent the most abundant hydrated minerals stable under pressure. The amount of water that can be stored in the mantle and mobilized during melting ranges from 1 to up to 4wt% at the wet solidus. Hydrous melt has also been analyzed in an experiment at 920°C and 5.2GPa and is roughly andesitic, consistent with the findings of others that partial melting of peridotite produces high silica melts. Based on our experimental data and considering both impact and radioactive heat sources, we propose a thermal model of Mars accretion. We assume that Mars formed very rapidly (3.6 Myr or less according to recent studies) and accreted initially from a mix of chondrites (85%H, 11%CV, 4%CI) that contain a bulk water content of 1.1 wt.% H2O. Because Mars accreted quickly and early in solar system history, 26Al decay played an important role in the thermal evolution of the planet. We found that at 20% of its present mass (corresponding to ~60% of its size), the planet is cool enough to retain the water stored in hydrous minerals. At 30% (~70% of its size), melting starts at -but is not limited to- a shallow depth (1-3GPa) and water can still be bound in crystalline solids. The critical stage is at 50% (~80% of its size), where Mars is now above the wet and dry solidi with most of its interior melted. Water allows melting to occur earlier in the accretion process and the presence of water promotes the formation of a significant amount of melt, contrasting with dry accretion scenarios. Interestingly, the 50 % accretion step matches with the time estimated for core formation by recent Hf/W isotopic studies [1]. Therefore, we suggest that water may have promoted early core formation on Mars and rapidly extended melting over a large portion of Mars interior. [1] Dauphas, N., Pourmand, A., 2011. Hf-W-Th evidence for rapid growth of Mars and its status as a planetary embryo. Nature, 473, doi:10.1038/nature10077.

Pommier, A.; Grove, T. L.; Charlier, B.

2011-12-01

223

Differentiation and core formation in accreting planetesimals  

NASA Astrophysics Data System (ADS)

Aims: The compositions of meteorites and the morphologies of asteroid surfaces provide strong evidence that partial melting and differentiation were widespread among the planetesimals of the early solar system. However, it is not easily understood how planetesimals can be differentiated. To account for significantly smaller radii, masses, gravity and accretion energies early, intense heat sources are required, e.g. the short-lived nuclides 26Al and 60Fe. Here, we investigate the process of differentiation and core formation in accreting planetesimals taking into account the effects of sintering, melt heat transport via porous flow and redistribution of the radiogenic heat sources. Methods: We use a spherically symmetric one-dimensional model of a partially molten planetesimal consisting of iron and silicates, which considers the accretion by radial growth. The common heat conduction equation has been modified to consider also melt segregation. In the initial state, the planetesimals are assumed to be highly porous and consist of a mixture of Fe,Ni-FeS and silicates consistent to an H-chondritic composition. The porosity change due to the so called hot pressing is simulated by solving a corresponding differential equation. Magma segregation of iron and silicate melt is treated according to the flow in porous media theory by using the Darcy flow equation and allowing a maximal melt fraction of 50%. Results: We show that the differentiation in planetesimals depends strongly on the formation time, accretion duration, and accretion law and cannot be assumed as instantaneous. Iron melt segregation starts almost simultaneously with silicate segregation and lasts between 0.4 and 10 Ma. The degree of differentiation varies significantly and the most evolved structure consists of an iron core, a silicate mantle, which are covered by an undifferentiated but sintered layer and an undifferentiated and unsintered regolith - suggesting that chondrites and achondrites can originate from the same parent body.

Neumann, W.; Breuer, D.; Spohn, T.

2012-07-01

224

Proton spin dynamics in polymer melts: new perspectives for experimental investigations of polymer dynamics  

E-print Network

Significant progress was made in recent years in the understanding of the proton spin kinetics in polymer melts. Generally, the proton spin kinetics is determined by intramolecular and intermolecular magnetic dipole-dipole contributions of proton spins. During many decades it was postulated that the main contribution is a result of intramolecular magnetic dipole-dipole interactions of protons belonging to the same polymer segment. It appears that this postulate is far from reality. The relative weights of intra- and intermolecular contributions are time dependent and sensitive to details of polymer chain dynamics. It is shown that for isotropic models of polymer dynamics the influence of the intermolecular magnetic dipole-dipole interactions increases faster with increasing evolution time (i.e. decreasing frequency) than the corresponding influence of the intramolecular counterpart. On the other hand, an inverted situation is predicted by the tube-reptation model: here the influence of the intramolecular magnetic dipole-dipole interactions increases faster with time than the contribution from intermolecular interactions. The intermolecular contribution in the proton relaxation of polymer melts can experimentally be isolated using the isotope dilution technique and this opens a new perspective for experimental investigations of polymer dynamics by proton NMR.

N. Fatkullin; S. Stapf; M. Hofmann; R. Meierc; E. A. Roessler

2014-05-25

225

Melting, freezing, and coalescence of gold nanoclusters  

Microsoft Academic Search

We present a detailed molecular-dynamics study of the melting, freezing, and coalescence of gold nanoclusters within the framework of the embedded-atom method. Concerning melting, we find the process first to affect the surface (``premelting''), then to proceed inwards. The curve for the melting temperature vs cluster size is found to agree reasonably well with predictions of phenomenological models based on

Laurent J. Lewis; Pablo Jensen; Jean-Louis Barrat

1997-01-01

226

Melt-spinning (Materials Preparation Center)  

SciTech Connect

Melt-spinning is a method used for producing amorphous ribbon, which can then be converted to powder. The quality of the ribbon is controlled by several processing factors. This video shows the melt stream, melt pool, and ribbon formation in slow motion.

None

2010-01-01

227

Planetary science. Shock compression of stishovite and melting of silica at planetary interior conditions.  

PubMed

Deep inside planets, extreme density, pressure, and temperature strongly modify the properties of the constituent materials. In particular, how much heat solids can sustain before melting under pressure is key to determining a planet's internal structure and evolution. We report laser-driven shock experiments on fused silica, ?-quartz, and stishovite yielding equation-of-state and electronic conductivity data at unprecedented conditions and showing that the melting temperature of SiO2 rises to 8300 K at a pressure of 500 gigapascals, comparable to the core-mantle boundary conditions for a 5-Earth mass super-Earth. We show that mantle silicates and core metal have comparable melting temperatures above 500 to 700 gigapascals, which could favor long-lived magma oceans for large terrestrial planets with implications for planetary magnetic-field generation in silicate magma layers deep inside such planets. PMID:25613887

Millot, M; Dubrovinskaia, N; ?ernok, A; Blaha, S; Dubrovinsky, L; Braun, D G; Celliers, P M; Collins, G W; Eggert, J H; Jeanloz, R

2015-01-23

228

Experimental investigation of stress-driven melt segregation and electrical conductivity of partially molten mantle rocks with low carbonated melt fractions  

NASA Astrophysics Data System (ADS)

The mechanical and thermal properties of the mantle are of prime concern since they play a major part in Earth's global geodynamics such as mantle convection, crustal flow and plate shifting. Several magnetotelluric and seismic campaigns, such as the MELT experiment, have shown high conductivity and low velocity zones that can be interpreted in terms of partial melting. Depending on the geological context, interactions between partial melting, deformation and melt-rock reactions can influence the nature of the produced melt and its segregation from the host rock. Recent experimental studies have shown that the high conductivity zones beneath mid-ocean ridges are best explained by low carbonated melt fractions (< 1 wt.%). Although recent experimental and theoretical studies have shown that shear stress gradients in initially homogeneous basaltic melt-bearing aggregates promote melt redistribution (Takei and Holtzman, 2009; Caricchi et al., 2011), little is known on the impact of shear stress gradients in samples containing less than 1 wt. % carbonated melts. All these studies lead to unanswered questions: how do these gradients influence melt mobility and therefore melt interconnectivity in partially molten samples with < 1 wt. % melt? How do low melt fractions impact on physical properties such as the bulk viscosity of partially molten rocks, on the deformation regime? How does melt segregation resulting from an applied shear stress impact on electrical and seismic anisotropy? To answer these questions, we have synthesized by spark plasma sintering large volume samples of forsterite and enstatite aggregates containing an initial homogeneous distribution of Na-rich carbonated melts (1 wt. %), which will be deformed under torsion in an internally heated Paterson-type apparatus coupled to an impedance spectrometer. These experiments will enable us to directly measure the bulk viscosity of these partially molten samples as well as collect continuous electrical measurements during deformation. We will similarly investigate carbonated melt migration velocities by deforming samples under torsion in a source/sink geometry. The source consisting of Na-rich carbonated melt, which will form the inner core, will be coupled with a nominally melt-free sink of forsterite and enstatite forming the outer ring. Our novel approach consisting in an internally coherent set of petrological-geophysical-rheological constraints will enable us to better interpret the anomalies detected by geophysical probing beneath mid-ocean ridges. Takei, Y., Holtzman, B., 2009. Viscous constitutive relations of solid-liquid composites in terms of grain boundary contiguity: 3. Causes and consequences of viscous anisotropy, J. Geophys. Res. 114, B06207, doi:10.1029/2008JB005852. Caricchi, L., Gaillard, F., Mecklenburgh, J., Le Trong, E., 2011. Experimental determination of electrical conductivity during deformation of melt-bearing olivine aggregates: Implications for electrical anisotropy in the oceanic low velocity zone. Earth Planet. Sci. Lett. 302, 81-94.

Hashim, Leila; Gaillard, Fabrice; Gardes, Emmanuel; Scaillet, Bruno

2013-04-01

229

Application of In-Flight Melting Technology by RF Induction Thermal Plasmas to Glass Production  

NASA Astrophysics Data System (ADS)

An innovative in-flight glass melting technology with induced thermal plasmas was developed for the purpose of energy conservation and environmental protection. Two-dimensional modeling was used to simulate the thermofluid fields in the plasma torch. The in-flight melting behavior of glass raw material was investigated by various analysis methods. Results showed that the plasma temperature was up to 10000 K with a maximum velocity over 30 m/s, which made it possible to melt the granulated glass raw material within milliseconds. The carbonates in the raw material decomposed completely and the compounds in the raw material attainted 100% vitrification during the in-flight time from the nozzle exit to substrate. The particle melting process is similar to the unreacted-core shrinking model.

Yao, Yaochun; M. Hossain, M.; Watanabe, T.; Funabiki, F.; Yano, T.

2008-06-01

230

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

Microsoft Academic Search

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

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

1994-01-01

231

Coeval Ar40\\/Ar39 ages of 65.0 million years ago from Chicxulub crater melt rock and Cretaceous-Tertiary boundary tektites  

Microsoft Academic Search

Ar-40\\/Ar-39 dating of drill-core samples of a glassy melt rock recovered from beneath a massive impact breccia contained with the 180-kilometer subsurface Chicxulub crater yields well-behaved incremental heating spectra with a mean plateau age of 64.98 +\\/- 0.05 million years ago (Ma). The glassy melt rock of andesitic composition was obtained from core 9 (1390 to 1393 meters) in the

Carl C. Swisher III; Jose M. Grajales-Nishimura; Alessandro Montanari; Stanley V. Margolis; Philippe Claeys; Walter Alvarez; Paul Renne; Esteban Cedillo-Pardo; Florentin J.-M. R. Maurrasse; Garniss H. Curtis; J. Smit; M. O. McWilliams

1992-01-01

232

The behavior of ANGRA 2 nuclear power plant core for a small break LOCA simulated with RELAP5 code  

NASA Astrophysics Data System (ADS)

This work discusses the behavior of Angra 2 nuclear power plant core, for a postulate Loss of Coolant Accident (LOCA) in the primary circuit for Small Break Loss Of Coolant Accident (SBLOCA). A pipe break of the hot leg Emergency Core Cooling System (ECCS) was simulated with RELAP 5 code. The considered rupture area is 380 cm2, which represents 100% of the ECCS pipe flow area. Results showed that the cooling is enough to guarantee the integrity of the reactor core.

Sabundjian, Gaianê; Andrade, Delvonei A.; Belchior, Antonio, Jr.; da Silva Rocha, Marcelo; Conti, Thadeu N.; Torres, Walmir M.; Macedo, Luiz A.; Umbehaun, Pedro E.; Mesquita, Roberto N.; Masotti, Paulo H. F.; de Souza Lima, Ana Cecília

2013-05-01

233

Martian mantle primary melts - An experimental study of iron-rich garnet lherzolite minimum melt composition  

NASA Technical Reports Server (NTRS)

The minimum melt composition in equilibrium with an iron-rich garnet lherzolite assemblage is ascertained from a study of the liquidus relations of iron-rich basaltic compositions at 23 kb. The experimentally determined primary melt composition and its calculated sodium content reveal that Martian garnet lherzolite minimum melts are picritic alkali olivine basalts. Martian primary melts are found to be more picritic than terrestrial garnet lherzolite primary melts.

Bertka, Constance M.; Holloway, John R.

1988-01-01

234

Fe-based nanocrystalline powder cores with ultra-low core loss  

NASA Astrophysics Data System (ADS)

Melt-spun amorphous Fe73.5Cu1Nb3Si15.5B7 alloy strip was crushed to make flake-shaped fine powders. The passivated powders by phosphoric acid were mixed with organic and inorganic binder, followed by cold compaction to form toroid-shaped bonded powder-metallurgical magnets. The powder cores were heat-treated to crystallize the amorphous structure and to control the nano-grain structure. Well-coated phosphate-oxide insulation layer on the powder surface decreased the the core loss with the insulation of each powder. FeCuNbSiB nanocrystalline alloy powder core prepared from the powder having phosphate-oxide layer exhibits a stable permeability up to high frequency range over 2 MHz. Especially, the core loss could be reduced remarkably. At the other hand, the softened inorganic binder in the annealing process could effectively improve the intensity of powder cores.

Wang, Xiangyue; Lu, Zhichao; Lu, Caowei; Li, Deren

2013-12-01

235

Refining of niobium by levitation melting technique  

SciTech Connect

The refining behavior of niobium, produced by an aluminothermic reduction reaction of Nb/sub 2/O/sub 5/, is studied using an electromagnetic levitation and melting technique. Under experimental conditions, significant refinement of niobium thermite occurs during levitation melting. Residence time plays a significant role in the refining process, and the refining kinetics, during levitation melting, correlate well with the approximate equations for desorption of nitrogen and carbon. The purity of the levitation-melted product is compared to that of niobium processed by the conventional EB drip-melting process.

Asfahani, R.I.; Abbaschian, G.J.; Murty, Y.V.; Patchett, J.A.; Shahapurkar, D.S.

1985-04-01

236

Theory of melted flux liquids  

NASA Astrophysics Data System (ADS)

Novel intermediate flux states should be accessible in high-Tc superconductors, where it appears that the conventional Abrikosov flux lattice is melted over a significant portion of the (H,T) plane. We discuss the Lindemann criterion, and argue that fluctuations in a flux crystal are highly anisotropic, so that an asymptotically two-dimensional melting transition is possible as the shear modulus drops toward zero for many sample geometries and field orientations. We then describe the ``entangled flux liquid'' which arises at high-flux densities or thick samples. The statistical mechanics of this liquid is closely related to the physics of two-dimensional superfluids. The decay of vortex line correlations along the field direction is controlled by the superfluid excitation spectrum. A renormalization-group analysis shows how line wandering changes the nature of the B(H) constitutive relation near Hc1. We suggest that a heavily entangled flux liquid could exhibit a shear modulus on experimental time scales, in analogy with viscoelastic behavior in dense polymer melts.

Nelson, David R.; Seung, H. Sebastian

1989-05-01

237

Fe 2+-Mg partitioning between olivine and basaltic melts: Applications to genesis of olivine-phyric shergottites and conditions of melting in the Martian interior  

NASA Astrophysics Data System (ADS)

Fe 2+-Mg partitioning between olivine and basaltic melt, expressed by the exchange coefficient, K Dol - melt Fe - Mg [=( XmeltMg/ XolivineMg)/( XmeltFe 2 + / XolivineFe 2 + )] is widely used to check if a rock composition may represent a mantle-derived magma, to demonstrate equilibrium between coexisting olivine and groundmass in mafic-ultramafic systems, both in experiments and in natural assemblages, and to constrain liquid lines of descent where olivine is the dominant fractionating phase. However, K Dol - melt Fe - Mg of 0.30, which is appropriate for understanding most terrestrial basalts petrogenesis may not apply for Martian basalts as K Dol - melt Fe - Mg is known to depend strongly on the melt compositions and Martian systems produce basalts that are distinctly richer in iron than terrestrial basalts. Here we compiled experimental data on olivine-melt equilibria of Martian and terrestrial basalt compositions to parameterize the effect of magma composition on K Dol - melt Fe - Mg and derive the K Dol - melt Fe - Mg applicable for Martian magmatic systems. We find that the equilibrium relationship between olivine and basaltic melt in Martian systems is described by K Dol - melt Fe - Mg of 0.35 ± 0.01. Applying the newly parameterized values of K Dol - melt Fe - Mg to olivine-phyric shergottites suggest that the only known Martian meteorites where the olivine cores and the bulk composition are in equilibrium and therefore could represent magma compositions are: Yamato 980459, NWA 5789, and NWA 2990. LAR 06319, which has been suggested to represent a near magma composition, actually contains ~ 11 wt.% excess olivine. All other ol-phyric shergottites contain significant excess olivine (20-52 wt.%). Further, assuming that the basalts analyzed by the Mars Exploration Rovers at Gusev crater and the Bounce Rock in Meridiani Planum lie on olivine control lines, we have used our newly parameterized K Dol - melt Fe - Mg to estimate primary magmas in equilibrium with the model Martian mantle. Application of geothermobarometers to new primitive magma compositions suggest that basalt generation in the Martian mantle occurs at greater depths and higher temperatures than previously thought.

Filiberto, Justin; Dasgupta, Rajdeep

2011-04-01

238

Rheology of Earth's Inner Core  

NASA Astrophysics Data System (ADS)

Here I use mineral physics constraints to evaluate the viscosity and creep mechanisms of iron at the conditions of the inner core. At low to intermediate stresses and temperatures near the melting point solid materials may deform by any of three mechanisms: power law creep, diffusion creep and Harper-Dorn creep. Both power law and Harper-Dorn creep are dislocation processes, and the transition between the two occurs at a stress level on the order of the Peierls stress, with power law creep dominating at higher stresses. The transition stress is predicted to be ~3 MPa for hcp-Fe at inner core conditions, which is far higher than the stresses of ~102 to 103 Pa expected from magnetic or gravitational forces. Harper-Dorn creep dominates diffusion creep above a certain grain size, which is predicted to be ~200 microns for hcp-Fe. At the high temperatures and low stresses of the inner core the grain size is expected to be several orders of magnitude larger than the transition value. Harper-Dorn creep is therefore predicted to be the dominant deformation mechanism in the inner core. Harper-Dorn creep is accomplished by the motion of dislocations and can lead to strong lattice preferred orientation. The viscosity in this regime is Newtonian and is given by ? = (kT)/(ADb) where k is Boltzmann's constant, T is temperature, D is the self-diffusion coefficient, b is the Burgers vector and A is a dimensionless constant predicted to have a value of ~1.7 x 1011 for hcp-Fe. No diffusion data exist for hcp-Fe, but metals with similar structure all have nearly the same self-diffusion coefficient at the same homologous temperature. Assuming an inner core temperature of 5700 K and melting temperature for pure iron of 6200 K, the diffusivity is predicted to be ~4 × 10-13 m2 s-1 and the viscosity ~6 × 1013 Pa s. The corresponding strain rate for a shear stress of 100 Pa is ~2 × 10-12 s-1, implying that large strains are possible on timescales less than 100,000 years. It is therefore likely that the anisotropy in the inner core is the result of lattice preferred orientation developed during active or very recent deformation.

van Orman, J. A.

2004-05-01

239

High-Mg carbonatitic melts in diamonds, kimberlites and the sub-continental lithosphere  

NASA Astrophysics Data System (ADS)

The trace elements of high-Mg carbonatitic high-density fluids (HDFs) trapped in six fibrous diamonds from Siberia exhibit patterns that are highly similar to those of Group I kimberlites, but are slightly more fractionated. The patterns of both are similar to the average pattern of post-Archaean xenoliths from the sub-continental lithospheric mantle (SCLM). The Siberian high-Mg carbonatitic HDFs are highly enriched in incompatible elements and have compositions comparable to those of high-Mg HDFs from Kankan, Guinea. However, in detail the latter show depletion of K, Rb, Cs, Nb and Ta and enrichment in Ba, Th, U and LREE relative to the Siberian HDFs. These differences correspond closely to those between the patterns of Group II and Group I kimberlites, respectively. Mixing, fractionation and melting were explored as possible scenarios to explain these similarities and to constrain the possible genetic relationships between HDFs, kimberlites and the SCLM. Addition of 2.5% of Group I kimberlitic magma or 0.5% of the Udachnaya high-Mg HDFs to a depleted peridotite closely reproduces the post-Archaean SCLM pattern. The formation of high-Mg HDFs through fractionation of kimberlitic magma calls for 80% crystallization of olivine, clinopyroxene, garnet, carbonate and ilmenite. However, mismatches in K, Rb, Y and Ho abundances, and absence of the postulated fractionating minerals as inclusions suggest other petrogenetic scenarios are more likely. High-Mg HDFs and kimberlites can be produced by melting of a common source. The pattern of the calculated source for Siberian HDF and Group I kimberlites resembles that of average post-Archean, rather than Archean, SCLM. Batch melting of such a source can produce high-Mg HDFs at 0.5% partial melting and Group I kimberlites at ~ 2%. Kankan HDFs and Group II kimberlites can be produced by 0.1 and 0.8% melting of average Archaean SCLM that carries phlogopite ± Fe-Ti oxides. The close correspondence between the trace-element composition of surface kimberlites and HDFs that were trapped at depth indicates that kimberlitic melts do not change their incompatible trace element contents much on their way to the surface (except for a possible loss of alkalis). The new data on the HDFs suggest a close genetic relation between high-Mg carbonatitic HDFs and kimberlites and reveals the similarity of the trace element of both to that of the post-Archaean SCLM. This similarity may reflect the interaction of such melts with the lithospheric keel, its melting to produce HDF and/or kimberlites or melting of deeper sources that led to formation of HDFs and kimberlite and to widespread metasomatism of the SCLM.

Weiss, Y.; Griffin, W. L.; Bell, D. R.; Navon, O.

2011-09-01

240

Small particle melting of pure metals  

NASA Technical Reports Server (NTRS)

Submicron-sized crystallites of lead, tin, indium and bismuth were melted in situ in the modified specimen chamber of a Siemens transmission e lectron microscope. Melting point and size determinations were made directly from the dark field images of the crystallites. Particles exhibited melting points that decreased with decreasing particle size. A near-linear relationship was observed for the melting point as a function of the reciprocal of the radius. Thermodynamnic expressions based on the significant contributions of the surface energy to the free energy of the system also suggest a linear relation. Other factors, such as shape and surface contamination, were also observed to affect the size-dependent melting of particles. Crystallites of extended platelet shape did not exhibit a significant depression in melting point. Elevated residual gas pressures were found to lessen the melting point depression of spherical particles.

Allen, G. L.; Bayles, R. A.; Gile, W. W.; Jesser, W. A.

1986-01-01

241

Garnet melt viscosity, surface tension and drainage  

NASA Technical Reports Server (NTRS)

Good surface morphology and layer uniformity of LPE-grown Bi YIG films are favored by fast melt removal after growth. Three flux modifying oxides: MoO3, V2O3, and WO3 are compared with respect to their effect on viscosity, surface tension and melt drainage. All three oxides increased the viscosities of Bi-garnet melts, but the viscosities and drainage times of V2O3 and MoO3 modified melts were smaller than those of WO3 modified melts. The liquid-gas surface tension was found to be temperature independent. The drainage process was strongly temperature dependent, 40 to 60 kcal/mol, whereas the viscosities of melts had activation energies of 11 to 16 kcal/mol. Contact angles of 16 + or - 2 deg were measured on frozen melt drops.

Luther, L. C.

1986-01-01

242

Impact melt products of chondritic material  

NASA Astrophysics Data System (ADS)

A large variety of objects in chondritic meteorites formed as a result of impact melting: shock veins, metal-troilite mixtures, metal and sulfide nodules, melt pockets, vugs, agglutinates, glassy and crystalline spherules, and numerous types of melt-rock clasts. The type of object produced in an impact event is related to the interaction of the shock waves with the particular target rock. Impact melting has also affected large portions of several chondrite breccias. Some workers have suggested that various iron meteorites were formed from individual impact melt pools in chondritic regoliths. The Eagle Station Trio pallasites and several ungrouped meteorites may have formed from impact-melted chondritic material. It is also possible that the parent magmas of ureilites were derived from impact-melted metal-rich cabonaceous chondrite material.

Rubin, A. E.

1985-08-01

243

SCDAP/RELAP5 Modeling of Movement of Melted Material Through Porous Debris in Lower Head  

SciTech Connect

A model is described for the movement of melted metallic material through a ceramic porous debris bed. The model is designed for the analysis of severe accidents in LWRs, wherein melted core plate material may slump onto the top of a porous bed of relocated core material supported by the lower head. The permeation of the melted core plate material into the porous debris bed influences the heatup of the debris bed and the heatup of the lower head supporting the debris. A model for mass transport of melted metallic material is applied that includes terms for viscosity and turbulence but neglects inertial and capillary terms because of their small value relative to gravity and viscous terms in the momentum equation. The relative permeability and passability of the porous debris are calculated as functions of debris porosity, particle size, and effective saturation. An iterative numerical solution is used to solve the set of nonlinear equations for mass transport. The effective thermal conductivity of the debris is calculated as a function of porosity, particle size, and saturation. The model integrates the equations for mass transport with a model for the two-dimensional conduction of heat through porous debris. The integrated model has been implemented into the SCDAP/RELAP5 code for the analysis of the integrity of LWR lower heads during severe accidents. The results of the model indicate that melted core plate material may permeate to near the bottom of a 1m deep hot porous debris bed supported by the lower head. The presence of the relocated core plate material was calculated to cause a 12% increase in the heat flux on the external surface of the lower head.

Siefken, Larry James; Harvego, Edwin Allan

2000-04-01

244

SCDAP/RELAP5 modeling of movement of melted material through porous debris in lower head  

SciTech Connect

A model is described for the movement of melted metallic material through a ceramic porous debris bed. The model is designed for the analysis of severe accidents in LWRs, wherein melted core plate material may slump onto the top of a porous bed of relocated core material supported by the lower head. The permeation of the melted core plate material into the porous debris bed influences the heatup of the debris bed and the heatup of the lower head supporting the debris. A model for mass transport of melted metallic material is applied that includes terms for viscosity and turbulence but neglects inertial and capillary terms because of their small value relative to gravity and viscous terms in the momentum equation. The relative permeability and passability of the porous debris are calculated as functions of debris porosity, particle size, and effective saturation. An iterative numerical solution is used to solve the set of nonlinear equations for mass transport. The effective thermal conductivity of the debris is calculated as a function of porosity, particle size, and saturation. The model integrates the equations for mass transport with a model for the two-dimensional conduction of heat through porous debris. The integrated model has been implemented into the SCDAP/RELAP5 code for the analysis of the integrity of LWR lower heads during severe accidents. The results of the model indicate that melted core plate material may permeate to near the bottom of a 1m deep hot porous debris bed supported by the lower head. The presence of the relocated core plate material was calculated to cause a 12% increase in the heat flux on the external surface of the lower head.

L. J. Siefken; E. A. Harvego

2000-04-02

245

Environmental consequences of postulated plutonium releases from Exxon Nuclear MOFP, Richland, Washington, as a result of severe natural phenomena  

SciTech Connect

Potential environmental consequences in terms of radiation dose to people are presented for postulated plutonium releases caused by severe natural phenomena at the Exxon Nuclear Company Mixed Oxide Fabrication Plant (MOFP), Richland, Washington. The severe natural phenomena considered are earthquakes, tornadoes, high straight-line winds, and floods. Maximum plutonium deposition values are given for significant locations around the site. All important potential exposure pathways are examined. The most likely 50-year committed dose equivalents are given for the maximum-exposed individual and the population within a 50-mile radius of the plant. The maximum plutonium deposition values most likely to occur offsite are also given.

Jamison, J.D.; Watson, E.C.

1980-02-01

246

A Monazite-bearing clast in Apollo 17 melt breccia  

NASA Technical Reports Server (NTRS)

A phosphate-rich clast in a pigeonite-plagioclase mineral assemblage occurs in Apollo 17 impact-melt breccia 76503,7025. The clast, measuring 0.9 x 0.4 mm in thin section, contains 3.3 percent (volume) apatite (Ca5P3O12(F,Cl)), 0.8 percent whitlockite (Ca16(Mg,Fe)2REE2P14O56), and trace monazite ((LREE)PO4). Major minerals include 26 percent pigeonite, En53-57FS34-35W08-13, and 69 percent plagioclase, An84-92Ab7-15Oro.6-1.1. Troilite, ilmenite, and other accessory minerals constitute less than 1 percent of the assemblage and Fe-metal occurs along fractures. Also present in the melt breccia as a separate clast is a fragment of felsite. Based on the association of these clasts and their assemblages, a parent lithology of alkali-anorthositic monzogabbro is postulated. Monazite occurs in the phosphate-bearing clast as two less than 10 micron grains intergrown with whitlockite. The concentration of combined REE oxides in monazite is 63.5 percent and the chondrite-normalized REE pattern is strongly enriched in LREE, similar to lunar monazite in 10047,68 and terrestrial monazite. Thorium concentration was not measured in monazite, but based on oxide analyses of approximately 100 percent (including interpolated values for REE not measured), substantial Th concentration is not indicated, similar to monazite in 10047,68. Measured monazite/whitlockite REE ratios are La: 11, Ce: 8, Sm: 3.6, Y: 0.9, and Yb: 0.5. Compositions of monazite and coexisting whitlockite and apatite are given.

Jolliff, Bradley L.

1993-01-01

247

Parallel channel effects and long-term cooling during emergency core cooling in a BWR\\/4  

Microsoft Academic Search

The effectiveness of the core spray cooling system and the low pressure coolant injection system during a design basis accident in a boiling water nuclear reactor (BWR) was investigated. This investigation considered a BWR\\/4 with both intact and broken jet pumps during the short-term and long-term core cooling of a postulated loss of coolant accident (LOCA). The experiments were performed

Fakory

1983-01-01

248

Is formation segregation melts in basaltic lava flows a viable analogue to melt generation in basaltic systems?  

NASA Astrophysics Data System (ADS)

Pahoehoe sheet lobes commonly exhibit a three-fold structural division into upper crust, core and lower crust, where the core corresponds to the liquid portion of an active lobe sealed by crust. Segregations are common in pahoehoe lavas and are confined to the core of individual lobes. Field relations and volume considerations indicate that segregation is initiated by generation of volatile-rich melt at or near the lower crust to core boundary via in-situ crystallization. Once buoyant, the segregated melt rises through the core during last stages of flow emplacement and accumulates at the base of the upper crust. The segregated melt is preserved as vesicular and aphyric, material within well-defined vesicle cylinders and horizontal vesicle sheets that make up 1-4% of the total lobe volume. We have undertaken a detailed sampling and chemical analysis of segregations and their host lava from three pahoehoe flow fields; two in Iceland and one in the Columbia River Basalt Group (CRBG). The Icelandic examples are: the olivine-tholeiite Thjorsa lava (24 cubic km) of the Bardarbunga-Veidivotn volcanic system and mildly alkalic Surtsey lavas (1.2 cubic km) of the Vestmannaeyjar volcanic system. The CRBG example is the tholeiitic ‘high-MgO group' Levering lava (>100? cubic km) of the N2 Grande Ronde Basalt. The thicknesses of the sampled lobes ranges from 2.3 to 14 m and each lobe feature well developed network of segregation structures [1,2,3]. Our whole-rock analyses show that the segregated melt is significantly more evolved than the host lava, with enrichment factors of 1.25 (Thjorsa) to 2.25 (Surtsey) for incompatible trace elements (Ba, Zr). Calculations indicate that the segregation melt was formed by 20 to 50% closed-system fractional crystallization of plagioclase (plus minor pyroxene and/or olivine). A more striking feature is the whole-rock composition of the segregations. In the olivine-tholeiite Thjorsa lava the segregations exhibit quartz tholeiite composition that is identical to the magma compositions produced by the nearby Grimsvotn and Kverkfjoll volcanic systems during the Holocene. The Surtsey segregations have whole-rock composition remarkably similar to the FeTi basalts from adjacent Katla volcanic system, whereas the segregations of the Levering flow are identical to the ‘low-MgO group' basalts of the CRBG. Is this a coincidence or does volatile induced liquid transfer, as inferred for the formation of the segregations, play an important role in magma differentiation in basaltic systems? [1]Thordarson & Self The Roza Member, Columbia River Basalt Group. J Geophys Res - Solid Earth [2] Sigmarsson, et al, 2009. Segregations in Surtsey lavas (Iceland). In Studies in Volcanology: The Legacy of George Walker. Special Publication of IAVCEI No 3. [3] Hartley & Thordarson, 2009, Melt segregations in a Columbia River Basalt lava flow. Lithos

Thordarson, Thorvaldur; Sigmarsson, Olgeir; Hartley, Margaret E.; Miller, Jay

2010-05-01

249

Molecular dynamics simulation of Coulomb explosion, melting and shock wave creation in silicon after an ionization pulse  

SciTech Connect

Strong electronic stopping power of swift ions in a semiconducting or insulating substrate can lead to localized electron stripping. The subsequent repulsive interactions among charged target atoms can cause Coulomb explosion. Using molecular dynamics simulation, we simulate Coulomb explosion in silicon by introducing an ionization pulse lasting for different periods, and at different substrate temperatures. We find that the longer the pulse period, the larger the melting radius. The observation can be explained by a critical energy density model assuming that melting required thermal energy density is a constant value and the total thermal energy gained from Coulomb explosion is linearly proportional to the ionization period. Our studies also show that melting radius is larger at higher substrate temperatures. The temperature effect is explained due to a longer structural relaxation above the melting temperature at original ionization boundary due to lower heat dissipation rates. Furthermore, simulations show the formation of shock waves, created due to the compression from the melting core.

Li, Zhongyu; Shao, Lin, E-mail: lshao@tamu.edu [Fundamental Science on Nuclear Safety and Simulation Technology Laboratory, Harbin Engineering University, Harbin 150001 (China); Chen, Di [Department of Nuclear Engineering, Texas A and M University, College Station, Texas 77843 (United States); Wang, Jing [Department of Materials Science and Engineering, Texas A and M University, College Station, Texas 77843 (United States)

2014-04-14

250

Translation and convection of Earth's inner core  

NASA Astrophysics Data System (ADS)

The image of the inner core growing slowly at the center of the Earth by gradual cooling and solidification of the surrounding liquid outer core is being replaced by the more vigorous image of a ``deep foundry'', where melting and crystallization rates exceed by many times the net growth rate. Recently, a particular mode of convection, called translation, has been put forward as an important mode of inner core dynamics because this mechanism is able to explain the observed East-West asymmetry of P-wave velocity and attenuation (Monnereau et al. 2010). Translation is a pure solid displacement of the inner core material (solid iron) within its envelop, implying crystallization of entering iron on one side of the inner core and melting on the opposite side. Translation is consistent with multiple scattering models of wave propagation. If they do not experience deformation, iron crystals grow as they transit from one hemisphere to the other. Larger crystals constituting a faster and more attenuating medium, a translation velocity of some cm/yr (about ten times the growth rate) is enough to account for the superficial asymmetry observed for P-wave velocity and attenuation, with grains of a few hundred meters on the crystallizing side (West) growing up to a few kilometers before melting on the East side, and a drift direction located in the equatorial plane. Among all hypotheses that have been proposed to account for the seismic asymmetry, translation is the only one based on a demonstrated link between the seismic data and the proposed dynamics, notably through a model of seismic wave propagation. This mechanism was also proposed to be responsible for the formation of a dense layer at the bottom of the outer core, since the high rate of melting and crystallization would release a liquid depleted in light elements at the surface of the inner core (Alboussiere et al 2010). This would explain the anomalously low gradient of P wave velocity in the lowermost 200 km of the outer core. Translation is a particular solution of Navier-Stokes equation with permeable boundary conditions, but depending on the viscosity of the solid core, modes with higher spherical harmonics degree can develop. At low viscosity, these modes can be dominant and dissipate the degree l=1 of thermal heterogeneities. Hence, a viscosity threshold may be expected below which translation cannot take place, thereby constraining the viscosity of iron at inner core conditions. Using a hybrid finite-difference spherical harmonics Navier-Stokes solver, we investigate the interplay between translation and convection in a 3D spherical model with permeable boundary conditions. Our numerical simulations show the dominance of pure translation for viscosities of the inner core higher than 5 x 1018 Pas. Translation is almost completely hampered by convective motions for viscosities lower than 1017 Pas and the phase change becomes an almost impermeable boundary. Between these values, a well developed circulation at the harmonic degree l=1 persists, but composed of localized cold downwellings, a passive upward flow taking place on the opposite side (the melting side). Such a convective structure remains compatible with the seismic asymmetry. Alboussiere, T., Deguen, R., Melzani, M., 2010. Nature 466 (7307), 744-U9. Monnereau, M., Calvet, M., Margerin, L., Souriau, A., 2010. Science 328 (5981), 1014-1017.

Monnereau, M.; Calvet, M.; Margerin, L.; Mizzon, H.; Souriau, A.

2012-12-01

251

Crystallization and melting kinetics of oligomer under confinement  

NASA Astrophysics Data System (ADS)

Crystallization and melting kinetics of oligomer of polyethylene glycol (PEG, Mn=400 g/mol) under confinement was studied by Differential Scanning Calorimetry (DSC). Liquid oligomer was surrounded by polysulfone sheath in core-shell configuration of co-electrospun nanofibers with core diameters in the range of 0.5-1;?m. Oligomer under confinement demonstrates a noticeable decrease in the crystallization and melting temperatures in comparison to the bulk: from -15^oC to -45^oC and from 8^oC to 5^oC, respectively (cooling rate of 5^oC/min). These temperature shifts increase with a decrease in fiber internal diameter. Repeated cooling of the oligomer confined inside nanofibers, after heating up to room temperature results in a decrease in crystallization temperature, whereas bulk oligomer demonstrates an opposite behavior, i.e. an increase of the crystallization temperature. Annealing at 70^oC of bulk oligomer for 5 min results in the same crystallization kinetics at each consequent cooling, thus the thermal history of the system is erased. However, in case of oligomer under confinement annealing even for a period of 30 min at 70^oC did not result in full relaxation of the system. These observations demonstrate suppressed mobility of oligomer molecules within nanofibers, caused by confinement effect.

Gradys, Arkadiusz; Arinstein, Arkadii; Zussman, Eyal

2012-02-01

252

EBR-II core damage potential for double pump faults  

SciTech Connect

The simultaneous failure of the two main coolant pumps in the Experimental Breeder Reactor II (EBR-II) is an event that could conceivably pose a serious threat to reactor safety. Potential core damage due to double pump faults depends on the duration of the pump coastdowns and the response of the reactor shutdown system. Previous studies have investigated the thermal response of cores loaded with Mark-II fuel elements to specific loss-of-flow transients under protected and unprotected conditions. In the current investigation, a systematic study of core damage potential for a core predominantly loaded with Mark-III fuel elements was performed for postulated and idealized double pump faults under protected and unprotected conditions. The analysis was performed with the SASSYS liquid-metal reactor (LMR) systems analysis code. Determination of core damage potential is an important component of a level 1 probabilistic risk assessment of EBR-II. By combining accident sequence frequencies with associated core damage potential, the probability of core damage can be estimated. This paper summarizes the analysis of core damage potential for a group of accident sequences that are anticipated to be important contributors to core damage risk.

Herzog, J.P. (Argonne National Lab., IL (United States))

1990-01-01

253

Polymer Micelles with Crystalline Cores for Thermally Triggered Release  

PubMed Central

Interest in the use of poly(ethylene glycol)-b-polycaprolactone diblock copolymers in a targeted, magnetically triggered drug delivery system has led to this study of the phase behavior of the polycaprolactone core. Four different diblock copolymers were prepared by the ring opening polymerization of caprolactone from the alcohol terminus of poly(ethylene glycol) monomethylether, Mn ~ 2,000. The critical micelle concentration depended on the degree of polymerization for the polycaprolactone block and was in the range of 2.9 to 41 mg/L. Differential scanning calorimetry curves for polymer solutions with a concentration above the critical micelle concentration showed a melting endotherm in the range of 40 to 45°C, indicating the polycaprolactone core was semicrystalline. Pyrene was entrapped in the micelle core without interfering with the ability of the polycaprolactone to crystallize. When the polymer solution was heated above the melting point of the micelle core, the pyrene was free to leave the core. Temperature dependent measurements of the critical micelle concentration and temperature dependent dynamic light scattering showed the micelles remain intact at temperatures above the melting point of the polycaprolactone core. PMID:22726124

Glover, Amanda L.; Nikles, Sarah M.; Nikles, Jacqueline A.; Brazel, Christopher S.; Nikles, David E.

2012-01-01

254

Transcrystalline melt migration and Earth's mantle.  

PubMed

Plate tectonics and volcanism involve the formation, migration, and interaction of magma and gas. Experiments show that melt inclusions subjected to a thermal gradient migrate through olivine crystals, under the kinetic control of crystal-melt interface mechanisms. Exsolved gas bubbles remain fixed and eventually separate from the melt. Scaled to thermal gradients in Earth's mantle and geological times, our results account for the grain-scale segregation of primitive melts, reinterpret CO2-rich fluid inclusions as escaped from melt, and question the existence of a free, deeply percolating fluid phase. Melt migration experiments also allow us to quantify crystal growth kinetics at very low undercoolings in conditions appropriate to many natural systems. PMID:17095697

Schiano, Pierre; Provost, Ariel; Clocchiatti, Roberto; Faure, François

2006-11-10

255

Melting a Sample within TEMPUS  

NASA Technical Reports Server (NTRS)

One of the final runs of the TEMPUS experiment shows heating of a sample on STS-94, July 15, 1997, MET:14/11:01 (approximate) and the flows on the surface. At the point this image was taken, the sample was in the process of melting. The surface of the sample is begirning to flow, looking like the motion of plate tectonics on the surface of a planet. During this mission, TEMPUS was able to run than 120 melting cycles with zirconium, with a maximum temperature of 2,000 degrees C, and was able to undercool by 340 degrees -- the highest temperature and largest undercooling ever achieved in space. The TEMPUS investigators also have provided the first measurements of viscosity of palladium-silicon alloys in the undercooled liquid alloy which are not possible on Earth. TEMPUS (stands for Tiegelfreies Elektromagnetisches Prozessiere unter Schwerelosigkeit (containerless electromagnetic processing under weightlessness). It was developed by the German Space Agency (DARA) for flight aboard Spacelab. The DARA project scientist was Igon Egry. The experiment was part of the space research investigations conducted during the Microgravity Science Laboratory-1R mission (STS-94, July 1-17 1997). DARA and NASA are exploring the possibility of flying an advanced version of TEMPUS on the International Space Station.(176KB JPEG, 1350 x 1516 pixels; downlinked video, higher quality not available) The MPG from which this composite was made is available at http://mix.msfc.nasa.gov/ABSTRACTS/MSFC-0300193.html.

2003-01-01

256

Does Hydrogen Pre-Melt Palladium Clusters?  

Microsoft Academic Search

We use molecular dynamics simulations to study the influence of an ambient atmosphere on the melting process in small palladium clusters, Pd_13, Pd_55 and Pd_147. The onset of the melting transition is monitored by both thermodynamical and structural observables. We find that heating by collisions with inert gas atoms or alternatively using a Nosé-Hoover thermostat both yield very similar melting

Henrik Grönbeck; Arne Rosén; David Tománek; Seonggon Kim

1996-01-01

257

Does hydrogen pre-melt palladium clusters?  

Microsoft Academic Search

We use molecular dynamics simulations to study the influence of an ambient atmosphere on the melting process in the icosahedral palladium clusters Pd13, Pd55 and Pd147. Novel methods to capture the character of melting in finite systems are presented. The signature of melting in clusters heated by inert carrier gas collisions closely resembles that in systems heated in a Nosé-Hoover

H. Gronbeck; D. Tománek; S. G. Kim; A. Rosén

1997-01-01

258

Impact Melt in Small Lunar Highlands Craters  

NASA Technical Reports Server (NTRS)

Impact-melt deposits are a typical characteristic of complex impact craters, occurring as thick pools on the crater floor, ponds on wall terraces, veneers on the walls, and flows outside and inside the rim. Studies of the distribution of impact melt suggested that such deposits are rare to absent in and around small (km to sub-km), simple impact craters. noted that the smallest lunar crater observed with impact melt was approximately 750 m in diameter. Similarly, theoretical models suggest that the amount of melt formed is a tiny fraction (<1%) of the total crater volume and thus significant deposits would not be expected for small lunar craters. LRO LROC images show that impact-melt deposits can be recognized associated with many simple craters to diameters down to approximately 200 m. The melt forms pools on the crater floor, veneer on the crater walls or ejecta outside the crater. Such melt deposits are relatively rare, and can be recognized only in some fresh craters. These observations indicate that identifiable quantities of impact melt can be produced in small impacts and the presence of such deposits shows that the material can be aggregated into recognizable deposits. Further, the present of such melt indicates that small craters could be reliably radiometrically dated helping to constrain the recent impact flux.

Plescia, J. B.; Cintala, M. J.; Robinson, M. S.; Barnouin, O.; Hawke, B. R.

2011-01-01

259

Lunar Simple Crater Impact Melt Volumes  

NASA Technical Reports Server (NTRS)

Impact melt is observed in simple lunar craters having diameters as small as less than 200 m. The presence of ponds of impact melt on the floor of such small craters is interpreted to indicate vertical impacts. Data from the LRO LROC and LOLA experiments allow quantitative estimates of the volume of impact melt in simple crater. Such estimates allow for validation of theoretical models of impact melt generation and examination of target effects. Preliminary data have considerable scatter but are broadly consistent with the models.

Plescia, Jeffrey B.; Barnouin, O. S.; Cintala, Mark J.

2013-01-01

260

Melting and diffusion under nanosecond laser pulse  

NASA Astrophysics Data System (ADS)

A computer simulation study of the melting process in Si, Ge and Sb under an UV laser beam was performed by means of the Finite Element Method (FEM). The melting threshold and melt duration of Si, Ge and Sb crystals were determined and a very good agreement with the Real Time Reflectivity (RTR) measurements is presented. Sb/Ge-Si substrate multilayer systems are also studied. The simulated melt duration was lifted to the experimental data assuming 400 K undercooling of the molten layer prior to the solidification. Ge diffusion in the sample is also presented and the diffusion constant D = 7.5 × 10 -5cm 2/s was determined.

Szyszko, W.

1995-11-01

261

Quantum melting of the vortex lattice in high-Tc superconductors  

NASA Astrophysics Data System (ADS)

In the new high-Tc superconductors both thermal as well as quantum fluctuations are large. The latter smear the vortex cores over a distance of the order of the coherence length and thereby strongly affect the melting transition. Taking account of quantum fluctuations, the shape of the melting line is given by a universal function which is different from a simple power law in 1 - T/Tc and is in excellent agreement with recent experiments on YBa2Cu3O(7-delta) single crystals. Above a crossover field of the order of a few tesla the resulting high-temperature phase is a quantum liquid.

Blatter, Gianni; Ivlev, Boris

1993-04-01

262

Melting of Iron - Light-Element Alloys in the Laser Heated DAC  

NASA Astrophysics Data System (ADS)

Seismic data indicate that the Earth's outer core is ~10% less dense than pure iron at the pertinent conditions of pressure and temperature based on the experimentally determined equation of state of iron (Shanker et al., 2004). This core density deficit can be explained by the presence of a light element component such as H, C, N, O, S or Si, or a mixture of these. Constraints on core composition, phase relations and temperature can be derived from knowledge of the melting relations in relevant iron - light-element systems using a thermodynamic approach coupled with observations from seismology (Helffrich & Kaneshima, 2004). Here we make a progress report on our systematic effort to determine melting phase relations in binary Fe-alloy systems at high pressures using laser-heated DAC techniques. Foils of compressed powder or pre-fabricated chips of Fe alloys are loaded into ~100 micron holes in pre- indented stainless steel or rhenium gaskets. We use a variety of pressure media including sapphire, ruby, alumina gel, NaCl, and Argon, which also serve as thermal insulators. Pressures are measured before and after experiments using the fluorescence shift of ruby. Samples are heated using a 60W Nd:YLF laser with a double- sided heating geometry, and temperatures are measured using standard spectro-radiometric techniques (Walter & Koga, 2004). Melting is deduced from sudden, obvious and repeatable discontinuities in the temperature and emissivity vs. laser power functions as expected from invariant melting. In some cases clear visual observation of melt motion is coincident with these discontinuities. Our results to date show good correspondence with previous measurements where data overlap for Fe, Pt, the Fe-S eutectic, the Fe-Fe3C eutectic and Fe3C. Our melting curve for Fe3C up to ~75 GPa is considerably lower in temperature at high pressures than previously predicted (Wood, 1993), yielding an extrapolated temperature of about 4000 K at the core mantle boundary using a Simon fit to the data. We predict a singular point along the Fe3C melting curve at ~ 20 GPa where congruent melting begins, and possibly another singular point at ~ 70 GPa where the Fe-Fe3C eutectic may intersect the Fe3C liquidus indicating that the eutectic composition has risen to become equal to that of Fe3C. We will present these and other new results.

Lord, O. T.; Walter, M. J.; Helffrich, G.

2007-12-01

263

NREL Scientists Reveal Origin of Diverse Melting Behaviors of Aluminum Nanoclusters (Fact Sheet)  

SciTech Connect

Research reveals active role of cluster symmetries on the size-sensitive, diverse melting behaviors of metallic nanoclusters, providing insight to understanding phase changes of nanoparticles for thermal energy storage. Unlike macroscopic bulk materials, intermediate-sized nanoclusters with around 55 atoms inherently exhibit size-sensitive melting changes: adding just a single atom to a nanocluster can cause a dramatic change in melting behavior. Microscopic understanding of thermal behaviors of metal nanoclusters is important for nanoscale catalysis and thermal energy storage applications. However, it is a challenge to obtain a structural interpretation at the atomic level from measured thermodynamic quantities such as heat capacity. Using ab initio molecular dynamics simulations, scientists at the National Renewable Energy Laboratory (NREL) revealed a clear correlation between the diverse melting behaviors of aluminum nanoclusters and cluster core symmetries. These simulations reproduced, for the first time, the size-sensitive heat capacities of aluminum nanoclusters, which exhibit several distinctive shapes associated with the diverse melting behaviors of the clusters. The size-dependent, diverse melting behaviors of the aluminum clusters are attributed to the reduced symmetry (from Td {yields} D2d {yields} Cs) with increasing the cluster sizes and can be used to help design thermal storage materials.

Not Available

2011-10-01

264

Mineralogy of Impact Melt at Copernicus Crater: Insights into Melt Evolution and Diversity  

NASA Astrophysics Data System (ADS)

Mineralogy of impact melt is deciphered by remote spectral analysis to determine its implication on crustal diversity. The observed variation in composition and crystallinity is assessed in context of the melt morphology and target lithology.

Dhingra, D.; Pieters, C. M.

2013-08-01

265

Thermocapillary flow and natural convection in a melt column with an unknown melt/solid interface  

NASA Technical Reports Server (NTRS)

A vertical melt column set up between an upper heating rod and a lower sample rod, i.e., the so-called half-zone system, is a convenient experimental tool for studying convection in the melt in floating-zone crystal growth. In order to help understand the convection observed in the melt column, a computer model has been developed to describe steady state, axisymmetrical thermocapillary flow and natural convection in the melt. The governing equations and boundary conditions are expressed in general non-orthogonal curvilinear coordinates in order to accurately treat the unknown melt/solid interface as well as all other physical boundaries in the system. The effects of key dimensionless variables on the following items are discussed: (1) convection and temperature distribution in the melt; (2) the shape of the melt/solid interface; (3) the height of the melt column. These dimensionless variables are the Grashof, Marangoni and Prandtl numbers.

Lan, C. W.; Kou, Sindo

1991-01-01

266

Trace Element Partitioning Between Metal and Melt at High Pressure  

NASA Astrophysics Data System (ADS)

Fractionations between siderophile trace elements are produced during crystallization of solid metal from a molten planetary core. It has been proposed (e.g., Brandon et al., 2003) that fractionations of Re/Os and Pt/Os produced during crystallization of Earth's inner core are recorded in rocks whose source regions lie at the core-mantle boundary. However, the possible effects of pressure, temperature, composition, and metal crystal structure on metal-melt partitioning have not been fully evaluated experimentally. Accordingly, we have begun to measure the partitioning of major and trace siderophile elements between Fe-rich metal and metal-sulfide melt at high pressures and temperatures using laser ablation ICP-MS of multi-anvil press samples. The starting materials included iron meteorite powder (having natural abundances of PGEs at the /sim10 ppm level) and troilite. In some cases Ru powder was also added to the starting material to promote transformation of the Fe-rich metal to the hcp structure, as described by Campbell et al. (2003). The powders were loaded into an MgO or BN sample capsule in a 10/5 multi-anvil press assembly, and pressurized to 14.5 GPa. The sample chamber thickness was held to <0.4 mm to minimize the temperature gradient experienced by the samples. Melting was achieved at temperatures of 975 C or above, and run durations were 6 to 24 hours. The recovered run products were polished and examined by SEM or electron microprobe before LA-ICP-MS analysis. Laser ablation spot sizes ranged from 15 to 50 microns, depending on the available grain size. Partition coefficients (D) were determined for Co, Ni, Ru, Re, Os, Ir, and Pt. Errors on the D values were based on the reproduceability of at least 3 measurements in each phase, and were <10% for major elements and <25% for trace elements. The effects of temperature and composition were evaluated and implications on the chemistry of the core will be discussed. Brandon A. D. et al. (2003) EPSL 206:411-426. Campbell A. J. et al. (2003) Fall AGU Meeting.

Campbell, A. J.; Moses, M.; Fei, Y.

2004-12-01

267

Systematics of melt stagnation in peridotites from the Godzilla Megamullion  

NASA Astrophysics Data System (ADS)

The Godzilla Megamullion (GM) Massif is the largest known example of an Oceanic Core Complex (OCC) or the exhumed footwall of a low angle-large offset oceanic detachment fault. It lies on the extinct Parece Vela Rift spreading center within the Parece Vela Back-arc Basin of the Philippine Sea. This has thus allowed for sampling of a young back-arc mantle section. Sampling of the massif has returned a dominantly ultramafic lithology, divided petrographically into depleted, fertile, and melt-percolated groups (1). Petrographic analysis of the extant peridotite thin section collection found that 44% of all GM peridotites (71 out of 161) exhibit evidence of plagioclase impregnation compared to the worldwide abyssal peridotite average of ~20% (2). The mullion is divided up into three regions, the proximal region ( closest to termination of spreading), the medial region, and the distal region (furthest from the termination of spreading)(3).Observations by region provide that 53% ( 62 out of 116 samples) in the proximal region (15 dredges), 12% ( 2 out of 17 samples) in the medial mullion (3 dredges), and 25% (7 out of 28) in the distal mullion (5 dredges) show of evidence of plagioclase impregnation (4). Major element analyses of spinels were completed using the Cameca SX-50 Electron Microprobe facility at the University of Houston. The Cr# [100 x Cr/(Cr + Al)] ranges from 10 to 65 with TiO2 concentrations ranging from less than 0.01 up to 1.6 wt%. When the Cr#s of the samples are plotted along the massif, a pattern of melt depletion exists that is consistent with the degree of plagioclase impregnation. In the distal region, Cr#s start at around an average of 35 and range up to 65 for melt percolated samples. In the medial region, a drop off in Cr# of about 1 Cr# per kilometer is observed with the trend bottoming out at around a Cr# of 10. In the proximal region, Cr#s closer to the medial region are observed as having more fertile values of around 20 but are found amongst melt-impregnated samples with values ranging up to 50. This range is seen as having increasing minimum and maximum values with distance away from the medial section until it reaches its peak at a base Cr# of 30 with a maximum of 65. From this trend, a general model for the secular evolution of the GM mantle section can be established (5). The ridge segment experienced normal mid-oceanic ridge growth with robust mantle melting during the time period represented by the distal region. At the boundary to the medial region, a steep drop-off in melt productivity was experienced, leading to minimal mantle melting during the time period represented by the medial region. Soon thereafter, melting began again, but was trapped in a thickened and cooling lithosphere, causing the melt to pool and react with its host peridotite. (1) Ohara, et al., (2003) G3. 4 (7), 8611, 10.1029/2002GC000469. (2) Dick (1989) Geol Soc. Lond. Spec. Pub. 42:71-105. (3) Ohara, et al., (2009), Eos Trans. AGU, 90(52), Fall Meet. Suppl. Abst.Num. T33D-06 (4) Loocke, et al., (2009), Eos Trans. AGU, 90(52), Fall Meet. Suppl. Abst.Num. T21A-1776 (5) Snow, et al., (2009), Eos Trans. AGU, 90(52), Fall Meet. Suppl. Abst.Num. T33D-07

Loocke, M.; Snow, J. E.; Ohara, Y.

2010-12-01

268

Partitioning REE between minerals and coexisting melts during partial melting of a garnet lherzolite  

NASA Technical Reports Server (NTRS)

Partition coefficients for Ce, Sm, and Tm between garnet, clinopyroxene, orthopyroxene, olivine, and melt are determined at 35 kbar for 2.3, 8, 20, and 37.7% melting of a garnet lherzolite nodule with chondritic REE abundances. Partition coefficients are found to increase as the degree of partial melting increases. From 2.3 to 8% melting, this increase is for the most part a consequence of non-Henry's law behavior of REE in minerals.

Harrison, W. J.

1981-01-01

269

Main results of study on the interaction between the corium melt and steel in the VVER-1000 reactor vessel during a severe accident performed under the MASCA project  

NASA Astrophysics Data System (ADS)

The interactions that take place in the corium melt in the reactor vessel in the case of a severe accident at a nuclear power plant were investigated in accordance with the MASCA international program. Results of the interaction between the oxide melt and iron (steel), partition of the main components [U, Zr, Fe (stainless steel)] between the oxide and the metal phases of the melt, partition of low-volatile simulators of fission products between the phases of the stratified core melt pool, and impact of the oxidizing atmosphere on the melt stratification are presented. The results obtained were used for prediction of thermodynamic properties of the melts belonging to the U-Zr-Fe-O system.

Asmolov, V. G.; Zagryazkin, V. N.; Tsurikov, D. F.; Vishnevsky, V. Yu.; D'Yakov, Ye. K.; Kotov, A. Yu.; Repnikov, V. M.

2010-12-01

270

Potential health risks from postulated accidents involving the Pu-238 RTG on the Ulysses solar exploration mission  

NASA Technical Reports Server (NTRS)

Potential radiation impacts from launch of the Ulysses solar exploration experiment were evaluated using eight postulated accident scenarios. Lifetime individual dose estimates rarely exceeded 1 mrem. Most of the potential health effects would come from inhalation exposures immediately after an accident, rather than from ingestion of contaminated food or water, or from inhalation of resuspended plutonium from contaminated ground. For local Florida accidents (that is, during the first minute after launch), an average source term accident was estimated to cause a total added cancer risk of up to 0.2 deaths. For accidents at later time after launch, a worldwide cancer risk of up to three cases was calculated (with a four in a million probability). Upper bound estimates were calculated to be about 10 times higher.

Goldman, Marvin; Hoover, Mark D.; Nelson, Robert C.; Templeton, William; Bollinger, Lance; Anspaugh, Lynn

1991-01-01

271

Potential health risks from postulated accidents involving the Pu-238 RTG (radioisotope thermoelectric generator) on the Ulysses solar exploration mission  

SciTech Connect

Potential radiation impacts from launch of the Ulysses solar exploration experiment were evaluated using eight postulated accident scenarios. Lifetime individual dose estimates rarely exceeded 1 mrem. Most of the potential health effects would come from inhalation exposures immediately after an accident, rather than from ingestion of contaminated food or water, or from inhalation of resuspended plutonium from contaminated ground. For local Florida accidents (that is, during the first minute after launch), an average source term accident was estimated to cause a total added cancer risk of up to 0.2 deaths. For accidents at later times after launch, a worldwide cancer risk of up to three cases was calculated (with a four in a million probability). Upper bound estimates were calculated to be about 10 times higher. 83 refs.

Goldman, M. (California Univ., Davis, CA (USA)); Nelson, R.C. (EG and G Idaho, Inc., Idaho Falls, ID (USA)); Bollinger, L. (Air Force Inspection and Safety Center, Kirtland AFB, NM (USA)); Hoover, M.D. (Lovelace Biomedical and Environmental Research Inst., Albuquerque, NM (USA). Inhalation Toxicology Research Inst.); Templeton, W. (Pacific Northwest Lab., Richland, WA (USA)); Anspaugh, L. (Lawren

1990-11-02

272

Manufacturing by combining Selective Laser Melting and Selective Laser Erosion\\/laser re-melting  

Microsoft Academic Search

This study presents an experimental investigation to improve Selective Laser Melting (SLM) regarding aspects such as surface roughness, density, precision and micro machining capability by employing secondary processes such as Selective Laser Erosion (SLE) and laser re-melting. SLM is a layered additive manufacturing technique for the direct fabrication of functional parts by fusing together metal powder particles. Laser re-melting, applied

E. Yasa; J.-P. Kruth; J. Deckers

2011-01-01

273

Quantum model for psychological measurements: from the projection postulate to interference of mental observables represented as positive operator valued measures  

E-print Network

Recently foundational issues of applicability of the formalism of quantum mechanics (QM) to cognitive psychology, decision making, and psychophysics attracted a lot of interest. In particular, in \\cite{DKBB} the possibility to use of the projection postulate and representation of "mental observables" by Hermitian operators was discussed in very detail. The main conclusion of the recent discussions on the foundations of "quantum(-like) cognitive psychology" is that one has to be careful in determination of conditions of applicability of the projection postulate as a mathematical tool for description of measurements of observables represented by Hermitian operators. To represent some statistical experimental data (both physical and mental) in the quantum(-like) way, one has to use generalized quantum observables given by positive operator-valued measures (POVMs). This paper contains a brief review on POVMs which can be useful for newcomers to the field of quantum(-like) studies. Especially interesting for cognitive psychology is a variant of the formula of total probability (FTP) with the interference term derived for incompatible observables given by POVMs. We present an interpretation of the interference term from the psychological viewpoint. As was shown before, the appearance of such a term (perturbing classical FTP) plays the important role in cognitive psychology, e.g., recognition of ambiguous figures and the disjunction effect. The interference term for observables given by POVMs has much more complicated structure than the corresponding term for observables given by Hermitian operators. We elaborate cognitive interpretations of different components of the POVMs-interference term and apply our analysis to a quantum(-like) model of decision making.

Andrei Khrennikov; Irina Basieva

2014-05-06

274

Transition metals in superheat melts  

NASA Technical Reports Server (NTRS)

A series of experiments with silicate melts doped with transition element oxides was carried out at atmospheric pressures of inert gas at temperatures exceeding liquidus. As predicted from the shape of fO2 buffer curves in T-fO2 diagrams the reducing conditions for a particular oxide-metal pair can be achieved through the T increase if the released oxygen is continuously removed. Experimental studies suggest that transition metals such as Cr or V behave as siderophile elements at temperatures exceeding liquidus temperatures if the system is not buffered by the presence of other oxide of more siderophile element. For example the presence of FeO prevents the reduction of Cr2O3. The sequence of decreasing siderophility of transition elements at superheat conditions (Mo, Ni, Fe, Cr) matches the decreasing degree of depletion of siderophile elements in mantle rocks as compared to chondrites.

Jakes, Petr; Wolfbauer, Michael-Patrick

1993-01-01

275

Glass-clad semiconductor core optical fibers  

NASA Astrophysics Data System (ADS)

Glass-clad optical fibers comprising a crystalline semiconductor core have garnered considerable recent attention for their potential utility as novel waveguides for applications in nonlinear optics, sensing, power delivery, and biomedicine. As research into these fibers has progressed, it has become evident that excessive losses are limiting performance and so greater understanding of the underlying materials science, coupled with advances in fiber processing, is needed. More specifically, the semiconductor core fibers possess three performance-limiting characteristics that need to be addressed: (a) thermal expansion mismatches between crystalline core and glass cladding that lead to cracks, (b) the precipitation of oxide species in the core upon fiber cooling, which results from partial dissolution of the cladding glass by the core melt, and (c) polycrystallinity; all of which lead to scattering and increased transmission losses. This dissertation systematically studies each of these effects and develops both a fundamental scientific understanding of and practical engineering methods for reducing their impact. With respect to the thermal expansion mismatch and, in part, the dissolution of oxides, for the first time to our knowledge, oxide and non-oxide glass compositions are developed for a series of semiconductor cores based on two main design criteria: (1) matching the thermal expansion coefficient between semiconductor core and glass cladding to minimize cracking and (2) matching the viscosity-temperature dependences, such that the cladding glass draws into fiber at a temperature slightly above the melting point of the semiconductor in order to minimize dissolution and improve the fiber draw process. The x[Na 2O:Al2O3] + (100 - 2x)SiO2 glass compositional family was selected due to the ability to tailor the glass properties to match the aforementioned targets through slight variations in composition and adjusting the ratios of bridging and non-bridging oxygen; experimental results show a decrease in fiber core oxygen content in the fibers drawn with the tailored glass composition. In a further attempt to reduce the presence of oxide species in the core, a reactive molten core approach to semiconductor optical fibers are developed. Specifically, the addition of silicon carbide (SiC) into a silicon (Si) core provides an in-situ reactive getter of oxygen during the draw process to achieve oxygen-free silicon optical fibers. Elemental analysis and x-ray diffraction of fibers drawn using this reactive chemistry approach show negligible oxygen concentration in the highly crystalline silicon core, a significant departure from the nearly 18 atom percent oxygen in previous fibers. Scattering of light out of the core is shown qualitatively to have been reduced in the process. The role of the cross-sectional geometry on the resultant core crystallography with respect to the fiber axis is explored in a continued effort to better understand the nature of the crystal formation and structural properties in these semiconductor core optical fibers. A square cross-sectional geometry was explored to determine if core non-circularity can enhance or promote single crystallinity, as the semiconductors studied have a preference to form cubic crystals. Resultant crystallography of the non-circular core showed a significant improvement in maintaining a preferred crystallographic orientation, with the square core fibers exhibiting a 90% preference for the < 1 1 0 > family of directions occurring closest to the longitudinal direction of the fiber. The ability to orient the crystallography with respect to the fiber axis could be of great value to future nonlinear optical fiber-based devices. In summary, this dissertation begins to elucidate some of the microstructural features, not present in conventional glass optical fibers, which could be important for future low-loss single crystalline semiconductor optical fibers. Additionally, this dissertation offers novel insight into the various aspects of mate

Morris, Stephanie Lynn

276

SCDAP/RELAP5 Modeling of Movement of Melted Material through Porous Debris in Lower Head (Rev. 2)  

SciTech Connect

A model is described for the movement of melted metallic material through a ceramic porous debris bed. The model is designed for the analysis of severe accidents in LWRs, wherein melted core plate material may slump onto the top of a porous bed of relocated core material supported by the lower head. The permeation of the melted core plate material into the porous debris bed influences the heatup of the debris bed and the heatup of the lower head supporting the debris. A model for mass transport of melted metallic material is applied that includes terms for viscosity and turbulence but neglects inertial and capillary terms because of their small value relative to gravity and viscous terms in the momentum equation. The relative permeability and passability of the porous debris are calculated as functions of debris porosity, particle size, and effective saturation. An iterative numerical solution is used to solve the set of nonlinear equations for mass transport. The effective thermal conductivity of the debris is calculated as a function of porosity, particle size, and saturation. The model integrates the equations for mass transport with a model for the two-dimensional conduction of heat through porous debris. The integrated model has been implemented into the SCDAP/RELAP5 code for the analysis of the integrity of LWR lower heads during severe accidents. The results of the model indicate that melted core plate material my permeate in about 120 s to the bottom of a 1 m deep hot porous debris bed supported by the lower head. The presence of the relocated core plate material at the bottom of the debris bed decreases the thermal resistance of the interface between the debris bed and the lower head. This report is a revision of the report with the identifier of INEEL/EXT-98-01178 REV 1, entitled "SCDAP/RELAP5 Modeling of Movement of Melted Material Through Porous Debris in Lower Head."

Siefken, Larry James

1999-10-01

277

The speciation of water in silicate melts  

Microsoft Academic Search

Previous models of water solubility in silicate melts generally assume essentially complete reaction of water molecules to hydroxyl groups. In this paper a new model is proposed that is based on the hypothesis that the observed concentrations of molecular water and hydroxyl groups in hydrous silicate glasses reflect those of the melts from which they were quenched. The new model

Edward Stolper

1982-01-01

278

Purification of tantalum by plasma arc melting  

DOEpatents

Purification of tantalum by plasma arc melting. The level of oxygen and carbon impurities in tantalum was reduced by plasma arc melting the tantalum using a flowing plasma gas generated from a gas mixture of helium and hydrogen. The flowing plasma gases of the present invention were found to be superior to other known flowing plasma gases used for this purpose.

Dunn, Paul S. (Santa Fe, NM); Korzekwa, Deniece R. (Los Alamos, NM)

1999-01-01

279

Solid Clusters above the Bulk Melting Point  

Microsoft Academic Search

The fact that the melting points of nanoparticles are always lower than those of the corresponding bulk material is a paradigm supported by extensive experimental data for a large number of systems and by numerous calculations. Here we demonstrate that tin cluster ions with 10-30 atoms remain solid at ~50 K above the melting point of bulk tin. This behavior

Alexandre A. Shvartsburg; Martin F. Jarrold

2000-01-01

280

Stabilizing Crystal Oscillators With Melting Metals  

NASA Technical Reports Server (NTRS)

Heat of fusion provides extended period of constant temperature and frequency. Crystal surrounded by metal in spherical container. As outside temperature rises to melting point of metal, metal starts to liquefy; but temperature stays at melting point until no solid metal remains. Potential terrestrial applications include low-power environmental telemetering transmitters and instrumentation transmitters for industrial processes.

Stephens, J. B.; Miller, C. G.

1984-01-01

281

Oceanic slab melting and mantle metasomatism.  

PubMed

Modern plate tectonic brings down oceanic crust along subduction zones where it either dehydrates or melts. Those hydrous fluids or melts migrate into the overlying mantle wedge trigerring its melting which produces arc magmas and thus additional continental crust. Nowadays, melting seems to be restricted to cases of young (< 50 Ma) subducted plates. Slab melts are silicic and strongly sodic (trondhjemitic). They are produced at low temperatures (< 1000 degrees C) and under water excess conditions. Their interaction with mantle peridotite produces hydrous metasomatic phases such as amphibole and phlogopite that can be more or less sodium rich. Upon interaction the slab melt becomes less silicic (dacitic to andesitic), and Mg, Ni and Cr richer. Virtually all exposed slab melts display geochemical evidence of ingestion of mantle material. Modern slab melts are thus unlike Archean Trondhjemite-Tonalite-Granodiorite rocks (TTG), which suggests that both types of magmas were generated via different petrogenetic pathways which may imply an Archean tectonic model of crust production different from that of the present-day, subduction-related, one. PMID:11838241

Scaillet, B; Prouteau, G

2001-01-01

282

Heterozygote PCR product melting curve prediction.  

PubMed

Melting curve prediction of PCR products is limited to perfectly complementary strands. Multiple domains are calculated by recursive nearest neighbor thermodynamics. However, the melting curve of an amplicon containing a heterozygous single-nucleotide variant (SNV) after PCR is the composite of four duplexes: two matched homoduplexes and two mismatched heteroduplexes. To better predict the shape of composite heterozygote melting curves, 52 experimental curves were compared with brute force in silico predictions varying two parameters simultaneously: the relative contribution of heteroduplex products and an ionic scaling factor for mismatched tetrads. Heteroduplex products contributed 25.7 ± 6.7% to the composite melting curve, varying from 23%-28% for different SNV classes. The effect of ions on mismatch tetrads scaled to 76%-96% of normal (depending on SNV class) and averaged 88 ± 16.4%. Based on uMelt (www.dna.utah.edu/umelt/umelt.html) with an expanded nearest neighbor thermodynamic set that includes mismatched base pairs, uMelt HETS calculates helicity as a function of temperature for homoduplex and heteroduplex products, as well as the composite curve expected from heterozygotes. It is an interactive Web tool for efficient genotyping design, heterozygote melting curve prediction, and quality control of melting curve experiments. The application was developed in Actionscript and can be found online at http://www.dna.utah.edu/hets/. PMID:24375593

Dwight, Zachary L; Palais, Robert; Kent, Jana; Wittwer, Carl T

2014-03-01

283

Temperature index melt modelling in mountain areas  

Microsoft Academic Search

Temperature index or degree-day models rest upon a claimed relationship between snow or ice melt and air temperature usually expressed in the form of positive temperatures. Since air temperature generally is the most readily available data, such models have been the most widely used method of ice and snow melt computations for many purposes, such as hydrological modelling, ice dynamic

Regine Hock

2003-01-01

284

Melt electrospinning of biodegradable polyurethane scaffolds  

Microsoft Academic Search

Electrospinning from a melt, in contrast to from a solution, is an attractive tissue engineering scaffold manufacturing process as it allows for the formation of small diameter fibers while eliminating potentially cytotoxic solvents. Despite this, there is a dearth of literature on scaffold formation via melt electrospinning. This is likely due to the technical challenges related to the need for

Ari Karchin; Felix I. Simonovsky; Buddy D. Ratner; Joan E. Sanders

2011-01-01

285

Natural melting within a spherical shell  

NASA Technical Reports Server (NTRS)

Fundamental heat transfer experiments were performed on the melting of a phase change medium in a spherical shell. Free expansion of the medium into a void space within the sphere was permitted. A step function temperature jump on the outer shell wall was imposed and the timewise evolution of the melting process and the position of the solid-liquid interface was photographically recorded. Numerical integration of the interface position data yielded information about the melted mass and the energy of melting. It was found that the rate of melting and the heat transfer were significantly affected by the movement of the solid medium to the base of the sphere due to gravity. The energy transfer associated with melting was substantially higher than that predicted by the conduction model. Furthermore, the radio of the measured values of sensible energy in the liquid melt to the energy of melting were nearly proportional to the Stefan number. The experimental results are in agreement with a theory set forth in an earlier paper.

Bahrami, Parviz A.

1990-01-01

286

Laser depolarisation 'bright band' from melting snowflakes  

Microsoft Academic Search

In investigations of linear depolarization ratios with continuous wave laser systems it has been found that melting snowflakes backscatter unexpectedly large amounts of depolarized energy. An apparatus employing a vertically polarized CW helium-neon laser has been designed to perform measurements comparable to those made with lidar in the study of snowflake melting.

KENNETH SASSEN

1975-01-01

287

Multiple applications of cold crucible melting  

Microsoft Academic Search

Induction-heated cold crucible melting is an increasingly promising technique in the international scientific and technical radioactive waste management community. It is capable of achieving high temperatures and power densities with virtually no melter corrosion, making it an ideal solution for many applications, from simple melting of metals, molten salts, or glass, to complex processes involving chemical reactions in molten baths,

A. Jouan; J. P. Monocouyoux; S. Merlin; P. Roux

1996-01-01

288

Metallic Recovery and Ferrous Melting Processes  

SciTech Connect

The effects of melting atmosphere and charge material type on the metallic and alloy recovery of ferrous charge materials were investigated in two sets of experiments (Tasks 1 and 2). In addition, thermodynamic studies were performed (Task 3) to determine the suitability of ladle treatment for the production of ductile iron using scrap charge materials high in manganese and sulfur. Task 1--In the first set of experiments, the charge materials investigated were thin steel scrap, thick steel scrap, cast iron scrap, and pig iron in the rusty and clean states. Melting atmospheres in this set of experiments were varied by melting with and without a furnace cover. In this study, it was found that neither covered melting nor melting clean (non-rusty) ferrous charge materials improved the metallic recovery over the recovery experienced with uncovered melting or rusty charge materials. However, the silicon and manganese recoveries were greater with covered melting and clean materials. Silicon and manganese in the molten iron react with oxygen dissolved in the iron from uncovered melting and oxidized iron (surface rust). Silica and manganese silicates are formed which float to the slag decreasing recoveries of silicon and manganese. Cast iron and pig iron had higher metallic recoveries than steel scrap. Carbon recovery was affected by the carbon content of the charge materials, and not by the melting conditions. Irons with higher silicon contents had higher silicon recovery than irons with lower silicon contents. Task 2--In the second set of experiments, briquetted turnings and borings were used to evaluate the effects of briquette cleanliness, carbon additions, and melting atmosphere on metallic and alloy recovery. The melting atmosphere in this set of experiments was varied by melting in air and with an argon atmosphere using the SPAL process. In this set of experiments, carbon additions to the briquettes were found to have the greatest effect on metallic and alloy recovery. The use of an argon atmosphere was also found to increase recoveries, but to a lesser extent than with carbon additions to the briquettes. Task 3--Finally, thermodynamic studies were carried out to evaluate the potential for removing manganese and sulfur from iron melts for the production of ferritic ductile iron. Thermodynamic calculations indicated that manganese and sulfur might be removed from iron melts by careful control of the temperature and slag. In laboratory tests however, it was shown that the removal of sulfur was much less successful than that indicated by the thermodynamic analyses.

Luis Trueba

2004-05-30

289

Melt Rate Improvement for DWPF MB3: Melt Rate Furnace Testing  

SciTech Connect

The Defense Waste Processing Facility (DWPF) would like to increase its canister production rate. The goal of this study is to improve the melt rate in DWPF specifically for Macrobatch 3. However, the knowledge gained may result in improved melting efficiencies translating to future DWPF macrobatches and in higher throughput for other Department of Energy's (DOE) melters. Increased melting efficiencies decrease overall operational costs by reducing the immobilization campaign time for a particular waste stream. For melt rate limited systems, a small increase in melting efficiency translates into significant hard dollar savings by reducing life cycle operational costs.

Stone, M.E.

2001-07-24

290

Core formation, evolution, and convection - A geophysical model  

NASA Technical Reports Server (NTRS)

A model for the formation and evolution of the earth's core, which provides an adequate energy source for maintaining the geodynamo, is proposed. A modified inhomogeneous accretion model is proposed which leads to initial iron and refractory enrichment at the center of the planet. The probable heat source for melting of the core is the decay of Al-26. The refractory material is emplaced irregularly in the lowermost mantle with uranium and thorium serving as a long-lived heat source. Fluid motions in the core are driven by the differential heating from above and the resulting cyclonic motions may be the source of the geodynamo.

Ruff, L.; Anderson, D. L.

1980-01-01

291

Ice-Shelf Melting Around Antarctica  

NASA Astrophysics Data System (ADS)

We compare the volume flux divergence of Antarctic ice shelves in 2007 and 2008 with 1979 to 2010 surface accumulation and 2003 to 2008 thinning to determine their rates of melting and mass balance. Basal melt of 1325 ± 235 gigatons per year (Gt/year) exceeds a calving flux of 1089 ± 139 Gt/year, making ice-shelf melting the largest ablation process in Antarctica. The giant cold-cavity Ross, Filchner, and Ronne ice shelves covering two-thirds of the total ice-shelf area account for only 15% of net melting. Half of the meltwater comes from 10 small, warm-cavity Southeast Pacific ice shelves occupying 8% of the area. A similar high melt/area ratio is found for six East Antarctic ice shelves, implying undocumented strong ocean thermal forcing on their deep grounding lines.

Rignot, E.; Jacobs, S.; Mouginot, J.; Scheuchl, B.

2013-07-01

292

Surface melting and sintering of metallic nanoparticles.  

PubMed

The melting and sintering of two different-sized metallic nanoparticles are simulated by a molecular dynamics method in this work. The particles are partitioned into different regimes where tracing atoms are arranged to investigate the melting and sintering kinetics. The melting of individual particles is firstly investigated and compared with established studies, where the size-dependent melting depression and surface melting phenomenon are revealed. The detailed sintering process of two nickel nanoparticles, 3.52 and 1.76 nanometers in diameter respectively, is subsequently examined by the gyration radius, mean square displacement (MSD), root mean square displacement (RMSD), sintering diffusivity and activation energy. A three-stage sintering scenario is illustrated, and the layered structure shows the regime dependent behavior of diffusivity during the sintering process. Beside the surface diffusion, sintering of different-sized nanoparticles is found to be affected by a few other mechanisms. PMID:21121291

Song, Pengxiang; Wen, Dongsheng

2010-12-01

293

The contribution of glacier melt to streamflow  

SciTech Connect

Ongoing and projected future changes in glacier extent and water storage globally have lead to concerns about the implications for water supplies. However, the current magnitude of glacier contributions to river runoff is not well known, nor is the population at risk to future glacier changes. We estimate an upper bound on glacier melt contribution to seasonal streamflow by computing the energy balance of glaciers globally. Melt water quantities are computed as a fraction of total streamflow simulated using a hydrology model and the melt fraction is tracked down the stream network. In general, our estimates of the glacier melt contribution to streamflow are lower than previously published values. Nonetheless, we find that globally an estimated 225 (36) million people live in river basins where maximum seasonal glacier melt contributes at least 10% (25%) of streamflow, mostly in the High Asia region.

Schaner, Neil; Voisin, Nathalie; Nijssen, Bart; Lettenmaier, D. P.

2012-09-13

294

Melting point, boiling point, and symmetry.  

PubMed

The relationship between the melting point of a compound and its chemical structure remains poorly understood. The melting point of a compound can be related to certain of its other physical chemical properties. The boiling point of a compound can be determined from additive constitutive properties, but the melting point can be estimated only with the aid of nonadditive constitutive parameters. The melting point of some non-hydrogen-bonding, rigid compounds can be estimated by the equation MP = 0.772 * BP + 110.8 * SIGMAL + 11.56 * ORTHO + 31.9 * EXPAN - 240.7 where MP is the melting point of the compound in Kelvin, BP is the boiling point, SIGMAL is the logarithm of the symmetry number, EXPAN is the cube of the eccentricity of the compound, and ORTHO indicates the number of groups that are ortho to another group. PMID:2235894

Abramowitz, R; Yalkowsky, S H

1990-09-01

295

Viscosity of flux-rich pegmatitic melts  

NASA Astrophysics Data System (ADS)

Viscosity experiments were conducted with two flux-rich pegmatitic melts PEG0 and PEG2. The Li2O, F, B2O3 and P2O5 contents of these melts were 1.04, 4.06, 2.30 and 1.68 and 1.68, 5.46, 2.75 and 2.46 wt%, respectively. The water contents varied from dry to 9.04 wt% H2O. The viscosity was determined in internally heated gas pressure vessels using the falling sphere method in the temperature range 873-1,373 K at 200 and 320 MPa pressure. At 1,073 K, the viscosity of water-rich (~9 wt% H2O) melts is in the range of 3-60 Pa s, depending on the melt composition. Extrapolations to lower temperature assuming an Arrhenian behavior indicate that highly fluxed pegmatite melts may reach viscosities of ~30 Pa s at 773 K. However, this value is a minimum estimation considering the strongly non-Arrhenian behavior of hydrous silicate melts. The experimentally determined melt viscosities are lower than the prediction of current models taking compositional parameters into account. Thus, these models need to be improved to predict accurately the viscosity of flux-rich water bearing melts. The data also indicate that Li influences significantly the melt viscosity. Decreasing the molar Al/(Na + K + Li) ratio results in a strong viscosity decrease, and highly fluxed melts with low Al/(Na + K + Li) ratios (~0.8) have a rheological behavior which is very close to that of supercritical fluids.

Bartels, Alexander; Vetere, Francesco; Holtz, Francois; Behrens, Harald; Linnen, Robert L.

2011-07-01

296

High-pressure melting of MgO from (Mg,Fe)O solid solutions  

NASA Astrophysics Data System (ADS)

oxide (MgO) is a significant component of planetary interiors, particularly Earth's mantle and other rocky planets within and beyond our solar system; thus its high-pressure, high-temperature behavior is important to understanding the thermochemical evolution of planets. Laser-heated diamond-anvil cell (DAC) experiments on (Mg,Fe)O ferropericlase up to ~40 GPa show that previous DAC experiments on MgO melting are too low, while previous multi-anvil experiments yield melting temperatures too high. Instead, our quasi-static experimental results are consistent with recent ab initio predictions as well as dynamic shock measurements. Extrapolated to the core-mantle boundary (CMB) of the Earth, MgO is expected to melt at ~8000 ± 500 K, much greater than expected geotherm temperatures.

Du, Zhixue; Lee, Kanani K. M.

2014-11-01

297

Melt and Chemical Transport in the Mantle: Insights from Deglaciation-Induced Melting Perturbations in Iceland  

NASA Astrophysics Data System (ADS)

Eruptive products represent a time-averaged view of the melting region and melt migration processes, making numerous fundamental parameters of the melt system difficult to constrain. Temporal and spatial variations in melting provide potential windows into this obscure region of the Earth by preferentially sampling melts from different regions of the mantle or mixing melts over different length-scales. We present a newly extended geochemical time series from the Western Volcanic Zone (WVZ) of Iceland, which experienced a short-lived melting perturbation due to glacial unloading during the last major deglaciation (~15-10 ka). Glacial unloading during this period led to increased degrees of melting particularly in the shallow mantle, which is manifest as an observed increase in volcanic production up to 30 times the steady-state value, decreased levels of highly to moderately incompatible element ratios (e.g., a 35-50% decrease in Nb/Y, with the greatest change occurring in the northernmost WVZ), and elevated SiO2 and CaO concentrations (~0.8 wt. % and ~1.9 wt. % increase in average oxide concentrations respectively) during and immediately following deglaciation. Although eruptive productivity returns to steady-state values within ~3000 yr following deglaciation, the incompatible element concentrations in erupted lavas gradually increase throughout the post-glacial period. We exploit this short-lived melting perturbation to examine and constrain knowledge of fundamental characteristics of melt generation and transport, including mantle permeability, melt ascent rates, depth-dependent melting functions (dF/dP), and the nature of chemical transport and melt mixing in the system. Using conservation equations describing the generation and porous flow of melt in a viscous matrix, we model melt migration in the mantle during and after ice sheet removal, as well as trace element transport for both equilibrium and disequilibrium transport end members. The predicted geochemical time series at the surface is particularly sensitive to the mode of chemical transport, with trace element compositions predicted for disequilibrium transport exhibiting a greater dependency on melt ascent rate than for equilibrium transport, as well as a greater overall magnitude of compositional change. We propose and examine other potential geologic settings in which short-lived perturbations in the melting region might be exploited to examine time- and depth-dependent melt processes. The results of this case study emphasize the potential importance of the nature and rate of melt migration and chemical transport in controlling compositional variability at spreading centers and ocean islands.

Eason, D. E.; Ito, G.; Sinton, J. M.

2011-12-01

298

Water solubility in rhyolitic silicate melts at atmospheric pressure  

NASA Astrophysics Data System (ADS)

High temperature (900-1100 °C) experiments have been conducted to measure the solubility of water in a rhyolitic melt at atmospheric pressure (1 atm) and to quantify the magnitude of retrograde solubility at low pressure. Individual cores (1 cm x 1 cm) of crystal- and bubble-free rhyolitic obsidian from Hrafntinnugryggur, Krafla (Iceland) were held in a furnace at 900-1100 °C for 0.25 to 20 hours. During this time, the uniform bubble-free cores vesiculate to produce variably swollen bubble-rich run products. The volume change in each core reflects the volume of bubbles produced in each experiment and depends on the experimental temperature and the time held at that temperature. The run product volumes for isothermal experiments (e.g., 950 °C) increase non-linearly with increasing time (e.g., 0.18 cm3 at 1.5 h, 0.96 cm3 at 12.5 h) until reaching a maximum value, after which the volume does not change appreciably. We take this plateau in the isothermal volume:time curve as coinciding with the 1 atm. solubility limit for the rhyolite at this temperature. With increasing temperature, the slope and final horizontal plateaus of the volume:time curves increase such that samples from the higher temperature suites vesiculate more, as well as more rapidly (e.g., 0.85 cm3 after 0.5 hours, 1.78 cm3 after 1 hour at 1100 °C). The variations in the maximum volume of bubbles produced for each temperature constrain the retrograde solubility of water in the melt at 1 atm. Fourier transform infrared spectroscopy (FTIR) analyses of the residual water content of the glass in the starting material and in the most vesiculated sample from each temperature suite shows a decrease in the water content of the glass from an initial 0.114 wt% (? 0.013) to 0.098 wt% (? 0.010), 0.087 wt% (? 0.009), 0.093 wt% (? 0.008), 0.090 wt% (? 0.006) and 0.108 wt% (? 0.010) for 900 °C, 950 °C, 1000 °C, 1050 °C and 1100 °C respectively. This change in the solubility of water at different temperatures, though slight, produces a marked change in maximum run product porosity from 50 to 70% through the temperature series, illuminating the effect of retrograde solubility at conduit- and surface-relevant pressures. The readiness of a rhyolitic silicate melt not only to produce more bubbles at higher temperatures, but also to resorb existing bubbles during cooling has important implications for magmatic fragmentation, flow of lava, and welding processes.

Ryan, Amy; Russell, Kelly; Nichols, Alexander; Porritt, Lucy; Friedlander, Elizabeth

2014-05-01

299

Core-core and core-valence correlation  

NASA Technical Reports Server (NTRS)

The effect of (1s) core correlation on properties and energy separations was analyzed using full configuration-interaction (FCI) calculations. The Be 1 S - 1 P, the C 3 P - 5 S and CH+ 1 Sigma + or - 1 Pi separations, and CH+ spectroscopic constants, dipole moment and 1 Sigma + - 1 Pi transition dipole moment were studied. The results of the FCI calculations are compared to those obtained using approximate methods. In addition, the generation of atomic natural orbital (ANO) basis sets, as a method for contracting a primitive basis set for both valence and core correlation, is discussed. When both core-core and core-valence correlation are included in the calculation, no suitable truncated CI approach consistently reproduces the FCI, and contraction of the basis set is very difficult. If the (nearly constant) core-core correlation is eliminated, and only the core-valence correlation is included, CASSCF/MRCI approached reproduce the FCI results and basis set contraction is significantly easier.

Bauschlicher, Charles W., Jr.; Langhoff, Stephen R.; Taylor, Peter R.

1988-01-01

300

Terrestrial impact melt rocks and glasses  

NASA Astrophysics Data System (ADS)

The effects of meteorite and comet impact on Earth are rock brecciation, the formation of shock metamorphic features, rock melting, and the formation of impact structures, i.e. simple craters, complex craters, and multi-ring basins. Large events, such as the 65-Ma Chicxulub impact, are believed to have had catastrophic environmental effects that profoundly influenced the development of life on Earth. In this review, an attempt is made to summarize some of the voluminous literature on impact melting, one important aspect of planetary impact, provide some comments on this process, and to make suggestions for future research. The products of impact melting are glasses, impact melt rocks, and pseudotachylites. Our treatise deals mainly with the geological setting, petrography, and major-element chemistry of melt rocks and glasses. Impact glasses, in several petrographic aspects, are similar to volcanic glasses, but they are associated with shock metamorphosed mineral and rock fragments and, in places, with siderophile element anomalies suggestive of meteoritic contamination. They are found in allogenic breccia deposits within (fall-back 'suevite') and outside (fall-out 'suevite') impact craters and, as spherules, in distal ejecta. Large events, such as the K/T boundary Chicxulub impact, are responsible for the formation of worldwide ejecta horizons which are associated with siderophile element anomalies and shock metamorphosed mineral and rock debris. Impact glasses have a bulk chemical composition that is homogeneous but exemptions to this rule are common. On a microscopic scale, however, impact glasses are commonly strikingly heterogeneous. Tektites are glasses ejected from craters over large distances. They are characterized by very low water and volatile contents and element abundances and ratios that are evidence that tektites formed by melting of upper crustal, sedimentary rocks. Four tektite strewn-fields are known, three of which can be tied to specific impact craters. Impact melt rocks form sheets, lenses, and dike-like bodies within or beneath allogenic fallback breccia deposits in the impact crater and possibly on crater terraces and flanks. Dikes of impact melt rocks also intrude the rocks of the crater floor. They commonly contain shock metamorphosed target rock and mineral fragments in various stages of assimilation and are glassy or fine- to coarse-grained. Chemically, they are strikingly homogeneous, but as with impact glasses, exemptions to this rule do exist. Large and thick melt bodies, such as the Sudbury Igneous Complex (SIC), are differentiated or may represent a combination of impact melt rocks sensu-strictu and impact-triggered, deep-crustal melts. A concerted, multidisciplinary approach to future research on impact melting and on other aspects of meteorite and comet impact is advocated. Impact models are models only and uncritical reliance on their validity will not lead to a better understanding of impact processes—especially of melting, excavation, and deposition of allogenic breccias and the spatial position of breccias in relation to sheets and lenses of melt rocks within the crater. Impact-triggered pressure-release melting of target rocks beneath the excavation cavity may be responsible for the existence of melt rocks beneath the impact melt rocks sensu-strictu. This controversial idea needs to be tested by a re-evaluation of existing data and models, be they based on field or laboratory research. Only a relatively small number of terrestrial impact structures has been investigated in sufficient detail as it relates to geological and geophysical mapping. In this review, we summarize observations made on impact melt rocks and impact glasses in a number of North American (Brent, Haughton, Manicouagan, New Quebec, Sudbury, Wanapitei, all in Canada), Asian (Popigai, Russia; Zhamanshin, Kazakhstan), two South African structures (Morokweng and Vredefort), the Henbury crater field of Australia, and one European crater (Ries, Germany). Our tables listing major-element chemical compositions of impact

Dressler, B. O.; Reimold, W. U.

2001-12-01

301

Late-Phase Melt Conditions Affecting the Potential for In-Vessel Retention in High Power Reactors  

SciTech Connect

If cooling is inadequate during a reactor accident, a significant amount of core material could become molten and relocate to the lower head of the reactor vessel, as happened in the Three Mile Island Unit 2 accident. In such a case, concerns about containment failure and associated risks can be eliminated if it is possible to ensure that the lower head remains intact so that relocated core materials are retained within the vessel. Accordingly, in-vessel retention (IVR) of core melt as a key severe accident management strategy has been adopted by some operating nuclear power plants and planned for some advanced light water reactors. However, it is not clear that currently proposed external reactor vessel cooling (ERVC) without additional enhancements can provide sufficient heat removal to assure IVR for high power reactors (i.e., reactors with power levels up to 1500 MWe). Consequently, a joint United States/Korean International Nuclear Energy Research Initiative (I-NERI) has been launched to develop recommendations to improve the margin of success for in-vessel retention in high power reactors. This program is initially focussed on the Korean Advanced Power Reactor—1400 MWe (APR1400) design. However, recommendations will be developed that can be applied to a wide range of existing and advanced reactor designs. The recommendations will focus on modifications to enhance ERVC and modifications to enhance in-vessel debris coolability. In this paper, late-phase melt conditions affecting the potential for IVR of core melt in the APR1400 were established as a basis for developing the I-NERI recommendations. The selection of ‘bounding’ reactor accidents, simulation of those accidents using the SCDAP/RELAP5-3D© code, and resulting late-phase melt conditions are presented. Results from this effort indicate that bounding late-phase melt conditions could include large melt masses (>120,000 kg) relocating at high temperatures (3400 K). Estimated lower head heat fluxes associated with this melt could exceed the maximum critical heat flux, indicating additional measures such as the use of a core catcher and/or modifications to enhance external reactor vessel cooling may be necessary to ensure in-vessel retention of core melt.

D. L. Knudson; J. L. Rempe; K. G. Condie; K. Y. Suh; F. B.Cheung; S. B. Kim

2004-05-01

302

Melt migration through Io's convecting mantle  

NASA Astrophysics Data System (ADS)

The extensive volcanism occurring on the surface of Io suggests that its interior must contain at least some partial melt. Unlike Earth, Io cannot lose its internal heat through convection alone [1]. Instead, melt moving through the solid mantle helps remove heat from Io's interior by carrying its latent heat towards the surface as it buoyantly ascends through the mantle. We investigate this process by considering melt migration in a column of rock rising through the mantle between downwelling plumes. Convective scaling laws provide the upwelling velocity and the temperature of the rising mantle. Properties of melt migration in this rising mantle are calculated using porous flow equations and an equation for the conservation of energy which includes latent heat consumption, heat advection and heat conduction [2]. This combination of convective scaling laws and porous flow laws allows us to self-consistently determine the radial melt fraction profile in Io's interior, the average melt fraction in Io's interior and the heat flux due to advection of melt. The average melt fraction can be compared to the melt fraction constraints calculated by [3] from Galileo magnetometer measurements. The surface heat flux calculations can be compared to the value of Io's observed surface heat flux which ranges with observation from 1.5-4 W m-2 [4]. [1] Moore W. B. (2003) J. Geophys. Res., 108, E8, 15-1. [2] Hewitt I. J. and Fowler A. C. (2008) Proc. R. Soc. A., 464, 2467-2491. [3] Khurana K. K. et al. (2011) Science, 332, 1186-1189. [4] Moore, W. B. et al. (2007) In: Io After Galileo, Springer-Praxis, 89-108.

Elder, C. M.; Showman, A. P.

2013-12-01

303

Variations in Melt Generation and Migration along the Aleutian Arc (Invited)  

NASA Astrophysics Data System (ADS)

The generation and ascent of mantle melt beneath volcanic arcs sets the course for how magmas differentiate to form the continental crust and erupt explosively from volcanoes. Although the basic framework of melting at subduction zones is understood to involve the convective influx of hot mantle (Tp ? 1300°C) and advective transport of water-rich fluids from the subducting slab, the P-T paths that melts follow during melt generation and migration are still not well known. The Aleutian Arc provides an opportunity to explore the conditions of mantle melting in the context of volcanoes that span an unusually large range in the depth to the slab, from Seguam island, with among the shallowest depths to the slab worldwide (~65 km, [1]) to Bogoslof island, behind the main volcanic front and twice the depth to the slab (~130 km). Here we combine thermal models tuned to Aleutian subduction parameters [after 2] with petrological estimates of the T and P of mantle-melt equilibration, using a major element geothermometer [3] and estimates of H2O and fO2 from olivine-hosted melt inclusion measurements [4] for basaltic magmas from 6 volcanoes in the central Aleutians (Korovin, Seguam, Bogoslof, Pakushin, Akutan, Shishaldin). We find mantle-melt equilibration conditions to vary systematically as a function of the depth to the slab, from 30 km and 1220°C (for Seguam) to 60 km and 1300°C (for Bogoslof). Such shallow depths, which extend up to the Moho, define a region perched well above the hot core of the mantle wedge predicted from thermal models, even considering the shallow depths of slab-mantle coupling (< 60 km) required to supply hot mantle beneath Seguam. Thus, even though the greatest melt production will occur in the hot core of the wedge (50-100 km depth), melts apparently ascend and re-equilibrate in the shallowest mantle. Volcanoes that overlie the greatest depth to the slab, and lie furthest from the wedge corner, stall at greater depths (~60 km), at the base of the conductive upper plate (i.e., lithosphere). The conductive lid and isotherms shallow toward the wedge corner. This leads to shallower depths of melt equilibration at shallower depths to the slab. A second effect is infiltration of melt into the thinning lithosphere, likely due to the increase in strain-rate toward the wedge corner, which favors melt segregation, migration, and shallow equilibration [5]. Such a process is developed most beneath Seguam, where melts collect at the Moho (~ 30km), but are still > 1200°C. Such equilibration depths in the uppermost mantle (30-60 km) and temperatures typical of the base of the conductive lid appear to characterize most modeled primary arc magmas [6], and point to a final re-setting point in the mantle that controls the composition of bulk arc crust. [1] Syracuse & Abers, 2006, G3. [2] Syracuse, van Keken, Abers, (2010) PEPI. [3] Lee, Luffi, Plank, Dalton, Leeman (2009) EPSL. [4] Zimmer et al. (2010) J.Pet. [5] Holzman & Kendall (2010). [6] Ruscitto et al. (2012) G3.

Plank, T. A.; Van Keken, P. E.

2013-12-01

304

Atomistic modeling of femtosecond laser-induced melting and atomic mixing in Au film Cu substrate system  

E-print Network

, including laser surface alloying, cladding, annealing, and hardening, e.g. [1­6]. The improvement of surfaceAtomistic modeling of femtosecond laser-induced melting and atomic mixing in Au film ­ Cu substrate modification by laser irradiation is in the core of many modern processing and fabrication techniques

Zhigilei, Leonid V.

305

Electrohydrodynamic quenching in polymer melt electrospinning  

NASA Astrophysics Data System (ADS)

Infrared thermal measurements on polymer melt jets in electrospinning have revealed rapid quenching by ambient air, an order of magnitude faster than predicted by the classical Kase and Matsuo correlation. This drastic heat transfer enhancement can be linked to electrohydrodynamic (EHD) effects. Analysis of EHD-driven air flow was performed and included into a comprehensive model for polymer melt electrospinning. The analysis was validated by excellent agreement of both predicted jet radius and temperature profiles with experimental results for electrospinning of Nylon-6 (N6), polypropylene (PP), and polylactic acid (PLA) melts. Based on this analysis, several methods that can be used to inhibit or enhance the quenching are described.

Zhmayev, Eduard; Cho, Daehwan; Lak Joo, Yong

2011-07-01

306

Physics of the Lindemann melting rule  

SciTech Connect

We investigate the thermodynamics of melting for 74 distinct chemical elements including several actinides and rare earths. We find that the observed melting points are consistent with a linear relationship between the correlation entropy of the liquid and the Grueneisen constant of the solid, and that the Lindemann rule is well obeyed for the elements with simple structures and less well obeyed for the less symmetric more open structures. No special assumptions are required to explain the melting points of the rare earths or light actinides.

Lawson, Andrew C [Los Alamos National Laboratory

2008-01-01

307

Models and correlations of the DEBRIS Late-Phase Melt Progression Model  

SciTech Connect

The DEBRIS Late Phase Melt Progression Model is an assembly of models, embodied in a computer code, which is designed to treat late-phase melt progression in dry rubble (or debris) regions that can form as a consequence of a severe core uncover accident in a commercial light water nuclear reactor. The approach is fully two-dimensional, and incorporates a porous medium modeling framework together with conservation and constitutive relationships to simulate the time-dependent evolution of such regions as various physical processes act upon the materials. The objective of the code is to accurately model these processes so that the late-phase melt progression that would occur in different hypothetical severe nuclear reactor accidents can be better understood and characterized. In this report the models and correlations incorporated and used within the current version of DEBRIS are described. These include the global conservation equations solved, heat transfer and fission heating models, melting and refreezing models (including material interactions), liquid and solid relocation models, gas flow and pressure field models, and the temperature and compositionally dependent material properties employed. The specific models described here have been used in the experiment design analysis of the Phebus FPT-4 debris-bed fission-product release experiment. An earlier DEBRIS code version was used to analyze the MP-1 and MP-2 late-phase melt progression experiments conducted at Sandia National Laboratories for the US Nuclear Regulatory Commission.

Schmidt, R.C.; Gasser, R.D. [Sandia National Labs., Albuquerque, NM (United States). Reactor Safety Experiments Dept.

1997-09-01

308

On the thermal and magnetic histories of Earth and Venus: Influences of melting, radioactivity, and conductivity  

NASA Astrophysics Data System (ADS)

The study of the thermal evolution of Earth's interior is uncertain and controversial in many respects, from the interpretation of petrologic observations used to infer the temperature and dynamics of the interior, to the physics and material properties governing heat transport. The thermal history of Venus is even more uncertain, but the lack of a dynamo at present in an otherwise similar planet may provide additional constraints on terrestrial planet evolution. In this paper a one dimensional thermal history model is derived that includes heat loss due to mantle melt eruption at the surface to explore its influence on the thermal and magnetic history of Earth and Venus. We show that the thermal catastrophe of Earth's mantle, which occurs for a present day Urey ratio of 1/3 and convective heat loss exponent of ?=1/3, can be avoided by assuming a rather high core heat flow of ?15 TW. This core heat flow also avoids the new core paradox by allowing for the geodynamo to be thermally powered prior to inner core growth for core thermal conductivities as high as 130 Wm K. Dynamo regime diagrams demonstrate that the mantle melt eruption rate has a minor effect on the history of mobile lid planets due to the efficiency of plate tectonic convective heat loss. However, if Earth were in a stagnant lid regime prior to 2.5 Ga, as has been proposed, then at least ?5% of mantle melt is required to erupt in order to thermally power the paleodynamo at that time. Dynamo regime diagrams for stagnant lid Venus models indicate that more than half of the melt generated in the mantle is required to erupt in order to overcome the insulation imposed by the stagnant lid and drive a dynamo. This implies that with an Earth-like mantle radioactivity the Venusian dynamo shut down ?0.3 Ga for an eruption efficiency of 50%, and ?3 Ga for an eruption efficiency of zero. Consequently, a stagnant lid alone does not prevent a core dynamo if melting of the upper mantle provides a substantial mantle heat sink.

Driscoll, P.; Bercovici, D.

2014-11-01

309

Microstructures and petrology of melt inclusions in the anatectic sequence of Jubrique (Betic Cordillera, S Spain): Implications for crustal anatexis  

NASA Astrophysics Data System (ADS)

We report a new occurrence of melt inclusions in polymetamorphic granulitic gneisses of the Jubrique unit, a complete though strongly thinned crustal section located above the Ronda peridotite slab (Betic Cordillera, S Spain). The gneissic sequence is composed of mylonitic gneisses at the bottom and in contact with the peridotites, and porphyroblastic gneisses on top. Mylonitic gneisses are strongly deformed rocks with abundant garnet and rare biotite. Except for the presence of melt inclusions, microstructures indicating the former presence of melt are rare or absent. Upwards in the sequence, garnet decreases whereas biotite increases in modal proportion. Melt inclusions are present from cores to rims of garnets throughout the entire sequence. Most of the former melt inclusions are now totally crystallized and correspond to nanogranites, whereas some of them are partially made of glass or, more rarely, are totally glassy. They show negative crystal shapes and range in size from ? 5 to 200 ?m, with a mean size of ? 30-40 ?m. Daughter phases in nanogranites and partially crystallized melt inclusions include quartz, feldspars, biotite and muscovite; accidental minerals include kyanite, graphite, zircon, monazite, rutile and ilmenite; glass has a granitic composition. Melt inclusions are mostly similar throughout all the gneissic sequence. Some fluid inclusions, of possible primary origin, are spatially associated with melt inclusions, indicating that at some point during the suprasolidus history of these rocks granitic melt and fluid coexisted. Thermodynamic modeling and conventional thermobarometry of mylonitic gneisses provide peak conditions of ? 850 °C and 12-14 kbar, corresponding to cores of large garnets with inclusions of kyanite and rutile. Post-peak conditions of ? 800-850 °C and 5-6 kbar are represented by rim regions of large garnets with inclusions of sillimanite and ilmenite, cordierite-quartz-biotite coronas replacing garnet rims, and the matrix with oriented sillimanite. Previous conventional petrologic studies on these strongly deformed rocks have proposed that anatexis started during decompression from peak to post-peak conditions and in the field of sillimanite. The study of melt inclusions shows, however, that melt was already present in the system at peak conditions, and that most garnet grew in the presence of melt.

Barich, Amel; Acosta-Vigil, Antonio; Garrido, Carlos J.; Cesare, Bernardo; Taj?manová, Lucie; Bartoli, Omar

2014-10-01

310

Extreme mineral-scale Sr isotope heterogeneity in granites by disequilibrium melting of the crust  

NASA Astrophysics Data System (ADS)

The broadest ranges of initial Sr isotopic ratios (87Sr/86Sri) ever reported within a single igneous rock (?2×10-2) are preserved within the late Miocene laccolith-pluton-dyke felsic complex of Elba Island (Italy). For these units, the integration of textural and crystal-scale isotope data allows tracing the evolution of the 87Sr/86Sri of the melt from the emplacement level back to the earliest pre-emplacement crystallization stage. The rock matrix minerals record the 87Sr/86Sri composition of the magma at the emplacement level (0.715-0.716). K-feldspar megacrysts, representing an earlier phase crystallized at depth, record a rim-to-core increase of Sr-isotopic ratios from values similar to those of the matrix to significantly higher ones (?0.719). Remarkably, biotites hosted within megacrysts, representing the first crystallization stage, have extreme and contrasting 87Sr/86Sri values in the different intrusive units: biotites within megacrysts from the laccolith record the lowest ratio in the intrusive complex (?0.710), while those in the megacrysts from the pluton and associated felsic dyke have the highest 87Sr/86Sri(?0.732). This time-transgressive record of isotopic variation in the magma reflects episodic recharge and mixing of magma batches formed by disequilibrium melting of crustal sources that produced melts through different reactions as temperature was increasing. The progression from muscovite- to biotite-dominated fluid-absent melting generates melts with increasing 87Sr/86Sr, while at higher temperatures, the progression from biotite- to hornblende-dominated melting reactions results in a decrease in the 87Sr/86Sr of the melt.

Farina, Federico; Dini, Andrea; Rocchi, Sergio; Stevens, Gary

2014-08-01

311

Monoclinic tridymite in clast-rich impact melt rock from the Chesapeake Bay impact structure  

USGS Publications Warehouse

X-ray diffraction and Raman spectroscopy confirm a rare terrestrial occurrence of monoclinic tridymite in clast-rich impact melt rock from the Eyreville B drill core in the Chesapeake Bay impact structure. The monoclinic tridymite occurs with quartz paramorphs after tridymite and K-feldspar in a microcrystalline groundmass of devitrified glass and Fe-rich smectite. Electron-microprobe analyses revealed that the tridymite and quartz paramorphs after tridymite contain different amounts of chemical impurities. Inspection by SEM showed that the tridymite crystal surfaces are smooth, whereas the quartz paramorphs contain irregular tabular voids. These voids may represent microporosity formed by volume decrease in the presence of fluid during transformation from tridymite to quartz, or skeletal growth in the original tridymite. Cristobalite locally rims spherulites within the same drill core interval. The occurrences of tridymite and cristobalite appear to be restricted to the thickest clast-rich impact melt body in the core at 1402.02-1407.49 m depth. Their formation and preservation in an alkali-rich, high-silica melt rock suggest initially high temperatures followed by rapid cooling.

Jackson, J.C.; Horton, J.W., Jr.; Chou, I.-M.; Belkin, H.E.

2011-01-01

312

Melting temperature and thermal conductivity of irradiated (U,Pu)O[sub 2] fuel  

SciTech Connect

Both melting temperature and thermal conductivity are important physical properties to evaluate the thermal behavior of fast breeder reactor (FBR) fuel. Core design for commercialization of the FBR has to realize high burnup, a long refueling interval, and high power density conditions. This means that the internal conversion ratio of the core fuel becomes high and depression of the linear heat generation rate becomes small. Therefore, evaluation of fuel temperature at the end of fuel life is essential to the design of a large FBR core. It is generally accepted that the melting temperature and thermal conductivity of irradiated (U,Pu)O[sub 2] fuel decrease with increasing burnup because of the buildup of fission products in a fuel matrix. However, because of large uncertainties of measured values, little postirradiation examination data are available on irradiation effects. In this study, the effect of irradiation on melting temperature and thermal conductivity with small measurement uncertainties is investigated by modified measurement system on (U,Pu)O[sub 2] fuels irradiated in the JOYO fast reactor and other foreign reactors.

Yamamoto, Kazuya; Hirosawa, Takashi; Yoshikawa, Katsunori; Morozumi, Katsuhumi; Nomura; Shigeo (Power Reactor and Nuclear Fuels Development Corp., Ibaraki-ken (Japan))

1992-01-01

313

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

SciTech Connect

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.

Principal Investigator Kent Peaslee; Co-PIà ƒ  ¢Ã ‚  € à ‚  ™ s: Von Richards, Jeffrey Smith

2012-07-31

314

Beyond the Melting Pot: 35 Years Later.  

ERIC Educational Resources Information Center

Introduces a set of essays that revisit, "Beyond the Melting Pot," a book about ethnicity, race, and the American city, first published in 1963. The essays assess how well the book's interpretations apply to the contemporary immigration metropolis. (SM)

Alba, Richard

2000-01-01

315

A Study of Melt Inclusions in Tin-Mineralized Granites From Zinnwald, Germany  

NASA Astrophysics Data System (ADS)

We have analyzed silicate melt inclusions from drill core samples from the eastern Erzgebirge region, Germany, to investigate magmatic-hydrothermal and mineralizing processes in compositionally evolved, tin-bearing granitic magmas. Silicate melt inclusions are small blebs of glass that are trapped or locked within phenocrysts and may contain high concentrations of volatiles that usually leave magma via degassing. Quartz phenocrysts were carefully hand picked from crushed samples of albite-, zinnwaldite- +/- lepidolite-bearing granitic dikes from Zinnwald and soaked in cold dilute HF to remove any attached groundmass. The cleaned phenocrysts were loaded into precious metal capsules with several drops of immersion oil to create a reducing environment at high temperature. The quartz-bearing capsules were inserted into quartz glass tubes, loaded into a furnace for heating at temperatures of 1025\\deg and 1050\\deg C (1atm) for periods of 20 to 30 hours, and subsequently the inclusions were quenched to glass. The inclusions were analyzed for major and minor elements (including F, Cl, and P) by electron microprobe and for H2O, trace elements, and ore elements by ion microprobe. The melt inclusion compositions are similar to that of the whole-rock sample from which the quartz separates were extracted. The average melt inclusion and whole-rock compositions are peraluminous, high in silica and rare alkalis, and low in MgO, CaO, FeO, MnO, and P2O5. Unlike the whole-rock sample, the melt inclusions contain from 0.5 to more than 4 wt.% F. The Cl contents of the inclusions are variable and range from hundreds of ppm to several thousand ppm. The variable and strong enrichments in F of the melt inclusions may correlate with (Na2O/Na2O+K2O) in the inclusions which is consistent with crystal fractionation of feldspars which drives the residual melt to increasing Na contents. Overall, the compositions of these melt inclusions are different from melt inclusions extracted from the highly peraluminous, tin-mineralized granites of the western Erzgebirge region. The latter represent extreme compositional evolution of P- and F-rich magmas. The inclusions from the albite-, zinnwaldite-, +/- lepidolite-bearing granitic dikes of Zinnwald are more similar, compositionally, to those in tin-mineralized rhyolites of Mexico and New Mexico; the Erzgebirge dike melt inclusions container comparatively greater abundances of Li, Sn, and F, however.

Sookdeo, C. A.; Webster, J. D.; Eschen, M. L.; Tappen, C. M.

2001-12-01

316

Debris Covered Glaciers: Melt Modeling and Characterization  

NASA Astrophysics Data System (ADS)

Debris-covered glaciers occur in many mountainous regions throughout the world. Melt water from these glaciers is important for nearby populations, e.g. for hydropower and drinking water, however it can also be potentially dangerous in the form of a glacial lake outburst flood (GLOF). Accurate melt models are needed to calculate present and future mass balance of debris-covered glaciers. One widely used method assumes a constant 24-hour thermal gradient (CTG), although this approach remains largely untested. We assess the physical basis of the CTG method using a fully time-dependent 1-dimensional heat flux model and field data from Longyear Glacier, Svalbard, gathered during the 2010 melt season. An indirect correlation between debris thickness and linearity of the average daily temperature profile has been found. Melt rates modeled using the CTG method show a convergence with the results using our full physically based model for debris thickness > 0.5m. For debris thicknesses < 0.5m the CTG method calculates melt rates as low as twice the physical model. These differences arise out of the CTG method's assumption of a constant thermal gradient with depth as well as a 0°C debris-ice interface. Results have shown that only under stable weather conditions does the average daily debris thermal gradient approach constant. Furthermore, in reality the debris-ice interface undergoes higher temperatures than those calculated by the CTG method and it is only with increasing debris thickness that the two converge. The model was also used to generate an Østrem curve for the Longyear Glacier. Three Østrem curves were generated using data from early, peak and late melt to assess the differences that may arise from using data from only a small part of the melt season. Curves calculated from data collected during early and late melt season are very similar to the full season curve whereas the curve generated using data from the peak of the melt season overestimates daily melt rates by up to double. The results have significant implications when using Østrem curves to compare glacial sub-debris melt rates.

Mertes, J. R.; Benn, D.

2011-12-01

317

Melting points of synthetic wax esters  

Microsoft Academic Search

Saturated, monoenoic and dienoic wax esters, C26?C40, have been synthesized from even-numbered fatty alcohols and acids. In homologous series of saturated esters, the increments\\u000a of melting points follow a regular trend except for those esters which have an acid moiety two carbon atoms shorter than the\\u000a alcohol moiety. These wax esters have melting points higher than interpolation would predict. Monoenoic

B. T. R. Iyengar; H. Schlenk

1969-01-01

318

Congruent Melting Kinetics: Constraints on Chondrule Formation  

NASA Technical Reports Server (NTRS)

The processes and mechanisms of melting and their applications to chondrule formation are discussed A model for the kinetics of congruent melting is developed and used to place constraints on the duration and maximum temperature experienced by the interiors of relict-bearing chondrules. Specifically, chondrules containing relict forsteritic olivine or enstatitic pyroxene cannot have been heated in excess of 1901 C or 1577 C, respectively, for more than a few seconds.

Greenwood, James P.; Hess, Paul C.

1995-01-01

319

Automatic melting point determination of fats  

Microsoft Academic Search

The Mettler FP3 automatic dropping point apparatus was used for the determination of melting points of a variety of edible\\u000a fat products. The instrument was particularly suitable for this purpose because of the availability-of different heating rates.\\u000a Advantages were the fully automatic heating, the automatic and objective endpoint determination, the application for melted\\u000a as well as solidified samples (shortening, margarine,

W. G. Mertens; J. M. DeMan

1972-01-01

320

Volcanism by melt-driven Rayleigh-Taylor instabilities and possible consequences of melting for admittance ratios on Venus  

NASA Technical Reports Server (NTRS)

A large number of volcanic features exist on Venus, ranging from tens of thousands of small domes to large shields and coronae. It is difficult to reconcile all these with an explanation involving deep mantle plumes, since a number of separate arguments lead to the conclusion that deep mantle plumes reaching the base of the lithosphere must exceed a certain size. In addition, the fraction of basal heating in Venus' mantle may be significantly lower than in Earth's mantle reducing the number of strong plumes from the core-mantle boundary. In three-dimensional convection simulations with mainly internal heating, weak, distributed upwellings are usually observed. We present an alternative mechanism for such volcanism, originally proposed for the Earth and for Venus, involving Rayleigh-Taylor instabilities driven by melt buoyancy, occurring spontaneously in partially or incipiently molten regions.

Tackley, P. J.; Stevenson, D. J.; Scott, D. R.

1992-01-01

321

On melting criteria for complex plasma  

NASA Astrophysics Data System (ADS)

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-Hückel 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.

Klumov, Boris A.

2010-10-01

322

Melt inclusions in pegmatite quartz: complete miscibility between silicate melts and hydrous fluids at low pressure  

Microsoft Academic Search

Fluorine-, boron- and phosphorus-rich pegmatites of the Variscan Ehrenfriedersdorf complex crystallized over a temperature\\u000a range from about 700 to 500?°C at a pressure of about 1?kbar. Pegmatite quartz crystals continuously trapped two different\\u000a types of melt inclusions during cooling and growth: a silicate-rich H2O-poor melt and a silicate-poor H2O-rich melt. Both melts were simultaneously trapped on the solvus boundaries of

R. Thomas; J. D. Webster; W. Heinrich

2000-01-01

323

The Energy Crisis in the Earth's Core (Invited)  

NASA Astrophysics Data System (ADS)

Calculations of the core's thermal history and power required to drive the dynamo have, in the past, suffered from uncertainties in some of the key physical properties. Recent ab initio calculations, some of which have been confirmed by high pressure experiments, have removed much of this uncertainty. Unfortunately the new numbers require a large amount of heat to cross the core-mantle boundary (CMB) into the mantle: the Gruneissen constant and melting point at the inner core boundary determine a steep adiabatic gradient and the thermal and electrical conductivities are 2-4 times higher than the values in recent use. High electrical conductivity means the dynamo requires less power to sustain the magnetic field, but high thermal conductivity means more heat leaks away down the steep adiabatic gradient. It is hard to explain current geomagnetic secular variation without fluid upwelling within about 100 km of the core surface, requiring the core to be adiabatic throughout most of its depth. Here we calculate the cooling rate required to balance the entropy of thermal conduction down the adiabat. This is a lower bound because it ignores all other entropy changes associated with diffusion, notably magnetic and molecular. The heat flux across the CMB is then found from the cooling rate. The largest remaining uncertainty is the seismologically-determined density jump at the inner core boundary, which governs the fraction of light elements in the outer core, the strength of compositional convection, the melting temperature of the mixture at the inner core boundary (ICB), and the adiabatic gradient. A high density jump means more light elements are released on freezing, the higher concentration of light elements lowers the melting point, which in turn lowers the temperature throughout the core and shallows the adiabatic gradient. Unfortunately, calculations of the acoustic velocity of candidate mixtures corresponding to a high density jump do not fit the seismic models well, limiting how high the jump can be. Our minimum heat flux is less than the heat conducted down the adiabat at the CMB. Compositional convection could stir the core to within 100 km of the surface, although the severe thermal stratification makes this seem unlikely. However, heat flux across the CMB, as determined by mantle convection, can vary from place to place by a factor of 10 or more. The adiabat only needs to be exceeded in one spot for convection to stir the core everywhere, albeit weakly, the mean heat flux remaining subadiabatic. This mode of convection could explain the low secular variation in the Pacific, where the mantle is hot and heat flux is low. The dynamo is be driven deep within the core where compositional convection is most vigorous.

Gubbins, D.; Davies, C.; Alfe, D.

2013-12-01

324

Review of experiments to evaluate the ability of electrical heater rods to simulate nuclear fuel rod behavior during postulated loss-of-coolant accidents in light water reactors  

SciTech Connect

Issues related to using electrical fuel rod simulators to simulate nuclear fuel rod behavior during postulated loss-of-coolant accident (LOCA) conditions in light water reactors are summarized. Experimental programs which will provide a data base for comparing electrical heater rod and nuclear fuel rod LOCA responses are reviewed.

McPherson, G D; Tolman, E L

1980-01-01

325

Microstructural evidence of melting in crustal rocks (Invited)  

Microsoft Academic Search

The signature of the former presence of melt on a microscopic scale is highly variable, subject to modification both during the melting event and during its subsequent history. Static pyrometamorphism results in melt films on grain boundaries between reactant phases. If a volume increase is involved, melting results in hydrofracture. On a longer timescale, as demonstrated by fragments of the

M. B. Holness; B. Cesare; E. W. Sawyer

2010-01-01

326

Melting of multilayer colloidal crystals confined between two walls  

Microsoft Academic Search

Video microscopy is employed to study the melting behaviors of multilayer colloidal crystals composed of diameter-tunable microgel spheres confined between two walls. We systematically explore film thickness effects on the melting process and on the phase behaviors of single crystal and polycrystalline films. Thick films (>4 layers) are observed to melt heterogeneously, while thin films (<=4 layers) melt homogeneously, even

Y. Peng; Z.-R. Wang; A. M. Alsayed; A. G. Yodh; Y. Han

2011-01-01

327

Creep measuring device for low melting point metals  

E-print Network

for low melting point metals Metal Lithium Tin Lead Cadmium Melting Temperature C 180. 54 231. 96 327. 5 320. 9 Metal Na Indium Melting Temperature C 63. 25 97. 81 156. 61 33 near the melting point. No literature has been identified...

Portal, Marc-Emmanuel Gilbert

2012-06-07

328

Partial Melting and Liquefaction of Granular Fault Gouge During Earthquake Slip  

NASA Astrophysics Data System (ADS)

Gouge particles interact by friction and must heat significantly in large earthquake slip (> 1 m) accommodated by a narrow fault core. For very impermeable border zones of a water-infiltrated core, and when gouge dilation is small compared to differential thermal expansion, pore pressure p rises towards the ambient fault-normal stress ? n and the frictional resistance drops, reducing strength, and hence the rate of continuing temperature rise, to negligible values before the onset of melting (Sibson, Lachenbruch, Mase and Smith). However, those border zones will have just experienced the high stress fluctuations associated with passage of the rupture front and will be extensively cracked with renewed, high permeability k. (k measured by Lockner et al. for the Nojima fault zone, active in the 1995 Kobe earthquake, is of order 500 times higher for the damage zones than for the sheared ultracataclastic core within them.) In presence of such high k border zones, the time tr to relax away thermally elevated p scales as h2/? where h is core thickness and ? is its poroelastic diffusivity. Using core permeability k = 10-19 m2 like for Nojima, we roughly estimate tr < 0.1 s for h < 10 mm. Thus thermal pressurization of water will sometimes be insufficient to eliminate frictional strength, and temperature will continue to rise so that the gouge begins to melt. We must then confront the problem of describing the rheology of a gouge with particles that are in frictional contact, at least in the earliest stages of melting, but with a pore fluid (mixture of melt and residual water) that sustains large shear stress. The Terzaghi effective stress procedure treats the fluid as if under hydrostatic pressure and is then not fully applicable. Within it, p is predicted to rapidly rise towards ? n in the early stages of partial melting because ? scales inversely with the then very large viscosity of the pore fluid, so tr is large and the pressure increase, due to differential expansion and conversion of solid to fluid, cannot diffuse away. Because of the viscosity of the fluid there will remain a shear strength of the gouge aggregate, albeit one that we cannot very confidently characterize, and the sustained shear heating necessarily drives further melting (conductive heat losses are negligible in the situation considered). Ultimately, melt comes to occupy enough volume fraction that the still-solid gouge particles are effectively suspended in the fluid, and the entire mass is liquefied under a pressure p = ? n and can be rapidly squeezed into large enough crack spaces in the damaged fault borders (refreezing occurs in narrow spaces affected by conduction). When the fault-parallel stress < ? n =p, a condition which will sometimes be met only transiently in the stress field near the rupture front, liquefied gouge can hydraulically crack into the border zones, later solidifying into pseudotachylyte injection vein structures seen in some geologic exposures. We describe also a local steady state in this fully liquefied range, with the melt rate balanced by the loss rate into the border zones; shear strength then varies inversely with slip rate. Our description of the process also supports the concept that natural pseudotachylytes result from rapid solidification of an only partially melted granular material.

Jacques, L. M.; Rice, J. R.

2002-12-01

329

The determination of partial melt compositions of peridotitic systems by melt inclusion synthesis  

NASA Astrophysics Data System (ADS)

An experimental method of melt inclusion synthesis within olivine crystals has been developed to determine the composition of the melt present in a partially molten peridotite assemblage. Trace element doped peridotite was equilibrated with 5wt% of a C-O-H volatile source at 20kbar/1175°C in a piston-cylinder apparatus under buffered oxygen and sulphur fugacity conditions [log(fO2) IW +1 log unit, log (fS2) Fe/FeS > +1 log unit]. A single crystal of olivine, which had been cut to a disc shape, was included in the sample capsule. At run conditions the peridotite charge formed olivine, orthopyroxene, clinopyroxene, Fe-Ni sulphide and a volatile-bearing melt. The melt phase is preserved as homogeneous glass inclusions up to 50?m in size, trapped in situ in the olivine disc. The major element composition of the glass inclusions showed them to be of broadly basaltic character, but with a low Mg/(Mg+?Fe), which is associated with precipitation of olivine from the melt inclusion onto the walls of the olivine disc during quenching. Thus the equilibrium melt composition has been calculated from the glass inclusion composition by addition of olivine component using the Fe/Mg exchange coefficient of Roeder and Emslie (1970); the desired Mg/(Mg+?Fe) being determined from the composition of olivine formed at run conditions in the peridotite section of the charge. The melt composition obtained is close to the trend for dry melting established by Falloon and Green (1988), and it is evident that although the reduced volatiles in this case have induced a liquidus depression of some 250°C, there has been only a small shift in melt composition. Trace element, carbon and hydrogen contents of thirteen melt inclusions have been determined by secondary ion mass spectrometry (SIMS). The trace element signature is consistent with 29% melting in equilibrium with a lherzolitic assemblage. The equilibrium melt has a C/H of 0.48 by weight. Carbon solubility in partial melts is thus significant under reducing conditions in the presence of dissolved ``water components'' and establishes a major melt fluxing role for carbon in the upper mantle. The ubiquitous presence of carbon and hydrogen in basaltic magmas underscores the importance of determining both the position of vapour-present solidi and the composition of melts generated, when developing petrogenetic models.

Odling, N. W. A.; Green, D. H.; Harte, B.

330

Statistical extraction of volcanic sulphate from nonpolar ice cores  

NASA Astrophysics Data System (ADS)

Ice cores from outside the Greenland and Antarctic ice sheets are difficult to date because of seasonal melting and multiple sources (terrestrial, marine, biogenic and anthropogenic) of sulfates deposited onto the ice. Here we present a method of volcanic sulfate extraction that relies on fitting sulfate profiles to other ion species measured along the cores in moving windows in log space. We verify the method with a well dated section of the Belukha ice core from central Eurasia. There are excellent matches to volcanoes in the preindustrial, and clear extraction of volcanic peaks in the post-1940 period when a simple method based on calcium as a proxy for terrestrial sulfate fails due to anthropogenic sulfate deposition. We then attempt to use the same statistical scheme to locate volcanic sulfate horizons within three ice cores from Svalbard and a core from Mount Everest. Volcanic sulfate is <5% of the sulfate budget in every core, and differences in eruption signals extracted reflect the large differences in environment between western, northern and central regions of Svalbard. The Lomonosovfonna and Vestfonna cores span about the last 1000 years, with good extraction of volcanic signals, while Holtedahlfonna which extends to about AD1700 appears to lack a clear record. The Mount Everest core allows clean volcanic signal extraction and the core extends back to about AD700, slightly older than a previous flow model has suggested. The method may thus be used to extract historical volcanic records from a more diverse geographical range than hitherto.

Moore, J. C.; Beaudon, E.; Kang, Shichang; Divine, D.; Isaksson, E.; Pohjola, V. A.; van de Wal, R. S. W.

2012-02-01

331

Diffusion of Water in Silicate Melts  

NASA Astrophysics Data System (ADS)

Diffusion of water in silicate melts and glasses has significant impact on both high temperature igneous and low temperature alteration processes. Water diffusivity in silicates is complicated by its strong, complex dependence on composition, including water content, which has been used to infer molecular level mechanisms of water diffusion. Very little has been done on mafic melts, but such studies are important both for their petrologic significance and because their molecular structures differ considerably (e.g., they are less polymerized) from more extensively studied acidic compositions. We have measured diffusion of water in high-Al basalt, Ab50Di50, Ab75Di25 (the last two modeling haplo-basalt to andesite), and rhyolite. Hydration (water-poor melt in contact with water vapor) and diffusion couple experiments (two glasses with different water contents placed in contact) were run in an internally heated pressure vessel or a rapid-quench TZM pressure vessel (1250-1300°C, 0.5-1 kbar, up to 25 minutes for intermediate to mafic compositions; 600-950°C, 0.5-1 kbar, up to 44 hours for rhyolite). Concentration profiles, obtained by FTIR spectroscopy, were fit using water diffusion coefficients with various functional forms for the dependence on water content. The dependence of water diffusivity on water content was also determined directly using a modified Boltzmann-Matano method for calculating diffusion coefficients along profiles. Key results include: (1) Hydration and diffusion couple experiments give similar results. (2) Diffusivity of water in basaltic melts at high water contents is consistent with the single previous study. (3) The concentration dependence of water diffusivity in these melts is consistent with previous studies and with simple models that assume water diffuses as water molecules in equilibrium with immobile hydroxyl groups. (4) Diffusivity of water over a wide range of melt compositions (at 1 wt.% water) correlates well with calculated melt viscosity.

Newman, S.; Persikov, E.; Stolper, E.; Bukhtiyarov, P.; Zhang, Y.

2005-12-01

332

An empirical method for calculating melt compositions produced beneath mid-ocean ridges: Application for axis and off-axis (seamounts) melting  

NASA Astrophysics Data System (ADS)

We present a new method for calculating the major element compositions of primary melts parental to mid-ocean ridge basalt (MORB). This model is based on the experimental data of Jaques and Green (1980), Falloon et al. (1988), and Falloon and Green (1987, 1988) which are ideal for this purpose. Our method is empirical and employs solid-liquid partition coefficients (Di) from the experiments. We empirically determine Di = ƒ(P,F) and use this to calculate melt compositions produced by decompression-induced melting along an adiabat (column melting). Results indicate that most MORBs can be generated by 10-20% partial melting at initial pressures (P0) of 12-21 kbar. Our primary MORB melts have MgO = 10-12 wt %. We fractionate these at low pressure to an MgO content of 8.0 wt % in order to interpret natural MORB liquids. This model allows us to calculate Po, Pƒ, To, Tƒ, and F for natural MORB melts. We apply the model to interpret MORB compositions and mantle upwelling patterns beneath a fast ridge (East Pacific Rise (EPR)8°N to 14°N), a slow ridge (mid-Atlantic Ridge (MAR) at 26°S), and seamounts near the EPR (Lament seamount chain). We find mantle temperature differences of up to 50°-60°C over distances of 30-50 km both across axis and along axis at the EPR. We propose that these are due to upward mantle flow in a weakly conductive (versus adiabatic) temperature gradient. We suggest that the EPR is fed by a wide (-100 km) zone of upwelling due to plate separation but has a central core of faster buoyant flow. An along-axis thermal dome between the Siqueiros transform and the 11°45' Overlapping Spreading center (OSC) may represent such an upwelling; however, in general there is a poor correlation between mantle temperature, topography, and the segmentation pattern at the EPR. For the Lament seamounts we find regular across-axis changes in Po and F suggesting that the melt zone pinches out off axis. This observation supports the idea that the EPR is fed by a broad upwelling which diminishes in vigor off axis. In contrast with the EPR axis, mantle temperature correlates well with topography at the MAR, and there is less melting under offsets. The data are consistent with weaker upwelling under offsets and an adiabatic temperature gradient in the sub axial mantle away from offsets. The MAR at 26°S exhibits the so-called local trend of Klein and Langmuir (1989). Our model indicates that the local trend cannot be due solely to intracolumn melting processes. The local trend seems to be genetically associated with slow-spreading ridges, and we suggest it is due to melting of multiple individual domains that differ in initial and final melting pressure within segments fed by buoyant focused mantle flow.

Niu, Yaoling; Batiza, Rodey

1991-12-01

333

An empirical method for calculating melt compositions produced beneath mid-ocean ridges: for axis and off-axis (seamounts) melting application  

NASA Astrophysics Data System (ADS)

We present a new method for calculating the major element compositions of primary melts parental to mid-ocean ridge basalt (MORB). This model is based on the experimental data of Jaques and Green (1980), Falloon et al. (1988), and Falloon and Green (1987, 1988) which are ideal for this purpose. Our method is empirical and employs solid-liquid partition coefficients (Di) from the experiments. We empirically determine Di=f(P,F) and use this to calculate melt compositions produced by decompression-induced melting along an adiabat (column melting). Results indicate that most MORBs can be generated by 10-20% partial melting at initial pressures (P0) of 12-21 kbar. Our primary MORB melts have MgO=10-12 wt %. We fractionate these at low pressure to an MgO content of 8.0 wt% in order to interpret natural MORB liquids. This model allows us to calculate Po, Pf, To, Tf, and F for natural MORB melts. We apply the model to interpret MORB compositions and mantle upwelling patterns beneath a fast ridge (East Pacific Rise (EPR) 8°N to 14°N), a slow ridge (mid-Atlantic Ridge (MAR) at 26°S), and seamounts near the EPR (Lamont seamount chain). We find mantle temperature differences of up to 50°-60°C over distances of 30-50 km both across axis and along axis at the EPR. We propose that these are due to upward mantle flow in a weakly conductive (versus adiabatic) temperature gradient. We suggest that the EPR is fed by a wide (~100 km) zone of upwelling due to plate separation but has a central core of faster buoyant flow. An along-axis thermal dome between the Siqueiros transform and the 11°45' Overlapping Spreading Center (OSC) may represent such an upwelling; however, in general there is a poor correlation between mantle temperature, topography, and the segmentation pattern at the EPR. For the Lamont seamounts we find regular across-axis changes in Po and F suggesting that the melt zone pinches out off axis. This observation supports the idea that the EPR is fed by a broad upwelling which diminishes in vigor off axis. In contrast with the EPR axis, mantle temperature correlates well with topography at the MAR, and there is less melting under offsets. The data are consistent with weaker upwelling under offsets and a adiabatic temperature gradient in the subaxial mantle away from offsets. The MAR at 26°S exhibits the so-called local trend of Klein and Langmuir (1989). Our model indicates that the local trend cannot be due solely to intracolumn melting processes. The local trend seems to be genetically associated with slow-spreading ridges, and we suggest it is due to melting of multiple individual domains that differ in initial and final melting pressure within segments fed by buoyant focused mantle flow.

Batiza, Rodey

1991-12-01

334

Powder Cores s Molypermalloy  

E-print Network

-2 Temperature Rise Calculations 2-3 Core Selector Charts TECHNICAL DATA 3-1 Material Properties 3-2 Conversion Tables 3-3 Normal Magnetization Curves 3-5 Core Loss Density Curves 3-12 Permeability versus Temperature versus Frequency Curves 3-21 Wire Table CORE DATA 4-1 Toroid Data 4-31 Kool Mµ® E Core Data 4-33 MPP

335

Forsterite-bearing type B refractory inclusions from CV3 chondrites: From aggregates to volatilized melt droplets  

NASA Astrophysics Data System (ADS)

Detailed petrologic and oxygen isotopic analysis of six forsterite-bearing Type B calcium-aluminum-rich inclusions (FoBs) from CV3 chondrites indicates that they formed by varying degrees of melting of primitive precursor material that resembled amoeboid olivine aggregates. A continuous evolutionary sequence exists between those objects that experienced only slight partial melting or sintering through objects that underwent prolonged melting episodes. In most cases, melting was accompanied by surface evaporative loss of magnesium and silicon. This loss resulted in outer margins that are very different in composition from the cores, so much so that in some cases, the mantles contain mineral assemblages that are petrologically incompatible with those in the cores. The precursor objects for these FoBs had a range of bulk compositions and must therefore have formed under varying conditions if they condensed from a solar composition gas. Five of the six objects show small degrees of mass-dependent oxygen isotopic fractionation in pyroxene, spinel, and olivine, consistent with the inferred melt evaporation, but there are no consistent differences among the three phases. Forsterite, spinel, and pyroxene are 16O-rich with ?17O ˜ -24‰ in all FoBs. Melilite and anorthite show a range of ?17O from -17‰ to -1‰.

Bullock, Emma S.; MacPherson, Glenn J.; Nagashima, Kazuhide; Krot, Alexander N.; Petaev, Michail I.; Jacobsen, Stein B.; Ulyanov, Alexander A.

2012-12-01

336

Explosive volcanism and the compositions of the cores of differentiated asteroids  

NASA Technical Reports Server (NTRS)

Eleven iron meteorite groups showing correlations between Ni and siderophile trace elements that are predictable by distribution coefficients between liquid and solid metal of fractionally crystallizing metal magmas, are interpreted to be fragments of the fractionally crystallized cores of 11 differentiated asteroids. Many of these groups crystallized from S-depleted magmas which we propose resulted from removal of the first partial melt (a Fe,Ni-FeS cotectic) by explosive pyroclastic volcanism. It is shown that these dense, negatively buoyant melts can be driven to asteroidal surfaces by the combination of an excess pressure in the melt and the presence of buoyant bubbles of gas which decrease the bulk density of the melt. It is also shown that in typical asteroidal materials, veins will form which grow into dikes and serve as pathways for migration of melt and gas to asteroidal surfaces. Since cotectic Fe,Ni-FeS melt consists of about 85 wt. percent FeS and 15 wt. percent Fe,Ni, removal of small volumes of eutectic melts results in major loss of S but only minor loss of Fe,Ni, thus leaving sufficient Fe,Ni to form sizeable asteroidal cores.

Keil, Klaus; Wilson, Lionel

1993-01-01

337

Shock-induced melting of MgSiO3 perovskite and implications for melts in Earth's lowermost mantle  

E-print Network

Shock-induced melting of MgSiO3 perovskite and implications for melts in Earth's lowermost mantle) data for enstatite and MgSiO3 glass constrain the density change upon melting of Mg-silicate perovskite up to 200 GPa. The melt becomes denser than perovskite near the base of Earth's lower mantle

Stewart, Sarah T.

338

Materials Science and Engineering A 442 (2006) 170174 Contrasting viscoelastic behavior of melt-free and melt-bearing olivine  

E-print Network

-free and melt-bearing olivine: Implications for the nature of grain-boundary sliding Ian Jacksona,, Ulrich H bstract Melt-free and basaltic (complex alumino-silicate) melt-bearing specimens of fine oscillation and microcreep, display markedly different behavior. For the melt-bearing aterials, superimposed

339

Materials Science and Engineering A 442 (2006) 170174 Contrasting viscoelastic behavior of melt-free and melt-bearing olivine  

E-print Network

-free and melt-bearing olivine: Implications for the nature of grain-boundary sliding Ian Jacksona,, Ulrich H Abstract Melt-free and basaltic (complex alumino-silicate) melt-bearing specimens of fine oscillation and microcreep, display markedly different behavior. For the melt-bearing materials, superimposed

340

The Bloomington (LL6) chondrite and its shock melt glasses  

NASA Astrophysics Data System (ADS)

The shock melt glasses of the Bloomington LL-group chondrite were examined using electron-beam microscopy and compared with data from studies of other shock melt glasses. Petrologic and mineralogic characterizations were also performed of the samples. The metal contents of the meteorite were almost wholly Ni-rich martensite. The glasses resembled shock melt glasses in L-group chondrites, and were indicative of isochemical melting during one melt phase, i.e., a very simple history.

Dodd, R.; Olsen, E. J.; Clarke, R. S., Jr.

1985-09-01

341

Constraints on The Coupled Thermal Evolution of the Earth's Core and Mantle, The Age of The Inner Core, And The Origin of the 186Os/188Os Core(?) Signal in Plume-Derived Lavas  

NASA Astrophysics Data System (ADS)

Thermal and chemical interaction between the core and mantle has played a critical role in the thermal and chemical evolution of the Earth's interior. Outer core convection is driven by core cooling and inner core crystallization. Core/mantle heat transfer also buffers mantle potential temperature, resulting in slower rates of mantle cooling (~50-100 K/Ga) than would be predicted from the discrepancy between current rates of surface heat loss (~44 TW) and internal radioactive heat production (~20 TW). Core/mantle heat transfer may also generate thermal mantle plumes responsible for ocean island volcanic chains such as the Hawaiian Islands. Several studies suggest that mantle plumes, in addition to transporting heat from the core/mantle boundary, also carry a chemical signature of core/mantle interaction. Elevated 186Os/188Os ratios in lavas from Hawaii, Gorgona, and in the 2.8 Ga Kostomuksha komatiites have been interpreted as reflecting incorporation of an outer core component with high time-integrated Pt/Os and Re/Os ( Brandon et al., 1999, 2003; Puchtel et al., 2005). Preferential partitioning of Os relative to Re and Pt into the inner core during inner core growth may generate elevated Re/Os and Pt/Os ratios in the residual outer core. Because of the long half-life of 190Pt (the parent of 186Os, t1/2 = 489 Ga), an elevated 186Os/188Os outer core signature in plume lavas requires that inner core crystallization began early in Earth history, most likely prior to 3.5 Ga. This in turn requires low time-averaged core/mantle heat flow (<~2.5 TW) or large quantities of heat-producing elements in the core. Core/mantle heat flow may be estimated using boundary-layer theory, by measuring the heat transported in mantle plumes, by estimating the heat transported along the outer core adiabat, or by comparing the rates of heat production, surface heat loss, and secular cooling of the mantle. All of these independent methods suggest time-averaged core/mantle heat flow of ~5-14 TW. In the absence of heat-producing elements in the core, such high heat flow rates require an inner core younger than ~1 Ga and preclude the development of significant 186Os enrichment in the outer core. Experimental studies suggest that potassium may partition into Fe-S-O liquids during core formation. Radioactive decay of potassium in the core could provide an additional heat source and reconcile geophysical evidence for high core/mantle heat flow with apparent geochemical evidence for an ancient inner core. However, high concentrations of chalcophile elements such as Cu in the mantle are inconsistent with significant segregation of a S-rich liquid during core formation, precluding K partitioning into the core by this mechanism. Furthermore, core formation scenarios that would lead to high K content in the core (e.g., core formation prior to terrestrial volatile depletion) also result in high core Pb concentrations. Core/mantle interaction would then produce strong negative correlations between 186Os/188Os and 207Pb/204Pb ratios, but such correlations are not observed. In summary, elevated 186Os/188Os ratios in some plume-derived lavas are unlikely to reflect core/mantle interaction because the inner core is too young for this isotopic signature to have developed in the outer core. Melt generation from pyroxenite or fractionation of PGEs between sulfide melts and monosulfide solid solutions provide alternative mechanisms for generating ancient mantle reservoirs with elevated Pt/Os and 186Os/188Os.

Lassiter, J. C.

2005-12-01

342

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

SciTech Connect

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.

David Schwam

2012-12-15

343

Trapped Melt in theJosephine Peridotite: Implications for Permeability and Melt  

E-print Network

Trapped Melt in theJosephine Peridotite: Implications for Permeability and Melt Extraction NOVEMBER 25, 2009 ADVANCE ACCESS PUBLICATION JANUARY 15, 2010 Tabular dunites in the Josephine peridotite within these channels during cooling and exhumation of the peridotite massif was calculated using a mass

344

Preparation of the melting tank for melting magnesite in an electric-arc furnace  

Microsoft Academic Search

In the appropriate technology for the production of periclase, melting processes which provide an increased furnace productivity by changing the diameter of the electrode discharge are commonly employed. With an increase in the diameter of the electrode discharge, the area of the cross section of the melted block increases wh~le the yield of periclase is raised 15-20% [i]. However, in

V. V. Skorodumov; Yu. I. Storozhev; V. V. Mechev; N. M. Vlasov; G. P. Zhilin

1985-01-01

345

Internal stress-induced melting below melting temperature at high-rate laser heating  

SciTech Connect

In this Letter, continuum thermodynamic and phase field approaches (PFAs) predicted internal stress-induced reduction in melting temperature for laser-irradiated heating of a nanolayer. Internal stresses appear due to thermal strain under constrained conditions and completely relax during melting, producing an additional thermodynamic driving force for melting. Thermodynamic melting temperature for Al reduces from 933.67?K for a stress-free condition down to 898.1?K for uniaxial strain and to 920.8?K for plane strain. Our PFA simulations demonstrated barrierless surface-induced melt nucleation below these temperatures and propagation of two solid-melt interfaces toward each other at the temperatures very close to the corresponding predicted thermodynamic equilibrium temperatures for the heating rate Q?1.51×10{sup 10}K/s. At higher heating rates, kinetic superheating competes with a reduction in melting temperature and melting under uniaxial strain occurs at 902.1?K for Q?=?1.51?×?10{sup 11?}K/s and 936.9?K for Q?=?1.46?×?10{sup 12?}K/s.

Hwang, Yong Seok, E-mail: yshwang@iastate.edu [Department of Aerospace Engineering, Iowa State University, Ames, Iowa 50011 (United States); Levitas, Valery I., E-mail: vlevitas@iastate.edu [Departments of Aerospace Engineering, Mechanical Engineering, and Material Science and Engineering, Iowa State University, Ames, Iowa 50011 (United States)

2014-06-30

346

Calculating melting temperatures and pressures of peridotite protoliths: Implications for the origin of cratonic mantle  

NASA Astrophysics Data System (ADS)

The old, stable cores of continents - cratons - are underlain by thick and cold mantle keels, composed of melt-depleted and low density peridotite residues. The origins of these thick keels are debated. Were these thick keels formed in situ, by orogenic thickening, or by underplating of buoyant residual mantle? Key to this debate is determining the temperature and pressure at which the protoliths of cratonic peridotites melted (igneous protolith conditions) and comparing to their metamorphic (subsolidus) temperatures and pressures within the keel. This paper presents a method for explicit calculation of the temperatures and pressures at which the peridotite protoliths melted. The approach relies only on the bulk FeO and MgO of residual peridotites. A system of equations consisting of mass balance and new calibrations of Mg peridotite/melt partitioning and melt productivity is then solved simultaneously. The igneous protoliths of abyssal peridotites are found to have melted at effective pressures of 1-2 GPa and temperatures of 1300-1400 °C, within error of the magmatic temperatures and pressures of melt extraction inferred independently from the SiO2 and MgO contents of mid-ocean ridge basalts. Archean cratonic peridotites, after filtering for the secondary effects of refertilization and orthopyroxene-metasomatism, give igneous protolith pressures and temperatures of 1-5 GPa (30-150 km) and 1400-1750 °C, similar to magmatic temperatures and pressures determined for Archean basalts thought to be representative of the thermal state of the Archean ambient mantle. Most importantly, cratonic peridotite protolith pressures and temperatures are shallower and hotter than their subsolidus equilibration pressures (3-7.5 GPa; 90-200 km) and temperatures (900-1300 °C), which reflects the recent thermal state of the cratonic lithosphere. Specifically, for individual samples with both melting and subsolidus thermobarometric constraints, we find that subsolidus pressures are 1-2 GPa (30-60 km) higher than their igneous protolith pressures although some of the deepest samples experienced minor increases in pressure. Collectively, these results support the suggestion that the building blocks of cratons were generated by hot shallow melting with a mantle potential temperature 200-300 °C warmer than the present. This shallowly generated mantle was subsequently thickened during orogenic episodes, culminating in the formation of a thick, stable craton. Whether such thickening has any modern analogs cannot be answered from this work alone.

Lee, Cin-Ty A.; Chin, Emily J.

2014-10-01

347

Seismogenic frictional melting in the magmatic column  

NASA Astrophysics Data System (ADS)

Lava dome eruptions subjected to high extrusion rates commonly evolve from endogenous to exogenous growth and limits to their structural stability hold catastrophic potential as explosive eruption triggers. In the conduit, strain localisation in magma, accompanied by seismogenic failure, marks the onset of brittle magma ascent dynamics. The rock record of exogenous dome structures preserves vestiges of cataclastic processes and thermal anomalies, key to unravelling subsurface processes. Here, a combined structural, thermal and magnetic investigation of a shear band crosscutting a large block erupted in 2010 at Soufrière Hills volcano (SHV) reveals evidence of faulting and frictional melting within the magmatic column. The mineralogy of this pseudotachylyte vein offers confirmation of complete recrystallisation, altering the structure, porosity and permeability of the material, and the magnetic signature typifies local electric currents in faults. Such melting events may be linked to the step-wise extrusion of magma accompanied by repetitive long-period (LP) drumbeat seismicity at SHV. Frictional melting of Soufrière Hills andesite in a high velocity rotary shear apparatus highlights the small slip distances (< 15 cm) thought to be required to bring 800 °C magma to melting point at upper conduit stress conditions (10 MPa). We conclude that frictional melting is a common consequence of seismogenic magma fracture during dome building eruptions and that it may govern the ascent of magma in the upper conduit.

Kendrick, J. E.; Lavallée, Y.; Hess, K.-U.; De Angelis, S.; Ferk, A.; Gaunt, H. E.; Meredith, P. G.; Dingwell, D. B.; Leonhardt, R.

2014-04-01

348

The body has a brake: micrin is a postulated new gonadal hormone curbing tissue overgrowth and restricting reproduction.  

PubMed

There is evidence for an unrecognised classical hormone secreted by the mammalian gonad. This postulated hormone - 'micrin' (pronounced 'my-crin') - represents the body's brake against tissue overgrowth. When oestrogens are administered in high doses to female rats there is a considerable (non-artefactual) increase in the relative size and weight of organs such as the pituitary, adrenals, uterus and liver - suggesting an organotrophic (organ-building) role for endogenous oestrogens. This effect is exaggerated if the animals are first ovariectomized, indicating the removal of a negative ovarian factor, micrin. These organ enlargements can be reduced by pretreating the rats with large doses of antioestrogens such as clomiphene and tamoxifen. This antiestrogenic blockade of exogenous oestrogens is itself blunted by prior removal of the ovaries. It is proposed that antioestrogens (e.g. tamoxifen in breast cancer treatment) antagonize the organotrophic effects of oestrogens by competing for the oestrogen receptor peripherally and centrally and via an increase in the secretion of ovarian micrin. It is deduced that micrin is the testicular 'inhibin' proposed in the 1930s, not the molecule that now bears that name, which acts at the pituitary tier as a downregulator of follicle-stimulating hormone. The hallmark of micrin deficiency in the male rat is a pituitary hypertrophy that follows castration. This is reversible with a steroid-depleted aqueous bovine testicular extract, the micrin within which suppresses the hypothalamus, normalizing the pituitary. Micrin probably acts as a brake on peripheral tissues directly but also indirectly at the meta-level via the hypothalamic-pituitary axis, resetting a hypothalamic 'organostat' controlling organ and tissue masses, part of the 'organotrophic system' of internal size regulation. Besides endocrine (circulating) micrin from the gonads there is probably paracrine (locally acting) micrin produced in the brain. This is involved in a somatic cueing system for puberty: the brake comes off at an appropriate body tissue mass disinhibiting the hypothalamus and accelerating the organism towards sexual maturity and full adult stature. This suggests the use in reproductive disorders of micrin-related drugs. These could also be inhibitors of breast, prostate and other cancers, while protecting the bone marrow via a trophic effect on the adrenals (the lack of which protection causes lethal bone marrow depression in oestrogen-treated ferrets and dogs). Benign prostatic hyperplasia is asserted to be a micrin deficiency disorder, involving insufficiently opposed androgen. The rise in cancers with age could be associated with a reduction in micrin protection and a relative lack of this hormone could partly explain why men die younger than women. Micrin is dissimilar in activity to any known molecule and could usefully be isolated, characterised and exploited therapeutically. PMID:25456786

Hart, John E

2014-10-19

349

partial melting yields magmas of different composition than melting rock at zones of upwelling (oceanic ridges) ultramafic rock (peridotite) partially melts  

E-print Network

(oceanic ridges) ultramafic rock (peridotite) partially melts to form mafic magma (basalt) mafic rock All oceanic crust is produced at mid-ocean ridges by seafloor spreading. Partial melting of peridotite

Siebel, Wolfgang

350

Testing the ureilite projectile hypothesis for the El'gygytgyn impact: Determination of siderophile element abundances and Os isotope ratios in ICDP drill core samples  

E-print Network

Testing the ureilite projectile hypothesis for the El'gygytgyn impact: Determination of siderophile element abundances and Os isotope ratios in ICDP drill core samples and melt rocks S. GODERIS1,2* , A with that of impact melt rock fragments collected near the western rim of the structure and literature data

Claeys, Philippe

351

A TEM analysis of nanoparticulates in a Polar ice core  

SciTech Connect

This paper explores the prospect for analyzing nanoparticulates in age-dated ice cores representing times in antiquity to establish a historical reference for atmospheric particulate regimes. Analytical transmission electron microscope (TEM) techniques were utilized to observe representative ice-melt water drops dried down on carbon/formvar or similar coated grids. A 10,000-year-old Greenland ice core was melted, and representative water drops were transferred to coated grids in a clean room environment. Essentially, all particulates observed were aggregates and either crystalline or complex mixtures of nanocrystals. Especially notable was the observation of carbon nanotubes and related fullerene-like nanocrystal forms. These observations are similar with some aspects of contemporary airborne particulates including carbon nanotubes and complex nanocrystal aggregates.

Esquivel, E.V.; Murr, L.E

2004-03-15

352

Ice Core Secrets  

NSDL National Science Digital Library

In this activity, students will explore the characteristics of ice and explain the influencing factors by using Internet connections to polar field experiences, making their own ice cores and taking a field trip for obtaining a local ice core. The students will practice scientific journaling to document their observations. They will assemble their findings, develop a poster of their ice core and explain their observations. The 'ice is ice' misconception will be dispelled. Students will explain what scientists learn from ice cores and define basic vocabulary associated with ice cores.

Kolb, Sandra

353

Banded transformer cores  

NASA Technical Reports Server (NTRS)

A banded transformer core formed by positioning a pair of mated, similar core halves on a supporting pedestal. The core halves are encircled with a strap, selectively applying tension whereby a compressive force is applied to the core edge for reducing the innate air gap. A dc magnetic field is employed in supporting the core halves during initial phases of the banding operation, while an ac magnetic field subsequently is employed for detecting dimension changes occurring in the air gaps as tension is applied to the strap.

Mclyman, C. W. T. (inventor)

1974-01-01

354

In-situ Elasticity and Density Measurements on Melts and Amorphous Materials at High Pressures  

NASA Astrophysics Data System (ADS)

Physical properties of melts are of great importance for understanding the dynamics and differentiation at various stages of the Earth's evolution. While elasticity and density equation of state of crystalline phases now can be consistently measured to the conditions of the core-mantle boundaries, precise measurements of these properties on melts at high pressure are still under extensive investigations. With the application of synchrotron X-radiation sources, new developments have emerged to facilitate the study properties and structures of melts and amorphous materials at the conditions of the deep interior of the Earth. For example, the application of X-radiography/ X-ray tomography enables the in-situ measurement of viscosity and density in multi-anvil and diamond anvil cell apparatus using falling sphere/sink-float, X-ray absorption and X-ray microtomography methods. In this study, we present a new technique for density measurements on melts and amorphous materials by using simultaneous synchrotron X-radiation and ultrasonic interferometry measurements in a cubic type multi-anvil apparatus installed at X-17B2, NSLS of Brookhaven National Lab. By directly measuring the length(thickness) of the sample using X-radiography, a precise determination of sound velocities can be obtained at high pressures, from which the density of melts and/or amorphous materials at high pressures can be calculated through an integration with respect to pressure. This technique opens a unique opportunity for the study of melts and amorphous materials, which will be demonstrated using results obtained from our recent studies on ceramic and metallic materials.

Li, B.; Liu, W.; Liu, Q.; Whitaker, M.

2008-12-01

355

Petrogenesis of Hawaiian tholeiites: 2, aspects of dynamic melt segregation  

NASA Astrophysics Data System (ADS)

To Hawaiian magma genesis, dynamic melt segregation offers a potential resolution of conflict arising between trace-element evidence and phase-equilibria evidence, for deep garnet-present melting versus shallow garnet-absent melting. In this study comprehensive dynamic melting models, which incorporate phase-equilibria constraints and variable partition coefficients, have been applied in efforts to simulate decompression melting of a mantle plume. These models specifically endeavour to reproduce Hawaiian REE (rare-earth-element) patterns from a peridotitic upper mantle source with chondritic relative abundances of middle and HREE (heavy REE). If the flow of both melt and solid mantle is vertical through the partially molten source region, and melting proceeds beyond the stability limit of garnet in peridotite, dynamic melting processes are unable to produce the fractionated REE patterns of Hawaiian tholeiites. Instead, three-dimensional dynamic melting modles need to be invoked, in which lateral migration of the melt relative to the residual matrix also takes place. This enables the derivation of small garnet-equilibrated melt fractions from a larger source volume than that supplying more extensive melt fractions from shallower garnet-absent levels of melting (i.e ‘melting shapes’ with a mean degree of melting smaller than the maximum extent of melting). This can be achieved by either drawing small-degree melt fractions, formed in the presence of garnet at the plume peripheries, toward the plume centre, or by advecting the mantle residue away from the plume centre as it ascends. Fluid dynamic theory supports a plume model incorporating the latter, with melt flow occurring vertically through a matrix flow which is deflected by the lithosphere and diverges away from the plume centre. In this framework, the generation of melting shapes dominated by small-degree garnetpresent melt fractions, requires a decrease in the rate of melting with progressive melting and height along melt-flow paths within the plume. This is consistent with a decrease in vertical velocity of the matrix (and thus decompression melting rate) upwards through the plume and, with diminishing melting rates upon exhaustion of garnet and clinopyroxene as melting progresses. Providing melt segregation occurs by percolation, equilibrium between the segregating melt and residual peridotite matrix may be maintained throughout the plume. In this way, primary melts extracted from the Hawaiian plume have their bulk compositions determined by phase equilibrium with the extensively melted matrix residue (harzburgite) at the plume top and shallowest level of melting (˜2.0 GPa), and their incompatible-trace-element characteristics determined by smaller-degree melt fractions derived from deeper, garnet-present levels of melting (?3.0 GPa). Simple unidimensional models for melt segregation by percolation or via channels are shown to produce incompatible-trace-element abundances and ratios which are similar to those generated by equivalent degrees of batch melting. Moreover, contrary to a common belief held for dynamic melting, the enrichment of more-incompatible elements over less-incompatible elements is not always greater than that produced by an equivalent amount of batch melting.

Eggins, S. M.

1992-04-01

356

On meson melting in the quark medium  

E-print Network

We consider a heavy quark-antiquark $(q\\bar{q})$ pair as a heavy meson in the medium composed of light quarks and gluons. By using the AdS/CFT correspondence, the properties of this system are investigated. In particular, we study the inter-quark distance and it is shown that the mechanism of melting in the quark-gluon plasma and in the hadronic phase are the same. It is found that by considering finite coupling corrections, the inter-quark distance of a heavy meson decreases. As a result a heavy meson like $J/ \\psi$ will melt at higher temperatures. By considering rotating heavy mesons, we discuss melting of exited states like $\\chi_c$ and $\\psi'$.

K. Bitaghsir Fadafan; E. Azimfard

2012-03-18

357

Melting Points (ChemPages Lab)  

NSDL National Science Digital Library

Melting Points: this is a resource in the collection "ChemPages Laboratory Resources". The melting point is a characteristic property of a substance. It can be used for sample identification and purity determination. The melting point is observed by slowly heating a sample and observing the temperature when the sample has changed from a solid to a liquid. The ChemPages Laboratory Resources are a set of web pages that include text, images, video, and self check questions. The topics included are those that are commonly encountered in the first-year chemistry laboratory. They have been put together for use as both a pre-laboratory preparation tool and an in-laboratory reference source.

358

Segregation effects during solidification in weightless melts  

NASA Technical Reports Server (NTRS)

Two types of melt segregation effects were studied: (1) evaporative segregation, or segregation due to surface evaporation; and (2) freezing segregation, or segregation due to liquid-solid phase transformation. These segregation effects are closely related. In fact, evaporative segregation always precedes freezing segregation to some degree and must often be studied prior to performing meaningful solidification experiments. This is particularly true since evaporation may cause the melt composition, at least at the critical surface regions or layers to be affected manyfold within seconds so that the surface region or layer melting point and other thermophysical properties, nucleation characteristics, base for undercooling, and critical velocity to avoid constitutional supercooling, may be completely unexpected. An important objective was, therefore, to develop the necessary normal evaporation equations for predicting the compositional changes within specified times at temperature and to correlate these equations with actual experimental data collected from the literature.

Li, C.

1973-01-01

359

On meson melting in the quark medium  

NASA Astrophysics Data System (ADS)

We consider a heavy quark-antiquark (qq¯) pair as a heavy meson in the medium composed of light quarks and gluons. By using the AdS/CFT correspondence, the properties of this system are investigated. In particular, we study the inter-quark distance and it is shown that the mechanism of melting in the quark-gluon plasma and in the hadronic phase is the same. It is found that by considering finite-coupling corrections, the inter-quark distance of a heavy meson decreases. As a result a heavy meson like J/? will melt at higher temperatures. By considering rotating heavy mesons, we discuss melting of exited states like ?c and ?'.

Fadafan, K. Bitaghsir; Azimfard, E.

2012-10-01

360

Melting Mechanisms of 3D Colloidal Crystals  

NASA Astrophysics Data System (ADS)

We study the melting mechanisms of 3D colloidal crystals using aqueous suspensions of thermally responsive NIPA microgel colloidal particles. Below 32 ^oC, the particle radius decreases approximately linearly with increasing temperature. We use this effect to tune the volume fraction of nearly hard-sphere aqueous NIPA colloidal suspensions from 0.74 to 0.54. Using video tracking microscopy, we measured the Lindemann parameter of particles within the crystal as a function of temperature. Interestingly, we find that melting of the 3D colloidal crystals starts at grain boundaries and free surfaces, rather than isolated vacancies or dislocations. Very near the melting temperature, the Lindemann parameter for particles near the grain boundaries and free surfaces was ˜0.16; the parameter decreased approximately exponentially with distance into the bulk crystal. These works has been partially supported by NSF through MRSEC DMR-0203378 and DMR-079909 and by NASA grant NAG8- 2172.

Alsayed, A. M.

2005-03-01

361

Compositions of Magmatic and Impact Melt Sulfides in Tissint And EETA79001: Precursors of Immiscible Sulfide Melt Blebs in Shergottite Impact Melts  

NASA Technical Reports Server (NTRS)

Immiscible sulfide melt spherules are locally very abundant in shergottite impact melts. These melts can also contain samples of Martian atmospheric gases [1], and cosmogenic nuclides [2] that are present in impact melt, but not in the host shergottite, indicating some components in the melt resided at the Martian surface. These observations show that some regolith components are, at least locally, present in the impact melts. This view also suggests that one source of the over-abundant sulfur in these impact melts could be sulfates that are major constituents of Martian regolith, and that the sulfates were reduced during shock heating to sulfide. An alternative view is that sulfide spherules in impact melts are produced solely by melting the crystalline sulfide minerals (dominantly pyrrhotite, Fe(1-x)S) that are present in shergottites [3]. In this abstract we report new analyses of the compositions of sulfide immiscible melt spherules and pyrrhotite in the shergottites Tissint, and EETA79001,507, and we use these data to investigate the possible origins of the immiscible sulfide melt spherules. In particular, we use the metal/S ratios determined in these blebs as potential diagnostic criteria for tracking the source material from which the numerous sulfide blebs were generated by shock in these melts.

Ross, D. K.; Rao, M. N.; Nyquist, L.; Agee, C.; Sutton, S.

2013-01-01

362

HYDRATE CORE DRILLING TESTS  

SciTech Connect

The ''Methane Hydrate Production from Alaskan Permafrost'' project is a three-year endeavor being conducted by Maurer Technology Inc. (MTI), Noble, and Anadarko Petroleum, in partnership with the U.S. DOE National Energy Technology Laboratory (NETL). The project's goal is to build on previous and ongoing R&D in the area of onshore hydrate deposition. The project team plans to design and implement a program to safely and economically drill, core and produce gas from arctic hydrates. The current work scope includes drilling and coring one well on Anadarko leases in FY 2003 during the winter drilling season. A specially built on-site core analysis laboratory will be used to determine some of the physical characteristics of the hydrates and surrounding rock. Prior to going to the field, the project team designed and conducted a controlled series of coring tests for simulating coring of hydrate formations. A variety of equipment and procedures were tested and modified to develop a practical solution for this special application. This Topical Report summarizes these coring tests. A special facility was designed and installed at MTI's Drilling Research Center (DRC) in Houston and used to conduct coring tests. Equipment and procedures were tested by cutting cores from frozen mixtures of sand and water supported by casing and designed to simulate hydrate formations. Tests were conducted with chilled drilling fluids. Tests showed that frozen core can be washed out and reduced in size by the action of the drilling fluid. Washing of the core by the drilling fluid caused a reduction in core diameter, making core recovery very difficult (if not impossible). One successful solution was to drill the last 6 inches of core dry (without fluid circulation). These tests demonstrated that it will be difficult to capture core when drilling in permafrost or hydrates without implementing certain safeguards. Among the coring tests was a simulated hydrate formation comprised of coarse, large-grain sand in ice. Results with this core showed that the viscosity of the drilling fluid must also be carefully controlled. When coarse sand was being cored, the core barrel became stuck because the drilling fluid was not viscous enough to completely remove the large grains of sand. These tests were very valuable to the project by showing the difficulties in coring permafrost or hydrates in a laboratory environment (as opposed to a field environment where drilling costs are much higher and the potential loss of equipment greater). Among the conclusions reached from these simulated hydrate coring tests are the following: Frozen hydrate core samples can be recovered successfully; A spring-finger core catcher works best for catching hydrate cores; Drilling fluid can erode the core and reduces its diameter, making it more difficult to capture the core; Mud must be designed with proper viscosity to lift larger cuttings; and The bottom 6 inches of core may need to be drilled dry to capture the core successfully.

John H. Cohen; Thomas E. Williams; Ali G. Kadaster; Bill V. Liddell

2002-11-01

363

Molecular dynamics simulation of zirconia melting  

NASA Astrophysics Data System (ADS)

The melting point for the tetragonal and cubic phases of zirconia (ZrO2) was computed using Z-method microcanonical molecular dynamics simulations for two different interaction models: the empirical Lewis-Catlow potential versus the relatively new reactive force field (ReaxFF) model. While both models reproduce the stability of the cubic phase over the tetragonal phase at high temperatures, ReaxFF also gives approximately the correct melting point, around 2900 K, whereas the Lewis-Catlow estimate is above 6000 K.

Davis, Sergio; Belonoshko, Anatoly B.; Rosengren, Anders; van Duin, Adri C. T.; Johansson, Börje

2010-10-01

364

Rock melting tool with annealer section  

DOEpatents

A rock melting penetrator is provided with an afterbody that rapidly cools a molten geological structure formed around the melting tip of the penetrator to the glass transition temperature for the surrounding molten glass-like material. An annealing afterbody then cools the glass slowly from the glass transition temperature through the annealing temperature range to form a solid self-supporting glass casing. This allows thermally induced strains to relax by viscous deformations as the molten glass cools and prevents fracturing of the resulting glass liner. The quality of the glass lining is improved, along with its ability to provide a rigid impermeable casing in unstable rock formations.

Bussod, Gilles Y. (Santa Fe, NM); Dick, Aaron J. (Oakland, CA); Cort, George E. (Montrose, CO)

1998-01-01

365

Scleral melt following Retisert intravitreal fluocinolone implant  

PubMed Central

Intravitreal fluocinolone acetonide implant (Retisert) has a high potency, a low solubility, and a very short duration of action in the systemic circulation, enabling the steroid pellet to be small and reducing the risk of systemic side effects. Scleral melt has not been reported as a possible complication of Retisert implant. The authors describe the occurrence of scleral melt 18 months after the implantation of fluocinolone acetonide implant in a 42-year-old Caucasian woman. To the authors’ knowledge, this is the first report of this possible complication. PMID:25489235

Georgalas, Ilias; Koutsandrea, Chrysanthi; Papaconstantinou, Dimitrios; Mpouritis, Dimitrios; Petrou, Petros

2014-01-01

366

REE Modeling of Melting and Crystallization  

NSDL National Science Digital Library

In this activity, students are led through some introductory lecture material on rare earth elements, distribution coefficients, and the derivation of equations relating element concentrations in solids and liquids during processes of both equilibrium and fractional melting and crystallization. This lecture material is interspersed with class discussion questions that seek to actively query the students' stepwise understanding of concepts. The activity culminates in the students' construction of rare earth element diagrams for rock samples, a fractional crystallization numerical model (e.g. a spreadsheet) for forward modeling and comparison to data, and an equilibrium modal melting model, again for comparison to a real data set.

Schmitz, Mark

367

Experimental correlation of melt structures, nucleation rates, and thermal histories of silicate melts  

NASA Technical Reports Server (NTRS)

The theory and measurement of the structure of liquids is an important aspect of modern metallurgy and igneous petrology. Liquid structure exerts strong controls on both the types of crystals that may precipitate from melts and on the chemical composition of those crystals. An interesting aspect of melt structure studies is the problem of melt memories; that is, a melt can retain a memory of previous thermal history. This memory can influence both nucleation behavior and crystal composition. This melt memory may be characterized quantitatively with techniques such as Raman, infrared and NMR spectroscopy to provide information on short-range structure. Melt structure studies at high temperature will take advantage of the microgravity conditions of the Space Station to perform containerless experiments. Melt structure determinations at high temperature (experiments that are greatly facilitated by containerless technology) will provide invaluable information for materials science, glass technology, and geochemistry. In conjunction with studies of nucleation behavior and nucleation rates, information relevant to nucleation in magma chambers in terrestrial planets will be acquired.

Boynton, W. V.; DRAKE; HILDEBRAND; JONES; LEWIS; TREIMAN; WARK

1987-01-01

368

Melt segregation from partially molten source regions - The importance of melt density and source region size  

NASA Technical Reports Server (NTRS)

An investigation is conducted regarding the changes expected in the density contrast between basic melts and peridotites with increasing pressure using the limited data available on the compressibilities of silicate melts and data on the densities of mantle minerals. It is concluded that since compressibilities of silicate melts are about an order of magnitude greater than those of mantle minerals, the density contrast between basic melts and mantle minerals must diminish significantly with increasing pressure. An earlier analysis regarding the migration of liquid in partially molten source regions conducted by Walker et al. (1978) is extended, giving particular attention to the influence of the diminished density contrast between melt and residual crystals with increasing source region depth and to the influence of source region size. This analysis leads to several generalizations concerning the factors influencing the depths at which magmas will segregate from their source regions and the degrees of partial melting that can be achieved in these source regions before melt segregation occurs.

Stolper, E.; Hager, B. H.; Walker, D.; Hays, J. F.

1981-01-01

369

Early planetesimal melting from an age of 4.5662 Gyr for differentiated meteorites.  

PubMed

Long- and short-lived radioactive isotopes and their daughter products in meteorites are chronometers that can test models for Solar System formation. Differentiated meteorites come from parent bodies that were once molten and separated into metal cores and silicate mantles. Mineral ages for these meteorites, however, are typically younger than age constraints for planetesimal differentiation. Such young ages indicate that the energy required to melt their parent bodies could not have come from the most likely heat source-radioactive decay of short-lived nuclides ((26)Al and (60)Fe) injected from a nearby supernova-because these would have largely decayed by the time of melting. Here we report an age of 4.5662 +/- 0.0001 billion years (based on Pb-Pb dating) for basaltic angrites, which is only 1 Myr younger than the currently accepted minimum age of the Solar System and corresponds to a time when (26)Al and (60)Fe decay could have triggered planetesimal melting. Small (26)Mg excesses in bulk angrite samples confirm that (26)Al decay contributed to the melting of their parent body. These results indicate that the accretion of differentiated planetesimals pre-dated that of undifferentiated planetesimals, and reveals the minimum Solar System age to be 4.5695 +/- 0.0002 billion years. PMID:16121173

Baker, Joel; Bizzarro, Martin; Wittig, Nadine; Connelly, James; Haack, Henning

2005-08-25

370

Constraints on the Parental Melts of Enriched Shergottites from Image Analysis and High Pressure Experiments  

NASA Technical Reports Server (NTRS)

Martian basalts can be classified in at least two geochemically different families: enriched and depleted shergottites. Enriched shergottites are characterized by higher incompatible element concentrations and initial Sr-87/Sr-86 and lower initial Nd-143/Nd-144 and Hf-176/Hf-177 than depleted shergottites [e.g. 1, 2]. It is now generally admitted that shergottites result from the melting of at least two distinct mantle reservoirs [e.g. 2, 3]. Some of the olivine-phyric shergottites (either depleted or enriched), the most magnesian Martian basalts, could represent primitive melts, which are of considerable interest to constrain mantle sources. Two depleted olivine-phyric shergottites, Yamato (Y) 980459 and Northwest Africa (NWA) 5789, are in equilibrium with their most magnesian olivine (Fig. 1) and their bulk rock compositions are inferred to represent primitive melts [4, 5]. Larkman Nunatak (LAR) 06319 [3, 6, 7] and NWA 1068 [8], the most magnesian enriched basalts, have bulk Mg# that are too high to be in equilibrium with their olivine megacryst cores. Parental melt compositions have been estimated by subtracting the most magnesian olivine from the bulk rock composition, assuming that olivine megacrysts have partially accumulated [3, 9]. However, because this technique does not account for the actual petrography of these meteorites, we used image analysis to study these rocks history, reconstruct their parent magma and understand the nature of olivine megacrysts.

Collinet, M.; Medard, E.; Devouard, B.; Peslier, A.

2012-01-01

371

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

NASA Technical Reports Server (NTRS)

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.

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

2010-01-01

372

Modeling and analysis framework for core damage propagation during flow-blockage-initiated accidents in the Advanced Neutron Source Reactor at Oak Ridge National Laboratory  

Microsoft Academic Search

This paper describes modeling and analysis to evaluate the extent of core damage during flow blockage events in the Advanced Neutron Source (ANS) reactor planned to be built at the Oak Ridge National Laboratory (ORNL). Damage propagation is postulated to occur from thermal conduction between damaged and undamaged plates due to direct thermal contact. Such direct thermal contact may occur

S. H. Kim; R. P. Taleyarkhan; S. Navarro-Valenti; V. Georgevich

1995-01-01

373

The re-evaluation of the AVR melt-wire experiment with specific focus on different modeling strategies and simplifications  

SciTech Connect

The AVR is a pebble-bed type reactor that operated in Germany for 21 years and was closed down in December 1988. The AVR melt-wire experiments, where graphite spheres with melt wires of different melting temperatures were introduced into the core, indicate that measured pebble temperatures significantly exceeded temperatures calculated with the analysis codes available at the time. The reason for these discrepancies are often attributed to the special design features of the AVR, in particular the control rod “noses” protruding into the core, and to inherent features of the pebble bed reactor. In a previous study different possible bypass flows were investigated. This study investigates different modeling strategies and assumptions for the solution of the core neutronics. Due to the complexities specific to the AVR there is not currently a code system that can take into account the noses while simultaneously solving the burnup and diffusion equations in three dimensions. A number of modeling simplifications were therefore made in the historic analysis of the AVR. The aim of this study is to quantify the effects these different simplifications have on the results. This includes the effects of modeling the core neutronics, burn-up and thermo-hydraulics in both two and three dimensions, as well as other simplifications of the geometry. The comparison of the most realistic case to the one comparable to historic calculations show that the difference in temperature predicted with these two models can be as high as 300 degrees C. The gas temperature distribution at the top of the core, where the maximum temperatures occur, is in fair agreement with the melt-wire experiment data even though few simplifications are introduced to the models and the power history has not been simulated. The results also serve as input to the final modeling strategy to repeat the modeling of the operational history of the AVR, which is planned for the future.

R. Sonat Sen; Carel F. Viljoen

2012-10-01

374

The Results From the First High-Pressure Melt Ejection Test Completed in the Molten Fuel Moderator Interaction Facility at Chalk River Laboratories  

SciTech Connect

A high-pressure melt ejection test using prototypical corium was conducted at Atomic Energy of Canada Limited Chalk River Laboratories. This test was planned by the CANDU Owners Group to study the potential for an energetic interaction between molten fuel and water under postulated single-channel flow-blockage events. The experiments were designed to address regulator concerns surrounding this very low probability postulated accident events in CANDU Pressurized Heavy Water Reactors. The objective of the experimental program is to determine whether a highly energetic 'steam explosion' and associated high-pressure pulse, is possible when molten material is finely fragmented as it is ejected from a fuel channel into the heavy-water moderator. The finely fragmented melt particles would transfer energy to the moderator as it is dispersed, creating a modest pressure pulse in the calandria vessel. The high-pressure melt ejection test consisted of heating up a {approx} 5 kg thermite mixture of U, U{sub 3}O{sub 8}, Zr, and CrO{sub 3} inside a 1.14-m length of insulated pressure tube. When the molten material reached the desired temperature of {approx} 2400 deg C, the pressure inside the tube was raised to 11.6 MPa, failing the pressure tube at a pre-machined flaw, and releasing the molten material into the surrounding tank of 68 deg C water. The experiment investigated the dynamic pressure history, debris size, and the effects of the material interacting with tubes representing neighbouring fuel channels. The measured mean particle size was 0.686 mm and the peak dynamic pressures were between 2.54 and 4.36 MPa, indicating that an energetic interaction between the melt and the water did not occur in the test. (authors)

Nitheanandan, T.; Kyle, G.; O'Connor, R.; Sanderson, DB. [Chalk River Laboratories, Atomic Energy of Canada Limited, Chalk River, Ontario, Canada, K0J 1J0 (Canada)

2006-07-01

375

Tectonic and source controls on granite melt chemistry  

NASA Astrophysics Data System (ADS)

The composition and microstructure of the source, P-T evolution, degree of melting and number of melt extraction events, and whether melting is an equilibrium or disequilibrium process dictate the initial chemistry of granite melt at P and T, whereas this chemistry may be modified by physico-chemical processes during migration through the source and ascent through the crust. In addition to determining P-T evolution, tectonic setting determines any juvenile input to melt generation. Assuming melt extraction occurs at the melt connectivity transition (MCT), multiple cycles of melt build-up and loss are predicted along suprasolidus prograde P-T paths. Melt extraction changes the composition of the source and solid solution phases, so that successive melt batches have different chemistries. During migration, melt composition evolves by interaction with residue and crystallization-fractionation; glass compositions from melting experiments on crustal rocks do not match mafic granites, suggesting that natural melts selectively entrain peritectic minerals from the source, which equilibrate during ascent by dissolution-precipitation cycling. For CW P-T paths, decompression across hydrate-breakdown melting reactions is commonly invoked as important in the production of late orogenic granites, yet the amount of melt produced during decompression is dependent on the fertility of the crust at the T of interest and the amount may be quite small if melt is lost along the prograde P-T path. Rock-forming and accessory mineral behavior during melting is critical to the composition and isotopic fingerprint of the melt. Although various accessory minerals are the main hosts for Zr, U, Th and the REE it is not clear that breakdown of these under suprasolidus conditions necessarily will lead to saturation of the melt, since rock-forming minerals in the granulite facies become enriched these elements. Furthermore, in fluid absent melting, melt pockets may be located along hydrate grain boundaries, so equilibrium is possible for elements concentrated in minerals located along these boundaries or sequestered close to the edges of the hydrate, whereas in fluid present melting, melt pockets form at Qtz-Flds grain junctions, which may limit the opportunity for equilibration with trace elements in accessory minerals associated with or sequestered in hydrate phases. Syn-anatectic deformation is important; diffusion accommodated grain-boundary sliding allows melt migration along grain boundaries, which enables better interaction between mineral grains and melt, whereas diffusion creep by dissolution-precipitation favors equilibration of grain surface compositions with melt. Deformation also assists rapid melt migration, which may inhibit equilibration between melt and residue. Commonly, leucosomes exhibit either strong positive Eu anomalies with low Zr, recording early crystallization of Flds and Qtz, or compositions with strong negative Eu anomalies and high Zr, representing fractionated melt. This contrast is generated as melt passes through crust that is cooler than the liquidus, causing crystallization on channel walls. There is a continuous process of crystallization/fractionation during migration until evolved melt crosses the solidus at a melt extraction point, after which if the volume is sufficient it ascends rapidly to the upper crust. Thus, residual source rocks were both zones of melt generation and zones of melt transfer from the deeper crust.

Brown, M.

2012-12-01

376

Core sample extractor  

NASA Technical Reports Server (NTRS)

The problem of retrieving and storing core samples from a hole drilled on the lunar surface is addressed. The total depth of the hole in question is 50 meters with a maximum diameter of 100 millimeters. The core sample itself has a diameter of 60 millimeters and will be two meters in length. It is therefore necessary to retrieve and store 25 core samples per hole. The design utilizes a control system that will stop the mechanism at a certain depth, a cam-linkage system that will fracture the core, and a storage system that will save and catalogue the cores to be extracted. The Rod Changer and Storage Design Group will provide the necessary tooling to get into the hole as well as to the core. The mechanical design for the cam-linkage system as well as the conceptual design of the storage device are described.

Akins, James; Cobb, Billy; Hart, Steve; Leaptrotte, Jeff; Milhollin, James; Pernik, Mark

1989-01-01

377

Supplementary Material: Glacier melt contribution to streamflow  

E-print Network

variations in the surface mass balance of 18 Svalbard glaciers from the Moderate Resolution Imaging of direct mass balance of Hintereisferner. Global and Planetary Change, 71, 13-26. Greuell, W., Kohler, J, J.-E. and Carenzo, M. 2008. A study of the energy balance and melt regime on Juncal Norte Glacier

Washington at Seattle, University of

378

Scrap uranium recycling via electron beam melting  

Microsoft Academic Search

A program is underway at the Lawrence Livermore National Laboratory (LLNL) to recycle scrap uranium metal. Currently, much of the material from forging and machining processes is considered radioactive waste and is disposed of by oxidation and encapsulation at significant cost. In the recycling process, uranium and uranium alloys in various forms will be processed by electron beam melting and

McKoon

1993-01-01

379

Energy Savings in Electric Arc Furnace Melting  

E-print Network

Arc furnace melting which at one time was almost exclusively used to produce alloy steel and steel castings is now widely accepted in the industry as an efficient process to produce all types of steel and iron. Presently, about 28% of steel...

Lubbeck, W.

1982-01-01

380

High-pressure melting curve of hydrogen  

Microsoft Academic Search

The melting curve of hydrogen was computed for pressures up to 200 GPa, using molecular dynamics. The inter- and intramolecular interactions were described by the reactive force field (ReaxFF) model. The model describes the pressure-volume equation of state solid hydrogen in good agreement with experiment up to pressures over 150 GPa, however the corresponding equation of state for liquid deviates

Sergio M. Davis; Anatoly B. Belonoshko; Börje Johansson; Natalia V. Skorodumova; Adri C. T. van Duin

2008-01-01

381

Can Text Messages Mitigate Summer Melt?  

ERIC Educational Resources Information Center

Higher education officials have long been familiar with the concept of "summer melt," where students who have paid a deposit to attend one college or university instead matriculate at a different institution, usually presumed to be of comparable quality. In previous research, drawing on longitudinal data from various urban school districts…

Castleman, Benjamin L.; Page, Lindsay C.

2013-01-01

382

DETERMINATION OF MELTING OF WATER CLUSTERS USING  

E-print Network

a formidable array of unusual physical and chemical properties in its condensed phases. Micro clusters of water are being undertaken to investigate the properties of small water clusters. Our aim is to simulate the melting temperature of water clusters (H2O)n of selected sizes and show how their properties evolve

Entel, P.

383

Frictional Melting Processes in Planetary Materials  

E-print Network

online as a Review in Advance on January 28, 2010 The Annual Review of Earth and Planetary SciencesFrictional Melting Processes in Planetary Materials: From Hypervelocity Impact to Earthquakes John G. Spray Planetary and Space Science Centre, University of New Brunswick, Fredericton, New Brunswick

Jellinek, Mark

384

Water and the viscosity of andesite melts  

Microsoft Academic Search

The viscosity of a synthetic andesite-like melt has been measured between 1010 and 1014 P for water contents in the range 0–3.5 wt%. The very slow kinetics of water exsolution over this viscosity range allowed the measurements to be made at 1 bar with a high precision. After a steep viscosity decrease of > 5 orders of magnitude for 1

Pascal Richet; Anne-Marie Lejeune; François Holtz; Jacques Roux

1996-01-01

385

Melting and breaking of ultrathin copper nanobridges  

NASA Astrophysics Data System (ADS)

Thermal properties of Cu nanobridges were investigated using a classical molecular dynamics simulation and a many-body potential function of the second-moment approximation of tight-binding scheme. The caloric curve and the diffusivity of nanobridges showed the information on the melting and breaking of nanobridges.

Hwang, Ho Jung; Kang, Jeong Won

2003-06-01

386

Causes and Effects of Melting Ice  

NSDL National Science Digital Library

In this activity, learners explore the concept of density-driven currents (thermohaline circulation) and how these currents are affected by climate change. Learners use colored ice cubes, water, and salt to explore density as it relates to salinity. This activity helps learners to understand the impact of glacial melt on sea level rise.

Bell, Elizabeth V.; Marshall, Brittney; Bliss, Angela

2012-11-14

387

BATCH CALCINATION STUDIES-MELT FORMATION  

Microsoft Academic Search

It is shown that the formation of a meltable calcine by batch ; calcination of an acidic waste solution containing primary sodium, iron, and ; aluminum sulfate and nitrate can be predicted. Calcine melting at temperatures ; less than 900 deg C can be correlated with the sodium to metal ion ratio and the ; sulfate to salt nitrate ratio.

Shefcik

1961-01-01

388

Educating Multicultural Citizens: Melting Pot or Mosaic?  

ERIC Educational Resources Information Center

Explores the educational metaphors of the melting pot (immigrants must assimilate into the mainstream culture) and the cultural mosaic (immigrants should retain their cultural identifies). Focuses on such issues as multiculturalism and justice for immigrants, social cohesion, the notion of cultural relativism, and differing conceptions of culture.…

Entwistle, Harold

2000-01-01

389

Static Compression of Hydrous Silicate Melts and Density Crossovers in the Mantle  

NASA Astrophysics Data System (ADS)

High pressure experiments using the sink/float method have bracketed the density of hydrous iron-rich ultrabasic silicate melt from 1.35 to 10.0 GPa at temperatures from 1400 to 1860C. The silicate melt composition was a 50- 50 mixture of natural komatiite and synthetic fayalite. Water was added in the form of brucite Mg(OH)2 and was present in the experimental run products at 2 wt% and 5 wt% levels as confirmed by microprobe analyses of total oxygen. Samples were contained in compression-sealed molybdenum capsules. Sink/float marker spheres implemented were gem quality synthetic forsterite (Fo100), San Carlos olivine (Fo91), and several types of natural pyrope-almandine garnet crystals with compositions in the range Py74-62. Experimental run times were 30 seconds, thus minimizing sphere-liquid reactions and liquid reaction with capsule and pressure media. All experiments were carried out in a Walker multi-anvil apparatus or a Quick Press piston-cylinder device at the Institute of Meteoritics, University of New Mexico. The density of the silicate melt with 5 wt% water at 2 GPa and 1500C is 0.192 g/cc less than the anhydrous form of this melt at the same P and T. This density difference gives a partial molar volume of water in silicate melt of approximately 7 cc/mol, which is similar to previous studies at high pressure. However, much work is still needed to determine the effect of pressure and composition on the partial molar volume of water in magma. Future studies should require precise density measurements of the same melt composition with and without water, observing numerous sink/float brackets, over a wide pressure range. The komatiite-fayalite liquids with 0 and 2 wt% H2O, have extrapolated density crossovers with equilibrium liquidus olivine at 8 and 9 GPa respectively, but there is no crossover for the liquid with 5 wt% H2O. These results are consistent with the hypothesis that dense hydrous melts could be gravitationally stable atop the 410 km discontinuity in the Earth. The results also support the notion that equilibrium liquidus olivine could float in a FeO- rich hydrous martian magma ocean. Extrapolation of the data suggests that FeO-rich hydrous melt could be negatively buoyant in the Earth's D-double-prime region or atop the core-mantle-boundary (CMB), although experiments at higher pressure are needed to confirm this prediction.

Agee, C. B.

2007-12-01

390

Melt segregation in a gabbroic intrusion studied by means of AMS  

NASA Astrophysics Data System (ADS)

The Miocene Muroto Gabbroic Intrusion (MGI) at Cape Muroto, Japan is a layered sill and displays spectacular evidence of melt segregation (Yoshizawa, 1953). Felsic melts separated from the mafic mush to form individual, anorthositic melt lenses in the central portions of the 230m thick sill. We sampled across the entire sill at intervals of 10m, with a special focus on the zone displaying melt lenses (5m sample interval). Oriented hand specimens were cored in the lab for measurement of the Anisotropy of Magnetic Susceptibility (AMS). Bulk susceptibilities range between 2.7x10-3 and 37.7x10-3 SI with a mean value of 16.3x10-3 ± 7.2x10-3 SI. The degree of anisotropy (Pj) is predominantly low (<1.12) and the highest values can be found in the center of the MGI. The shape parameter (T) ranges from oblate (0.95) to prolate (-0.9) but its distribution is not random throughout the sill. T switches from predominantly prolate to oblate at around 75m from the bottom of the sill. From 150m above the bottom to the top of the sill, T is more variable. The orientation of the major axis of the AMS ellipsoid (K1) is relatively variable throughout the sill but steadily converges to a sub-horizontal orientation between 50m and 110m from the bottom. The minor axis (K3) is mainly subvertical, when K1 is horizontal. Field and thin section observations suggest that the sill did not record intense deformation after solidification. Bulk susceptibilities and thermomagnetic curves suggest that the AMS signal is dominated by titaniferous magnetite. MELTS (Gualda et al. 2012) modeling indicates the crystallization of Fe-Ti oxide at 1075°C upon cooling of the sill, a temperature corresponding to a crystal fraction of ~0.55. Hence, crystallization of the AMS signal carrier occurs once the silicates formed a rigid framework. Crystallization of the AMS signal carrier in the residual, melt-filled pore space may record valuable information about the separation of melt from a partially crystallized mush. In the MGI, this is supported by the conspicuous AMS parameters and orientations towards the central portion of the sill, where melt segregation is evident from field observations. Gualda et al., 2012, J.Pet, v. 53, p. 875-890. Yoshizawa, 1953, Mem.Col.Sci.Univ.Kyoto, v. 20, p. 271-284.

Floess, David; Caricchi, Luca; Wallis, Simon

2014-05-01

391

Crystallization of An-rich plagioclase in 'dacitic' melt at Arenal volcano: Natural occurrence and experiments  

NASA Astrophysics Data System (ADS)

High-An plagioclase (An85-94) is ubiquitous in crystal-rich basaltic andesitic lavas of the current eruption and of the entire eruptive history of Arenal volcano, Costa Rica. An85-91 plagioclase was found to host glassy melt inclusions of dacitic composition suggesting that high An plagioclase may also crystallize in melts as silicic as ~63 wt.% SiO2 (Streck &Wacaster, 2006). Such dacitic melt inclusion compositions resemble dacite tephra units that erupted a few times in Arenal's history. We investigated one pumice clast from the dacitic ET2 tephra (e.g. Borgia et al., 1988) to shed light on the possibility to crystallize high An plagioclase from dacitic melt. The natural ET2 pumice sample is phenocryst poor (~7 wt.%) with a fine-grained, vesicular, and mostly crystalline matrix. Phenocrysts are dominated by plagioclase with subordinate amphibole, pyroxenes and oxides. Apatite occurs as accessory phase. Plagioclase cores indeed display high An between An94 to An85. On the other hand, rim compositions tend to be significantly less anorthitic (~An75 to 65). A natural glass made from a split of the natural ET2 pumice clast was utilized as starting material for an experimental investigation into phase equilibria of this dacite magma. The first experiments were carried out at high pressure (4 kbar), high temperature (900-950°C) and water-rich conditions (4-9 wt.% H2O in melt) in an internally heated pressure vessel (?logfO2~NNO+3). Plagioclase with up to 83 mole % anorthite crystallizes at 900°C and for H2Omelt=9 wt.% (water-saturated). An-rich plagioclase coexists with amphibole (Mg#~70) and magnetite (Xulvo=10) in 60 wt.% SiO2 melt. As expected, An content increases with increasing temperature and water content in the melt. At 950°C, current experiments found plagioclase (An75) to be stable with H2Omelt<6.4 wt.% (no plagioclase at water-saturated conditions, only magnetite crystallizes). We infer that plagioclase begins crystallizing at H2Omelt = 8 wt.% and is stable at lower H2Omelt cocrystallizing with orthopyroxene (Mg#=60-75), clinopyroxene (Mg#<76) and magnetite (Xulvo=11-29) with the anorthite content decreasing to An55 at H2Omelt = 4.9 wt.%. Our results to date already show that water-rich dacitic melt at relatively high pressure and high temperature may indeed crystallize An-rich plagioclase at onset of plagioclase crystallization with or without amphibole depending on temperature. Borgia et al. 1988-Bull Volcanol, 50,86-105; Streck &Wacaster, 2006-JVGR, in press.

Parat, F.; Streck, M.; Holtz, F.; Almeev, R.

2006-12-01

392

Partial melting in a thermo-chemical boundary layer at the base of the mantle  

NASA Astrophysics Data System (ADS)

Seismological detections of complex structures in the lowermost mantle boundary layer (the D? region) motivate a conceptual model of a compositionally stratified thermo-chemical boundary layer (TCBL) within which lateral temperature variations (sustained by large-scale mid-mantle flow) cause variations of partial melt fraction. Partial melt fractions of from 0 to 30% in the TCBL occur due to the eutectic of the boundary layer material lying below the high temperature at the core-mantle boundary (CMB), coupled with the presence of steep thermal gradients across the boundary layer. Regions of the TCBL with the highest temperatures have extensive partial melting, producing lateral chemical variations and strong effects on seismic velocities and boundary layer dynamics. This TCBL concept provides a relatively simple framework that can plausibly account for diverse seismological observations such as: predominance of large-scale volumetric elastic wave velocity heterogeneity in the boundary layer, laterally extensive, but intermittent abrupt shear and compressional velocity increases and decreases at the top of the D? region, small-scale topography of D? velocity discontinuities, thin ultra-low velocity zones at the CMB, widespread shear wave anisotropy in D?, bulk sound velocity anomalies detected in low shear velocity regions of D?, and large-scale upwellings from the most extensively melted regions of the boundary layer. Neutral or negative buoyancy of the partial melt in the TCBL is required, along with an increase in bulk modulus and some density increase of the boundary layer material relative to the overlying mantle. More complex models, in which the partially melted chemical boundary layer is laterally displaced by mid-mantle downwellings are also viable, but these appear to require additional special circumstances, such as a phase change, efficient segregation of slab crustal material, or abrupt onset of anisotropy, in order to account for rapid velocity increases at the top of D?. The precise nature of the compositional anomaly, or anomalies, in D? and the eutectic composition of this zone are yet to be determined, but it appears likely that partial melting within the lowermost mantle plays a paramount role in the observed seismic velocity heterogeneity. Increased resolution geodynamic calculations of dense boundary layer structures with partial melting (and attendant viscosity reductions and chemical heterogeneity) are needed to quantify this TCBL concept.

Lay, Thorne; Garnero, Edward J.; Williams, Quentin

2004-09-01

393

Theory of core excitons  

Microsoft Academic Search

The major chemical trends in the binding energies of intrinsic and extrinsic core excitons are predicted for zinc-blende semiconductors using an empirical tight-binding theory and localized empirical core-hole potentials. A transition from a shallow Wannier exciton to a deep Frenkel exciton is predicted for an exciton at a core-exciton absorption edge, depending on the chemical structure of the excited atom

Harold P. Hjalmarson; Helmut Büttner; John D. Dow

1981-01-01

394

Core structure heatup and material relocation in a BWR short-term station blackout accident  

SciTech Connect

Recent safety assessment studies have identified the short-term station blackout accident sequence as an important contributor to the overall plant risk of currently operating boiling water reactors (BWRs). In this hypothetical scenario, the loss of all off- and on-site alternating-current power is coupled with the loss of the capability for water injection to the reactor vessel (caused by, for example, the independent failure of the high-pressure core injection and reactor coolant inventory control). At present, the outcome of this accident sequence is not well understood, primarily due to uncertainty in the relevant core melt progression path. Of interest in this study is the core-structure heatup and subsequent melt relocation leading to the possible formation of core blockages. The results of one-dimensional heat transfer analysis and three-dimensional heat transfer and material relocation modeling are summarized.

Schmidt, R.C.; Dosanjh, S.S.

1990-01-01

395

Metamorphism and melting of picritic crust in the early Earth  

NASA Astrophysics Data System (ADS)

Partial melting experiments with models of Archean oceanic crust (MAOC; with 11, 13 and 15 wt.% MgO) are used to investigate the role of metamorphism and melting of primary picritic compositions in the formation of TTG-like melts and continental crust on the early Earth. The approach investigates the possibility that the average early crust composition was comparatively MgO-rich and evolved to lower magnesium content during the secular cooling of the Earth. High-pressure partial melting experiments indicate a transition of melt compositions from aluminous basaltic melts in MAOC 15 to predominantly tonalitic melts in MAOC 11 and higher melting temperatures with increasing magnesium in the bulk composition. Tonalitic melts were generated in MAOC 11 and 13 at pressures ? 12.5 kbar along with the residual phases garnet + clinopyroxene + plagioclase ± quartz (± orthopyroxene in the presence of quartz and at lower pressures) in the absence of amphibole. Basaltic melts were generated at pressures ? 15 kbar predominantly in the presence of granulite facies residues such as amphibole ± garnet ± plagioclase + orthopyroxene that lack quartz in all MAOC compositions. The tonalitic melts generated in MAOC 11 and 13 indicate that thicker oceanic crust with more magnesium than that of a modern MORB is a viable source for the generation of early Archean high-Si, low-MgO melts, and therefore TTG-like continental crust in the Archean. The favoured settings for the generation of these melts at pressures up to 15 kbar are the base of oceanic crust much thicker than today or melting of slabs in shallow subduction zones, both without interaction of the melts with the mantle during passage to the surface. Tonalitic melts may have formed in deeper subduction zones at 20 kbar beyond plagioclase stability but it is unlikely that such melts could migrate to shallower levels without further mantle interaction. This process may have become more important during the progressive cooling of the Earth.

Ziaja, Karen; Foley, Stephen F.; White, Richard W.; Buhre, Stephan

2014-02-01

396

Subduction: The Gatekeeper for Mantle Melting.  

NASA Astrophysics Data System (ADS)

Geodynamic models are used to show the importance of subduction in controlling vertical thermal and chemical fluxes from Earth's interior to surface. In our models subduction-induced circulation produces conditions favorable to both steady-state and episodic melt production and also plays the role of gatekeeper in thwarting large scale melt production from rising plumes. We use laboratory experiments to characterize three-dimensional (3D) flow fields in convergent margins in response to a range of subduction and back-arc deformation styles, and how these flows interact with upwellings. Models utilize a glucose working fluid with a temperature dependent viscosity to represent the upper 2000 km of the mantle. Subducting lithosphere is modeled with a descending Phenolic plate and back-arc extension is produced by moving Mylar sheets. Thermal plumes are generated from a pressurized, temperature controlled source. Our results show that naturally occurring transitions from downdip- to rollback-dominated subduction produce conditions that favor both widespread decompression melting in the mantle wedge and short-lived pulses of extensive slab melting. For cases of plume-subduction interaction, 3D slab-induced flow quickly converts the active upwelling to a passive thermal anomaly that bears little to no resemblance to traditional models for plume surface expressions. Instead of rising to make LIPs with age-progressive chains, the bulk of the original plume material is trapped below depths of melt production before being re-subducted by the slab. A limited volume of this passive, former plume material is capable of surfacing. Interestingly, this is seen to occur through a range of morphologies that are consistently offset from the original rise location (e.g., conduit). Surface expressions include anything from small circular patches to long, linear features with complex age trends (e.g., progressive or regressive) resulting from the competition between plate motions and deeper mantle flow. Spatial-temporal patterns in melt production, beyond those from background 3D flow, are extremely sensitive to the position of the deep plume relative to the trench. For example, the timing, volume and distribution of melt for upwellings originating beneath the back-arc plate (e.g. Yellowstone) are fundamentally different from those rising under the ocean side of the slab (e.g. Samoa).

Kincaid, C. R.; Druken, K. A.; Griffiths, R. W.

2011-12-01

397

Lithospheric Architecture, Heterogenities, Instabilities, Melting - insight form numerical modelling  

NASA Astrophysics Data System (ADS)

The seismological structure of the Earth's lithosphere is identified to be strongly heterogeneous in terms of thermal and rheological structures. Lithospheric discontinuities (sharp changes in the thermal and/or compositional structure) are thought to be long lived and are mostly correlated with major tectonic boundaries that commonly have been reactivated and which subsequently are the foci of magma intrusion and major mineralization. Resent studies have shown that mantle metasomatism is also controlled by such boundaries. This paper explores the control that lithospheric heterogeneity exerts on the thermal and chemical evolution during deformation subsequent to the development of the heterogeneity. We explore the behaviour of the rheological heterogeneous lithosphere in a compressional regime. The occurrence of such variations may be caused for instance by amalgamation of micro-continents such as is thought to be characteristic of the Yilgarn, Western Australia or South Africa. Theses micro-continents, due to diverse histories may be characterised by various thermal and rheological structures. The models are simplistic but illustrate the basic principles. The code used in this study is based on a conservative finite-difference, multi-grid, marker in cell method. Devolatilisation reactions and melting can affect the physical properties of rocks and are incorporated in a self-consistent manner. We use a petrological-thermomechanical modelling approach with all rock properties including mechanical properties calculated in the Lagrangian scheme for rock markers at every time step based on Gibbs free energy minimization as a function of the local pressure, temperature and rock composition. The results illustrate that initial structural complexity is necessary for and has a dramatic effect on fault and development, the growth of deep basins, core complex formation, melting and devolatilisation within the lithosphere. The horizontal and vertical variation in plastic yield stress of the blocks (representing heterogeneous fused material) nucleates localised deformation and creates conditions for delamination via a Rayleigh-Taylor instability. Above the site of localised delamination of the mantle lithosphere, a series of deep crustal faults develop that may extend into the upper mantle. These deep structures can act as the pathways for mantle derived CO2±H2O fluids and alkaline igneous complexes. Isotherms are commonly elevated throughout the lithosphere in the hanging wall of deep through-going structures and are depressed in the footwalls. This means that some architectures favour devolatilisation and melting in the hanging wall. A large spectrum of behaviour is observed and results from minor changes in the orientation and strength of the blocks.

Gorczyk, Weronika; Hobbs, Bruce; Ord, Alison; Gessner, Klaus; Gerya, Taras V.

2010-05-01

398

Analysis of Pu Isotopes in Melted Fuel by Neutron Resonance Transmission: Examination by Linear Absorption Model  

NASA Astrophysics Data System (ADS)

We have been studying the feasibility of neutron resonance transmission analysis (NRTA) for quantifying nuclear materials (Pu/U isotopes) in particle-like debris of melted fuel for nuclear material accountability and safeguards. The achievable measurement accuracy of NRTA was examined using a linear absorption model for the sample which contain substances other than nuclear fuel materials, such as boron and iron. The impurities (boron and iron etc.) in melted fuel are from the support structure and criticality control materials of the reactor core, and should be included to study the feasibility of NRTA for actual application. Neutron transmission spectra were calculated using the total neutron cross-sections in JENDL-4.0. The transmission spectra together with their uncertainties were evaluated. The study showed quantitatively that the statistical uncertainty in the determination of atomic number density of each isotope depends on the impurity density in the sample. The optimal thickness of the sample was determined for various impurity densities.

Kitatani, F.; Harada, H.; Takamine, J.; Kureta, M.; Seya, M.

2014-04-01

399

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

NASA Technical Reports Server (NTRS)

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.

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

1994-01-01

400

Melt detection of Fe-Ni at high-pressures using atomic dynamics measurements and a fast temperature readout spectrometer  

NASA Astrophysics Data System (ADS)

Cosmochemical studies suggest that the cores of terrestrial planetary bodies are primarily composed of Fe with ~5-10 wt% Ni (e.g., McDonough and Sun 1995). The P-T conditions of the cores of Mars, Mercury, Earth's moon, Io and Ganymede are thought to lie in the stability field of fcc-structured Fe alloyed with ~10 wt% Ni (e.g., Fei et al. 2005). Geomagnetic surveys suggest these terrestrial bodies either have or once had a magnetic dynamo (e.g., Margot et al. 2007), which likely requires the presence of a liquid metallic core surrounding a solid inner core. Therefore, an accurate determination of the melting temperature of fcc-structured Fe-Ni at high pressure will provide constraints on the thermal structure of these small terrestrial bodies, and in turn, may provide insight to their magnetic dynamo and interior evolution history. We have developed a new metric for detecting the solid-liquid phase boundary of Fe-bearing materials at high-pressures using synchrotron Mössbauer spectroscopy (SMS). Focused synchrotron radiation with 1 meV bandwidth passes through a laser-heated Fe-bearing sample inside a diamond-anvil cell. The characteristic SMS time signal vanishes when melting occurs. This process is described by the Lamb-Mössbauer factor, a quantity that is directly related to the mean-square displacement of the Fe atoms. Therefore, we measure the atomic dynamics in the material, in contrast to a static diffraction measurement. The SMS technique provides a new and independent means of melting point determination for materials under high-pressure, as well as access to vibrational properties of the solid near its melting point (Jackson et al. 2013). Accurate melting temperatures of the sample are also necessary factors in constructing reliable melting curves. However, most conventional temperature measurement methods in laser-heated diamond-anvil cell studies are often too slow (~0.3 Hz) to capture the sample's transient temperature fluctuations, which can be significant for materials near their melting points. To accurately capture this effect and reduce uncertainties in melting temperatures, we have developed a Fast Temperature Readout (FasTeR) spectrometer in-line with nuclear resonance scattering measurements under extreme conditions at Sector 3-ID-B of the Advanced Photon Source. Dedicated to determining the sample's temperature near its melting point, FasTeR features a fast readout rate (~100 Hz), high sensitivity, large dynamic range and well-constrained focus. FasTeR may also be ideal for a variety of short time-scale measurements conducted at high-temperatures. FasTeR has been successfully combined with SMS measurements on compressed fcc-structured Fe alloyed with 10 wt% Ni to determine the melting curve by monitoring the dynamics of the atoms. References: Fei, Y., Bertka, C.M. (2005): The interior of Mars. Science 308, 1120-1121 Jackson et al. (2013): Melting of compressed iron by monitoring atomic dynamics, EPSL, 362, 143-150 Margot et al. (2007): Large longitude libration of Mercury reveals a molten core. Science 316, 710-714 McDonough, W.F., Sun, S.S. (1995): The composition of the Earth. Chem. Geol. 120, 223-253

Zhang, D.; Jackson, J. M.; Zhao, J.; Sturhahn, W.; Alp, E. E.; Hu, M.; Toellner, T. S.

2013-12-01

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In situ determination of binary alloy melt compositions in the LHDAC by X- Radiography  

NASA Astrophysics Data System (ADS)

Constraining the light element in Earth's molten outer core requires an understanding of the melting