These are representative sample records from Science.gov related to your search topic.
For comprehensive and current results, perform a real-time search at Science.gov.
1

Large spreading of core melt for melt retention—stabilization  

Microsoft Academic Search

For future nuclear power plants possible core melt scenarios have to be taken into account in the plant layout. Different solutions for core melt retention are proposed in the literature. The core melt retention devices should as far as possible be simple in construction, to minimize the deepness of sophistication of the physical problems connected with it and to minimize

H. A. Weisshäupl; D. Bittermann

1995-01-01

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

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

4

The Annular Core Research Reactor (ACRR) postulated limiting event initial and building source terms  

SciTech Connect

As part of the update of the Safety analysis Report (SAR) for the Annular Core Research Reactor (ACRR), operational limiting events under the category of inadvertent withdrawal of an experiment while at power or during a power pulse were determined to be the most limiting event(s) for this reactor. This report provides a summary of the assumptions, modeling, and results in evaluation of: Reactivity and thermal hydraulics analysis to determine the amount of fuel melt or fuel damage ratios; The reactor inventories following the limiting event; A literature review of post NUREG-0772 release fraction experiment results on severe fuel damages; Decontamination factors due to in-pool transport; and In-building transport modeling and building source term analysis.

Restrepo, L F

1992-08-01

5

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

6

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

7

Core melt/coolant interactions: modelling. [PWR; BWR  

SciTech Connect

If there is not adequate cooling water in the core of a light-water reactor (LWR), the fission product decay heat would eventually cause the reactor fuel and cladding to melt. This could lead to slumping of the molten core materials into the lower plenum of the reactor vessel, possibly followed by failure of the vessel wall and pouring of the molten materials into the reactor cavity. When the molten core materials enter either region, there is a strong possibility of molten core contacting water. This paper focuses on analysis of recent FITS experiments, mechanistic and probabilistic model development, and the application of these models to reactor considerations.

Berman, M.; McGlaun, J.M.; Corradini, M.L.

1983-01-01

8

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

9

Disequilibrium melting and melt migration driven by impacts: Implications for rapid planetesimal core formation  

NASA Astrophysics Data System (ADS)

The ?182W ages of magmatic iron meteorites are largely within error of the oldest solar system particles, apparently requiring a mechanism for segregation of metals to the cores of planetesimals within 1.5 million years of initial condensation. Currently favoured models involve equilibrium melting and gravitational segregation in a static, quiescent environment, which requires very high early heat production in small bodies via decay of short-lived radionuclides. However, the rapid accretion needed to do this implies a violent early accretionary history, raising the question of whether attainment of equilibrium is a valid assumption. Since our use of the Hf-W isotopic system is predicated on achievement of chemical equilibrium during core formation, our understanding of the timing of this key early solar system process is dependent on our knowledge of the segregation mechanism. Here, we investigate impact-related textures and microstructures in chondritic meteorites, and show that impact-generated deformation promoted separation of liquid FeNi into enlarged sulfide-depleted accumulations, and that this happened under conditions of thermochemical disequilibrium. These observations imply that similar enlarged metal accumulations developed as the earliest planetesimals grew by rapid collisional accretion. We suggest that the nonmagmatic iron meteorites formed this way and explain why they contain chondritic fragments in a way that is consistent with their trace element characteristics. As some planetesimals grew large enough to develop partially molten silicate mantles, these enlarged metal accumulations would settle rapidly to form cores leaving sulfide and small metal particles behind, since gravitational settling rate scales with the square of metal particle size. Our model thus provides a mechanism for more rapid core formation with less radiogenic heating. In contrast to existing models of core formation, the observed rarity of sulfide-dominant meteorites is an expected consequence of our model, which promotes early and progressive separation of metal and sulfide. We suggest that the core formation models that assume attainment of equilibrium in the Hf-W system underestimate the core formation time.

Tomkins, Andrew G.; Weinberg, Roberto F.; Schaefer, Bruce F.; Langendam, Andrew

2013-01-01

10

Holocene climate in West Antarctica from the Siple Dome ice core melt-layer record  

Microsoft Academic Search

Summer climate conditions in West Antarctica changed significantly during the Holocene, as recorded by frequency of occurrence of rare melt layers in the Siple Dome deep ice core. We present a record of millennial-scale melt-layer frequency through the Holocene from the Siple Dome ice-core which we interpret as a significant record of changing summer climate conditions for West Antarctica. Melting

S. B. Das; R. B. Alley; J. W. C. White

2003-01-01

11

Hydrogen generation during a core melt-coolant interactions. [PWR; BWR  

SciTech Connect

If a reactor accident leads to core melt, interaction of this material with coolant can produce hydrogen by steam oxidation of the metallic content of the melt. Experimental results are presented for hydrogen generation from both explosive and non-explosive melt-coolant interactions, using either iron-alumina or corium A + R as the melt simulant. Use of a simple model gives predictions for hydrogen generation rates that are in reasonable agreement with the experimental results.

Corradini, M.L.; Mitchell, D.E.; Evans, N.A.

1983-01-01

12

Water isotopic ratios from a continuously melted ice core sample  

E-print Network

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 simultaneous water isotopic analysis of $\\delta^{18}$O and $\\delta$D on a continuous stream of liquid water as generated from a continuously melted ice rod. Injection of sub ${\\mu}$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. A calibration procedure allows for proper reporting of the data on the VSMOW--SLAP scale. Application of spectral methods yields the combined uncertainty of the system at below 0.1 permil and 0.5 permil for $\\delta^{18}$O and $\\delta$D, respectively. This performance is comparable to that achieved with mass spectrometry. Dispersion of the sampl...

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

2014-01-01

13

Core-melt materials interactions evaluations. Final report, April 1980April 1983  

Microsoft Academic Search

This final report describes work performed on a variety of topics related to the materials interactions that would occur following a postulated core-meltdown accident in a Light Water Reactor. The main topics addressed include: (1) an evaluation of candidate core-retention-system materials for the Zion and Indian Point (Z\\/IP) nuclear reactors; (2) an examination of various core-retention-system concepts with emphasis on

D. G. Swanson; J. N. Castle; P. D. Anderson; I. Catton

1983-01-01

14

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

15

Melting of Iron under Earth's Core Conditions from Diffusion MonteCarlo Free Energy Calculations  

Microsoft Academic Search

The temperature of Earth's core is a parameter of critical importance to model the thermal structure of Earth. Since the core is mainly made of iron, with a solid liquid boundary (the inner core boundary) at 1220 km from the center of the Earth, the melting temperature of iron at the pressure of the ICB provides constraints on the temperature

Ester Sola; Dario Alfè

2009-01-01

16

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

17

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

18

Development of Melting Device for Measurement of Traceable Proxies in Ice Core  

NASA Astrophysics Data System (ADS)

It has been well known that various proxies in ice core can provide useful information about climate change and atmospheric environment in the past. However, ice core sample can be easily contaminated during drilling, shipping, cutting, and handling and especially, its breaks are the primary source of contamination of the inner core. Therefore, decontamination procedure of ice core sample to remove contaminants of outer layers in ice core is very important. Until now, as a decontamination method of ice core sample, conventional method has been broadly used. This indicates removal of pollutants by mechanical scraping with stainless steel knives or by a series of washing-baths with ultra-pure distilled water. It has advantages such as minimization of interferences between samples, flexible adaptation of extraction time, and stable instrumental analysis. As a disadvantage, there have been also reported as low efficiencies of ice core preparation owing to strict and complicated procedures, low resolution (10-20 cm/sample), and difficulties of application to on-line measurement system. As a result, the melting device was developed as an alternative of conventional decontamination method in the early 1990s. Contrary to conventional method, this represented high efficiencies of decontamination, high resolution (? 5 cm/sample), and the possibilities of application to on-line measurement system. However, the artifacts from melting head made of metals, the interferences between samples melted in series, recovery efficiencies of traceable element, and instability of instrumental analysis owing to short extraction time and scanning time have to be overcome. Even if various melting devices have been developed, prior to this study, little researches had been undertaken examining systematically them which would be expected to be important in on-line measurement system. In this study, melting head made of Ti and with 3-channels was constructed to decontaminate discrete ice core samples. The results of performance test of melting device conducted systematically and preliminary results applied to ice core drilled at Alpine and Antarctica will be presented.

Hong, S.; Hwang, H.; Lee, K.; Hur, S.; Hong, S.; Chung, J.; Yoon, A.; Yoon, H.

2009-12-01

19

Melting relationships in the Fe-Fe3S system up to the outer core conditions  

NASA Astrophysics Data System (ADS)

In situ X-ray diffraction experiments in the Fe-Fe3S system were performed up to 175 GPa and 3500 K using a laser-heated diamond anvil cell to investigate melting relationships in the system. Partial melting in the Fe-Fe3S system was observed based on the disappearance of X-ray diffraction peaks of solid Fe3S and texture observation of the recovered samples. The melting relationship of the Fe-Fe3S system as a function of pressure is evaluated based on Kraut-Kennedy law. Our results of melting relationships suggest that the temperature at the inner core boundary is between 4700(160) and 4930(330) K if sulfur is the only light element in the Earth's core. Assuming the adiabatic temperature gradient in the outer core, the temperature at the core-mantle boundary is estimated to be in the range of 3600-3770 K. The present temperature profile of the core is consistent with the core-mantle boundary temperature that can explain the core heat flux to maintain the core dynamo and the seismic structure at the base of the lower mantle.

Kamada, Seiji; Ohtani, Eiji; Terasaki, Hidenori; Sakai, Takeshi; Miyahara, Masaaki; Ohishi, Yasuo; Hirao, Naohisa

2012-12-01

20

Melting of the Fe-O-S system and reaction between olivine and iron melt at the lunar core conditions: Implications for the structure of the lunar core  

NASA Astrophysics Data System (ADS)

Despite recent observations on the Moon from satellite sensing and analyses of Apollo-era seismic data, there are still several unsolved issues on the deep lunar interior. Recent studies suggest the presence of a solid inner core and liquid outer core in the Moon (1). If we could constrain the temperature and composition of the lunar outer core, this would help us to better understand the lunar interior. Here, we focused on the interaction between liquid iron-alloys and solid silicates, and revealed the nature of the core of the Moon. The lunar mantle is characterized by high FeO content (2). This implies that the Moon is more oxidizing compared to the Earth and thus the lunar core could be composed of Fe-O-S alloys. It is known that there is a liquid immiscibility in the Fe-O-S system, thus one of the aims of our study is to clarify whether the Moon has an immiscible liquid core or not. We performed oxygen partition experiments between the lunar silicate mantle and molten metal at 5 GPa and calculated the distribution coefficient, D, of oxygen between liquid metal and olivine crystals. Using this value, the amount of O in the lunar liquid core is calculated to be 4.45 at.% at 1000 °C and 5.56 at.% at 1400 °C when the mantle Mg number is 80, which is the assumed lunar core (2). This high amount of oxygen strongly indicates that the lunar core coexisting with the FeO-rich mantle is composed of the two immiscible liquids (FeO-rich melt and Fe-FeS melt). Estimations from the existing data on the density of FeO-rich melt and liquid Fe-FeS indicate that the liquid Fe-FeS is denser than the FeO-rich melt suggesting that the lunar liquid core is stratified to an upper FeO-rich layer and a lower Fe-FeS layer. The upper FeO-rich layer is reactive with the olivine rich lunar mantle to form magnesiowustite and could cause the partially molten low Q (high damping) region at the CMB of the Moon. (1) Weber, R.C., Lin. P., Garnero, E.J., Williams, Q., Lognonné, P., Science 331, 309-312, (2011) (2) Taylor, S.R., Solar system evolution, A new Perspective. Cambridge University Press, New York, 307 (1992)

Akamatsu, H.; Ohtani, E.; Suzuki, A.

2013-12-01

21

Acceleration of snow melt in an Antarctic Peninsula ice core during the twentieth century  

NASA Astrophysics Data System (ADS)

Over the past 50 years, warming of the Antarctic Peninsula has been accompanied by accelerating glacier mass loss and the retreat and collapse of ice shelves. A key driver of ice loss is summer melting; however, it is not usually possible to specifically reconstruct the summer conditions that are critical for determining ice melt in Antarctic. Here we reconstruct changes in ice-melt intensity and mean temperature on the northern Antarctic Peninsula since AD 1000 based on the identification of visible melt layers in the James Ross Island ice core and local mean annual temperature estimates from the deuterium content of the ice. During the past millennium, the coolest conditions and lowest melt occurred from about AD 1410 to 1460, when mean temperature was 1.6°C lower than that of 1981-2000. Since the late 1400s, there has been a nearly tenfold increase in melt intensity from 0.5 to 4.9%. The warming has occurred in progressive phases since about AD 1460, but intensification of melt is nonlinear, and has largely occurred since the mid-twentieth century. Summer melting is now at a level that is unprecedented over the past 1,000 years. We conclude that ice on the Antarctic Peninsula is now particularly susceptible to rapid increases in melting and loss in response to relatively small increases in mean temperature.

Abram, Nerilie J.; Mulvaney, Robert; Wolff, Eric W.; Triest, Jack; Kipfstuhl, Sepp; Trusel, Luke D.; Vimeux, Françoise; Fleet, Louise; Arrowsmith, Carol

2013-05-01

22

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

23

Crystallization of ion clouds in octupole traps: Structural transitions, core melting, and scaling laws  

SciTech Connect

The stable structures and melting properties of ion clouds in isotropic octupole traps are investigated using a combination of semianalytical and numerical models, with a particular emphasis at finite-size scaling effects. Small-size clouds are found to be hollow and arranged in shells corresponding approximately to the solutions of the Thomson problem. The shell structure is lost in clusters containing more than a few thousands of ions, the inner parts of the cloud becoming soft and amorphous. While melting is triggered in the core shells, the melting temperature follows the rule expected for three-dimensional dense particles, with a depression scaling linearly with the inverse radius.

Calvo, F.; Champenois, C.; Yurtsever, E. [LASIM, Universite Claude Bernard Lyon 1 and CNRS, UMR 5579, 43 Boulevard du 11 Novembre 1918, F69622 Villeurbanne Cedex (France); PIIM, UMR 6633, Universite de Provence and CNRS, Campus Universitaire de Saint-Jerome C21, F13397 Marseille Cedex 20 (France); Koc University, Rumelifeneriyolu, Sariyer, Istanbul 34450 (Turkey)

2009-12-15

24

Crystallization of ion clouds in octupole traps: structural transitions, core melting, and scaling laws  

E-print Network

The stable structures and melting properties of ion clouds in isotropic octupole traps are investigated using a combination of semi-analytical and numerical models, with a particular emphasis at finite size scaling effects. Small-size clouds are found to be hollow and arranged in shells corresponding approximately to the solutions of the Thomson problem. The shell structure is lost in clusters containing more than a few thousands of ions, the inner parts of the cloud becoming soft and amorphous. While melting is triggered in the core shells, the melting temperature unexpectedly follows the rule expected for three-dimensional dense particles, with a depression scaling linearly with the inverse radius.

Calvo, Florent; Yurtsever, Ersin

2009-01-01

25

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

26

Melting of iron under Earth's core conditions from diffusion Monte Carlo free energy calculations.  

PubMed

The temperature of Earth's core is a parameter of critical importance to model the thermal structure of Earth. Since the core is mainly made of iron, with a solid liquid boundary (the inner core boundary) at 1220 km from the center of the Earth, the melting temperature of iron at the pressure of the ICB provides constraints on the temperature of the core. These constraints are based either on extrapolations to ICB pressure of experimental measurements, or on theoretical calculations which employed various flavors of quantum mechanics, most notably density functional theory. Significant disagreement between estimates obtained with different methods calls for calculations based on more accurate techniques. Here we used quantum Monte Carlo techniques to compute the free energies of solid and liquid iron at ICB conditions. We obtained an iron melting temperature at 330 GPa of 6900+/-400 K. PMID:19792692

Sola, Ester; Alfè, Dario

2009-08-14

27

Melting of Iron under Earth's Core Conditions from Diffusion Monte Carlo Free Energy Calculations  

E-print Network

Melting of Iron under Earth's Core Conditions from Diffusion Monte Carlo Free Energy Calculations Ester Sola1 and Dario Alfe`1,2 1 Thomas Young Centre@UCL, and Department of Earth Sciences, UCL, Gower. Here we used quantum Monte Carlo techniques to compute the free energies of solid and liquid iron

Alfè, Dario

28

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

29

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

E-print Network

We consider the phase behavior of two-dimensional ($2D$)system of particles with an isotropic core-softened potential introduced in our previous publications. As one can expect from the qualitative consideration for the three dimensional case, the system demonstrates a reentrant-melting transition at low densities along with waterlike anomalies in the fluid phase near the melting maximum. In contrast with the three dimensional case, in two dimensions melting is a continuous two-stage transition in the low density part of the phase diagram with an intermediate hexatic phase corresponding to the Kosterlitz-Thouless-Halperin-Nelson-Young (KTHNY) scenario. At the same time, at high densities the system melts through one first-order transition. We also show, that the order of the region of anomalous diffusion and the regions of density and structural anomalies are inverted in comparison with the $3D$ case and have silicalike sequence.

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

2013-11-29

30

Melting of iron at the physical conditions of the Earth's core.  

PubMed

Seismological data can yield physical properties of the Earth's core, such as its size and seismic anisotropy. A well-constrained iron phase diagram, however, is essential to determine the temperatures at core boundaries and the crystal structure of the solid inner core. To date, the iron phase diagram at high pressure has been investigated experimentally through both laser-heated diamond-anvil cell and shock-compression techniques, as well as through theoretical calculations. Despite these contributions, a consensus on the melt line or the high-pressure, high-temperature phase of iron is lacking. Here we report new and re-analysed sound velocity measurements of shock-compressed iron at Earth-core conditions. We show that melting starts at 225 +/- 3 GPa (5,100 +/- 500 K) and is complete at 260 +/- 3 GPa (6,100 +/- 500 K), both on the Hugoniot curve-the locus of shock-compressed states. This new melting pressure is lower than previously reported, and we find no evidence for a previously reported solid-solid phase transition on the Hugoniot curve near 200 GPa (ref. 16). PMID:14737164

Nguyen, Jeffrey H; Holmes, Neil C

2004-01-22

31

Melting of iron at the physical conditions of the Earth's core  

NASA Astrophysics Data System (ADS)

Seismological data can yield physical properties of the Earth's core, such as its size and seismic anisotropy. A well-constrained iron phase diagram, however, is essential to determine the temperatures at core boundaries and the crystal structure of the solid inner core. To date, the iron phase diagram at high pressure has been investigated experimentally through both laser-heated diamond-anvil cell and shock-compression techniques, as well as through theoretical calculations. Despite these contributions, a consensus on the melt line or the high-pressure, high-temperature phase of iron is lacking. Here we report new and re-analysed sound velocity measurements of shock-compressed iron at Earth-core conditions. We show that melting starts at 225 +/- 3GPa (5,100 +/- 500K) and is complete at 260 +/- 3GPa (6,100 +/- 500K), both on the Hugoniot curve-the locus of shock-compressed states. This new melting pressure is lower than previously reported, and we find no evidence for a previously reported solid-solid phase transition on the Hugoniot curve near 200GPa (ref. 16).

Nguyen, Jeffrey H.; Holmes, Neil C.

2004-01-01

32

NATURAL CONVECTION PHENOMENA IN A PROTOTYPIC PWR DURING A POSTULATED BEYOND-THE-DESIGN-BASIS ACCIDENTS  

Microsoft Academic Search

In a postulated beyond-the-design-basis accident scenario of a prototypic pressurized water reactor that may lead to a partial or total core melt, natural convection is an important phenomenon that can affect the accident progression and its consequence. Comparison between the results obtained from COMMIX code and Westinghouse's experimental data of 1\\/7 scale natural convection test, the agreement is good. We

William T. Sha

33

Melt stagnation in peridotites from the Godzilla Megamullion Oceanic Core Complex, Parece Vela Basin, Philippine Sea  

NASA Astrophysics Data System (ADS)

The Godzilla Megamullion, located in the Parece Vela Backarc Basin of the Izu-Bonin-Mariana (IBM) system, is the largest known example of an Oceanic Core Complex (OCC). Peridotites recovered from the megamullion are divided petrographically into fertile (e.g. lherzolites), depleted (e.g. harzburgites), and plagioclase-bearing groups (Ohara et al., 2003a). A total of 151 thin sections were studied from the Kairei KR03-01, Hakuho Maru KH07-02, and Yokosuka YK09-05 cruises. Melt stagnation is studied via the incidence of plagioclase-bearing peridotites and the major element chemistry of Cr-spinels in the plag-bearing samples. A distinct trend in melt stagnation is evident along the length of the megamullion representing a secular evolution in the entrapment of melts rising through the lithosphere. The distal (furthest from the termination of spreading), depleted portion of the mullion represents a robust mantle section that was still producing abundant melt and can be compared to typical oceanic spreading with its relatively “normal” percentage of plagioclase peridotites and average spinel Cr# of 0.35. The medial, fertile portion of the mullion represents a steep falloff in melt productivity represented by fertile spinel compositions (i.e. Cr# < 0.25) and the presence of plagioclase-free lherzolites. The proximal (closest to termination of spreading), heavily plagioclase impregnated portion (with spinel Cr#s covering nearly the entire range of abyssal peridotite spinel compositions) of the mullion then represents a period of increasing stagnation of melt into a lithosphere that was undergoing progressive thickening. We infer that the processes of mantle evolution through melt stagnation and impregnation, as evidenced by the systematic variations in plag-peridotites along Godzilla Megamullion, represent a possibly common way in which the mantle reacts to OCC formation. In this case, Godzilla Megamullion may represent an extreme endmember in OCC formation.

Loocke, Matthew; Snow, Jonathan E.; Ohara, Yasuhiko

2013-12-01

34

Melting of iron close to Earth's inner core boundary conditions and beyond  

E-print Network

Several important geophysical features such as heat flux at the Core-Mantle Boundary or geodynamo production are intimately related with the temperature profile in the Earth's core. However, measuring the melting curve of iron at conditions corresponding to the Earth inner core boundary under pressure of 330 GPa has eluded scientists for several decades. Significant discrepancies in previously reported iron melting temperatures at high pressure have called into question the validity of dynamic measurements. We report measurements made with a novel approach using X-ray absorption spectroscopy using an X-ray free electron laser source coupled to a laser shock experiment. We determine the state of iron along the shock Hugoniot up to 420 GPa (+/- 50) and 10800 K (+/- 1390) and find an upper boundary for the melting curve of iron by detecting solid iron at 130 GPa and molten at 260, 380 and 420 GPa along the shock Hugoniot. Our result establishes unambiguous agreement between dynamic measurement and recent extrapo...

Harmand, M; Mazevet, S; Bouchet, J; Denoeud, A; Dorchies, F; Feng, Y; Fourment, C; Galtier, E; Gaudin, J; Guyot, F; Kodama, R; Koenig, M; Lee, H J; Miyanishi, K; Morard, G; Musella, R; Nagler, B; Nakatsutsumi, M; Ozaki, N; Recoules, V; Toleikis, S; Vinci, T; Zastrau, U; Zhu, D; Benuzzi-Mounaix, A

2014-01-01

35

Sulfur Saturation Limits in Silicate Melts and their Implications for Core Formation Scenarios for Terrestrial Planets  

NASA Technical Reports Server (NTRS)

This study explores the controls of temperature, pressure, and silicate melt composition on S solubility in silicate liquids. The solubility of S in FeO-containing silicate melts in equilibrium with metal sulfide increases significantly with increasing temperature but decreases with increasing pressure. The silicate melt structure also exercises a control on S solubility. Increasing the degree of polymerization of the silicate melt structure lowers the S solubility in the silicate liquid. The new set of experimental data is used to expand the model of Mavrogenes and O'Neill(1999) for S solubility in silicate liquids by incorporating the influence of the silicate melt structure. The expected S solubility in the ascending magma is calculated using the expanded model. Because the negative pressure dependence of S solubility is more influential than the positive temperature dependence, decompression and adiabatic ascent of a formerly S-saturated silicate magma will lead to S undersaturation. A primitive magma that is S-saturated in its source region will, therefore, become S-undersaturated as it ascends to shallower depth. In order to precipitate magmatic sulfides, the magma must first cool and undergo fractional crystallization to reach S saturation. The S content in a metallic liquid that is in equilibrium with a magma ocean that contains approx. 200 ppm S (i.e., Earth's bulk mantle S content) ranges from 5.5 to 12 wt% S. This range of S values encompasses the amount of S (9 to 12 wt%) that would be present in the outer core if S is the light element. Thus, the Earth's proto-mantle could be in equilibrium (in terms of the preserved S abundance) with a core-forming metallic phase.

Holzheid, Astrid; Grove, Timothy L.

2002-01-01

36

Carbon in the Martian Interior: Core-Mantle Fractionation and Extraction by Mantle Melting at Oxidized Conditions  

NASA Astrophysics Data System (ADS)

The budget and origin of carbon in the martian mantle is discussed based on experimental prediction of carbon partitioning in a core-forming magma ocean. Experiments on carbonated martian mantle melting are also presented.

Dasgupta, R.; Nelson, J. D.; Chi, H.; Ding, S.; Li, Y.; Duncan, M. S.; Tsuno, K.

2014-11-01

37

Quantification of Dead-ice Melting in Ice-Cored Moraines at the High-Arctic Glacier Holmströmbreen, Svalbard  

NASA Astrophysics Data System (ADS)

An extensive dead-ice area has developed at the stagnant snout of the Holmströmbreen glacier on Svalbard following its Little Ice Age maximum. Dead-ice appears mainly as ice-cored moraines, ice-cored eskers and ice- cored kames. The most common dead-ice landform is sediment gravity flows on ice-cored slopes surrounding a large ice-walled, moraine-dammed lake. The lake finally receives the sediment from the resedimentation processes. Dead-ice melting is described and quantified through field studies and analyses of high-resolution, multi-temporal aerial photographs and satellite imagery. Field measurements of backwasting of ice-cored slopes indicate short-term melting rates of c. 9.2 cm/day. Long-term downwasting rates indicate a surface lowering of ice-cored moraines of c. 0.9 m/yr from 1984-2004. Different measures for dead-ice melting are assessed in relation to the temperature record from Svalbard since the termination of the Little Ice Age. The most prominent impact of dead-ice melting is the evolution of the ice-walled lake with an area increasing near-exponentially over the last 40 years. As long as backwasting and mass movement processes prevent build-up of an insulating debris-cover and expose ice-cores to melting, the de-icing continues even though the area is characterized by continuous permafrost.

Schomacker, A.; Kjaer, K. H.

2007-12-01

38

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

39

Diverse Melting Modes and Structural Collapse of Hollow Bimetallic Core-Shell Nanoparticles: A Perspective from Molecular Dynamics Simulations  

PubMed Central

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

40

How dimensionality changes the anomalous behavior and melting scenario of a core-softened potential system?  

PubMed

We present a computer simulation study of the phase diagram and anomalous behavior of two-dimensional (2D) and three-dimensional (3D) classical particles repelling each other through an isotropic core-softened potential. As in the analogous three-dimensional case, in 2D a reentrant-melting transition occurs upon compression under not too high pressure, along with a spectrum of thermodynamic and dynamic anomalies in the fluid phase. However, in two dimensions the order of the region of anomalous diffusion and the region of structural anomaly is inverted in comparison with the 3D case, where there exists a water-like sequence of anomalies, and has a silica-like sequence. In the low density part of the 2D 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. PMID:24888366

Dudalov, D E; Fomin, Y D; Tsiok, E N; Ryzhov, V N

2014-07-21

41

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

42

In-situ rock melting applied to lunar base construction and for exploration drilling and coring on the moon  

SciTech Connect

An excavation technology based upon melting of rock and soil has been extensively developed at the prototype hardware and conceptual design levels for terrestrial conditions. Laboratory and field tests of rock-melting penetration have conclusively indicated that this excavation method is insensitive to rock, soil types, and conditions. Especially significant is the ability to form in-place glass linings or casings on the walls of boreholes, tunnels, and shafts. These factors indicate the unique potential for in situ construction of primary lunar base facilities. Drilling and coring equipment for resource exploration on the moon can also be devised that are largely automated and remotely operated. It is also very likely that lunar melt-glasses will have changed mechanical properties when formed in anhydrous and hard vacuum conditions. Rock melting experiments and prototype hardware designs for lunar rock-melting excavation applications are suggested.

Rowley, J.C.; Neudecker, J.W.

1984-01-01

43

The timing of partial melting, Barrovian metamorphism and granite intrusion in the Naxos metamorphic core complex, Cyclades, Aegean Sea, Greece  

NASA Astrophysics Data System (ADS)

The relationship between partial melting and granite intrusion in a classic Barrovian metamorphic terrane has been assessed. Thirteen samples were dated by SHRIMP U-Pb zircon geochronology from the island of Naxos, Greece, one of the Aegean metamorphic core complexes. The effect of partial melting during peak Barrovian metamorphism on Naxos is recorded by fine (<30 ?m) zircon overgrowths surrounding older cores in seven of nine samples of migmatite analyzed. The ages of these overgrowths suggest that partial melting commenced prior to 20.7 Ma. The timing of partial melting on Naxos also constrains the onset of extensional tectonism in the area to pre-20.7 Ma. The preservation of zircon overgrowth rims with distinctly different concordant ages, ranging from 20.7 to 16.8 Ma, both from different samples and from within the one handspecimen, suggests that zircon precipitation, associated with the partial melting process, was episodic over this age range on both local (cm) and regional (km) scales. Zircons from four granite intrusives were also dated and range in age from 15.4 to 11.3 Ma, with the main period of magmatic activity at ca. 12 Ma, clearly post-dating metamorphism. The sequence of partial melting, Barrovian metamorphism and magmatism in the Naxos metamorphic core complex can be related to a change from overall crustal shortening to extensional tectonism in the Aegean region, caused by post-collisional roll-back of the subducting African slab along the Hellenic trench system.

Keay, Sue; Lister, Gordon; Buick, Ian

2001-12-01

44

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

45

Elastic moduli, dislocation core energy, and melting of hard disks in two dimensions  

NASA Astrophysics Data System (ADS)

Elastic moduli and dislocation core energy of the triangular solid of hard disks of diameter ? are obtained in the limit of vanishing dislocation-antidislocation pair density, from Monte Carlo simulations that incorporate a constraint, namely that all moves altering the local connectivity away from that of the ideal triangular lattice are rejected. In this limit we show that the solid is stable against all other fluctuations at least up to densities as low as ??2=0.88. Our system does not show any phase transition so diverging correlation lengths leading to finite size effects and slow relaxations do not exist. The dislocation pair formation probability is estimated from the fraction of moves rejected due to the constraint which yields, in turn, the core energy Ec and the (bare) dislocation fugacity y. Using these quantities, we check the relative validity of first order and Kosterlitz-Thouless-Halperin-Nelson-Young (KTHNY) melting scenarios and obtain numerical estimates of the typical expected transition densities and pressures. We conclude that a KTHNY transition from the solid to a hexatic phase preempts the solid to liquid first order transition in this system albeit by a very small margin, easily masked by crossover effects in unconstrained ``brute- force'' simulations with a small number of particles.

Sengupta, Surajit; Nielaba, Peter; Binder, K.

2000-06-01

46

Melting behavior of the iron-sulfur system and chemical convection in iron-rich planetary cores  

SciTech Connect

We present experimental data on the high-pressure melting behavior of the Fe-S system from a synchrotron x-ray radiography study using the large volume press, with implications for the role of chemical convection in sulfur-bearing planetary cores. At present, Earth, Mercury and Ganymede are the only three solid bodies in the Solar System that possess intrinsic global magnetic fields. Dynamo simulation reveal that chemical buoyancy force associated with the formation of a solid inner core is critical for sustaining the Earth's magnetic field. Fluid motions in Mercury and Ganymede may be partially driven by chemical buoyancy force as well. The style of chemical convection and its influence on the thermal and chemical state and evolution of iron-rich cores are determined in part by the melting behavior of potential core-forming materials. Sulfur is widely accepted as a candidate light element in iron-rich planetary cores. In order to understand the role of chemical convection in sulfur-bearing cores, we studied the high-pressure melting behavior of Fe-S mixtures containing 9 wt% sulfur using the synchrotron x-ray radiographic method in a large volume press.

Li, J.; Chen, B. (UIUC)

2009-03-26

47

Carbon solubility in core melts in a shallow magma ocean environment and distribution of carbon between the Earth’s core and the mantle  

NASA Astrophysics Data System (ADS)

The solubility of carbon in Fe and Fe-5.2 wt.% Ni melts, saturated with graphite, determined by electron microprobe analysis of quenched metal melts was 5.8 ± 0.1 wt.% at 2000 °C, 6.7 ± 0.2 wt.% at 2200 °C, and 7.4 ± 0.2 wt.% at 2410 °C at 2 GPa, conditions relevant for core/mantle differentiation in a shallow magma ocean. These solubilities are slightly lower than low-pressure literature values and significantly beneath calculated values for even higher pressures [e.g., Wood B. J. (1993) Carbon in the core. Earth Planet. Sci. Lett.117, 593-607]. The trend of C solubility versus temperature for Fe-5.2 wt.% Ni melt, within analytical uncertainties, is similar to or slightly lower (˜0.2-0.4 wt.%) than that of pure Fe. Carbon content of core melts and residual mantle silicates derived from equilibrium batch or fractional segregation of core liquids and their comparison with our solubility data and carbon content estimate of the present day mantle, respectively, constrain the partition coefficient of carbon between silicate and metallic melts, DCsilicate/metal in a magma ocean. For the entire range of possible bulk Earth carbon content from chondritic to subchondritic values, DCsilicate/metal of 10 -4 to 1 is derived. But for ˜1000 ppm bulk Earth carbon, DCsilicate/metal is between 10 -2 and 1. Using the complete range of possible DCsilicate/metal for a magma ocean at ˜2200 °C, we predict maximum carbon content of the Earth's core to be ˜6-7 wt.% and a preferred value of 0.25 ± 0.15 wt.% for a bulk Earth carbon concentration of ˜1000 ppm.

Dasgupta, Rajdeep; Walker, David

2008-09-01

48

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

49

The consequences of melting and melt segregation in the overturned ilmenite-bearing cumulates at the core-mantle boundary of the Moon  

NASA Astrophysics Data System (ADS)

Standard lunar evolution models involve giant impact, lunar magma ocean, and cumulate overturn. One potential outcome of lunar cumulate mantle overturn is the presence of an ilmenite-bearing cumulates (IBC) at the base of the lunar mantle. Because the IBC layer is enriched in heat producing elements, they may become thermally buoyant with respect to the overlying harzburgite cumulate mantle at a later time. Ascending of the ilmenite-bearing cumulate layer has been used to explain the petrogenesis of mare basalts. On the other hand, the ilmenite-rich cumulates may sink to form a stable outer core surrounding the small metallic lunar core. Inversion of lunar free oscillation data indicates a density structure that may be more compatible with a metallic core surrounded by stable ilmenite-rich cumulates. A seismically attenuation region has been shown to exist on the lunar CMB and have been attributed to the presence of partial melt. Here, we explore possible mechanisms that stabilize the overturned ilmenite-rich cumulates. The solidi of ilmenite-bearing harzburgite are considerably lower than those of harzburgites. Presence of high abundance of heat producing elements in the overturned IBC may result in partial melting which will lead to the redistribution of heat producing elements. Due to its high Fe-Ti abundances, the melt is likely denser than the solid matrix and will percolate downward, forming a new liquid layer on the CMB. Meanwhile, because the heat producing elements (U and Th) are incompatible, they will also sink down with the melt. This redistribution of heat producing elements can influence the instability of the IBC and the generation of mare volcanism. We first investigate the thermal evolution of the lunar cumulate mantle using a numerical convection model in a spherical geometry. When the temperature of the IBC exceeds the solidus of ilmenite-bearing harzburgite, the excess temperature is taken to produce the melt source. This melt source is used to estimate the melt segregation rate and the redistribution of the heat producing elements in the IBC. Preliminary calculations show that the melt can sink down to the CMB in 25 Ma, a time scale that is much shorter than the time needed to heat up the ilmenite-rich layer to neutral buoyant (~ 200 Ma). Results from the present study suggest that, given a relatively large radioactive production heat, the ilmenite-rich cumulate layer may be stable due to downward segregation of Fe-Ti rich melt . The melt layer with high concentrations of U and Th may freeze slowly and resulting in a low-velocity region above CMB to the present day. The mare vocalism may be generated from an asymmetrically distributed source in lunar mantle shallower than the ilmenite-rich cumulate layer.

Zhang, N.; Liang, Y.; Parmentier, E.

2012-12-01

50

Numerical and Experimental Model Studies on Thermal Hydraulic Behavior of FBR Internal Core Catcher Assembly  

Microsoft Academic Search

Core Catcher is provided as an in-vessel core debris retention device to collect, support, cool and maintain in sub-critical configuration, the generated core debris from fuel melting due to certain postulated Beyond Design Basis Events (BDBE) for Fast Breeder Reactor (FBR). This also acts as a barrier to prevent settling of debris on main vessel and keeps its maximum temperature

Sanjay Kumar Das; Anil Kumar Sharma; A. Jasmin Sudha; G. Punitha; G. Lydia; P. A. Somayajulu; S. S. Murthy; B. Malarvizhi; V. Gopalakrishnan; J. Harvey; N. Kasinathan; M. Rajan

2006-01-01

51

Melting of Fe and Fe120Si8 at the Earth's Core Pressures by ab Initio Molecular Dynamics  

NASA Astrophysics Data System (ADS)

The solid Earth's inner core (IC) consists mainly of iron likely alloyed with some light elements. At low temperature iron is stable in hexagonal close packed (hcp) phase up to very high pressures. However, there is an accumulating evidence that under pressures (~ 364 GPa) and temperatures (above 6000 K) in the Earth's IC iron, either pure or alloyed with light elements (e.g. Si), might be stable in the body-centred cubic (bcc) phase1,2. The melting temperature of this phase in the IC is unknown. Conditions of the IC are not achieved in experiment. Previous theoretical studies concentrated mostly on the melting of the hcp phase3. We show, by combination of ab initio molecular dynamics and Z-method4 that pure bcc Fe melts at at the pressure in the center of IC at ~7000 K. Iron, alloyed with 6.25% of Si, melts at a temperature of ~7200 K. While light elements depress hcp Fe melting temperatures5, we show that Si addition has opposite effect on bcc Fe. Melting temperatures of bcc and hcp 2,3 are within mutual error bars, even though bcc melts at a higher temperature. However, the melting temperature of Si-alloyed bcc iron is clearly above that of Si-alloyed hcp phase5. This is because of different bonding of Si-Fe within the bcc as compared to the hcp structure. Therefore, the existing estimates of core temperatures have to be corrected upwards. 1. Brown, J.M. & McQueen, R.G. J. Geophys. Res. 91, 7485(1986). 2. Belonoshko, A.B., Ahuja, R. & Johansson, B. Nature 424, 1032(2003); Belonoshko, A.B., Skorodumova, N.V., Rosengren, A. & Johansson, B. Science 319, 797(2008). 3. Belonoshko, A.B., Ahuja, R. & Johansson, B. Phys. Rev. Lett. 84, 3638(2000); Alfé, D., Gillan, M.J. & Price, G.D. Nature 401, 462(1999). 4. Kresse, G. & Furthmüller, J. J. Phys. Rev. B 54, 11169(1996); Belonoshko, A.B., Skorodumova, N.V., Rosengren, A. & Johansson, B. Phys. Rev. B 73, 012201(2006). 5. Alfé, D., Price, G.D. & Gillan, M.J. Cont. Phys. 48, 63 (2007).

Belonoshko, A. B.; Rosengren, A.; Burakovsky, L.; Preston, D. L.; Johansson, B.

2008-12-01

52

REVIEWS OF TOPICAL PROBLEMS: Universal viscosity growth in metallic melts at megabar pressures: the vitreous state of the Earth's inner core  

NASA Astrophysics Data System (ADS)

Experimental data on and theoretical models for the viscosity of various types of liquids and melts under pressure are reviewed. Experimentally, the least studied melts are those of metals, whose viscosity is considered to be virtually constant along the melting curve. The authors' new approach to the viscosity of melts involves the measurement of the grain size in solidified samples. Measurements on liquid metals at pressures up to 10 GPa using this method show, contrary to the empirical approach, that the melt viscosity grows considerably along the melting curves. Based on the experimental data and on the critical analysis of current theories, a hypothesis of a universal viscosity behavior is introduced for liquids under pressure. Extrapolating the liquid iron results to the pressures and temperatures at the Earth's core reveals that the Earth's outer core is a very viscous melt with viscosity values ranging from 102 Pa s to 1011 Pa s depending on the depth. The Earth's inner core is presumably an ultraviscous (>1011 Pa s) glass-like liquid — in disagreement with the current idea of a crystalline inner core. The notion of the highly viscous interior of celestial bodies sheds light on many mysteries of planetary geophysics and astronomy. From the analysis of the pressure variation of the melting and glass-transition temperatures, an entirely new concept of a stable metallic vitreous state arises, calling for further experimental and theoretical study.

Brazhkin, Vadim V.; Lyapin, A. G.

2000-05-01

53

A model for calculating composition and density of the core melt in the water-moderated water-cooled reactor in case of severe accident  

Microsoft Academic Search

Thermochemical behavior of the core melt in the VVER-type reactor at severe accident is discussed. Experimental information\\u000a gained made it possible to construct a thermodynamic model of the O-U-Zr-Fe system. The model describes the immiscibility\\u000a of the oxide and metal phases of the core melt and makes it possible to estimate their densities. Parameters of the model\\u000a were obtained by

V. D. Ozrin; O. V. Tarasov; V. F. Strizhov; A. S. Filippov

2010-01-01

54

A model for calculating composition and density of the core melt in the water-moderated water-cooled reactor in case of severe accident  

Microsoft Academic Search

Thermochemical behavior of the core melt in the VVER-type reactor at severe accident is discussed. Experimental information gained made it possible to construct a thermodynamic model of the O-U-Zr-Fe system. The model describes the immiscibility of the oxide and metal phases of the core melt and makes it possible to estimate their densities. Parameters of the model were obtained by

V. D. Ozrin; O. V. Tarasov; V. F. Strizhov; A. S. Filippov

2010-01-01

55

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

56

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 < Tmelt of the silicate phase), then based on the experimental results indicating DU increases with increasing P, 1 to 4 ppb U may have entered the core. The concentration of Si in liquid Fe also increases with pressure. The concentration of Ca is < 0.44 wt % for most samples and no relation with U concentration is found, which indicates that U may alloy with Fe directly. If Si concentration in the Fe phase can be used as an indicator of oxygen fugacity, then the increase in Si and U with pressure suggests a pressure dependent decrease in oxygen fugacity. This supports U (and possibly also Si) inclusion in the the core of Earth at the time of core formation. The implications for radioactive heating in the planetary cores are briefly discussed. Keywords: Uranium; partition coefficients; high pressure; dynamos; planetary cores; heat sources, LA-ICP-MS.

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

2006-06-25

57

High Pressure Melting of Iron with Nonmetals Sulfur, Carbon, Oxygen, and Hydrogen: Implications for Planetary Cores  

NASA Astrophysics Data System (ADS)

The earth's core consists of a solid metallic center surrounded by a liquid metallic outer layer. Understanding the compositions of the inner and outer cores allows us to better understand the dynamics of the earth's core, as well as the dynamics of the cores of other terrestrial planets and moons. The density and size of the earth's core indicate that it is approximately 90% metallic, predominantly iron, with about 10% light elements. Iron meteorites, believed to be the remnants of planetary cores, provide further constraints on the composition of the earth's core, indicating a composition of 86% iron, 4% nickel, and 10% light elements. Any potential candidate for the major light element core component must meet two criteria: first, it must have high cosmic abundances and second, it must be compatible with Fe. Given these two constraints there are five plausible elements that could be the major light element in the core: H, O, C, S, and Si. Of these five possible candidates this thesis focuses on S and C as well exploring the effect of minor amounts of O and H on the eutectic temperature in a Fe-FeS core. We look at two specific aspects of the Fe-FeS system: first, the shape of the liquidus as a function of pressure, second, a possible cause for the reported variations in the eutectic temperature, which draws on the effect of H and O. Finally we look at the effect of S and C on partitioning behavior of Ni, Pt, Re,Co, Os and W between cohenite and metallic liquid. We are interested in constraining the shape of the Fe-FeS liquidus because as a planet with a S-enriched core cools, the thermal and compositional evolution of its core is constrained by this liquidus. In Chapter 1 I present an equation that allows for calculation of the temperature along the liquidus as a function of pressure and composition for Fe-rich compositions and pressures from 1 bar to 10 GPa. One particularly interesting feature of the Fe --rich side of the Fe-FeS eutectic is the sigmoidal shape of the liquidus. This morphology indicates non-ideal liquid solution behavior and suggests the presence of a metastable solvus beneath the liquidus. An important consequence of such curved liquidi is that isobaric, uniform cooling requires substantial variations in the solidification rate of the core. Additionally, in bodies large enough for P variation within the core to be significant, solidification behavior is further complicated by the P dependence of the liquidus shape. Brett and Bell (1969) show that at 3 GPa, the liquidus curvature relaxes, implying that the liquid solution becomes more ideal. By 10 GPa, the liquidus approaches nearly ideal behavior (Chen et al., 2008b). However, at 14 GPa, the liquidus again assumes a sigmoidal curvature (Chen et al., 2008a; Chen et al., 2008b), suggesting a fundamental change in the thermodynamic behavior of the liquid. Chapter 1 of this thesis accounts for the observed complexity in the liquidus up to 10 GPa thus enabling more accurate modeling of the evolution of the cores of small planets (Buono and Walker, 2011). Accurately knowing the eutectic temperature for the Fe-FeS system is important because it places a minimum bound on the temperature of a S-enriched core that has a solid and liquid component which are in equilibrium. Unfortunately literature values for the 1 bar to 10 GPa eutectic temperature in the Fe-FeS system are highly variable making the estimation of core temperature, an important geodynamic parameter, very difficult. In Chapter 2 we look at a possible cause of this observed variation by experimentally investigating the effects of H on the eutectic temperature in the Fe-FeS system at 6 and 8 GPa. We find that H causes a decrease in the eutectic temperature (but that O does not) and that this decrease can explain some of the observed scatter in the available data. The effect of H on the eutectic temperature increases with increasing pressure (i.e. the eutectic temperature is more depressed at higher pressures), matching the trend reported for the Fe-FeS system (Fei et al., 1997). Our work suggests

Buono, Antonio Salvatore

58

Core melt progression and consequence analysis methodology development in support of the Savannah River Reactor PSA  

SciTech Connect

A three-level Probabilistic Safety Assessment (PSA) of production reactor operation has been underway since 1985 at the US Department of Energy's Savannah River Site (SRS). The goals of this analysis are to: Analyze existing margins of safety provided by the heavy-water reactor (HWR) design challenged by postulated severe accidents; Compare measures of risk to the general public and onsite workers to guideline values, as well as to those posed by commercial reactor operation; and Develop the methodology and database necessary to prioritize improvements to engineering safety systems and components, operator training, and engineering projects that contribute significantly to improving plant safety. PSA technical staff from the Westinghouse Savannah River Company (WSRC) and Science Applications International Corporation (SAIC) have performed the assessment despite two obstacles: A variable baseline plant configuration and power level; and a lack of technically applicable code methodology to model the SRS reactor conditions. This paper discusses the detailed effort necessary to modify the requisite codes before accident analysis insights for the risk assessment were obtained.

O'Kula, K.R.; Sharp, D.A. (Westinghouse Savannah River Co., Aiken, SC (United States)); Amos, C.N.; Wagner, K.C.; Bradley, D.R. (Science Applications International Corp., Albuquerque, NM (United States))

1992-01-01

59

The evaluation of RCS depressurization to prevent core melting in pressure tube reactors (CANDU-type)  

Microsoft Academic Search

Pressure tube reactors, especially of the CANDU-type, have a low-pressure vessel calandria – under an internal pressure near atmospheric. The calandria vessel is immersed into the water contained inside a concrete structure – the calandria vault. In the case of accidents with the loss of normal core heat sinks, the moderator inside the calandria (heavy water) could become the ultimate

Stefan Mehedinteanu

2009-01-01

60

The Influence of Lunar Mantle Convection on Partial Melting and the Cooling of a Small Core  

NASA Astrophysics Data System (ADS)

The Moon is one of the smaller terrestrial planetary bodies. However, heat transport by mantle convection must have played an important role during its early history. We present a thermal evolution model of the Moon that simulates axisymmetric mantle convection. The model assumes Newtonian rheology to determine the radial viscosity profile depending on the average radial temperature profile. Convection is heated internally by radioactive isotopes. The present day global average U abundance is assumed to be 30 ppb. The model considers a crust with a thickness of 60 km that is enriched in radioactive isotopes with respect to the mantle. The crustal U concentration is assumed to be 240 ppb. In addition to internal heating, a metallic core with a radius of 450 km containing 8 wt% S is assumed to have an initial temperature exceeding lower mantle temperatures by about 100 K. The existence of a similar core formed at high temperatures has been inferred from geochemical considerations. The initial thermal state of the model implies that the differentiation into core and mantle as well as the formation of the crust following the crystallization of the early magma ocean have been completed. Therefore, the starting point of the model is chosen at 0.2 b.y. after formation of the Moon. The initial temperature profile comprises a cold thermal boundary layer close to the surface, a zone in the upper mantle corresponding to a solidified magma ocean where the average radial temperature profile is close to the solidus, an adiabatic profile in the lower mantle, and a hot thermal boundary layer at the core mantle boundary.

Konrad, W.; Spohn, T.

1998-01-01

61

Melting and metallization of silica in the cores of gas giants, ice giants and super Earths  

E-print Network

The physical state and properties of silicates at conditions encountered in the cores of gas giants, ice giants and of Earth like exoplanets now discovered with masses up to several times the mass of the Earth remains mostly unknown. Here, we report on theoretical predictions of the properties of silica, SiO$_2$, up to 4 TPa and about 20,000K using first principle molecular dynamics simulations based on density functional theory. For conditions found in the Super-Earths and in ice giants, we show that silica remains a poor electrical conductor up to 10 Mbar due to an increase in the Si-O coordination with pressure. For Jupiter and Saturn cores, we find that MgSiO$_3$ silicate has not only dissociated into MgO and SiO$_2$, as shown in previous studies, but that these two phases have likely differentiated to lead to a core made of liquid SiO$_2$ and solid (Mg,Fe)O.

Mazevet, S; Taniuchi, T; Benuzzi-Mounaix, A; Guyot, F

2014-01-01

62

Stability and melting relations of Fe3C up to 3 Mbar: Implication for the carbon in the Earth's inner core  

NASA Astrophysics Data System (ADS)

The Earth's core is regarded as an Fe-Ni alloy but its density is lower than that of pure Fe at the core conditions. Therefore, the Earth's core is supposed to contain light elements and carbon is one of the candidates of the light elements to explain the density deficit of the Earth's core. Nakajima et al. (2009) reported the melting temperature of Fe3C up to around 30 GPa based on textual observations, the chemical analysis of the quenched run products and in situ X-ray diffraction experiments using a Kawai-type multi anvil apparatus. Lord et al. (2009) reported melting temperatures of Fe3C up to 70 GPa, which was determined by the temperature plateau during increasing laser power using a laser-heated diamond anvil cell. They also suggested Fe+Fe7C3 is a stable subsolidus phase. There are obvious discrepancies between the melting curve and the stable subsolidus phase reported by Nakajima et al. (2009) and those reported by Lord et al. (2009). In this study, the melting temperatures of Fe3C and a subsolidus phase relation were determined based on in situ X-ray diffraction experiments and observations of the recovered sample. This study aims to reveal the stability field of Fe3C and the melting temperature of Fe3C and to discuss the behaviors of carbon in the Earth's core. We have performed experiments using a laser-heated diamond anvil cell combined with in situ X-ray diffraction experiment at BL10XU beamline, SPring-8 synchrotron facility. We also conducted quench experiments for observation of the recovered sample at Tohoku University. Synthesized Fe3C or Fe+Fe3C (C = 5.2 wt.%) were sandwiched by NaCl or SiO2 glass layers, which were used as the thermal insulator and the pressure medium. Melting of the sample was determined by disappearance of the X-ray diffraction peaks and textual observations. We determined the melting relation of Fe3C up to 200 GPa by in situ X-ray diffraction experiments and textual observations of recovered samples. The melting temperature extrapolated to the ICB pressure, 330 GPa, is 5100 K. We also confirmed that Fe3C is stable as a subsolidus phase at least up to 340 GPa. This strongly suggests that Fe3C is a potential candidate of the Earth's inner core although we need further studies at the inner core conditions. However, if the core has a carbon-rich composition and the inner core crystalized by cooling of the outer core from above 5100 K, the inner core is indicated to be composed of Fe7C3, initially.

Takahashi, S.; Ohtani, E.; Sakai, T.; Mashino, I.; Kamada, S.; Miyahara, M.; Sakamaki, T.; Hirao, N.; Ohishi, Y.

2013-12-01

63

High Pressure Melting, Phase Diagrams, and Equations of State in the Fe-FeSi System with Application to Earth's Core  

NASA Astrophysics Data System (ADS)

The Earth's core is comprised mostly of iron, with some nickel and several weight percent of one or more light elements. The light element(s) dictate phase relations, structure, and dynamic behaviour, so it is crucial to evaluate various candidates at conditions of planetary interiors. We present results on high P-T phase diagrams and equations of state in the Fe-FeSi system with application to the structure and composition of Earth's core. X-ray diffraction measurements were performed on stoichiometric FeSi and on Fe-Si alloys containing 9 and 16 wt% silicon in a laser-heated diamond anvil cell at the APS, NSLS, and ALS. Pressures were determined from the lattice parameter of KBr. We have investigated the phase diagram of Fe-9Si to 100 GPa and over 3000 K. Our melting curve agrees with previous results on similar alloys [1,2], as demonstrated using multiple methods of detecting melting. Our subsolidus results are similar to those of Lin et al. [3], though we find the B2 structure instead of bcc, and a shallower slope for the hcp+B2 to fcc+B2 boundary. We studied phase relations of Fe-16Si to over 135 GPa, finding agreement with previous melting curves [2,4]. Below 45 GPa, this alloy has the D0_3 structure. At high pressures, Fe-16Si breaks down into a mixture of B2 and hcp phases, with this mixture stable to pressures of the Earth's outer core. This is the first study on the B2 phase of FeSi with in situ X-ray diffraction at high pressures and temperatures. We report a wide B2+B20 two-phase field in FeSi, with complete conversion to the B2 structure by ~42 GPa. A melting experiment on FeSi agrees with the results of Lord et al. [5]. We have synthesized our results with previous studies to construct T-X and P-X phase diagrams, and we have determined thermal equations of state of each alloy. Our measured densities can be used to constrain the maximum amount of silicon in the Earth's outer core by comparison to the equation of state of hcp-Fe [6] and the seismologically-determined density. Assuming a core-mantle boundary (CMB) temperature of 4000 +/- 500 K and a 1-2% density decrease upon melting, the amount of silicon in the outer core required to match PREM at the CMB is 11.3 +/- 1.5 weight percent, under the simplifying assumption of a purely Fe-Ni-Si outer core. The minimum temperature of an Fe-Si outer core is 4380 K, based on the eutectic melting point of Fe-FeSi alloys, and silicon is shown not to significantly depress the melting point of iron at core conditions. At the highest pressures reached, only the hcp and B2 structures are seen in the Fe-FeSi system. We predict that alloys containing more than ~4-8 wt% Si will convert to an hcp+B2 mixture and later to the hcp structure with increasing pressure, and that an iron-silicon alloy in the Earth's inner core would most likely be a mixture of hcp and B2 phases. [1] Kuwayama and Hirose (2004) Am Mineral 89, 273-276 [2] Morard et al. (2011) PCM 38, 767-776 [3] Lin et al (2002) Science 295, 313-315 [4] Asanuma et al. (2010) PCM 37, 353-359 [5] Lord et al. (2010) JGR 115, B06208 [6] Dewaele et al. (2006) PRL 97, 215504

Fischer, R. A.; Campbell, A. J.; Reaman, D. M.; Heinz, D. L.; Dera, P. K.; Prakapenka, V.

2012-12-01

64

Black carbon concentrations from a Tibetan Plateau ice core spanning 1843-1982: recent increases due to emissions and glacier melt  

NASA Astrophysics Data System (ADS)

Black carbon (BC) deposited on snow and glacier surfaces can reduce albedo and lead to accelerated melt. An ice core recovered from Guoqu glacier on Mt. Geladaindong and analyzed using a Single Particle Soot Photometer provides the first long-term (1843-1982) record of BC concentrations from the Central Tibetan Plateau. The highest concentrations are observed from 1975-1982, which corresponds to a 2.0-fold and 2.4-fold increase in average and median values, respectively, relative to 1843-1940. BC concentrations post-1940 are also elevated relative to the earlier portion of the record. Causes for the higher BC concentrations include increased regional BC emissions and subsequent deposition, and melt induced enrichment of BC, with the melt potentially accelerated due to the presence of BC at the glacier surface. A qualitative comparison of the BC and Fe (used as a dust proxy) records suggests that if changes in the concentrations of absorbing impurities at the glacier surface have influenced recent glacial melt, the melt may be due to the presence of BC rather than dust. Guoqu glacier has received no net ice accumulation since the 1980s, and is a potential example of a glacier where an increase in the equilibrium line altitude is exposing buried high impurity layers. That BC concentrations in the uppermost layers of the Geladaindong ice core are not substantially higher relative to deeper in the ice core suggests that some of the BC that must have been deposited on Guoqu glacier via wet or dry deposition between 1983 and 2005 has been removed from the surface of the glacier, potentially via supraglacial or englacial meltwater.

Jenkins, M.; Kaspari, S.; Kang, S.; Grigholm, B.; Mayewski, P. A.

2013-10-01

65

A 10 yr record of black carbon and dust from Mera Peak ice core (Nepal): variability and potential impact on Himalayan glacier melting  

NASA Astrophysics Data System (ADS)

A shallow ice core of the southern flank of Nepalese Himalaya range was extracted from the summit of Mera Peak at 6376 m a.s.l. in Nepal. From this core, we have reconstructed the seasonal deposition fluxes of dust and refractory black carbon (rBC) since 1999. This archive presents well preserved seasonal cycles based on monsoonal precipitation pattern. According to the seasonal precipitation regime, 80% of the annual precipitation between June and September, we estimated the surface snow concentrations evolution for these aerosols. The analyzes reveals that mass fluxes are a few orders of magnitude higher for dust (10.2±2.5 g m-2 yr-1) that for rBC (3.2±1.2 mg m-2 yr-1).These data were used to simulate the surface snow albedo changes with time and the induced potential melting related to these impurities. The potential melting associated to joint dust and rBC can reach 660 kg m-2 yr-1, and 220 kg m-2 yr-1 for rBC only under some assumptions. Compared to the melting rate measured by mass and energy balance at 5400 m a.s.l. on Mera glacier, close to the equilibrium altitude, the impact of rBC represents less than 7% of annual potential melting while the joint contribution of dust and rBC of the surface melting represents a maximum 18%. Furthermore, over this 10 yr time span, the fluxes variability in the ice core signal is rather reflecting the variability of the monsoon signal than that of emission intensity.

Ginot, P.; Dumont, M.; Lim, S.; Patris, N.; Taupin, J.-D.; Wagnon, P.; Gilbert, A.; Arnaud, Y.; Marinoni, A.; Bonasoni, P.; Laj, P.

2013-12-01

66

Thermodynamics of melting relations in the system Fe-FeO at high pressure: Implications for oxygen in the Earth's core  

NASA Astrophysics Data System (ADS)

thermodynamics of melting relations in the system Fe-FeO was investigated to the outer core-inner core boundary condition from a self-consistent thermodynamic database which was evaluated from the latest static high-pressure (P) and high-temperature (T) experiments. The evaluated database together with an existing nonideal mixing model for liquids reproduces experimental data on the eutectic composition and temperature to P = 50 GPa. On the other hand at the outer core pressures (136 to 330 GPa), employing an ideal solution model gives calculated eutectic temperatures of T = 2990-4330 K, which are also consistent with experimental data. Hence, the ideal solution model is applied to calculate the liquid property under outer core conditions and yields the eutectic compositions of Fe-7.2-9.1 wt % O. From the Gibbs free energy for the Fe-FeO liquids, I calculated the density, sound velocity, and isentropic temperature gradient of a hypothetical oxygen-bearing outer core. Under the outer core conditions, the addition of oxygen reduces the compressional wave velocity of iron liquid, moving it away from seismologically constrained values. An overall O-rich bulk outer core model is thus excluded. Seismological observations however suggest the presence of a low-velocity layer with a thickness of 60-70 km at the top of the outer core. The origin of such a low-velocity layer can be explained by an enrichment of oxygen which might be a consequence of chemical interactions between the core and mantle.

Komabayashi, Tetsuya

2014-05-01

67

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

68

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

69

Low energy nuclear reaction polyplasmon postulate  

Microsoft Academic Search

An explanation is proposed for the nuclear reactions that occur in the electrolysis class of LENR processes. The proposed explanation postulates that a proton, or deuteron, dissolved in the hydrogen bearing metal cathode, absorbs its associated atomic electron to become a short lived state of the neutron with the resulting neutrino in a singular wave function centered on the neutron.

John L. Russell

2008-01-01

70

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

71

A 10 year record of black carbon and dust from a Mera Peak ice core (Nepal): variability and potential impact on melting of Himalayan glaciers  

NASA Astrophysics Data System (ADS)

A shallow ice core was extracted at the summit of Mera Peak at 6376 m a.s.l. in the southern flank of the Nepalese Himalaya range. From this core, we reconstructed the seasonal deposition fluxes of dust and refractory black carbon (rBC) since 1999. This archive presents well preserved seasonal cycles based on a monsoonal precipitation pattern. According to the seasonal precipitation regime in which 80% of annual precipitation falls between June and September, we estimated changes in the concentrations of these aerosols in surface snow. The analyses revealed that mass fluxes are a few orders of magnitude higher for dust (10.4 ± 2.8 g m-2 yr-1 than for rBC (7.9 ± 2.8 mg m-2 yr-1). The relative lack of seasonality in the dust record may reflect a high background level of dust inputs, whether from local or regional sources. Over the 10-year record, no deposition flux trends were detected for any of the species of interest. The data were then used to simulate changes in the surface snow albedo over time and the potential melting caused by these impurities. Mean potential melting caused by dust and rBC combined was 713 kg m-2 yr-1, and for rBC alone, 342 kg m-2 yr-1 for rBC under certain assumptions. Compared to the melting rate measured using the mass and energy balance at 5360 m a.s.l. on Mera Glacier between November 2009 and October 2010, i.e. 3000 kg m-2 yr-1 and 3690 kg m-2 yr-1 respectively, the impact of rBC represents less than 16% of annual potential melting while the contribution of dust and rBC combined to surface melting represents a maximum of 26%. Over the 10-year period, rBC variability in the ice core signal primarily reflected variability of the monsoon signal rather than variations in the intensity of emissions.

Ginot, P.; Dumont, M.; Lim, S.; Patris, N.; Taupin, J.-D.; Wagnon, P.; Gilbert, A.; Arnaud, Y.; Marinoni, A.; Bonasoni, P.; Laj, P.

2014-08-01

72

Phase evolution study on the melting and recrystallization of ceramic core in the (Bi,Pb)-2223 tape  

E-print Network

;conductors work still. It is believed that (Bi,Pb)-2223 phase formation from a liquid being either stable into a 2212-like liquid and (Ca,Sr)-cuprates. 2:1 phase plays the most important role in (Bi,Pb)-2223 melt a slow increase in Jc of Bi-2223 conductors in spite of the remarkable progresses achieved. The Jc

Boyer, Edmond

73

Protoplanetary core formation by rain-out of iron drops. [coalesced melted metal transport to Jovian protoplanet center  

NASA Technical Reports Server (NTRS)

Using the stochastic collection equation we find that the time scale for rain out of liquid iron in a Saturn mass protoplanet is rapid compared with other evolutionary time scales and hence iron protoplanetary core formation is inevitable. The survival of this core during subsequent protoplanetary evolution and the consequences of the rain-out on the evolution are also discussed.

Slattery, W. L.

1978-01-01

74

Principia aetiologica: taking causality beyond Koch's postulates.  

PubMed

There is no single accepted method to establish a causal relationship between an infective agent and its corresponding infectious disease. Different biomedical disciplines use a patchwork of distinct but overlapping approaches. To a greater or lesser extent these are based on criteria known as the Koch-Henle postulates, or 'Koch's postulates' for short. Deficiencies in Koch's postulates were recognized by their principal author shortly after their formulation. Now, over a century later, a more rigorous method to test causality has still to be finalized. One contender is a method that uses molecular methods to establish a causal relationship ('molecular Koch's postulates'). Recognizing the wider range of contemporary approaches used to build an argument for a causal relationship, the use of a more inclusive approach to establish proof of causality is proposed. This method uses an argument built from a series of assertions. Assertion 1: congruence or reproducible correlation of a taxonomically defined life form with the clinico-pathological and epidemiological features of infection. Assertion 2: consistency of the demonstrable biological response in the subject to an encounter with the prospective infective agent. Assertion 3: progressive or cumulative dissonance as an explanation for pathophysiological processes at every known level of biological organization in the subject. Assertion 4: curtailment of that pathophysiological process on the deliberate introduction of a specified biomedical intervention. Evidence to implicate the candidate biological entity as an initiator of or primer for cumulative dissonance places it in a subcategory of micro-organisms to be known as 'priobes'. A priobe is the sufficient and necessary antecedent cause of a pathophysiological process evident as an infectious disease. PMID:17965339

Inglis, Timothy J J

2007-11-01

75

Status of the MELTSPREAD-1 computer code for the analysis of transient spreading of core debris melts  

SciTech Connect

A transient, one dimensional, finite difference computer code (MELTSPREAD-1) has been developed to predict spreading behavior of high temperature melts flowing over concrete and/or steel surfaces submerged in water, or without the effects of water if the surface is initially dry. This paper provides a summary overview of models and correlations currently implemented in the code, code validation activities completed thus far, LWR spreading-related safety issues for which the code has been applied, and the status of documentation for the code.

Farmer, M.T.; Sienicki, J.J.; Spencer, B.W.; Chu, C.C.

1992-04-01

76

Status of the MELTSPREAD-1 computer code for the analysis of transient spreading of core debris melts  

SciTech Connect

A transient, one dimensional, finite difference computer code (MELTSPREAD-1) has been developed to predict spreading behavior of high temperature melts flowing over concrete and/or steel surfaces submerged in water, or without the effects of water if the surface is initially dry. This paper provides a summary overview of models and correlations currently implemented in the code, code validation activities completed thus far, LWR spreading-related safety issues for which the code has been applied, and the status of documentation for the code.

Farmer, M.T.; Sienicki, J.J.; Spencer, B.W.; Chu, C.C.

1992-01-01

77

Melting of (Mg,Fe)2SiO4 at the Core-Mantle Boundary of the Earth  

PubMed

The lower mantle of the Earth is believed to be largely composed of (Mg,Fe)O (magnesiowustite) and (Mg,Fe)SiO3 (perovskite). Radiative temperatures of single-crystal olivine [(Mg0.9,Fe0.1)2SiO4] decreased abruptly from 7040 +/- 315 to 4300 +/- 270 kelvin upon shock compression above 80 gigapascals. The data indicate that an upper bound to the solidus of the magnesiowustite and perovskite assemblage at 4300 +/- 270 kelvin is 130 +/- 3 gigapascals. These conditions correspond to those for partial melting at the base of the mantle, as has been suggested occurs within the ultralow-velocity zone beneath the central Pacific. PMID:9054352

Holland; Ahrens

1997-03-14

78

Solubility of Uranium in Fe-S-Si Melts at High Pressure and Temperature and at Highly Reducing Conditions: Uranium as a heat source in the Earth's Core?  

NASA Astrophysics Data System (ADS)

The presence of Uranium and its role as a radioactive heat source in the Earth's Fe-metallic core has been controversial (e.g., Wheeler et al., 2006; Bao et al., 2005). We report here on partitioning of U between molten enstatite chondrite and Fe-S-Si melts at about 4 log units below the Iron-Wustite oxygen buffer and pressures between 3 and 8 GPa. All experiments were performed at super-liquidus temperatures in the range of 2000- 2400 C. Both the metal and silicates were completely molten, in keeping with the concept of an early global magma ocean. At these pressures and temperatures, the partition coefficient, DU (U concentration in metallic sulfide liquid/U concentration in molten silicate) is in the range of 0.03-0.08. DU is positively correlated with S as observed in prior studies (Bao et al., 2005; Wheeler et al., 2006), but is inversely correlated with Si in metallic liquid. In metal with little or no sulfur, DU is lower by an order of magnitude or more. In the range of our measurements, no strong effect of either T or P on the partition coefficient is observed. U shows no correlation with Ca suggesting that U is not carried via CaS at these highly reducing conditions, as has been suggested (Murrell and Burnett, 1982; Furst et al., 1982). Nor does the U content of metal-sulfide have any discernible dependency on the O content of the metallic liquid. Thus it appears that neither Ca nor O act as carriers or catalytic agents for the entry of U into Fe-S melts. Rather, we suggest that the reaction UO2 +2 FeS = US2 +2FeO proceeds to the right at elevated P and T and highly reducing conditions, facilitating the incorporation of U in Fe-S liquids. Assuming that the behavior of DU is not significantly changed at the much higher P and T relevant to the magma ocean, our data permit 0.6-1.8 ppb of U in the core with heat production capacity of 0.1-0.3 TW at present, a small fraction of the 6-12 TW total heat flux from the core (Buffet, 2003). We conclude that under highly reducing conditions uranium might be incorporated into the Earth's metallic core.

Murthy, V.; Draper, D. S.; Agee, C. B.

2006-12-01

79

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

80

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

81

Melt fracture revisited  

SciTech Connect

In a previous paper the author and Demay advanced a model to explain the melt fracture instability observed when molten linear polymer melts are extruded in a capillary rheometer operating under the controlled condition that the inlet flow rate was held constant. The model postulated that the melts were a slightly compressible viscous fluid and allowed for slipping of the melt at the wall. The novel feature of that model was the use of an empirical switch law which governed the amount of wall slip. The model successfully accounted for the oscillatory behavior of the exit flow rate, typically referred to as the melt fracture instability, but did not simultaneously yield the fine scale spatial oscillations in the melt typically referred to as shark skin. In this note a new model is advanced which simultaneously explains the melt fracture instability and shark skin phenomena. The model postulates that the polymer is a slightly compressible linearly viscous fluid but assumes no slip boundary conditions at the capillary wall. In simple shear the shear stress {tau}and strain rate d are assumed to be related by d = F{tau} where F ranges between F{sub 2} and F{sub 1} > F{sub 2}. A strain rate dependent yield function is introduced and this function governs whether F evolves towards F{sub 2} or F{sub 1}. This model accounts for the empirical observation that at high shears polymers align and slide more easily than at low shears and explains both the melt fracture and shark skin phenomena.

Greenberg, J. M.

2003-07-16

82

Megablocks and melt pockets in the Chesapeake Bay impact structure constrained by magnetic field measurements and properties of the Eyreville and Cape Charles cores  

USGS Publications Warehouse

We use magnetic susceptibility and remanent magnetization measurements of the Eyreville and Cape Charles cores in combination with new and previously collected magnetic field data in order to constrain structural features within the inner basin of the Chesapeake Bay impact structure. The Eyreville core shows the first evidence of several-hundred-meter-thick basement-derived megablocks that have been transported possibly kilometers from their pre-impact location. The magnetic anomaly map of the structure exhibits numerous short-wavelength (<2 km) variations that indicate the presence of magnetic sources within the crater fill. With core magnetic properties and seismic reflection and refraction results as constraints, forward models of the magnetic field show that these sources may represent basementderived megablocks that are a few hundred meters thick or melt bodies that are a few dozen meters thick. Larger-scale magnetic field properties suggest that these bodies overlie deeper, pre-impact basement contacts between materials with different magnetic properties such as gneiss and schist or gneiss and granite. The distribution of the short-wavelength magnetic anomalies in combination with observations of small-scale (1-2 mGal) gravity field variations suggest that basement-derived megablocks are preferentially distributed on the eastern side of the inner crater, not far from the Eyreville core, at depths of around 1-2 km. A scenario where additional basement-derived blocks between 2 and 3 km depth are distributed throughout the inner basin-and are composed of more magnetic materials, such as granite and schist, toward the east over a large-scale magnetic anomaly high and less magnetic materials, such as gneiss, toward the west where the magnetic anomaly is lower-provides a good model fi t to the observed magnetic anomalies in a manner that is consistent with both gravity and seismic-refraction data. ?? 2009 The Geological Society of America.

Shah, A.K.; Daniels, D.L.; Kontny, A.; Brozena, J.

2009-01-01

83

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

84

Melt transport - a personal cashing-up  

NASA Astrophysics Data System (ADS)

The flow of fluids through rocks transports heat and material and changes bulk composition. The large-scale chemical differentiation of the Earth is related to flow of partial melts. From the perspective of current understanding of tectonic processes, prominent examples of such transport processes are the formation of oceanic crust from ascending basic melts at mid-ocean ridges, melt segregation involved in the solidification of the Earth's core, and dissolution-precipitation creep in subduction channels. Transport and deformation cannot be separated for partially molten aggregates. Permeability is only defined as an instantaneous parameter in the sense that Darcy's law is assumed to be valid; it is not an explicit parameter in the fundamental mechanical conservation laws but can be derived from them in certain circumstances as a result of averaging schemes. The governing, explicit physical properties in the mechanical equations are the shear and bulk viscosities of the solid framework and the fluid viscosity and compressibility. Constraints on the magnitude of these properties are available today from experiments at specific loading configurations, i.e., more or less well constrained initial and boundary conditions. The melt pressure remains the least controlled parameter. While the fluid viscosity is often much lower than the solid's the two-phase aggregate may exhibit considerable strength owing to the difficulty of moving the fluid through the branched pore network. The extremes in behavior depend on the time scale of loading, as known from daily live experiences (spounge, Danish coffee-pot, human tissue between neighboring bones). Several theoretical approaches attempted to formulate mechanical constitutive equations for two-phase aggregates. An important issue is the handling of internal variables in these equations. At experimental conditions, grain size, melt pocket orientation and crystallographic orientation -prime candidates for internal variables- change considerably and potentially contribute significantly to the total dissipation of the external work. Theoretically founded evolution equations for these internal variables are lacking. In experiments, both the kinetics of grain growth but also the resultant shape of grains is affected by the presence of melt. The latter is linked to the alignment of melt pockets with the maximum principle stress. Thus, the melt redistribution causes direct anisotropy but also indirect through a shape-preferred orientation of solid grains. Notably, the foliation is parallel to the maximum principle stress in contrast to deformation controlled by crystal defects alone. Extremum principles developed for dissipation potentials in the framework of irreversible thermodynamics may allow us to postulate evolution equations. Owing to their significant effect on aggregate viscosities understanding the evolution of internal variables is mandatory for substantial large-scale modeling.

Renner, J.

2005-12-01

85

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

86

From the postulates of relativity to the law of inertia  

Microsoft Academic Search

While teaching special relativity, Newton's first law is usually assumed and then superimposed on the first postulate via the introduction of ``inertial reference frames.'' By contrast, taking Einstein's earliest and simplest statement of the postulates of relativity to be fundamentally true, it is possible to show that Newton's formulation of the law of inertia follows as a consequence.

Eugene Hecht

2000-01-01

87

A proof of von Neumann's postulate in Quantum Mechanics  

SciTech Connect

A Clifford algebraic analysis is explained. It gives proof of von Neumann's postulate on quantum measurement. It is of basic significance to explain the problem of quantum wave function reduction in quantum mechanics.

Conte, Elio [Department of Pharmacology and Human Physiology, TIRES-Center for Innovative Technologies for Signal Detection and Processing, Department of Physics, University of Bari (Italy) and School of Advanced International Studies for Applied Theoretical and Non Linear Methodologies of Physics, Bari (Italy)

2010-05-04

88

Stratigraphic analysis of an ice core from the Prince of Wales Icefield, Ellesmere Island, Arctic Canada, using digital image analysis: High-resolution density, past summer warmth reconstruction, and melt effect on ice core solid conductivity  

Microsoft Academic Search

High-resolution (1 mm) stratigraphic information was derived from digital image analysis of an ice core from the Prince of Wales (POW) Icefield, Central Ellesmere Island, Canada. Following careful image processing, a profile of ice core transmitted light was derived from the greyscale images and used to reconstruct high-resolution density variations for the unfractured sections of the core. Images were further

Christophe Kinnard; Roy M. Koerner; Christian M. Zdanowicz; David A. Fisher; Jiancheng Zheng; Martin J. Sharp; Lindsey Nicholson; Bernard Lauriol

2008-01-01

89

Experimental determination of carbon isotope fractionation between iron carbide melt and carbon: 12C-enriched carbon in the Earth's core?  

Microsoft Academic Search

We report here new experimental data on equilibrium carbon isotope fractionation between graphite\\/diamond and iron carbide melt at 5 and 10GPa and in the temperature range between 1200 and 2000°C. Carbon isotope equilibrium was tested using morphological features of graphite and also by performing a longer duration experiment, both of which suggested that equilibrium carbon isotope fractionation is present. The

Madhusoodhan Satish-Kumar; Hayato So; Takashi Yoshino; Mutsumi Kato; Yoshikuni Hiroi

2011-01-01

90

Melting Icebergs  

NSDL National Science Digital Library

This formative assessment item uncovers student ideas and misconceptions about melting icebergs. It determines if students believe that water levels will rise due to melting icebergs. Resources provided will assist teachers. It gives instructional support as well as information for teachers. This probe is aligned to National Science Education Standards (NSES).

Fries-Gaither, Jessica

91

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.

Consortium, The C.

2011-12-13

92

The Function 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. A free parameter in these equations, $k$, plays the part of $c^{-2}$ in special relativity. It is usual to claim that $k$ is determined by experiment and hence, that special relativity does not need the postulate of constancy of the speed of light. I analyze how one would go about determining $k$ empirically and find that all methods suffer from severe problems without further assumptions, none as simple and elegant as the postulate of constancy of the speed of light. I conclude that while the formal structure of the transformation equations can be determined without appeal to the second postulate, the theory is left without physical content if we ignore this postulate. Specifically, evaluating $k$ requires creating a signal that travels identically in opposite directions or ensuring that such a signa...

Drory, Alon

2014-01-01

93

Safely Teaching Koch's Postulates on the Causation of Infectious Disease.  

ERIC Educational Resources Information Center

Described is an activity in which the interactions between a parasite and its host may be demonstrated using the relationship between yogurt and two species of bacteria. Background information on Koch's postulates is provided. Materials, laboratory procedures, and results are discussed. (CW)

Stewart, Peter R.

1990-01-01

94

A Conceptual Derivation of Einstein's Postulates of Special Relativity.  

ERIC Educational Resources Information Center

This document presents a discussion and conceptual derivation of Einstein's postulates of special relativity. The perceptron approach appears to be a fundamentally new manner of regarding physical phenomena and it is hoped that physicists will interest themselves in the concept. (Author)

Bearden, Thomas E.

95

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

96

The Four Postulates of Freudian Unconscious Neurocognitive Convergences  

PubMed Central

In the 1980s, the terms “cognitive unconscious” were invented to denominate a perspective on unconscious mental processes independent from the psychoanalytical views. For several reasons, the two approaches to unconscious are generally conceived as irreducible. Nowadays, we are witnessing a certain convergence between both fields. The aim of this paper consists in examining the four basic postulates of Freudian unconscious at the light of neurocognitive sciences. They posit: (1) that some psychological processes are unconsciously performed and causally determine conscious processes, (2) that they are governed by their own cognitive rules, (3) that they set out their own intentions, (4) and that they lead to a conflicting organization of psyche. We show that each of these postulates is the subject of empirical and theoretical works. If the two fields refer to more or less similar mechanisms, we propose that their opposition rests on an epistemological misunderstanding. As a conclusion, we promote a conservative reunification of the two perspectives. PMID:21734896

Arminjon, Mathieu

2011-01-01

97

OPERA data and The Equivalence Postulate of Quantum Mechanics  

E-print Network

An interpretation of the recent results reported by the OPERA collaboration is that neutrinos propagation in vacuum exceeds the speed of light. It has been further been suggested that this interpretation can be attributed to the variation of the particle speed arising from the Relativistic Quantum Hamilton Jacobi Equation. I show that this is in general not the case. I derive an expression for the quantum correction to the instantaneous relativistic velocity in the framework of the relativistic quantum Hamilton-Jacobi equation, which is derived from the equivalence postulate of quantum mechanics. While the quantum correction does indicate deviations from the classical energy--momentum relation, it does not necessarily lead to superluminal speeds. The quantum correction found herein has a non-trivial dependence on the energy and mass of the particle, as well as on distance travelled. I speculate on other possible observational consequences of the equivalence postulate approach.

Alon E. Faraggi

2011-10-09

98

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

99

Prism reactor system design and analysis of postulated unscrammed events  

SciTech Connect

Key safety characteristics of the PRISM reactor system include the passive reactor shutdown characteristic and the passive shutdown heat removal system, RVACS. While these characteristics are simple in principle, the physical processes are fairly complex, particularly for the passive reactor shutdown. It has been possible to adapt independent safety analysis codes originally developed for the Clinch River Breeder Reactor review, although some limitations remain. In this paper, the analyses of postulated unscrammed events are discussed, along with limitations in the predictive capabilities and plans to correct the limitations in the near future. 6 refs., 4 figs.

Van Tuyle, G.J.; Slovik, G.C.

1991-08-01

100

PRISM reactor system design and analysis of postulated unscrammed events  

SciTech Connect

Key safety characteristics of the PRISM reactor system include the passive reactor shutdown characteristics and the passive shutdown heat removal system, RVACS. While these characteristics are simple in principle, the physical processes are fairly complex, particularly for the passive reactor shutdown. It has been possible to adapt independent safety analysis codes originally developed for the Clinch River Breeder Reactor review, although some limitations remain. In this paper, the analyses of postulated unscrammed events are discussed, along with limitations in the predictive capabilities and plans to correct the limitations in the near future. 6 refs., 4 figs.

Van Tuyle, G.J.; Slovik, G.C. (Brookhaven National Lab., Upton, NY (United States)); Rosztoczy, Z.; Lane, J. (Nuclear Regulatory Commission, Washington, DC (United States))

1991-01-01

101

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

102

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

103

[Pelletization of melts and liquids].  

PubMed

During the second half of the last century, pelletization methods based on wetting were developed, e.g. agglomeration in coating pans, pelletization plates or fluid-bed equipment, layering of the drug in solution or suspension on inactive spherical cores, extrusion/spheronization and later on also rotoagglomeration in rotogranulators or rotoprocessors. These technologies have become a requisite part of industrial production of solid dosage forms. At present, numerous experimental papers deal with pellet preparation from melts and liquids. These new pelletization methods are the topic of the present article. Pellet preparation from melts is represented by three methods, i.e. fluid hot melt agglomeration, hot melt extrusion, and freeze pelletization. Jet cutting and cryopelletization are the techniques dealing with pellet preparation from liquids. PMID:21650006

Rabisková, Miloslava

2011-04-01

104

Preliminary risks associated with postulated tritium release from production reactor operation  

SciTech Connect

The Probabilistic Risk Assessment (PRA) of Savannah River Plant (SRP) reactor operation is assessing the off-site risk due to tritium releases during postulated full or partial loss of heavy water moderator accidents. Other sources of tritium in the reactor are less likely to contribute to off-site risk in non-fuel melting accident scenarios. Preliminary determination of the frequency of average partial moderator loss (including incidents with leaks as small as .5 kg) yields an estimate of /approximately/1 per reactor year. The full moderator loss frequency is conservatively chosen as 5 /times/ 10/sup /minus/3/ per reactor year. Conditional consequences, determined with a version of the MACCS code modified to handle tritium, are found to be insignificant. The 95th percentile individual cancer risk is 4 /times/ 10/sup /minus/8/ per reactor year within 16 km of the release point. The full moderator loss accident contributes about 75% of the evaluated risks. 13 refs., 4 figs., 5 tabs.

O'Kula, K.R.; Horton, W.H.

1988-01-01

105

Analysis of postulated events for the revised ALMR/PRISM design  

SciTech Connect

The Nuclear Regulatory Commission (NRC) is continuing a pre-application review of the 471 MWt, Liquid Metal Reactor, PRISM by General Electric, with Brookhaven National Laboratory providing technical support. The revised design has been evaluated, using the SSC code, for an unscrammed loss of heat sink (ULOHS), an unscrammed loss of flow (ULOF) with and without the Gas Expansion Modules (GEMs), and a 40{cents} unscrammed transient overpower (UTOP) event. The feedback effects for U-27Pu-10Zr metal fuel were modeled in SSC. The ULOHS accident was determined to be a benign event for the design, with the reactor power transitioning down to a decay heat level within 500s. The power during the postulated ULOF events, with the GEMs functioning, transitioned to decay heat levels without fuel damage, and included a 300K margin to sodium saturation. The case without the GEMs had only a 160K margin to sodium saturation and higher fuel temperatures. In addition, the clad was predicted to quickly pass through the eutectic phase (between fuel and clad), and some clad wastage would result. The 40{cents} UTOP was predicted to raise the power to 1.8 rated, which later stabilized near 1.2 times full power. SSC predicted some localized fuel melting for the event, but the significance of this localized damage has not yet been determined. If necessary, the vendor has options to reduce the maximum reactivity insertion below 40{cents}.

Slovik, G.C.; Van Tuyle, G.J.

1991-01-01

106

Analysis of postulated events for the revised ALMR/PRISM design  

SciTech Connect

The Nuclear Regulatory Commission (NRC) is continuing a pre-application review of the 471 MWt, Liquid Metal Reactor, PRISM by General Electric, with Brookhaven National Laboratory providing technical support. The revised design has been evaluated, using the SSC code, for an unscrammed loss of heat sink (ULOHS), an unscrammed loss of flow (ULOF) with and without the Gas Expansion Modules (GEMs), and a 40{cents} unscrammed transient overpower (UTOP) event. The feedback effects for U-27Pu-10Zr metal fuel were modeled in SSC. The ULOHS accident was determined to be a benign event for the design, with the reactor power transitioning down to a decay heat level within 500s. The power during the postulated ULOF events, with the GEMs functioning, transitioned to decay heat levels without fuel damage, and included a 300K margin to sodium saturation. The case without the GEMs had only a 160K margin to sodium saturation and higher fuel temperatures. In addition, the clad was predicted to quickly pass through the eutectic phase (between fuel and clad), and some clad wastage would result. The 40{cents} UTOP was predicted to raise the power to 1.8 rated, which later stabilized near 1.2 times full power. SSC predicted some localized fuel melting for the event, but the significance of this localized damage has not yet been determined. If necessary, the vendor has options to reduce the maximum reactivity insertion below 40{cents}.

Slovik, G.C.; Van Tuyle, G.J.

1991-12-31

107

Melting Ice  

NSDL National Science Digital Library

In this lesson, students explore a discrepant event when they design an experiment to measure the rate that ice melts when in pure water versus salt water. It is designed to help students realize that a carefully-designed experiment may yield unexpected results, due to unseen events, even though the experiment is precisely planned and executed. The addition of a new technology may clarify factors in the experiment which were previously unknown. Note: the experiment requires advance preparation the day before: two buckets of water are set-up (one with plain tap water, the other with as much salt dissolved in it as possible), which need to be at room temperature. It also requires ice cubes of uniform shape (e.g., from an ice maker or ice trays filled to uniform capacity). This lesson is part of the Cosmic Times teachers guide and is intended to be used in conjunction with the 1993 Cosmic Times Poster.

108

Phenomenological studies on melt-coolant interactions in the ALPHA program  

Microsoft Academic Search

Two series of experiments to investigate melt-coolant interactions have been performed as part of the ALPHA program at JAERI. In the melt drop steam explosion experiments, melt simulating a molten core was dropped into a pool of water. Volume fractions of the melt, water and steam in the mixing region prior to the occurrence of spontaneous steam explosions were quantified.

N. Yamano; Y. Maruyama; T. Kudo; A. Hidaka; J. Sugimoto

1995-01-01

109

Bowing of core assemblies in advanced liquid metal fast reactors  

Microsoft Academic Search

Two alternative core restraint concepts are considered for a conceptual design of a 900 MWth liquid metal fast reactor core with a heterogeneous layout. The two concepts, known as limited free bowing and free flowering, are evaluated based on core bowing criteria that emphasize the echancement of inherent reactor safety. The core reactivity change during a postulated loss of flow

S. A. Kamal; Y. Orechwa

1986-01-01

110

The Postulates of Quantum Mechanics (from Quantum Mechanics by Claude Cohen-Tannoudji, Bernard Diu, and  

E-print Network

The Postulates of Quantum Mechanics (from Quantum Mechanics by Claude Cohen-Tannoudji, Bernard Diu, and Franck Lalo¨e) Introduction The postulates of quantum mechanics are the theory. Their physical content to the following questions: (i) How is the state of a quantum mechanical system at a given time described

Nielsen, Steven O.

111

Numerical and Experimental Model Studies on Thermal Hydraulic Behavior of FBR Internal Core Catcher Assembly  

SciTech Connect

Core Catcher is provided as an in-vessel core debris retention device to collect, support, cool and maintain in sub-critical configuration, the generated core debris from fuel melting due to certain postulated Beyond Design Basis Events (BDBE) for Fast Breeder Reactor (FBR). This also acts as a barrier to prevent settling of debris on main vessel and keeps its maximum temperature within acceptable creep range. Heat transfer by natural convection in the core catcher assembly has been assessed numerically and through water experiments using geometrically similar configuration. Resistive heating elements are used in experiment as heat source to simulate debris decay heat on core catcher. Series of experiments were carried out for two configurations referred as geometry A and geometry B. The later configuration showed enhanced natural convective heat transfer from the lower plenum of the vessel. Temperatures were monitored at critical positions and compared with numerical evaluation. Numerically evaluated flow fields and isotherms are compared with experimental data for specific steady state temperatures on heat source plate. Numerical results are found to be in good agreement with that obtained from experiments. The combined efforts of numerical and experimental work conclude core catcher assembly with geometry B to be more suitable. (authors)

Sanjay Kumar Das; Anil Kumar Sharma; Jasmin Sudha, A.; Punitha, G.; Lydia, G.; Somayajulu, P.A.; Murthy, S.S.; Malarvizhi, B.; Gopalakrishnan, V.; Harvey, J.; Kasinathan, N.; Rajan, M. [Indira Gandhi Centre for Atomic Research, Kalpakkam 603 102 (India)

2006-07-01

112

F-layer formation in the outer core with asymmetric inner core growth  

NASA Astrophysics Data System (ADS)

Numerical calculations of thermochemical convection in a rotating, electrically conducting fluid sphere with heterogeneous boundary conditions are used to model effects of asymmetric inner core growth. With heterogeneous inner core growth but no melting, outer core flow consists of intense convection where inner core buoyancy release is high, weak convection where inner core buoyancy release is low, and large scale, mostly westward flow in the form of spiraling gyres. With localized inner core melting, outer core flow includes a gravity current of dense fluid that spreads over the inner core boundary, analogous to the seismic F-layer. An analytical model for gravity currents on a sphere connects the structure of the dense layer to the distribution of inner core melting and solidification. Predictions for F-layer formation by asymmetric inner core growth include large-scale asymmetric gyres below the core-mantle boundary and eccentricity of the geomagnetic field.

Deguen, Renaud; Olson, Peter; Reynolds, Evan

2014-05-01

113

A model for core formation in the early Earth  

NASA Technical Reports Server (NTRS)

Two basic types exogenous models were proposed to account for siderophile and chalcophile element abundances in the Earth's upper mantle. The first model requires that the Earth be depleted in volatiles and that, after a core formation event which extracted the most siderophile elements into the core, additional noble siderophile elements (Pt, Ir, Au) were added as a late veneer and mixed into the mantle. The second model postulates a reduced Earth with approximately CI elemental abundances in which a primary core forming event depleted all siderophile elements in the mantle. The plausibility of models which require fine scale mixing of chondritic material into the upper mantle is analyzed. Mixing in liquids is more efficient, but large degrees of silicate partial melting will facilitate the separation of magma from residual solids. Any external events affecting the upper mantle of the Earth should also be evident in the Moon; but siderophile and chalcophile element abundance patterns inferred for the mantles of the Earth and Moon differ. There appear to be significant physical difficulties associated with chondritic veneer models.

Jones, J. H.; Drake, M. J.

1985-01-01

114

MACCS usage at Rocky Flats Plant for consequence analysis of postulated accidents  

SciTech Connect

The MELCOR Accident Consequence Code System (MACCS) has been applied to the radiological consequence assessment of potential accidents from a non-reactor nuclear facility. MACCS has been used in a variety of applications to evaluate radiological dose and health effects to the public from postulated plutonium releases and from postulated criticalities. These applications were conducted to support deterministic and probabilistic accident analyses for safety analyses for safety analysis reports, radiological sabotage studies, and other regulatory requests.

Foppe, T.L.; Peterson, V.L.

1993-10-01

115

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

116

Melting of MORB up to 130 GPa  

NASA Astrophysics Data System (ADS)

Though today Earth's mantle material is predominantly solid, presence of regions of anomalously low seismic wave velocity deep within the mantle, known as ultralow velocity zones (ULVZs), may be indicative of a remnant magma ocean[Labrosse et al., Nature 450, 866, 2007] or an accumulation of subducted oceanic crust. A recent study on peridotite melting [Fiquet et al., Science 329, 1516, 2010] showed that it is possible to melt peridotites at the base of the mantle, thus making the hypothesis of a remnant magma ocean thermodynamically feasible. It is thus important to know about the possible melting of the oceanic lithosphere at the base of the mantle and whether the partial melting products can significantly contribute to ULVZs. Data on the melting curve (solidus) of mid-ocean ridge basalt (MORB), here taken as a proxy of the oceanic crust, exist up to 64 GPa [Hirose et al.,Nature 397, 53, 1999]. Melting temperature at the core mantle boundary, however, is only estimated from extrapolations of low pressure data and composition of the liquids obtained from partial melting have been reported in multi-anvil experiments at pressures up to 27.5 GPa only [Hirose et al.,GCA 66, 2099, 2002]. We have therefore conducted a series of experiments using diamond-anvil cells and laser-heating and determined the melting curve for the MORB between 44 and 130 GPa. Thin (electron transparent) sections of recovered samples (quenched melt) were prepared by Focused Ion Beam (FIB) and further investigated by analytical transmission electron microscopy to check melting/crystallization sequences as well as variations of phase composition as a function of temperature and pressure. Our results also yield strong constraints on the solidus curve of the lower mantle.

Pradhan, G. K.; Fiquet, G.; Siebert, J.; Auzende, A.; Antonangeli, D.

2013-12-01

117

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

118

Report on large scale molten core/magnesia interaction test  

SciTech Connect

A molten core/material interaction experiment was performed at the Large-Scale Melt Facility at Sandia National Laboratories. The experiment involved the release of 230 kg of core melt, heated to 2923/sup 0/K, into a magnesia brick crucible. Descriptions of the facility, the melting technology, as well as results of the experiment, are presented. Preliminary evaluations of the results indicate that magnesia brick can be a suitable material for core ladle construction.

Chu, T.Y.; Bentz, J.H.; Arellano, F.E.; Brockmann, J.E.; Field, M.E.; Fish, J.D.

1984-08-01

119

Model of interfacial melting  

NASA Astrophysics Data System (ADS)

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

Mouritsen, Ole G.; Zuckermann, Martin J.

1987-01-01

120

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

121

The rock melting approach to drilling  

SciTech Connect

During the early and mid-1970`s the Los Alamos National Laboratory demonstrated practical applications of drilling and coring using an electrically-heated graphite, tungsten, or molybdenum penetrator that melts a hole as it is slowly pushed through the rock or soil. The molten material consolidates into a rugged glass lining that prevents hole collapse; minimizes the potential for cross-flow, lost circulation, or the release of hazardous materials without casing operations; and produces no cuttings in porous or low density (<1.7 g/cc) formations. Because there are no drilling fluids required, the rock melting approach reduces waste handling, treatment and disposal. Drilling by rock melting has been demonstrated to depths up to 30 m in caliche, clay, alluvium, cobbles, sand, basalt, granite, and other materials. Penetrating large cobbles without debris removal was achieved by thermal stress fracturing and lateral extrusion of portions of the rock melt into the resulting cracks. Both horizontal and vertical holes in a variety of diameters were drilled in these materials using modular, self-contained field units that operate in remote areas. Because the penetrator does not need to rotate, steering by several simple approaches is considered quite feasible. Melting is ideal for obtaining core samples in alluvium and other poorly consolidated soils since the formed-in-place glass liner stabilizes the hole, encapsulates volatile or hazardous material, and recovers an undisturbed core. Because of the relatively low thermal conductivity of rock and soil materials, the heat-affected zone beyond the melt layer is very small, <1 inch thick. Los Alamos has begun to update the technology and this paper will report on the current status of applications and designs for improved drills.

Cort, G.E.; Goff, S.J.; Rowley, J.C.; Neudecker, J.W. Jr.; Dreesen, D.S.; Winchester, W.

1993-09-01

122

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

2006-06-15

123

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

124

Melting Glaciers Threaten Peru  

NSDL National Science Digital Library

Thousands of people in the Andes mountains of Peru are having their lives affected in both a practical and cultural way by climate change, which is causing the region's glaciers to melt. This document explores the causes of the glacial melt and its impacts on the local cultures.

2003-10-09

125

Conditions for inner core translation, and possible observable consequences for the outer core dynamics  

NASA Astrophysics Data System (ADS)

The hemispherical asymmetry seen in the seismological properties of the inner core has recently been interpreted as resulting form a high-viscosity mode of inner core thermal convection, consisting in a translation of the inner core with melting on one hemisphere and solidification on the other. Inner core translation can potentially explain a significant part of the inner core structure, but its existence depends critically on the value of poorly constrained parameters. Being a thermal convection mode, a prerequisite for the existence of convective translation is that a superadiabatic temperature profile is maintained with the inner core. The necessary conditions for inner core superadiabaticity will be discussed, in particular in view of recent work suggesting a core thermal conductivity much larger than previously thought. If the inner core is indeed superadiabatic, linear stability analysis, asymptotic calculations, and direct numerical simulations consistently show that the convective translation mode dominates only if the viscosity is large enough, with a critical viscosity value estimated to be ˜ 3 × 1018 Pa~s. Inner core translation imposes highly asymmetric boundary conditions for the outer core flow, with a negative buoyancy flux in the melting hemisphere and a high positive flux in the crystallizing hemisphere. This might have profound - and potentially observable - implications for the outer core dynamics. The excessively asymmetric buoyancy release imposed by inner core translation would be expected to induce a persisting asymmetry in the outer core flow and the geomagnetic field. Numerical dynamos suggest a hemispherical pattern of buoyancy flux at the ICB would produce a large scale asymmetric anticyclonic jet reminiscent of the eccentric gyre inferred in the core from quasi-geostrophic core flow inversions. In addition, the large melt production associated with inner core translation may be at the origin of the seismic F-layer, with inner core melting providing the dense iron-rich melt necessary for the formation of the layer.

Deguen, R.; Alboussiere, T.; Olson, P.; Cardin, P.

2012-12-01

126

Fitting Straight Lines with Replicated Observations by Linear Regression: The Least Squares Postulates  

Microsoft Academic Search

The results obtained by statistical techniques are valid if the assumed conditions are satisfied. Fitting straight lines with replicated observations by linear regression is considered in this article paying special attention to the compliance of the least squares postulates. Normality, robustness, independence, abscissa free from error, and proper weights are contemplated sequentially in this article. A detailed consideration of multiple

Ana Sayago; Maravillas Boccio; Agustin Asuero

2004-01-01

127

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

128

Are the non equilibrium thermodynamics postulates necessary in modeling coating formation by drying?  

NASA Astrophysics Data System (ADS)

In this work it is shown that it is necessary to apply the non equilibrium thermodynamics postulates in Fickian multi-component diffusion appearing in coating formation by drying. More specifically, two cases of solvent(s) evaporation from a ternary polymer solution were examined. The first case assumes given diffusion coefficients while in the second case the non-equilibrium thermodynamics postulates such as the Onsager Reciprocal Relations (ORR) and the quasi equilibrium postulate (Gibbs-Duhem equation) were applied. The coating drying was modeled as a coupled heat and mass problem with a moving boundary. The Galerkin Finite Element method was applied to numerically solve the drying problem. It was shown that the inclusion of quasi equilibrium postulates in calculating the ternary diffusion coefficients could explain the discrepancy of negative concentrations in the given diffusion coefficients case observed even if the restrictions of the second thermodynamic law are satisfied. It is believed that this work could have applications such as modeling coating formation by drying.

Verros, George D.; Xentes, George K.

2013-10-01

129

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

130

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

131

The Einstein Postulates: 1905-2005 A Critical Review of the Evidence  

E-print Network

The Einstein postulates assert an invariance of the propagation speed of light in vacuum for any observer, and which amounts to a presumed absence of any preferred frame. The postulates appear to be directly linked to relativistic effects which emerge from Einstein's Special Theory of Relativity, which is based upon the concept of a flat spacetime ontology, and which then lead to the General Theory of Relativity with its curved spacetime model for gravity. While the relativistic effects are well established experimentally it is now known that numerous experiments, beginning with the Michelson-Morley experiment of 1887, have always shown that the postulates themselves are false, namely that there is a detectable local preferred frame of reference. This critique briefly reviews the experimental evidence regarding the failure of the postulates, and the implications for our understanding of fundamental physics, and in particular for our understanding of gravity. A new theory of gravity is seen to be necessary, and this results in an explanation of the `dark matter' effect entailing the discovery that the fine structure constant is a 2nd gravitational constant.

Reginald T. Cahill

2004-12-07

132

Transient bowing of core assemblies in advanced liquid metal fast reactors  

Microsoft Academic Search

Two alternative core restraint concepts are considered for a conceptual design of a 900 MWth liquid metal fast reactor core with a heterogeneous layout. The two concepts, known as limited free bowing and free flowering, are evaluated based on core bowing criteria that emphasize the enhancement of inherent reactor safety. The core reactivity change during a postulated loss of flow

S. A. Kamal; Y. Orechwa

1986-01-01

133

Melting at dislocations and grain boundaries: A phase field crystal study  

Microsoft Academic Search

Dislocation and grain-boundary melting are studied in three dimensions using the phase field crystal method. Isolated dislocations are found to melt radially outward from their core, as the localized excess elastic energy drives a power-law divergence in the melt radius. Dislocations within low angle to intermediate angle grain boundaries melt similarly until an angle-dependent first-order wetting transition occurs when neighboring

Joel Berry; K. R. Elder; Martin Grant

2008-01-01

134

Martorell, B; Vocadlo, L; Brodholt, J; Wood, IG (2013); Strong pre-melting effect in the elastic properties of hcp-Fe under inner-core conditions, Science 342:6157; 466-468.  

E-print Network

. Martorell). Abstract: The observed shear wave velocity in the Earth's core is much lower than expected from% molar fraction in Si at 5000 K and 13000 kg m-3 , ref. 11) to solve the discrepancy. Another possible is in the range 6200 to 6900 K (15,17) using phase coexistence calculations (solid and liquid), with upper limit

Crawford, Ian

135

Rise in frequency of surface melting at Siple Dome through the Holocene: Evidence for increasing marine influence on the climate of West Antarctica  

Microsoft Academic Search

A new melt layer history from Siple Dome, West Antarctica, indicates notable late-Holocene summertime warming. Visual stratigraphic analyses of the 1004-m ice core identified 62 years with melt layers. Melting events began around 11.7 ka, followed by a period of no melting from 8.8–6.6 ka. Melt layer frequency increased from 6.6 ka to the present, with the 1000-year-average melt layer

Sarah B. Das; Richard B. Alley

2008-01-01

136

Molybdenum Valence in Basaltic Silicate Melts  

NASA Technical Reports Server (NTRS)

The moderately siderophile element molybdenum has been used as an indicator in planetary differentiation processes, and is particularly relevant to core formation [for example, 1-6]. However, models that apply experimental data to an equilibrium differentiation scenario infer the oxidation state of molybdenum from solubility data or from multivariable coefficients from metal-silicate partitioning data [1,3,7]. Partitioning behavior of molybdenum, a multivalent element with a transition near the J02 of interest for core formation (IW-2) will be sensitive to changes in JO2 of the system and silicate melt structure. In a silicate melt, Mo can occur in either 4+ or 6+ valence state, and Mo6+ can be either octahedrally or tetrahedrally coordinated. Here we present first XANES measurements of Mo valence in basaltic run products at a range of P, T, and JO2 and further quantify the valence transition of Mo.

Danielson, L. R.; Righter, K.; Newville, M.; Sutton, S.; Pando, K.

2010-01-01

137

Melting point of niobium  

Microsoft Academic Search

The melting point of 99.7% pure niobium was found to be 2469 deg C. This ; was the result of 21 measurements carried out using two EOP optical monochromatic ; pyrometers and a model of the absolute black body. (auth);

B. Ya. Berezin; M. M. Kenisarin; V. Ya. Chekhovskoi

1973-01-01

138

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

2012-02-13

139

Impact of Violations and Deviations in Hardy-Weinberg Equilibrium on Postulated Gene-Disease Associations  

Microsoft Academic Search

The authors evaluated whether statistically significant violations of Hardy-Weinberg equilibrium (HWE) or the magnitude of deviations from HWE may contribute to the problem of replicating postulated gene-disease associ- ations across different studies. Forty-two gene-disease associations assessed in meta-analyses of 591 studies were examined. Studies with disease-free controls in which HWE was violated gave significantly different results from HWE-conforming studies in

Thomas A. Trikalinos; Georgia Salanti; Muin J. Khoury; John P. A. Ioannidis

2006-01-01

140

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

141

Abyssal Peridotites and Mantle Melting Beneath Ocean Ridges  

NASA Astrophysics Data System (ADS)

Studies of abyssal peridotite from ultraslow and slow spreading ridges show significant regional variability; with a strong correlation between the compositions of peridotite averaged by locality and spatially associated MORB reflecting higher degrees of mantle melting near mantle hot spots. Local variability of peridotite compositions, however, is often large, and may equal the regional variability along ocean ridges. The latter is attributed to local melting and melt transport processes such as melt channelization or late-stage melt impregnation in the lithosphere. The observed regional correlation appears only when many samples are averaged to eliminate local and outcrop scale variability. Almost all the peridotites used in these correlations are from transforms, and therefore represent similar thermal and mantle melting histories. Thus, regional differences in mantle composition are preserved. Until recently, little data were available for peridotites away from transforms representing the central mantle environment beneath magmatic segments. This is key, as geophysical and geologic evidence suggest focused melt flow beneath slow spreading ridges. If so, beneath individual magmatic segments there should be a corresponding mantle melting cell in which melt is focused from a broad melting region to a melt transport zone at its mid-point that feeds an overlying crustal magmatic center. High melt fluxes in the transport zone would produce very depleted peridotites stripped of pyroxene by melt-rock reaction during magma ascent. Studies of peridotites far from transforms at ultraslow Gakkel and SW Indian Ridges indicate this is the case: with near-Cpx free intergranular harzburgite and dunite locally abundant in contrast to transform peridotites. Recent mapping of the plutonic foundation of an ancient 35-km long slow spreading ridge segment at the Kane Core Complex also found a narrow 10-km wide zone of focused melt flow through the mantle marked by abundant dunite and spatially associated troctolites. Abyssal peridotite studies show that melts are produced in a geometrically complex melting regime. Not all portions of the source region contribute equally, and the mantle itself is likely multi component, with different components contributing to different degrees depending on the melting regime. A geochemical conundrum, then, is that mantle compositions estimated by inverting MORB provide only a fictive mantle 'source' composition - and not its true composition. Average abyssal peridotite compositions from ultra-slow spreading ridges where little crust is produced are only slightly different than those from slow spreading ridges with normal crustal thickness - suggesting that the average mantle composition could be more depleted than has been thought, and that mantle veins may contribute in greater proportion to melt production than has been believed.

Dick, H. J.; Snow, J. E.; Hellebrand, E.; Shimizu, N.

2005-12-01

142

Melting experiments on peridotite to lowermost mantle conditions  

NASA Astrophysics Data System (ADS)

experiments on a pyrolitic mantle material were performed in a pressure range from 34 to 179 GPa based on laser-heated diamond-anvil cell (DAC) techniques. The textural and chemical characterizations of quenched samples were made by using field-emission-type electron microprobe (FE-EPMA). Melts formed by 46 to 77 wt.% partial melting in this study were ultrabasic in composition and became more depleted in SiO2 and more enriched in FeO with increasing pressure. Melting textures indicate that the liquidus phase changed from ferropericlase to MgSiO3-rich perovskite at least above 34 GPa and further to post-perovskite. The first phase to melt (disappear) changed from CaSiO3 perovskite to (Mg,Fe)O ferropericlase between 68 and 82 GPa. The stability of ferropericlase above solidus temperature shrinks with increasing pressure (melting last below 34 GPa and first 82 GPa), resulting in higher (MgO + FeO)/SiO2 ratio in partial melt at higher pressure. Additionally, the Fe-Mg distribution coefficients (KD) between perovskite/post-perovskite and melt decreased considerably with increasing pressure, leading to strong Fe-enrichment in partial melts. It supports dense partial melts in a deep lower mantle, which migrate downward to the core mantle boundary (CMB).

Tateno, Shigehiko; Hirose, Kei; Ohishi, Yasuo

2014-06-01

143

Polymer Melt Flow Visualization  

NASA Astrophysics Data System (ADS)

Melt flow during injection molding is non-Newtonian, non-isothermal, and unsteady. Software packages for the numerical simulation of such flows are prevalent in the plastics industry, but experimental data for benchmarking and verification of these programs are scarce. To address this situation, an optical access mold has been constructed with a rectangular mold cavity that can be illuminated from the top and bottom and viewed from the side. The mold has been placed in a Cincinnati Milacron VS-33 injection molding machine and has been used to study the flow of polyethylene melts. A digital CCD camera was used to record the progress of the melt as it filled the cavity from a gate near one of the cavity corners. The digital images were then processed to extract the melt front geometry as a function of time. Images of the flowing plastic, and polynomial fits to the melt front data for various sets of molding parameters are presented. In addition, the experimental data may be compared to the results of GOMA, a program developed at Sandia that can be used to simulate the flow of non-Newtonian fluids with free and fixed boundaries, if time allows.

Bress, Thomas; Dowling, David

2000-11-01

144

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 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. The Concord Consortium develops deeply digital learning innovations for science, mathematics, and engineering.

2011-05-17

145

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

146

Low melting mesophase pitches  

SciTech Connect

A low melting point, low molecular weight, heptane insoluble, 1,2,4-trichlorobenzene soluble mesophase pitch useful in carbon fiber spinning as such or as a plasticizer in a carbon fiber spinning composition is obtained by heating chrysene, triphenylene or paraterphenyl as well as mixtures thereof and hydrocarbon fractions containing the same, dissolving the resulting heat treated material with 1,2,4-trichlorobenzene, and separating the insolubles, and then contacting the 1,2,4-trichlorobenzene soluble fraction with a sufficient amount of heptane to precipitate the low melting point, low molecular weight mesophase pitch.

Diefendorf, R.J.; Chen, S.H.

1984-04-17

147

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

148

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

149

Varieties of Melt-Rock Interactions in Abyssal Peridotites  

NASA Astrophysics Data System (ADS)

Ocean Drilling Program cores of abyssal peridotite from Hess Deep (Leg 147) and near the Kane Fracture Zone (Leg 153) exhibit features suggesting that a variety of melt-rock interaction processes can influence their compositions. Shallow intrusion into peridotite by melt veins can produce small gabbroic intrusives, with local interaction with the host peridotite, leading to local enrichments in peridotite incompatible element budgets and changes in peridotite modes. This process reveals nothing about proposed reactive porous flow or melt-entrapment processes that might be influencing peridotite geochemistry at greater depth. Given the limited extent of our `outcrop' (one core diameter), it is possible that the gabbroic intrusive could be un-sampled, but that the chemical effects could be present in the core and mistaken for some other type of melt-rock reaction. The presence of these gabbroic veins in both suites of drilled peridotites shows that this type of process has demonstrably changed the geochemistry of parts of these cores. Other processes that could influence the geochemistry of these rocks include: 1. Melt-entrapment; the effects this have on the mode of peridotite will depend on the pressure at which the melt is entrapped and crystallizes and on the composition of the melt; if this occurs at shallow levels, then plagioclase will be present and the occurrence of melt-trapping will be obvious, but if it occurs at greater depths, then the melt will crystallize no plagioclase and the process will be cryptic. 2. Reactive porous flow; this process could also be cryptic, because in the absence of a set of samples that clearly represents simple melt-residues, the baseline against which modal and geochemical changes have occurred is lacking. Both suites of peridotites studied show evidence for Na enrichments, but in different styles. The Kane suite is pervasively enriched in Na above the amount that should be present based on fractional melting models, in samples that are distal from shallow gabbroic intrusives. The Hess Deep suite shows local enrichments in Na by a factor of > 30 over baseline Na levels. The causes of these different enrichment styles are being investigated and we are determining abundances of strongly incompatible trace elements in CPX by ion probe to constrain the histories of these suites.

Ross, K.; Elthon, D.

2003-12-01

150

Melt Processible Fluoropolymer Composites  

Microsoft Academic Search

A series of melt processible fluoropolymer resins including ETFE, PVF 2-TFE, ECTFE, PFA, and FEP containing reinforcing glass fiber, milled glass fiber, carbon fiber, minerals, graphite powder, and MoS2 have been prepared and characterized. The mechanical, physical, thermal and tribological properties of these composites have been compared and ranked for suitability in various applications. These composites represent the first comprehensive

J. M. Crosby; J. E. Theberge; K. L. Talley

1981-01-01

151

Melting of Phospholipid Tubules  

Microsoft Academic Search

The melting of lipid-based microcylinders (tubules) has been investigated for systems with single and multiple bilayer walls using high field, magnetic birefringence, and precision microcalorimetry. The pretransitional behavior of both the magnetic birefringence and the specific heat is very different in tubules with a single bilayer wall from that of tubules with multiple bilayers.

G. Nounesis; B. R. Ratna; S. Shin; R. S. Flugel; S. N. Sprunt; A. Singh; J. D. Litster; R. Shashidhar; Satyendra Kumar

1996-01-01

152

How do crystals melt?  

Microsoft Academic Search

Direct atomistic simulation of the melting of crystalline substances is discussed. Atomistic modeling is in the form of molecular-dynamics and Monte Carlo simulations and is a method of studying the cooperative and individual behavior of a system of atoms under well-prescribed conditions. Through the use of interatomic interaction potentials and border conditions, simulations can be made to represent the physical

Simon R. Phillpot; Sidney Yip; Dieter Wolf

1989-01-01

153

Is Greenland Melting?  

NSDL National Science Digital Library

Data-centric activity where students explore the connections between an observable change in the cryosphere and its potential impact in the hydrosphere and atmosphere. Students analyze the melt extents on the Greenland ice sheet from 1992-2003. Students also learn about how scientists collect the data.

Youngman, Betsy; Terc, Earth E.

154

An Improved Method for Postulating Fabrication Flaws in Reactor Pressure Vessels for Structural Integrity Evaluation  

SciTech Connect

This paper presents an improved model for postulating fabrication flaws in reactor pressure vessels (RPVs) and for the treatment of measured flaw data by probabilistic fracture mechanics (PFM) codes that are used for structural integrity evaluations. The model used to develop the current pressurized thermal shock (PTS) regulations conservatively postulated that all fabrication flaws were inner-surface breaking flaws. To reduce conservatisms and uncertainties in flaw-related inputs, the United States Nuclear Regulatory Commission (USNRC) has supported research at Pacific Northwest National Laboratory (PNNL) that has resulted in data on fabrication flaws from non-destructive and destructive examinations of actual RPV material. Statistical distributions have been developed to characterize the number and sizes of flaws in the various material regions of a vessel. The regions include the main seam welds, repair welds, base metal of plates and forgings, and the cladding that is applied to the inner surface of the vessel. Flaws are also characterized as being located within the interior of these regions or along the weld fusion lines that join the regions. Flaws are taken that occur at random locations relative to the embrittled inner region of the vessel. The probabilistic fracture mechanics model associates each of the simulated flaw types with the fracture properties of the region being addressed. (authors)

Simonen, F.A. [Pacific Northwest National Laboratory, P.O. Box 999 Richland, WA 99352 (United States); Dickson, T.L. [Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, TN 37831 (United States)

2002-07-01

155

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

156

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 ?-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 ?-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 ?-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 ?-clocks, exactly contradicts Lorentz transformations. 1

Wang Guowen

2005-01-01

157

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

158

Existence of an information unit as a postulate of quantum theory  

PubMed Central

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, Lluis; Muller, Markus P.; Augusiak, Remigiusz; Perez-Garcia, David

2013-01-01

159

Melting Beneath Our Feet  

NSDL National Science Digital Library

This radio broadcast discusses how permafrost (permanently frozen ground) in Alaska and the Arctic has been melting, and what the potential consequences might be. These include damage to many engineering structures and coastlines and the release of gases into the atmosphere which may compound the problem of climate warming. About two-thirds of Alaska is covered by permafrost and a recent report says a higher priority should be given to studying it. The clip is about 4 minutes in length.

160

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

161

Consolidation of zircaloy-4 end crops by induction melting  

SciTech Connect

The Oak Ridge Y-12 Plant is investigating the use of induction melting as a method of consolidating Zircaloy-4, a zirconium alloy used in the fabrication of submarine nuclear reactor cores. Knolls Atomic Power Laboratory (KAPL) furnished about 4000 lb of typical core material, also known as hardware, for use in evaluating induction melting as a method of consolidation. Three ingots were produced by the induction melting of hardware in a graphite crucible that was protected by a laminated coating specifically developed for this application. This report includes a description of both the equipment and the crucible coating materials used for this project, a discussion of results, and a production assessment of using this technique for full-scale consolidation.

Bird, E.L.

1994-01-25

162

Experiments on the behaviour of a hot melt injected into sodium  

Microsoft Academic Search

Molten fuel\\/coolant interaction has been recognized as a key issue in the event of a reactor core disruptive accident. To support the theoretical work in this field, a series of simulation experiments was carried out. 5 kg of thermite melt at 3270 K were injected from below into a sodium pool at 770 K. The melt consisted of either mainly

A. Kaiser; F. Huber; D. Wilhelm

1998-01-01

163

An integral approach to investigate planetary cores  

NASA Astrophysics Data System (ADS)

The same core-mantle differentiation process was in operation during the early formation of the terrestrial planets, but it led to unique cores for the Earth, Venus, Mars, and Mercury, with different magnetic fields, reflecting their different dynamic, physical, and chemical states. Assuming all terrestrial planets shared the same materials of the building block, the differences must be resulted from the different conditions of the early accretion and the subsequent planetary evolution unique to each planet. The pressures at the core-mantle boundary of the terrestrial planets range from as low as 7 GPa to 136 GPa. The physical state (liquid or solid) for each planetary core is closely tied to the melting and chemical composition of the cores. In order to determine the minimal temperature of a liquid core or the maximal temperature of a solid core, we have systematically investigated melting relations in the binary systems Fe-FeS, Fe-C, and Fe-FeSi, move toward unravelling the crystallization sequence and element partitioning between solid and liquid metal in the ternary and quaternary systems up to 25 GPa, using multi-anvil apparatus. We have developed new techniques to analyze the quenched samples recovered from laser-heating diamond-anvil cell experiments using combination of focus ion beam (FIB) milling, high-resolution SEM imaging, and quantitative chemical analysis with silicon drift detector EDS. With precision milling of the laser-heating spot, we determined melting using quenching texture criteria imaged with high-resolution SEM and the sulfur partitioning between solid and liquid at submicron spatial resolution. We have also re-constructed 3D image of the laser-heating spot at multi-megabar pressures to better constrain melting point and understanding melting process. The new techniques allow us to extend precise measurements of melting relations to core pressures in the laser-heating diamond-anvil cell. In addition to the static experiments, we also used shockwave compression to determine density, sound velocity, and melting of core materials up to liquid outer core conditions. The integration of the static and dynamic compression data provides an extensive dataset over a wide pressure and temperature range that is necessary for establishing a comprehensive model of the planetary cores, providing the best fit to the geophysical, cosmochemial, and geochemical observations.

Fei, Y.

2012-12-01

164

Experimental constraints on Mercury's core composition  

NASA Astrophysics Data System (ADS)

The recent discovery of high S concentrations on the surface of Mercury by spacecraft measurements from the MESSENGER mission provides the potential to place new constraints on the composition of Mercury's large metallic core. In this work, we conducted a set of systematic equilibrium metal-silicate experiments that determined the effect of different metallic compositions in the Fe-S-Si system on the S concentration in the coexisting silicate melt. We find that metallic melts with a range of S and Si combinations can be in equilibrium with silicate melts with S contents consistent with Mercury's surface, but that such silicate melts contain Fe contents lower than measured for Mercury's surface. If Mercury's surface S abundance is representative of the planet's bulk silicate composition and if the planet experienced metal-silicate equilibrium during planetary core formation, then these results place boundaries on the range of possible combinations of Si and S that could be present as the light elements in Mercury's core and suggest that Mercury's core likely contains Si. Except for core compositions with extreme abundances of Si, bulk Mercury compositions calculated by using the newly determined range of potential S and Si core compositions do not resemble primitive meteorite compositions.

Chabot, Nancy L.; Wollack, E. Alex; Klima, Rachel L.; Minitti, Michelle E.

2014-03-01

165

Consistently melting crystals  

E-print Network

Recently Ooguri and Yamazaki proposed a statistical model of melting crystals to count BPS bound states of certain D-brane configurations on toric Calabi--Yau manifolds [arXiv:0811.2801]. This construction relied on a set of consistency conditions on the corresponding brane tiling, and in this note I show that these conditions are satisfied for any physical brane tiling; they follow from the conformality of the low energy field theory on the D-branes. As a byproduct I also provide a simple direct proof that any physical brane tiling has a perfect matching.

Klaus Larjo

2009-02-04

166

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

167

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

168

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

169

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

170

Melt Redistribution in Dynamic Systems: Applications to Core Formation  

NASA Technical Reports Server (NTRS)

Samples of olivine + Fe-S were fabricated by hot-pressing a mechanical mixture of the two phases. Olivine powders with a starting grain size of approx. 10 microns were prepared by crushing crystals of San Carlos olivine followed by pulverization in a fluid energy mill. Iron sulfide powder with a particle size of approx. 5 microns was prepared from a 2:1 mixture of reagent grade iron sulfide (FeS) plus iron. Rods 20 mm in length by 10 mm in diameter were cold-pressed into iron capsules with a uniaxial stress of approx. 200 MPa. These rods were then hot-pressed at 1523 K and 300 MPa for 4 h to obtain a starting material with <2% porosity. Samples for shear experiments were cut perpendicular to the long axis of these rods. The discs were shaped into ellipses approx. 6 mm by approx. 8 mm with a thickness ranging from 0.6 to 1.0 mm. An iron foil strain marker was inserted into a cut made along the minor axis. The sample was placed between two thoriated tungsten pistons cut at 45 deg to the long axis and then placed into an iron sleeve capped by alumina discs. The sample was then sheared in a gas pressure-medium apparatus at a temperature of 1523 K and a confining pressure of 300 MPa.

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

2003-01-01

171

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.

172

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...

173

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.

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

2014-10-01

174

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

175

Waste glass melting stages  

SciTech Connect

Three different simulated nuclear waste glass feeds, consisting of dried waste and glass frit, were heat treated for 1 hour in a gradient furnace at temperatures ranging from approximately 600[degrees]C--1000[degrees]C. Simulated melter feeds from the Hanford Waste Vitrification Plant (HWVP), the Defense Waste Processing Facility (DWPF), and Kernforschungszentrum Karlsruhe (KfK) in Germany were used. The samples were thin-sectioned and examined by optical microscopy to investigate the stages of the conversion from feed to glass. Various phenomena were seen, such as frit softening, bubble formation, foaming, bubble motion and removal, convective mixing, and homogenization. Behavior of different feeds was similar, although the degree of gas generation and melt homogenization varied.

Anderson, L.D.; Dennis, T.; Elliott, M.L.; Hrma, P.

1993-04-01

176

Waste glass melting stages  

SciTech Connect

Three different simulated nuclear waste glass feeds, consisting of dried waste and glass frit, were heat treated for 1 hour in a gradient furnace at temperatures ranging from approximately 600{degrees}C--1000{degrees}C. Simulated melter feeds from the Hanford Waste Vitrification Plant (HWVP), the Defense Waste Processing Facility (DWPF), and Kernforschungszentrum Karlsruhe (KfK) in Germany were used. The samples were thin-sectioned and examined by optical microscopy to investigate the stages of the conversion from feed to glass. Various phenomena were seen, such as frit softening, bubble formation, foaming, bubble motion and removal, convective mixing, and homogenization. Behavior of different feeds was similar, although the degree of gas generation and melt homogenization varied.

Anderson, L.D.; Dennis, T.; Elliott, M.L.; Hrma, P.

1993-04-01

177

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

178

Westinghouse Small Modular Reactor passive safety system response to postulated events  

SciTech Connect

The Westinghouse Small Modular Reactor (SMR) is an 800 MWt (>225 MWe) integral pressurized water reactor. This paper is part of a series of four describing the design and safety features of the Westinghouse SMR. This paper focuses in particular upon the passive safety features and the safety system response of the Westinghouse SMR. The Westinghouse SMR design incorporates many features to minimize the effects of, and in some cases eliminates the possibility of postulated accidents. The small size of the reactor and the low power density limits the potential consequences of an accident relative to a large plant. The integral design eliminates large loop piping, which significantly reduces the flow area of postulated loss of coolant accidents (LOCAs). The Westinghouse SMR containment is a high-pressure, compact design that normally operates at a partial vacuum. This facilitates heat removal from the containment during LOCA events. The containment is submerged in water which also aides the heat removal and provides an additional radionuclide filter. The Westinghouse SMR safety system design is passive, is based largely on the passive safety systems used in the AP1000{sup R} reactor, and provides mitigation of all design basis accidents without the need for AC electrical power for a period of seven days. Frequent faults, such as reactivity insertion events and loss of power events, are protected by first shutting down the nuclear reaction by inserting control rods, then providing cold, borated water through a passive, buoyancy-driven flow. Decay heat removal is provided using a layered approach that includes the passive removal of heat by the steam drum and independent passive heat removal system that transfers heat from the primary system to the environment. Less frequent faults such as loss of coolant accidents are mitigated by passive injection of a large quantity of water that is readily available inside containment. An automatic depressurization system is used to reduce the reactor pressure in a controlled manner to facilitate the passive injection. Long-term decay heat removal is accomplished using the passive heat removal systems augmented by heat transfer through the containment vessel to the environment. The passive injection systems are designed so that the fuel remains covered and effectively cooled throughout the event. Like during the frequent faults, the passive systems provide effective cooling without the need for ac power for seven days following the accident. Connections are available to add additional water to indefinitely cool the plant. The response of the safety systems of the Westinghouse SMR to various initiating faults has been examined. Among them, two accidents; an extended station blackout event, and a LOCA event have been evaluated to demonstrate how the plant will remain safe in the unlikely event that either should occur. (authors)

Smith, M. C.; Wright, R. F. [Westinghouse Electric Company, 600 Cranberry Woods Drive (United States)

2012-07-01

179

Melting phenomena in polymer blending  

NASA Astrophysics Data System (ADS)

This study is focused on understanding of the melting process of polymer blends during blending. Four topics are addressed in this thesis: melting behavior of polymer blends in an extruder, heat transfer between a solid polymer pellet and polymer melt; rheological properties of polymer melt suspensions; and morphology development of polymer blends during melting. A barrel sliding mechanism and a perturbation method was used to investigate the melting behavior of polypropylene (PP) and polystyrene (PS) blends in the extruder. It was found that the melting process in the extruder could be divided into three distinct regions. Most of melting occurred in the transition region mainly due to mechanical energy input. Friction between solid polymer pellets played a critical role in converting mechanical energy into heat. The location of the transition region for each process could be determined from the on-line visualization results, temperature and pressure profiles, and the perturbation signals. A representative heat transfer coefficient between a solid polymer pellet and another polymer melt under shear flow was obtained as 250W/m2 · K through numerical simulations. The dynamics of thermocouple used in the experiment was captured using a first order process approximation. A good match was achieved between the simulation and experiment after taking the thermocouple dynamics into account. Suspensions of ethylene acrylate copolymer (EAC) melt with PS beads were used to study rheological properties of polymer flow during extrusion. It was found that deformation of PS beads under high local shear stress could result in the decrease of the relative viscosity with increasing volume fraction. On-line visualization in a TSE showed an "erosion" mechanism for polycarbonate (PC) drop deformation and breakup in polyethylene (PE) melt. This "erosion" mechanism was also found from corresponding numerical simulations. Stress peaks at the interface from simulation result could explain the "erosion" mechanism.

Chen, Hongbing

180

Previously postulated "ligand-independent" signaling of GPR4 is mediated through proton-sensing mechanisms.  

PubMed

GPR4 was initially identified as a receptor for sphingosylphosphorylcholine and lysophosphatidylcholine; however, lipid actions have not always been confirmed. Instead, ligand-independent actions have sometimes been observed in GPR4- and other OGR1 family receptor-expressing cells. Here, we examined the possible involvement of extracellular protons, which have recently been proposed as another ligand for GPR4. At pH 7.4, the epidermal growth factor-induced extracellular signal-regulated kinase activity was lower in GPR4-transfected RH7777 cells, in association with increased cAMP accumulation, than in vector-transfected cells. The serum response element (SRE)-driven transcriptional activity was also clearly higher in GPR4-expressing HEK293 cells than in vector-transfected cells at pH 7.4. These apparent ligand-independent actions were very small at alkalinic 7.8. The SRE activity was further increased by extracellular acidification in a manner dependent on the G13 protein/Rho signaling pathway in HEK293 cells expressing GPR4 or other OGR1 receptor family members. GPR4-expressing cells also showed a calcineurin-dependent nuclear factor of activated T cell (NFAT) promoter activation at pH 7.4, and this activity was further increased by pH below 7.2 in association with inositol phosphate production. In contrast to the cAMP and SRE responses, however, alkalinization to pH 7.8 hardly affected the high basal activity. Finally, the expression of GPR4 hardly modulated the sphingosylphosphorylcholine- or lysophosphatidylcholine-induced action. These results suggest that an extracellular proton play a role as a ligand in some of previously postulated ligand-independent actions through GPR4 receptors. Moreover, GPR4 may be a multi-functional receptor coupling to Gs, G13, and Gq/11 proteins in response to extracellular acidification. PMID:17462861

Tobo, Masayuki; Tomura, Hideaki; Mogi, Chihiro; Wang, Ju-Qiang; Liu, Jin-Peng; Komachi, Mayumi; Damirin, Alatangaole; Kimura, Takao; Murata, Naoya; Kurose, Hitoshi; Sato, Koichi; Okajima, Fumikazu

2007-08-01

181

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

182

Consequences of tritium release to water pathways from postulated accidents in a DOE production reactor  

SciTech Connect

A full-scale PRA of a DOE production reactor has been completed that considers full release of tritium as part of the severe accident source term. Two classes of postulated reactor accidents, a loss-of-moderator pumping accident and a loss-of-coolant accident, are used to bound the expected dose consequence from liquid pathway release. Population doses from the radiological release associated with the two accidents are compared for aqueous discharge and atmospheric release modes. The expectation values of the distribution of possible values for the societal effective dose equivalent to the general public, given a tritium release to the atmosphere, is 2.8 person-Sv/PBq (9.9 {times} 10{sup {minus}3} person-rem/Ci). The general public drinking water dose to downstream water consumers is 6.5 {times} 10{sup {minus}2} person-Sv/Pbq (2.4 {times} 10{sup {minus}4} person-rem/Ci) for aqueous releases to the surface streams eventually reaching the Savannah River. Negligible doses are calculated for freshwater fish and saltwater invertebrate consumption, irrigation, and recreational use of the river, given that an aqueous release is assumed to occur. Relative to the balance of fission products released in a hypothetical severe accident, the tritium-related dose is small. This study suggests that application of regional models (1610 km radius) will indicate larger dose consequences from short-term tritium release to the atmosphere than from comparable tritium source terms to water pathways. However, the water pathways assessment is clearly site-specific, and the overall aqueous dose will be dependent on downstream receptor populations and uses of the river.

O`Kula, K.R.; Olson, R.L.; Hamby, D.M.

1991-12-31

183

Consequences of tritium release to water pathways from postulated accidents in a DOE production reactor  

SciTech Connect

A full-scale PRA of a DOE production reactor has been completed that considers full release of tritium as part of the severe accident source term. Two classes of postulated reactor accidents, a loss-of-moderator pumping accident and a loss-of-coolant accident, are used to bound the expected dose consequence from liquid pathway release. Population doses from the radiological release associated with the two accidents are compared for aqueous discharge and atmospheric release modes. The expectation values of the distribution of possible values for the societal effective dose equivalent to the general public, given a tritium release to the atmosphere, is 2.8 person-Sv/PBq (9.9 {times} 10{sup {minus}3} person-rem/Ci). The general public drinking water dose to downstream water consumers is 6.5 {times} 10{sup {minus}2} person-Sv/Pbq (2.4 {times} 10{sup {minus}4} person-rem/Ci) for aqueous releases to the surface streams eventually reaching the Savannah River. Negligible doses are calculated for freshwater fish and saltwater invertebrate consumption, irrigation, and recreational use of the river, given that an aqueous release is assumed to occur. Relative to the balance of fission products released in a hypothetical severe accident, the tritium-related dose is small. This study suggests that application of regional models (1610 km radius) will indicate larger dose consequences from short-term tritium release to the atmosphere than from comparable tritium source terms to water pathways. However, the water pathways assessment is clearly site-specific, and the overall aqueous dose will be dependent on downstream receptor populations and uses of the river.

O'Kula, K.R.; Olson, R.L.; Hamby, D.M.

1991-01-01

184

An adult zebrafish model for Laribacter hongkongensis infection: Koch's postulates fulfilled  

PubMed Central

Laribacter hongkongensis is a gram-negative emerging bacterium associated with invasive bacteremic infections in patients with liver disease and fish-borne community-acquired gastroenteritis and traveler's diarrhea. Although the complete genome of L. hongkongensis has been sequenced, no animal model is available for further study of its pathogenicity mechanisms. In this study, we showed that adult zebrafish infected with L. hongkongensis by immersion following dermal abrasion or intraperitoneal injection suffered mortality in a dose-dependent manner, with lethal dose 50 (LD50) of 2.1×104 and 1.9×104?colony-forming units (CFU)/mL, respectively. All mortalities occurred in the first four days post-infection. Zebrafish that died showed characteristic clinicopathological features: swimming near water surface, marked lethargy and sidestroke; abdominal hemorrhage, ulcers and marked swelling with ascites; and hydropic degeneration and necrosis of hepatocytes around central vein and inflammatory cells infiltration. L. hongkongensis was recovered from the ascitic fluid and tissues of zebrafish that died. Of the 30 zebrafish infected with 2.1×104?CFU/mL (LD50) L. hongkongensis isolated from dead zebrafish using the immersion following dermal abrasion method, 18 (60%) died. All zebrafish that died also showed the characteristic clinical and pathological features. Histopathological studies also showed dilation of hepatic central vein and hydropic degeneration. L. hongkongensis was isolated from the zebrafish that died. The Koch's postulates for L. hongkongensis as an infectious agent have been fulfilled. This highly reproducible and effective zebrafish model is of crucial importance for future studies on virulence factors for L. hongkongensis infection.

Xie, Jun; He, Jia-Bei; Shi, Jia-Wei; Xiao, Qiang; Li, Ling; Woo, Patrick CY

2014-01-01

185

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

SciTech Connect

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 because of fuel plate swelling during fission product vapor release or plate buckling. Complex phenomena of damage propagation were modeled using a one-dimensional heat transfer model. A scoping study was conducted to learn what parameters are important for core damage propagation, and to obtain initial estimates of core melt mass for addressing recriticality and steam explosion events. The study included investigating the effects of the plate contact area, the convective heat transfer coefficient, thermal conductivity upon fuel swelling, and the initial temperature of the plate being contacted by the damaged plate. Also, the side support plates were modeled to account for their effects on damage propagation. The results provide useful insights into how various uncertain parameters affect damage propagation.

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

1995-09-01

186

Modeling of residual stresses in core shroud structures  

SciTech Connect

A BWR core shroud is a cylindrical shell that surrounds the reactor core. Feedwater for the reactor is introduced into the annulus between the reactor vessel wall and the shroud. The shroud separates the feedwater from the cooling water flowing up through the reactor core. The shroud also supports the top guide which provides lateral support to the fuel assemblies and maintains core geometry during operational transients and postulated accidents to permit control rod insertion and provides the refloodable volume needed to ensure safe shutdown and cooling of the core during postulated accident conditions. Core shrouds were fabricated from welded Type 304 or 304L stainless steel plates and are supported at the top and bottom by forged ring support structures. In 1990, cracking was reported in the core shroud of a non-U.S. BWR. The cracks were located in the heat-affected zone (HAZ) of a circumferential core shroud weld. Subsequent inspections in U.S. BWRs have revealed the presence of numerous flaw indications in some BWR core shrouds, primarily in weld HAZs. In several instances, this cracking was quite extensive, with the cracks extending 75% or more around the circumference of some welds. However, because the applied stresses on the shroud are low during operation and postulated accidents and because of the high fracture toughness of stainless steel, adequate structural margins can be preserved even in the presence of extensive cracking. Although assessments by the USNRC staff of the potential significance of this cracking have shown that core shroud cracking does not pose a high degree of risk in the short term, the staff concluded that the cracking was a safety concern for the long term because of the uncertainties associated with the behavior of core shrouds with complete 360{degrees} through-wall cracks under accident conditions and because it could eliminate a layer of defense-in-depth.

Zhang, J.; Dong, P.; Brust, F.W.; Mayfield, M.; McNeil, M.; Shack, W.J.

1997-10-01

187

Beyond the Melting Pot Reconsidered.  

ERIC Educational Resources Information Center

Discusses the 1963 book, "Beyond the Melting Pot," which suggested that eventually the problem of different ethnicities in the U.S. would be resolved and society would become one melting pot. Examines how changes in immigration and economic structures have affected the issue, noting the devastating effect of the dominant culture's denigration of…

Anderson, Elijah

2000-01-01

188

Manicouagan and the Moon: Reassessing Impact Melt - Crater Affiliations  

NASA Astrophysics Data System (ADS)

When Apollo samples were first returned to Earth, comparisons were made with several terrestrial impact melt sheets to aid in the interpretation of the samples. Manicouagan was considered representative of a 60 to 100 km size complex crater with a supposedly undifferentiated, chemically homogeneous, although somewhat texturally heterogeneous, impact-melt sheet. Based on the belief that craters in the size range of Manicouagan produced chemically homogeneous melt sheets, Simonds et al. (1976) identified four distinct compositions of lunar melt in Apollo 16 breccia samples, attributing each to four different impact-melt sheets formed during discrete cratering events. However, recent drilling activities at Manicouagan, combined with surface sampling and geochemical analysis, have revealed that its impact-melt sheet is not of uniform composition as suggested by past field work. This calls into question previously held assumptions regarding the identification and interpretation of lunar impact melts. Drilling has revealed an unexpectedly varied topography to the melt sheet-basement contact in the centre of the structure at Manicouagan. An elongate, impact-melt filled, N-S trough extending at least 8 km from the southern flanks of the uplifted Mont de Babel anorthosite has been identified. The trough varies in depth from 600 m at the northern and southern extremes, to 1430 m in the middle, resulting in substantially thicker melt sections than previously identified by field work, which estimated current impact-melt sheet thickness to be 200 to 300 m. Our geochemical analysis of 88 core and field impact melt samples reveal that the more typical 300 m thick sections and the newly discovered 600 m thick sections intersected within the central trough in drill holes MAN0501 and 0511, exhibit a homogeneous, quartz monzodiorite composition comparable with previous average impact melt compositions. In contrast, the 1100 m clast-free melt sequence encountered in the centre of the graben in hole MAN0608 is segregated into two compositionally distinct layers, separated by a transition zone: a 450 m thick lower monzodiorite; a 180 m thick transition zone of quartz monzodiorite (the same as the average composition of the impact-melt sheet intersected in the other drill holes), and a 450 m thick upper quartz monzonite. The identification of a thicker, fractionated impact-melt sheet section at a crater the size of Manicouagan (90 km) has implications for the interpretation of lunar samples. It is apparent that samples previously assigned to separate impact events on the Moon may be differentiates of a common impact-melt sheet. Critically, this may occur at smaller diameters than previously considered. Simonds, C.H., Warner, J.L. and Phinney, W.C. 1976. Thermal regimes in cratered terrains with emphasis on the role of impact melt. Am. Mineral. 61, 569-577.

Spray, J. G.; Thompson, L. M.; O'Connell-Cooper, C.

2009-05-01

189

Iron--what is melt?  

SciTech Connect

The melting point of iron reported from a variety of phenomena observed in the laser-heated diamond-anvil-cell (DAC) and in shock wave studies differs widely. Although three groups of investigators, observing the same phenomena in the DAC are in good agreement to about 40 GPa, they disagree significantly with other measurements of melting point based on observation of different phenomena in the DAC. These latter data are in substantial agreement with some of the reported melting temperatures from two groups of investigators who measured temperature along the Hugoniot. However, a third group of investigators observe a sound velocity discontinuity along the Hugoniot and calculate a significantly lower temperature for melting. Melting point determination in iron is subject to the interpretation of physical phenomena, experimental errors which are probably larger than estimated, and perhaps undetected chemical reactions.

Duba, A.G.

1993-06-01

190

Crystal Melting and Black Holes  

E-print Network

It has recently been shown that the statistical mechanics of crystal melting maps to A-model topological string amplitudes on non-compact Calabi-Yau spaces. In this note we establish a one to one correspondence between two and three dimensional crystal melting configurations and certain BPS black holes given by branes wrapping collapsed cycles on the orbifolds C^2/Z_n and C^3/Z_n x Z_n in the large n limit. The ranks of gauge groups in the associated gauged quiver quantum mechanics determine the profiles of crystal melting configurations and the process of melting maps to flop transitions which leave the background Calabi-Yau invariant. We explain the connection between these two realizations of crystal melting and speculate on the underlying physical meaning.

Jonathan J. Heckman; Cumrun Vafa

2006-10-02

191

24. A CORE WORKER DISPLAYS THE CORE BOX AND CORES ...  

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

24. A CORE WORKER DISPLAYS THE CORE BOX AND CORES FOR A BRASS GATE VALVE BODY MADE ON A CORE BOX, CA. 1950. - Stockham Pipe & Fittings Company, 4000 Tenth Avenue North, Birmingham, Jefferson County, AL

192

The Manicouagan impact melt sheet: Evidence for isotopic homogenization with limited assimilation  

NASA Astrophysics Data System (ADS)

The Rb-Sr, Pb-Pb and Sm-Nd isotope chemistry of impact-generated melt and target rocks has been determined from the 214 Ma, ˜90 km rim-diameter, Manicouagan impact structure of Canada. Fifty-seven samples were obtained from 8 field sites and 11 drill core sites across the impact melt sheet, located on the 55 km-diameter central island (Île René-Levasseur). The results reveal that the impact melt, though locally differentiated via fractional crystallization, was isotopically homogenized during its formation following its derivation primarily from charnockites and mesocratic gneisses. The isotopic signatures of the target rocks indicate that the protolith for the melt was the Proterozoic Manicouagan Imbricate Zone, and that the underlying Archean Gagnon Terrane was not involved in melt production, or its subsequent modification via assimilation, despite impact melt resting on Archean lithologies in the southwest sector of the melt sheet. Limited assimilation of the footwall in this sector is attributed to the relatively rapid cooling of a thinner peripheral melt body (<100 m), primarily through contact with cooler footwall and clasts. Assimilation at the base of the thicker (up to 1.4 km thick) melt sections, near the center of the structure is attributed to secondary melting of centrally uplifted anorthosite, which locally modified the original isotopic signature.

O'Connell-Cooper, Catherine D.; Dickin, Alan P.; Spray, John G.

2012-06-01

193

Granulite Migmatization and Retrogression: Result of Pervasive Melt Influx? (Invited)  

NASA Astrophysics Data System (ADS)

The Blanský les granulite massif (BLG) is large (ca. 270 km2) lower crust exposure in Bohemian Massif in Czech Republic. It consists of felsic granulites in various degrees of retrogression and small bodies of eclogites, mafic granulites and ultrabasites. Peak granulitic conditions were estimated at ca. 16-18 kbar and 850-1100°C. This granulite massif was later, during exhumation, heterogeneously retrogressed in amphibolite facies conditions (ca. 5-7 kbar and 700-800°C). The degree of granulite retrogression increases continuously from the core towards the margin of the BLG massif. The question raised in this work is the nature of the retrogression. In core of the massif retrogression is manifested only by plagioclase and spinel coronas around kyanite. Towards the margin granulite gets progressively hydrated, has gneissic look and stable mineral assemblage of Qtz + Kfs + Pl + Bt + Sill × Grt. Retrograde granulite reveals higher amount of biotite, which forms at expanse of garnet and kyanite break down to sillimanite. Along the margin the transformation is accompanied by presence of melt, resulting into formation of migmatitic gneisses. The detailed field and microstructural observations revealed a gradual transition from mylonitic gneiss with only incipient amount of melt to migmatitic gneisses with no relict of gneissosity and high proportion of melt. This transition is accompanied by textural changes as well as changes in mineral chemistry (increase of XFe in biotite and garnet, increase of Na in plagioclase) and mineral proportions (decrease of garnet %, increase of biotite and feldspars %). During the exhumation, the granulite was dry, thus melt present in the granulite cannot be produced in-situ. We suggest that the hot dry granulite released and 'attracted' water from colder underlying metasedimentary sequence. This water flux caused extensive melting along the massif margins. This melt then further pervasively migrated towards the core of the massif causing heterogeneous migmatization and retrogression of the granulite. Moreover, we suggest that at an outcrop-scale leucosome distribution controls the extent of the retrogression. Distribution gradient created by the water-saturated melt in leucosomes is spatially limited. Thus granulite closer to the leucosome will reveal higher degree of retrogression than further from the leucosome. Importantly, melt presence in the granulite will play important role for the rheology at lower-middle crust interface.

Hasalova, P.; Štípská, P.; Weinberg, R. F.; Fran?k, J.; Schulmann, K.

2013-12-01

194

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

195

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

196

Gravitationally driven inner core differential rotation  

NASA Astrophysics Data System (ADS)

A heterogeneous heat flux at the core-mantle boundary can maintain time-averaged convective structures in the fluid core. This includes a steady pattern of heterogeneous heat flux at the inner core boundary which leads to aspherical inner core growth. If this growth pattern is longitudinally misaligned with the mantle-induced geoid, the latter would impart a gravitational torque on the newly created topography of the inner core. Allowing for continuous melting/solidification and viscous deformation of the inner core, a steady gravitationally driven differential rotation of the inner core with respect to the mantle can be sustained. In this work, we present calculations of inner core rotation driven by such a mechanism using recently published models of the heat flux at the inner core boundary and of the geoid at the base of the mantle. We show that, for a fast mean inner core growth rate of 1 mm/yr and a bulk viscous relaxation time longer than 100 yr, the inner core differential rotation can be as high as 100 deg/Myr, in the westward direction. Although this is much too slow (and in the wrong direction) to explain the seismically inferred inner core rotation (eastward, of the order of 0.2 deg/yr), this mechanism by itself would rotate the inner core by one full rotation in only a few million years. This gravitational torque would then partly offset the viscomagnetic torque from the steady eastward zonal flow near the inner core boundary, the driving mechanism typically invoked to explain a steady inner core super-rotation. Under the combined action of these two torques, the overall steady differential rotation of the inner core may then be small. This would allow the development of an inner core texture with a distinct longitudinal pattern connected to its aspherical freezing rate, as has been suggested to explain seismic observations.

Dumberry, Mathieu

2010-09-01

197

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

198

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

199

Influence of Silicate Melt Composition on Metal/Silicate Partitioning of W, Ge, Ga and Ni  

NASA Technical Reports Server (NTRS)

The depletion of the siderophile elements in the Earth's upper mantle relative to the chondritic meteorites is a geochemical imprint of core segregation. Therefore, metal/silicate partition coefficients (Dm/s) for siderophile elements are essential to investigations of core formation when used in conjunction with the pattern of elemental abundances in the Earth's mantle. The partitioning of siderophile elements is controlled by temperature, pressure, oxygen fugacity, and by the compositions of the metal and silicate phases. Several recent studies have shown the importance of silicate melt composition on the partitioning of siderophile elements between silicate and metallic liquids. It has been demonstrated that many elements display increased solubility in less polymerized (mafic) melts. However, the importance of silicate melt composition was believed to be minor compared to the influence of oxygen fugacity until studies showed that melt composition is an important factor at high pressures and temperatures. It was found that melt composition is also important for partitioning of high valency siderophile elements. Atmospheric experiments were conducted, varying only silicate melt composition, to assess the importance of silicate melt composition for the partitioning of W, Co and Ga and found that the valence of the dissolving species plays an important role in determining the effect of composition on solubility. In this study, we extend the data set to higher pressures and investigate the role of silicate melt composition on the partitioning of the siderophile elements W, Ge, Ga and Ni between metallic and silicate liquid.

Singletary, S. J.; Domanik, K.; Drake, M. J.

2005-01-01

200

Melting of iron-aluminide alloys  

SciTech Connect

The melting of Fe{sub 3}Al-based alloys at the Oak Ridge National Laboratory (ORNL) and commercial vendors is described. The melting processes evaluated includes are melting, air-induction melting (AIM), vacuum-induction melting (VIM), and electroslag remelting (ESR). The quality of the ingots studied are base on internal soundness and the surface finish obtained. The ingots were analyzed for recovery of various elements during melting. The impurity levels observed in the alloys by various melting processes were compared. Recommendations are made for viable processes for commercial melting of these alloys. 1 ref., 5 figs., 3 tabs.

Sikka, V.K.

1990-01-01

201

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

202

Circulation and melting beneath the ross ice shelf.  

PubMed

Thermohaline observations in the water column beneath the Ross Ice Shelf and along its terminal face show significant vertical stratification, active horizontal circulation, and net melting at the ice shelf base. Heat is supplied by seawater that moves southward beneath the ice shelf from a central warm core and from a western region of high salinity. The near-freezing Ice Shelf Water produced flows northward into the Ross Sea. PMID:17734137

Jacobs, S S; Gordon, A L; Ardai, J L

1979-02-01

203

Thermochemical convection in Earth's inner core  

NASA Astrophysics Data System (ADS)

The dynamics of Earth's inner core depends critically on whether it is stably stratified or unstably stratified. We propose here a general analysis of the thermal evolution of the inner core. Whether the geotherm in the inner core is superadiabatic or not depends on the inner core solidification rate, on the thermal diffusivity of iron at inner core conditions, and on the ratio of the Clapeyron slope to the adiabatic gradient in the inner core. The temperature field within the inner core can be destabilizing—and could drive convection—if the growth of the inner core is fast enough. The effect of radiogenic heating is probably small, and, perhaps surprisingly, can even stabilize the inner core against convection. The uncertainties are such that it is not possible at present to conclude about the likelihood of thermal convection in the inner core, but recent estimates of the Core-Mantle Boundary (CMB) heat flux and inner core conductivity favour convection. Thermal convection is more likely early in the inner core history, a consequence of the secular decrease in cooling rate of the core. In addition, solidification-induced partitioning of the light elements may induce a stable density stratification within the inner core. We develop a numerical model of thermochemical convection in a growing inner core, which couples the evolution and dynamics of the inner core with the thermal and compositional evolution of the outer core. Melting and crystallization associated with deformation of the Inner Core Boundary (ICB) would be of importance for the style of convection if the viscosity is large, but we focus here on the case of low viscosity for which phase change associated with dynamic topography at the ICB is expected to play a secondary role. In this regime, convection is typical of high Rayleigh number internally heated convection, with cold plumes falling from the ICB. Several possible scenarios can lead to a layered inner core, either because of cessation of thermal convection due to the decrease in cooling rate of the core, or because of a compositional stratification which can confine convection in the deep inner core, or stabilize the whole inner core. For each of these scenarios, it is possible to find plausible sets of parameters (inner core age, viscosity, magnitude of the compositional stratification) for which the radius at which convection stops corresponds to the radius of the seismically inferred innermost inner core.

Deguen, Renaud; Cardin, Philippe

2011-12-01

204

Formation and characterization of fission-product aerosols under postulated HTGR accident conditions  

SciTech Connect

The paper presents the results of an experimental investigation on the formation mechanism and physical characterization of simulated nuclear aerosols that could likely be released during an HTGR core heat-up accident. Experiments were carried out in a high-temperature flow system consisting essentially of an inductively heated release source, a vapor deposition tube, and a filter assembly for collecting particulate matter. Simulated fission products Sr and Ba as oxides are separately impregnated in H451 graphite wafers and released at elevated temperatures into a dry helium flow. In the presence of graphite, the oxides are quantitatively reduced to metals, which subsequently vaporize at temperatures much lower than required for the oxides alone to vaporize in the absence of graphite. A substantial fraction of the released material is associated with particulate matter, which is collected on filters located downstream at ambient temperature. The release and transport of simulated fission product Ag as metal are also investigated.

Tang, I.N.; Munkelwitz, H.R.

1982-07-01

205

Melting points of lanthanide trichlorides  

Microsoft Academic Search

Summary  The melting temperatures and absolute values of melting enthalpies of lanthanide trichlorides decrease from LaCl3to TbCl3and then increase to LuCl3. The preceding decrease cannot be explained by the lattice energies of the trichlorides, since they increase continuously\\u000a from the lanthanum to the lutetium compounds. However, it may be attributed to the structural features of the liquid state.\\u000a The liquids near

H. J. Seifert

2005-01-01

206

A Wave Interpretation of the Compton Effect As a Further Demonstration of the Postulates of de Broglie  

E-print Network

The Compton effect is commonly cited as a demonstration of the particle feature of light, while the wave nature of matter has been proposed by de Broglie and demonstrated by Davisson and Germer with the Bragg diffraction of electron beams. In this investigation, we present an entirely different interpretation of the Compton effect based on the postulates of de Broglie and on an interaction between electromagnetic and matter waves. The speeds of interacting electrons in the Compton scattering are quite fast and its mechanism relies heavily on the mass variation. Thus, based on this wave interpretation, the Compton effect can be viewed as a further demonstration of the postulates of de Broglie for high-speed particles. In addition to the scattered wave, a direct radiation depending on the mass variation is predicted, which provides a means to test the wave interpretation.

Ching-Chuan Su

2005-06-29

207

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

208

Ferrocyanide Safety Program: Analysis of postulated energetic reactions and resultant aerosol generation in Hanford Site Waste Tanks  

SciTech Connect

This report reviews work done to estimate the possible consequences of postulated energetic reactions in ferrocyanide waste stored in underground tanks at the Hanford Site. The issue of explosive reactions was raised in the 1987 Environmental Impact Statement (EIS), where a detonation-like explosion was postulated for the purpose of defining an upper bound on dose consequences for various disposal options. A review of the explosion scenario by the General Accounting Office (GAO) indicated that the aerosol generation and consequent radioactive doses projected for the explosion postulated in the EIS were understated by one to two orders of magnitude. The US DOE has sponsored an extensive study of the hazard posed by uncontrolled exothermic reactions in ferrocyanide waste, and results obtained during the past three years have allowed this hazard to be more realistically assessed. The objective of this report is to summarize the improved knowledge base that now indicates that explosive or vigorous chemical reactions are not credible in the ferrocyanide waste stored in underground tanks. This improved understanding supports the decision not to proceed with further analyses or predictions of the consequences of such an event or with aerosol tests in support of such predictions. 53 refs., 2 tabs.

Postma, A.K. [G and P Consulting, Inc., Dallas, OR (United States); Dickinson, D.R. [Westinghouse Hanford Co., Richland, WA (United States)

1995-09-01

209

Core Challenge  

NSDL National Science Digital Library

This learning community provides a forum for teachers, parents, and students to share ideas about teaching and learning. The concept of this forum is centered around the Common Core Standards to aide in moving mathematics education forward through shared knowledge. The website provides opportunities for community members to contribute, review, and learn through "Educational Objects".

2012-01-01

210

Modeling energy balance and melt layer formation on the Kahiltna Glacier, Alaska  

NASA Astrophysics Data System (ADS)

Understanding melt on alpine glaciers is required both for accurate mass balance modeling and ice core paleoclimate reconstruction. In alpine regions with complex meteorology and topography, modeling melt through the quantification and balance of all identifiable energy fluxes is the most complete way of describing how local meteorology influences melt layer formation and snowpack evolution. To meet this goal at our field site on the Kahiltna glacier, located in the Central Alaska Range, Denali National Park, we have developed an energy balance model from two years of meteorological data from Kahiltna Base Camp (2100 m elevation, 63.25 degrees N, 151 degrees W). Current model results show the dominance of turbulent heat transfer at the study site and the importance of surface roughness and albedo in controlling melt. Preliminary data show a 30 percent overestimation of melt flux from the surface into the snowpack although an albedo submodel is being developed which may address this. Sampling of the snowpack across the glacier for analysis of stratigraphic and chemical evolution shows an isothermal near surface snowpack (to at least 1m) at 2100 meters in elevation in the early melt season with increasing density and melt layer abundance as the summer progresses. This suggests that a large amount of the meltwater remains in the snowpack after surface melting. We will discuss further the model’s accuracy in relation to ablation stake measurements as well as the major environmental controls on physical and chemical snowpack evolution into the melt season as additional results are processed.

Winski, D. A.; Kreutz, K. J.; Osterberg, E. C.; Campbell, S. W.; Denali Ice Core Team

2010-12-01

211

Frictional melting and stick-slip behavior in volcanic conduits  

NASA Astrophysics Data System (ADS)

Dome-building eruptions have catastrophic potential, with dome collapse leading to devastating pyroclastic flows with almost no precursory warning. During dome growth, the driving forces of the buoyant magma may be superseded by controls along conduit margins; where brittle fracture and sliding can lead to formation of lubricating cataclasite and gouge. Under extreme friction, pseudotachylyte may form at the conduit margin. Understanding the conduit margin processes is vital to understanding the continuation of an eruption and we postulate that pseudotachylyte generation could be the underlying cause of stick-slip motion and associated seismic "drumbeats", which are so commonly observed at dome-building volcanoes. This view is supported by field evidence in the form of pseudotachylytes identified in lava dome products at Soufrière Hills (Montserrat) and Mount St. Helens (USA). Both eruptions were characterised by repetitive, periodic seismicity and lava spine extrusion of highly viscous magma. High velocity rotary shear (HVR) experiments demonstrate the propensity for melting of the andesitic and dacitic material (from Soufrière Hills and Mount St. Helens respectively) at upper conduit stress conditions (<10 MPa). Starting from room temperature, frictional melting of the magmas occurs in under 1 s (<< 1 m) at 1.5 m/s (a speed that is achievable during stick-slip motion). At lower velocities melting occurs comparatively later due to dissipation of heat from the slip zone (e.g. 8-15 m at 0.1 m/s). Hence, given the ease with which melting is achieved in volcanic rocks, and considering the high ambient temperatures in volcanic conduits, frictional melting may thus be an inevitable consequence of viscous magma ascent. The shear resistance of the slip zone during the experiment is also monitored. Frictional melting induces a higher resistance to sliding than rock on rock, and viscous processes control the slip zone properties. Variable-rate HVR experiments which mimic rapid velocity fluctuations in stick-slip behavior demonstrate velocity-weakening behavior of melt, with a tendency for unstable slip. During ascent, magma may slip and undergo melting along the conduit margin. In the process the shear resistance of the slip zone is increased, acting as a viscous brake halting slip (the "stick" of stick-slip motion). Sufficient buoyancy-driven pressures from ascending magma below eventually overcome resistance to produce a rapid slip event (the "slip") along the melt-bearing slip zone, which is temporarily lubricated due to velocity-weakening. New magma below experiences the same slip event more slowly (as the magma decompresses) to produce a viscous brake and the process is repeated. This allows a fixed spatial locus that explains the repetitive drumbeat seismicity and the occurrence of "families" of similar seismic events. We conclude that stick-slip motion in volcanic conduits is a self-driving, frictional-melt-regulated force common to many dome building volcanoes.

Kendrick, Jackie Evan; Lavallee, Yan; Hirose, Takehiro; di Toro, Giulio; Hornby, Adrian Jakob; Hess, Kai-Uwe; Dingwell, Donald Bruce

2013-04-01

212

Possible use of Skull melting under microgravity  

Microsoft Academic Search

Skull melting is a special kind of direct inductive heating which allows quasi-crucible-free processing of materials with very high melting points (3000K and above). Under terrestrial gravity, the temperature gradients essential to the Skull technique cause buoyancy driven convection in the melt, which might interfere with crystal growth. Skull melting could therefore benefit from processing in a microgravity environment. We

C. Gross; W Assmus; A Muiznieks; A Mühlbauer; C Stenzel; O Schulz

1999-01-01

213

Electrical Conductivity Measurement of Oxides Melts  

Microsoft Academic Search

Notwithstanding on variety of existing processes of induction skull melting of oxides, electrical and thermal properties of oxides melts are practically unknown. From the other hand, liquid-phase synthesis of Hi-Tech oxides materials such as new ceramics, monocrystals and glasses, requires knowledge of melts properties up to 3700 K. Inasmuch as the main physical property, which influence to the melt power

I. Pozniak; A. Pechenkov; A. Shatunov

214

Novel melting investigations of iron at high-pressure using synchrotron Mossbauer spectroscopy  

NASA Astrophysics Data System (ADS)

Seismological observations show that Earth's iron-dominated core consists of a solid inner region surrounded by a liquid outer core. The melting temperature of iron at high-pressure therefore provides a bound on the temperature regime of the core. Previously, melting studies of iron metal at high-pressures were performed by shock-compression, resistive- and laser-heating in diamond anvil cells using visual observations or synchrotron x-ray diffraction, and theoretical methods. However, the melting curve of iron is still controversial, especially at very high pressures. Here we present a novel method of detecting the solid-liquid phase boundary of iron at high-pressure using 57Fe synchrotron Mössbauer spectroscopy (SMS). Focused synchrotron radiation with 1 meV bandwidth passes through a laser-heated sample inside a diamond anvil cell. The characteristic SMS time signature is observed by fast detectors and vanishes suddenly when melting occurs. This process is described by the Lamb-Mössbauer factor f = exp(-k2), where k is the wave number of the resonant x-rays and is the mean-square displacement of the iron atoms. We will discuss our melting results in comparison with previous data and also discuss future applications of this method to the study of melting of Earth materials under pressure. In addition to the detection of melt, the Lamb-Mössbauer factor is related to the phonon density of states (PDOS) of the material investigated. Results thus far indicate that the phonon density of states of fcc-structured iron softens with increasing temperature at high-pressure. We propose that the softening of the PDOS is related to a reduction of the shear modulus. This behavior that occurs at high-pressure near the melting point of iron should be considered when extrapolating the behavior of iron to the outermost inner core conditions.

Jackson, J. M.; Sturhahn, W.; Lerche, M.; Zhao, J.; Sinogeikin, S. V.; Lakshtanov, D. L.; Bass, J. D.; Murakami, M.

2005-12-01

215

An assessment of the radiological doses resulting from accidental uranium aerosol releases and fission product releases from a postulated criticality accident at the Oak Ridge Y-12 Plant  

Microsoft Academic Search

A dose assessment for two separate normalized source terms was conducted for the Oak Ridge Y-12 Plant. The first source term consisted of the noble gas and iodine fission products emanating from a postulated criticality with a magnitude of 10¹⁹ fissions. The second postulated source term was 1 kg of respirable highly enriched uranium. The MELCOR Accident Consequence Code System

S. E. Fisher; K. E. Lenox

1995-01-01

216

Explosive volcanism and the compositions of cores of differentiated asteroids  

NASA Technical Reports Server (NTRS)

Eleven iron meteorite groups show correlations between Ni and siderophile trace elements that are predictable by distribution coefficients between liquid and solid metal in fractionally crystallizing metal magmas. These meteorites are interpreted to be fragments of the fractionally crystallized cores of eleven differentiated asteroids. Many of these groups crystallized from S-depleted magmas which we propose resulted from removal of the first partial melt (the Fe,Ni-FeS cotectic melt) by explosive pyroclastic volcanism of the type envisaged by Wilson and Keil (1991). We show that these dense, negatively buoyant melts can be driven to asteroidal surfaces due to the presence of excess pressure in the melt and the presence of buoyant bubbles of gas which decrease the density of the melt. We also show 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 pct FeS and 15 wt pct 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

217

Automatic Control of Silicon Melt Level  

NASA Technical Reports Server (NTRS)

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

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

1982-01-01

218

Defects and particle motions in the nonuniform melting of a two-dimensional Coulomb cluster.  

PubMed

The defect excitation and nonuniform melting of a two-dimensional Coulomb cluster with 300 charged particles (interacting with 1/r type force) in a uniform neutralizing background are studied numerically. Intrinsic defects exist around the outer circular shells surrounding the inner triangular lattice. They are the source regions for anisotropic particle thermal vibrations and then cyclic hoppings with the increasing temperature. It leads to the nonuniform melting associated with the thermal motion of intrinsic defects, and then the thermal excitation of dislocation pairs and disclinations. The intrinsic defect free center core has the highest melting temperature. It shows the sequential losses of translational and then orientational orders. PMID:11461324

Lai, Y J; I, L

2001-07-01

219

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

220

Thermal convection in Earth's inner core with phase change at its boundary  

NASA Astrophysics Data System (ADS)

Inner core translation, with solidification on one hemisphere and melting on the other, provides a promising basis for understanding the hemispherical dichotomy of the inner core, as well as the anomalous stable layer observed at the base of the outer core-the so-called F-layer-which might be sustained by continuous melting of inner core material. In this paper, we study in details the dynamics of inner core thermal convection when dynamically induced melting and freezing of the inner core boundary (ICB) are taken into account. If the inner core is unstably stratified, linear stability analysis and numerical simulations consistently show that the translation mode dominates only if the viscosity ? is large enough, with a critical viscosity value, of order ˜3 × 1018 Pa s, depending on the ability of outer core convection to supply or remove the latent heat of melting or solidification. If ? is smaller, the dynamic effect of melting and freezing is small. Convection takes a more classical form, with a one-cell axisymmetric mode at the onset and chaotic plume convection at large Rayleigh number. ? being poorly known, either mode seems equally possible. We derive analytical expressions for the rates of translation and melting for the translation mode, and a scaling theory for high Rayleigh number plume convection. Coupling our dynamic models with a model of inner core thermal evolution, we predict the convection mode and melting rate as functions of inner core age, thermal conductivity, and viscosity. If the inner core is indeed in the translation regime, the predicted melting rate is high enough, according to Alboussière et al.'s experiments, to allow the formation of a stratified layer above the ICB. In the plume convection regime, the melting rate, although smaller than in the translation regime, can still be significant if ? is not too small. Thermal convection requires that a superadiabatic temperature profile is maintained in the inner core, which depends on a competition between extraction of the inner core internal heat by conduction and cooling at the ICB. Inner core thermal convection appears very likely with the low thermal conductivity value proposed by Stacey & Loper, but nearly impossible with the much higher thermal conductivity recently put forward by Sha & Cohen, de Koker et al. and Pozzo et al. We argue however that the formation of an iron-rich layer above the ICB may have a positive feedback on inner core convection: it implies that the inner core crystallized from an increasingly iron-rich liquid, resulting in an unstable compositional stratification which could drive inner core convection, perhaps even if the inner core is subadiabatic.

Deguen, Renaud; Alboussière, Thierry; Cardin, Philippe

2013-09-01

221

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

222

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

223

Partial Melting of the Indarch (EH4) Meteorite : A Textural, Chemical and Phase Relations View of Melting and Melt Migration  

NASA Technical Reports Server (NTRS)

To Test whether Aubrites can be formed by melting of enstatite Chondrites and to understand igneous processes at very low oxygen fugacities, we have conducted partial melting experiments on the Indarch (EH4) chondrite at 1000-1500 C. Silicate melting begins at 1000 C. Substantial melt migration occurs at 1300-1400 C and metal migrates out of the silicate change at 1450 C and approx. 50% silicate partial melting. As a group, our experiments contain three immiscible metallic melts 9Si-, and C-rich), two immiscible sulfide melts(Fe-and FeMgMnCa-rich) and Silicate melt. Our partial melting experiments on the Indarch (EH4) enstatite Chondrite suggest that igneous processes at low fO2 exhibit serveral unique features. The complete melting of sulfides at 1000 C suggest that aubritic sulfides are not relicts. Aubritic oldhamite may have crystallized from Ca and S complexed in the silicate melt. Significant metal-sulfide melt migration might occur at relatively low degrees of silicate partial melting. Substantial elemental exchange occurred between different melts (e.g., between sulfide and silicate, Si between silicate and metal), a feature not observed during experiments at higher fO2. This exchange may help explain the formation of aubrites from known enstatite chondrites.

McCoy, Timothy J.; Dickinson, Tamara L.; Lofgren, Gary E.

2000-01-01

224

What controls dead-ice melting under different climate conditions?  

NASA Astrophysics Data System (ADS)

In the geological record, hummocky dead-ice moraines represent the final product of the melt-out of dead- ice. Processes and rates of dead-ice melting in ice-cored moraines and at debris-covered glaciers are commonly believed to be governed by climate. Here, backwasting rates from 14 dead-ice areas are assessed in relation to mean annual air temperature, mean summer air temperature, mean annual precipitation, mean summer precipitation, and the sum of degree days > 0 deg. C. The highest correlation was found between backwasting rate and mean annual air temperature. However, the correlation between melt rates and climate parameters is low, stressing that processes and topography play a major role in governing the rates of backwasting. The rates of dead-ice melting from modern glacial environments should serve as input to de-icing models for ancient dead-ice areas in order to assess the mode and duration of deposition. A challenge for future explorations of dead-ice environments is to obtain long-term records of field-based monitoring of melt progression. Furthermore, many modern satellite-borne sensors have high potentials for recordings of multi-temporal Digital Elevation Models (DEMs) for detection and quantification of changes in dead-ice environments. However, time series of high-resolution aerial photographs remain essential for both visual inspection and high-resolution stereographic DEM production. Reference: Schomacker, A. 2008. What controls dead-ice melting under different climate conditions? Earth- Science Reviews, in press.

Schomacker, A.

2008-12-01

225

Challenges in Melt Furnace Tests  

NASA Astrophysics Data System (ADS)

Measurement is a critical part of running a cast house. Key performance indicators such as energy intensity, production (or melt rate), downtime (or OEE), and melt loss must all be understood and monitored on a weekly or monthly basis. Continuous process variables such as bath temperature, flue temperature, and furnace pressure should be used to control the furnace systems along with storing the values in databases for later analysis. While using measurement to track furnace performance over time is important, there is also a time and place for short-term tests.

Belt, Cynthia

2014-09-01

226

Core formation in silicate bodies  

NASA Astrophysics Data System (ADS)

Differentiation of a body into a metallic core and silicate mantle occurs most efficiently if temperatures are high enough to allow at least the metal to melt [1], and is enhanced if matrix deformation occurs [2]. Elevated temperatures may occur due to either decay of short-lived radio-isotopes, or gravitational energy release during accretion [3]. For bodies smaller than the Moon, core formation happens primarily due to radioactive decay. The Hf-W isotopic system may be used to date core formation; cores in some iron meteorites and the eucrite parent body (probably Vesta) formed within 1 My and 1-4~My of solar system formation, respectively [4]. These formation times are early enough to ensure widespread melting and differentiation by 26Al decay. Incorporation of Fe60 into the core, together with rapid early mantle solidification and cooling, may have driven early dynamo activity on some bodies [5]. Iron meteorites are typically depleted in sulphur relative to chondrites, for unknown reasons [6]. This depletion contrasts with the apparently higher sulphur contents of cores in larger planetary bodies, such as Mars [7], and also has a significant effect on the timing of core solidification. For bodies of Moon-size and larger, gravitational energy released during accretion is probably the primary cause of core formation [3]. The final stages of accretion involve large, stochastic collisions [8] between objects which are already differentiated. During each collision, the metallic cores of the colliding objects merge on timescales of a few hours [9]. Each collision will reset the Hf-W isotopic signature of both mantle and core, depending on the degree to which the impactor core re-equilibrates with the mantle of the target [10]. The re-equilibration efficiency depends mainly on the degree to which the impactor emulsifies [11], which is very uncertain. Results from N-body simulations [8,12] suggest that significant degrees of re- equilibration are required [4,10]. Re-equilibration is also suggested by mantle siderophile abundances [13], though simple partitioning models do not capture the likely complex P,T evolution during successive giant impacts. The timescale of Martian core formation is currently uncertain (0-10 My) [14], though it is clear that Martian core formation ended before that of the Earth. [1] Stevenson, in Origin of the Earth, 1990. [2] Groebner and Kohlstedt, EPSL 2006. [3] Rubie et al., Treatise Geophys. 2007. [4] Kleine et al., GCA submitted. [5] Weiss et al., LPSC 39, 2008. [6] Keil and Wilson, EPSL 1993 [7] Wanke and Dreibus, PTRSL, 1984. [8] Agnor et al. Icarus 1999 [9] Canup and Asphaug, Nature 2001 [10] Nimmo and Agnor, EPSL 2006. [11] Rubie et al., EPSL 2003 [12] O'Brien et al, Icarus 2006 [13] Righter, AREPS 2003. [14] Nimmo and Kleine, Icarus 2007.

Nimmo, F.; O'Brien, D. P.; Kleine, T.

2008-12-01

227

Effective charges along the melting line of colloidal crystals.  

PubMed

The shear modulus G of charged colloidal crystals was measured at several constant particle densities n and varying salt concentrations c up to the melting salt concentration cM using torsional resonance spectroscopy. Far from the phase boundary the samples are polycrystalline and the shear modulus stays roughly constant as a function of c. Upon approaching the melting transition an increasing amount of wall based crystal material is formed surrounding a shrinking polycrystalline core and G drops nearly linearly. When the transition is complete G again stays constant. The morphologic transitions may be scaled upon a single master curve. For the polycrystalline morphology, the elastic data are evaluated in terms of a pairwise additive screened Coulomb interaction yielding a particle effective charge Z(G)*. Under de-ionized conditions Z(0,G)* is independent of n and significantly lower than expected from charge renormalization theory. With increasing salt concentration Z(G)* increases. The increase becomes more pronounced at larger n. By extrapolation we further obtain the melting line effective elasticity charge Z(M,G)*. Z(M,G)* shows a steplike increase with increasing nM and cM to values consistent with charge renormalization theory. Interestingly, the increase coincides semi-quantitatively with the one expected from the universal melting line for charged spheres, thus facilitating a consistent description of phase behavior and elasticity over an extended range of the phase diagram. PMID:17129157

Shapran, Larysa; Schöpe, Hans Joachim; Palberg, Thomas

2006-11-21

228

Possible use of Skull melting under microgravity  

NASA Astrophysics Data System (ADS)

Skull melting is a special kind of direct inductive heating which allows quasi-crucible-free processing of materials with very high melting points (3000 K and above). Under terrestrial gravity, the temperature gradients essential to the Skull technique cause buoyancy driven convection in the melt, which might interfere with crystal growth. Skull melting could therefore benefit from processing in a microgravity environment. We report on results of a joint project under contract with the European Space Research and Technology Centre (ESTEC), which has evaluated the possible use of Skull melting in microgravity from two main viewpoints: the power efficiency and the expected effects of ?g environment on melt convection.

Gross, C.; Assmus, W.; Muiznieks, A.; Mühlbauer, A.; Stenzel, C.; Schulz, O.

1999-03-01

229

Melting curve of black phosphorous  

NASA Astrophysics Data System (ADS)

The melting curve of black phosphorus has been determined up to 5 GPa by a high-pressure high-temperature X-ray system using synchrotron radition. The curve has a maximum at 1 GPa and joins the orthorhombic-rhombohedral phase boundary at a triple point around 2.7 GPa and 900°C.

Akahama, Y.; Utsumi, W.; Endo, S.; Kikegawa, T.; Iwasaki, H.; Shimomura, O.; Yagi, T.; Akimoto, S.

1987-06-01

230

Transcrystalline melt migration in clinopyroxene  

NASA Astrophysics Data System (ADS)

Glass inclusions in clinopyroxene phenocrysts from La Sommata (Vulcano Island, Aeolian Arc) were reheated and submitted to a sustained thermal gradient. Each remelted inclusion undergoes a transient textural and chemical reequilibration and concomitantly begins to migrate along a crystallographic direction, at a small angle with the thermal gradient. The completion of morphological evolution requires a characteristic time that is governed by chemical diffusion. Chemical reequilibration results in the formation of a colored halo that delineates the former location and shape of the inclusion after it has migrated away. Transcrystalline migration proceeds by dissolution of the host clinopyroxene ahead and precipitation astern. Its rate is not limited by Fick's law, but by the crystal-melt interface kinetics. Clinopyroxene dissolution and growth are slower than for olivine in similar conditions but obey the same analytical law, which can be transposed to equally or more sluggish melting or crystallization events in nature. When a gas bubble is initially present, it responds to elastic forces by quickly shifting toward the cold end of the inclusion, where it soon becomes engulfed as an isolated fluid inclusion in the reprecipitated crystal. This study confirms that transcrystalline melt migration, beside its possible implications for small-scale melt segregation and fluid-inclusion generation in the Earth's mantle, provides an experimental access to interfacial kinetic laws in near-equilibrium conditions.

Sonzogni, Yann; Provost, Ariel; Schiano, Pierre

2011-03-01

231

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

232

Elongational rheology of polyethylene melts  

NASA Astrophysics Data System (ADS)

Elongational melt flow behavior is an important and fundamental concept underlying many industrial plastics operations which involve a rapid change of shape as for example fiber spinning and stretching, bottle blow molding, and film blowing and stretching. Under high process loads polymeric materials experience enormous stresses causing the molecular structure to gain considerable orientation. This event has significant effects on the melt flow behavior and can be measured in terms of elongational viscosity and changes in enthalpy and entropy. Different polymeric materials with unique molecular characteristics are expected to respond uniquely to the elongational deformation; hence, molecular parameters such as molecular weight and degree of branching were related to the measurable elongational flow variables. Elongational viscosities were measured for high and low density polyethylenes using an advanced capillary extrusion rheometer fitted with semi-hyperbolic dies. Said dies establish a purely elongational. flow field at constant elongational strain rate. The elongational viscosities were evaluated under influence of process strain rate, Hencky strain (natural logarithm of area reduction of the extrusion die), and temperature. Enthalpy and entropy changes associated with the orientation development of semi-hyperbolic processed melts were also determined. Results showed that elongational viscosities were primarily affected by differences in weight average molecular weight rather than degree of branching. This effect was process strain rate as well as temperature dependent. An investigation of melt relaxation and the associated first decay time constants revealed that with increasing strain rate the molecular field of the melt asymptotically gained orientation in approaching a limit. As a result of this behavior molecular uniqueness vanished at high process strain rates, yielding to orientation development and the associated restructuring of the melt's molecular morphology. Flow induced orientation was measured in form of enthalpy changes that were largest for the highest elongational strain rates and larger Hencky strain. The enthalpy changes were in magnitude one order lower than the polymer's heat of fusion. This explained why peak melt temperatures, evaluated by differential scanning calorimetry, remained unchanged in magnitude with a rise in process strain rate and Hencky strain.

Seyfzadeh, Bijan

233

Redox viscometry of ferropicrite melt  

NASA Astrophysics Data System (ADS)

The rheology governs the dynamics of magmas at all scales (i.e. partial melting, magmatic chamber emplacement, lava flow behavior). It is also a fundamental constraint on volcanic morphology and landforms. Most terrestrial volcanic flows have moderate iron contents up to 10 wt% but some basalts show contain up to 16 wt%. These ferropicrites range from the Archean to recent, typically forming thin isolated flows near the base of thick lava piles in large igneous provinces, are not well understood. Although ferropicrites are rare on Earth's surface they are believed to be abundant on Mars. Analyses of Martian rocks (from remote sensing data, in situ measurements and meteorite analyses) display up to 20 wt% FeO. Studying these compositions will help to constrain the physical nature and evolution of the volcanism on Mars. The influence of iron on the structure and properties of magmatic melts, remains controversial. Simple system investigations indicate an as yet insufficiently parameterized influence of the oxidation state of iron on the rheology and other properties of silicate melts. The dependence of shear viscosity on the oxidation state of ferrosilicate melts has been measured using the concentric cylinder method and a gas mixing furnace. Previously, two different simple Fe-bearing systems have been studied: (i) anorthite-diopside eutectic composition (AnDi) with variable amount of Fe (up to 20 wt%) as a basalt analog and (ii) sodium disilicate (NS2) with up to 30 wt % Fe. Two natural compositions have been previously investigated, a phonolite and a pantellerite. Here, the compositional range has been extended to the more complex ferropicrite composition using the Adirondack class rock, a typical martian basalt (with low Al content and Fe up to 18,7 wt%). The experimental procedure involves a continuous measurement of viscosity at constant temperature during stepwise reduction state. The melt is reduced by flowing CO2 and then successively reducing mixtures of CO2-CO. The composition and oxidation state of the melt is monitored by obtaining a melt sample after each redox equilibrium step. The melts are sampled by dipping an alumina rod into the sample and drawing out a drop of liquid, which is then plunged into water for quenching. The resulting glasses are analyzed by electron microprobe, and the volumetric potassium dichromate titration is employed to determine FeO content. So far we observed a very low viscosity for high iron content samples and a decrease of the viscosity with increasing Fe content. Moreover, the viscosity of all melts investigated to date decreases with melt reduction. The viscosity decrease is, in general, a nonlinear function of oxidation state expressed as Fe2+/Fetot and can be fitted using logarithmic equation. The range of viscosity is compared to previous experimental studies and will help to understand morphological observations.

Oryaëlle Chevrel, Magdalena; Potuzak, Marcel; Dingwell, Donald B.; Hess, Kai-Uwe

2010-05-01

234

Modeling and database for melt-water interfacial heat transfer  

SciTech Connect

A mechanistic model is developed to predict the transition superficial gas velocity between bulk cooldown and crust-limited heat transfer regimes in a sparged molten pool with a coolant overlayer. The model has direct applications in the analysis of ex-vessel severe accidents, where molten corium interacts with concrete, thereby producing sparging concrete decomposition gases. The analysis approach embodies thermal, mechanical, and hydrodynamic aspects associated with incipient crust formation at the melt/coolant interface. The model is validated against experiment data obtained with water (melt) and liquid nitrogen (coolant) simulants. Predictions are then made for the critical gas velocity at which crust formation will occur for core material interacting with concrete in the presence of water.

Farmer, M.T.; Spencer, B.W. (Argonne National Lab., IL (United States)); Schneider, J.P. (Illinois Univ., Urbana, IL (United States)); Bonomo, B. (Northwestern Univ., Evanston, IL (United States)); Theofanous, G. (California Univ., Berkeley, CA (United States))

1992-01-01

235

Modeling and database for melt-water interfacial heat transfer  

SciTech Connect

A mechanistic model is developed to predict the transition superficial gas velocity between bulk cooldown and crust-limited heat transfer regimes in a sparged molten pool with a coolant overlayer. The model has direct applications in the analysis of ex-vessel severe accidents, where molten corium interacts with concrete, thereby producing sparging concrete decomposition gases. The analysis approach embodies thermal, mechanical, and hydrodynamic aspects associated with incipient crust formation at the melt/coolant interface. The model is validated against experiment data obtained with water (melt) and liquid nitrogen (coolant) simulants. Predictions are then made for the critical gas velocity at which crust formation will occur for core material interacting with concrete in the presence of water.

Farmer, M.T.; Spencer, B.W. [Argonne National Lab., IL (United States); Schneider, J.P. [Illinois Univ., Urbana, IL (United States); Bonomo, B. [Northwestern Univ., Evanston, IL (United States); Theofanous, G. [California Univ., Berkeley, CA (United States)

1992-04-01

236

Osmium Solubility in Silicate Melts: New Efforts and New Results  

NASA Technical Reports Server (NTRS)

In a recent paper, Borisov and Palme reported the first experimental results on the partitioning of Os between metal (Ni-rich OsNi alloys) and silicate melt of anorthite-diopside eutectic composition at 1400 C and 1 atm total pressure and and at function of O2 from 10(exp -8) to 10(exp -12) atm. Experiments were done by equilibrating OsNi metal loops with silicate melt. Metal and glass were analyzed separately by INAA. D(sup 0s) ranged from 10(exp 6) to 10(exp 7), which is inconsistent with core/ mantle equilibrium for HSEs and favors the late veneer hypothesis. Unfortunately, there was practically no function of O2 dependence of Os partitioning, and the scatter of experimental results was quite serious, so the formation of Os nuggets was suspected. This new set of experiments was specifically designed to avoid of at least minimize the nugget problem

Borisov, A.; Walker, R. J.

1998-01-01

237

Formation of pseudotachylitic breccias in the central uplifts of very large impact structures: Scaling the melt formation  

NASA Astrophysics Data System (ADS)

The processes leading to formation of sometimes massive occurrences of pseudotachylitic breccia (PTB) in impact structures have been strongly debated for decades. Variably an origin of these pseudotachylite (friction melt)-like breccias by (1) shearing (friction melting); (2) so-called shock compression melting (with or without a shear component) immediately after shock propagation through the target; (3) decompression melting related to rapid uplift of crustal material due to central uplift formation; (4) combinations of these processes; or (5) intrusion of allochthonous impact melt from a coherent melt body has been advocated. Our investigations of these enigmatic breccias involve detailed multidisciplinary analysis of millimeter- to meter-sized occurrences from the type location, the Vredefort Dome. This complex Archean to early Proterozoic terrane constitutes the central uplift of the originally >250 km diameter Vredefort impact structure in South Africa. Previously, results of microstructural and microchemical investigations have indicated that formation of very small veinlets involved local melting, likely during the early shock compression phase. However, for larger veins and networks it was so far not possible to isolate a specific melt-forming mechanism. Macroscopic to microscopic evidence for friction melting is very limited, and so far chemical results have not directly supported PTB generation by intrusion of impact melt. On the other hand, evidence for filling of dilational sites with melt is abundant. Herein, we present a new approach to the mysterium of PTB formation based on volumetric melt breccia calculations. The foundation for this is the detailed analysis of a 1.5 × 3 × 0.04 m polished granite slab from a dimension-stone quarry in the core of the Vredefort Dome. This slab contains a 37.5 dm3 breccia zone. The pure melt volume in 0.1 m3 PTB-bearing granitic target rock outside of the several-decimeter-wide breccia zone in the granite slab was estimated at 5.2 dm3. This amount can be divided into 4.6 dm3 melt (88%), for which we have evidenced a limited material transport (at maximum, ?20 cm) and 0.6 dm3 melt (12%) with, at most, grain-scale material transport, which we consider in situ formed shock melt. The breccia zone itself contains about 10 dm3 of matrix (melt). Assuming melt exchange over 20 cm at the slab surface, between breccia zone and surrounding melt-bearing host rock volume, the outer melt volume is calculated to contain the same amount of melt as contained by the massive breccia zone. Meso- and microscopic observations indicate melt transport is more prominent from larger into smaller melt occurrences. Thus, melt of the breccia zone could have provided the melt fill for all the small-scale PTB veins in the surrounding target rock. Extrapolating this melt capacity calculation for 1 m3 PTB-bearing host rock shows that a host rock volume of this dimension is able to take up some 52 dm3 melt. Scaling up 1000-fold to the outcrop scale reveals that exchange between a host rock volume of 2 m radius around a 37 m3 breccia zone could involve some 10 m3 melt. These results demonstrate that large melt volumes (i.e., large breccia zones) can be derived, in principle, from local reservoirs. However, strong decompression would have to apply in order to exchange these considerable melt volumes, which would only be realistic during the decompression phase of impact cratering upon central uplift formation, or locally where compressive regimes acted during the subsequent down- and outward collapse of the central uplift.

Mohr-Westheide, Tanja; Reimold, Wolf Uwe

2011-04-01

238

Melt Fracture Revisited J. M. Greenberg #;  

E-print Network

the melt fracture instability observed when molten linear polymer melts are extruded in a cap- illary death is sadly mourned. #3; This research was partially supported by the Applied Mathematical Sciences

239

Summary of the first three in-core PAHR molten fuel pool experiments  

Microsoft Academic Search

Results from the first three Sandia in-core molten pool experiments are reviewed. Incipient melt of a fully enriched dry bed of UO was achieved in the first experiment while 30g of UO was melted in the second. The melting region developed a void surrounded by a dense crust as indicated by post-test x-radiographs. In the third experiment, a steel layer

H. G. Plein; R. J. Lipinski; G. A. Carlson; D. W. Varela

1979-01-01

240

Two-Stage Melting Of Mantle Plumes And The Origin Of Rejuvenescent Volcanism On Oceanic Islands  

NASA Astrophysics Data System (ADS)

Many mid-plate oceanic volcanoes experience a rejuvenescent, or "post-erosional" phase of volcanism that occurs hundreds of thousands or million years after the main shield-building phase of volcanism has ended. The Hawaiian Islands are the best-documented example, but rejuvenescent volcanism also occurs on the Society Islands, the Marquesas, the Australs, Samoa, and Mauritius. It does not occur on near-ridge islands such as the Galapagos, the Azores, and Iceland. Rejuvenescent lavas have a number of features in common: they are erupted in small volumes, they are highly enriched in incompatible elements, and they are highly alkalic, typically basanitic to nephelenitic. All these features suggest they are quite small degree melts. In addition, rejuvenescent magmas have more depleted isotopic signatures, implying they are melts of more depleted sources, despite their strong incompatible element enrichment. Although isotopic signatures of these lavas are more depleted that those of the corresponding shield stage lavas, they are nevertheless not as depleted as MORB. Furthermore, the isotopic compositions of the rejuvenescent magmas rule out their sources being mixtures of plume material and MORB-source material. Thus geochemical considerations rule out both the lithosphere and the asthenosphere surrounding the plume as the source of rejuvenescent magmas; this implies the plume itself must be the source of rejuvenescent magmas. This conclusion is consistent with geophysical models of plumes. Finite difference numerical models of plume-lithosphere interaction that include both temperature and compositional viscosity dependence reveal that while most melting is concentrated above the hot core of the plume, a melting "tail" extends hundreds of km downstream. In this tail region, lateral spreading of the plume results in a slight rising motion of the plume, and consequently, small extents of melting. The problem thus becomes that of deciphering why melts produced in this tail region are isotopically distinct from those produced in the main melting region. We propose the following model to explain this difference: Mantle plumes are lithologically heterogeneous, consisting of eclogite or pyroxenite "plums" that have a solidus temperature several tens of degrees lower than the more refractory peridotite "pudding" in which they are embedded. Complete isotopic equilibrium is not achieved during melting - either because the plums are large enough (>10-100m) or the extraction of plum melts is rapid after their generation. Both the plums and the peridotite are incompatible-element enriched relative to the average depleted upper mantle, but the plums are substantially more enriched. The plums melt entirely in the base of the main melting region and the heat so consumed initially suppresses melting of the peridotite pudding. Plum-derived melts mix as they rise with melts of the peridotite pudding produced higher in the main melting region. This mixture of eclogitic and peridotitic melts form the shield stage magmas. Material in the melting "tail" has had the plums melted out of it in the main melting region. Low degree melting of the plum-free peridotite in the melting tail gives rise to rejuvenescent magmas. Melt production in the tail is more or less continuous, but rejuvenescent volcanism is not. This suggests that some other factor is involved, such as lithospheric loading by adjacent volcanoes, that provides pathways to the surface for small degree tail melts.

White, W. M.; Morgan, J. P.

2004-12-01

241

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

242

Core and early crust formation on Mars  

NASA Astrophysics Data System (ADS)

One of the most striking surface features on Mars is the crustal dichotomy. It is the oldest geological feature on Mars and was formed more than 4.1 Ga ago by either exogenic or endogenic processes [1,2]. In order to find an internal origin of the crustal dichotomy, located within a maximum of 400 Ma of planetary differentiation, the thermal state of the planet resulting from core formation needs to be considered. Additionally, it was suggested that a primordial crust with up to 45 km thickness can be formed already during the Martian core formation [3]. We suggest that the sinking of iron diapirs delivered by predifferentiated impactors induced impact- and shear heating-related temperature anomalies in the mantle that fostered the formation of early Martian crust. Thus, the crustal thickness distribution would largely be a result of planetary core formation, late impact history and the onset of mantle convection. To test this hypothesis we use numerical models to simulate the formation of the Martian iron core and the resulting mantle convection pattern, while peridotite melting is enabled to track melting caused by shear and radioactive heating. We perform 2D simulations using the spherical-Cartesian code I2ELVIS for planetary accretion and the spherical code STAGYY for the consequent onset of mantle convection. We apply a temperature-, stress- and melt-fraction dependent viscoplastic rheology. Radioactive and shear heating as well as consumption of latent heat by silicate melting are taken into account. The depth of neutral buoyancy of silicate melt with respect to solid silicates is determined by the difference in compressibility of the liquid and solid phase. To self-consistently simulate the silicate phase changes expected inside a Mars-sized body, we use the thermodynamical database Perple_X. As initial condition for core formation, we apply randomly distributed iron diapirs with 75 km radius inside the planet, representing the cores of stochastically distributed impactors. Additionally, we explore the effect of one giant impactor core on the planetary evolution. Results indicate that the presence of a large impactor core induces hemispherically asymmetrical core formation. The amplitude of shear heating anomalies often exceeds the solidus of primitive mantle material and thus, the formation of a considerable amount of silicate melt is observed. The resulting temperature field after core formation is then read into the mantle convection code STAYY. The hemispherical magma ocean induced by one late giant impactor favours a dichotomous crust formation during and shortly after core formation. Afterwards, the extraction of excess heat produced by the sinking of the giant impactor through the mantle leads to a localized region of massive magmatism, comparable to Tharsis, which is sustained during later evolution by a single plume forming beneath the province. The rest of the mantle is dominated by a sluggish convection pattern with limited crust formation that preserves the early formed dichotomous crustal structure until recent time. References [1] Nimmo, F. et al., Nature, 453, 1220-1223, 2008. [2] Keller, T. & Tackley, P.J., Icarus, 202, 429-443, 2009. [3] Norman, M.D., Meteorit. Planet. Sci., 34, 439-449, 1999.

Golabek, G. J.; Keller, T.; Gerya, T.; Tackley, P. J.; Connolly, J.; Zhu, G.

2010-12-01

243

Climate variability, warming and ice melt on the Antarctic Peninsula over the last millennium (Invited)  

NASA Astrophysics Data System (ADS)

The Antarctic Peninsula has experienced rapid warming over the past 50 years, which has led to extensive summer ice melt, the collapse of ice shelves and the acceleration of glacial outflow. But the short observational records of Antarctic climate don't allow for an understanding of how unusual the recent conditions may be. We present reconstructions of temperature and melt history since 1000 AD from a highly resolved ice core record from James Ross Island on the northeastern Antarctic Peninsula. The spatial pattern of temperature variability across networks of palaeoclimate reconstructions demonstrates that the Southern Annular Mode (SAM) has been an important driver of Antarctic Peninsula climate variability over a range of time scales. Rapid warming of the Antarctic Peninsula since the mid-20th century is consistent with strengthening of the SAM by a combination of greenhouse and later ozone forcing. The rare reconstruction of summer melting, from visible melt layers in the ice core, demonstrates the non-linear response of ice melt to increasing summer temperatures. Melting in the region is now more intense than at any other time over the last 1000 years and suggests that the Antarctic Peninsula is now particularly susceptible to rapid increases in ice loss in response to relatively small increases in mean temperature.

Abram, N.; Mulvaney, R.; Wolff, E. W.; Triest, J.; Kipfstuhl, S.; Trusel, L. D.; Vimeux, F.; Fleet, L.; Arrowsmith, C.

2013-12-01

244

Melt transport - a personal cashing-up  

Microsoft Academic Search

The flow of fluids through rocks transports heat and material and changes bulk composition. The large-scale chemical differentiation of the Earth is related to flow of partial melts. From the perspective of current understanding of tectonic processes, prominent examples of such transport processes are the formation of oceanic crust from ascending basic melts at mid-ocean ridges, melt segregation involved in

J. Renner

2005-01-01

245

How Does Melting Ice Affect Sea Level?  

NSDL National Science Digital Library

In this activity, students investigate how sea levels might rise when ice sheets and ice caps melt by constructing a pair of models and seeing the effects of ice melt in two different situations. Students should use their markers to predict the increase of water in each box before the ice melts.

Dahlman, Luann; Andrill

246

Model for disequilibrium mantle melting incorporating melt transport by porous and channel flows  

Microsoft Academic Search

Attempts to understand melt transport in the Earth's mantle have focused on the two mechanisms of porous flow along grain boundaries and channel flow in fractures. To elucidate the contributions of these segregation processes to the chemical evolution of melt and solid, I have developed a disequilibrium melting model for a one-dimensional upwelling mantle in which melt is produced, transported

Hikaru Iwamori

1993-01-01

247

The influence of melting and melt drainage on crustal rheology during orogenesis  

NASA Astrophysics Data System (ADS)

Partial melting significantly weakens crustal rocks by introducing a low-viscosity liquid phase. However, near-concomitant melt drainage can remove this weak phase, potentially reversing the rheological effects such that the strength of a specific lithology depends on when the prograde pressure-temperature path intersects a melting reaction, how much melt is produced, and how long this melt is retained before it is lost. Phase equilibria and mixed rheology modeling of typical metapelite and metagreywacke compositions indicate that these rocks undergo continuous but pulsed melt production during prograde metamorphism. Depending on whether melt removal is continuous or episodic, and assuming geological strain rates, the lithologies can retain a very low strength less than 1 MPa or transiently strengthen to ˜5 MPa following melt loss. Lithologies undergoing episodic melt loss can therefore cycle between being relatively weak and relatively strong components within a composite crustal section. Melt production, retention, and weakening in the middle to lower crust as a whole is more sustained during heating and melt production, consistent with geodynamic inferences of weak, melt-bearing lower crust. However, the long-term consequence of melting and melt loss is a 50-400% increase in the strength of residual lithologies. The strengthening is more pronounced in metapelite than metagreywacke and is achieved through a combination of dehydration and the removal of the weak mica framework coupled to increased proportions of strong feldspars and garnet. Despite prolonged weakness, melting and melt loss therefore ultimately result in a dry and elastic lower crust.

Diener, Johann F. A.; Fagereng, Åke

2014-08-01

248

Experimental methods for determining the melting temperature and the heat of melting of clusters and nanoparticles  

Microsoft Academic Search

Unlike macroscopic objects, clusters and nanoparticles lack a definite melting temperature at a given pressure but rather have their solid and liquid phases coexistent in a certain temperature range and their melting temperature dependent on the particle size. As the particle size decreases, the melting temperature becomes fundamentally difficult to define. This review examines methods for measuring the melting temperature

Grigorii N Makarov

2010-01-01

249

How does the mantle melt?How does the mantle melt? 1) Increase the temperature  

E-print Network

the temperatureMelting by raising the temperature Solidus: Temperature of melting, increases with depth (P) #12 the solidus and traverses the shaded melting interval. Dashed lines represent approximate % melting. http amphibole, mica, serpentine minerals in subducting crust · Lowers solidus of overlying mantle · Magmas

Siebel, Wolfgang

250

Crystal melting on toric surfaces  

E-print Network

We study the relationship between the statistical mechanics of crystal melting and instanton counting in N=4 supersymmetric U(1) gauge theory on toric surfaces. We argue that, in contrast to their six-dimensional cousins, the two problems are related but not identical. We develop a vertex formalism for the crystal partition function, which calculates a generating function for the dimension 0 and 1 subschemes of the toric surface, and describe the modifications required to obtain the corresponding gauge theory partition function.

Michele Cirafici; Amir-Kian Kashani-Poor; Richard J. Szabo

2009-12-04

251

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

252

Melting and unzipping of DNA  

NASA Astrophysics Data System (ADS)

Existing experimental studies of the thermal denaturation of DNA yield sharp steps in the melting curve suggesting that the melting transition is first order. This transition has been theoretically studied since the early sixties, mostly within an approach in which the microscopic configurations of a DNA molecule consist of an alternating sequence of non-interacting bound segments and denaturated loops. Studies of these models neglect the repulsive, self-avoiding, interaction between different loops and segments and have invariably yielded continuous denaturation transitions. In the present study we take into account in an approximate way the excluded-volume interaction between denaturated loops and the rest of the chain. This is done by exploiting recent results on scaling properties of polymer networks of arbitrary topology. We also ignore the heterogeneity of the polymer. We obtain a first-order melting transition in d = 2 dimensions and above, consistent with the experimental results. We also consider within our approach the unzipping transition, which takes place when the two DNA strands are pulled apart by an external force acting on one end. We find that the under equilibrium condition the unzipping transition is also first order. Although the denaturation and unzipping transitions are thermodynamically first order, they do exhibit critical fluctuations in some of their properties. For instance, the loop size distribution decays algebraically at the transition and the length of the denaturated end segment diverges as the transition is approached. We evaluate these critical properties within our approach.

Kafri, Y.; Mukamel, D.; Peliti, L.

2002-05-01

253

Melt propagation and volcanism in mantle convection simulations, with applications for Martian volcanic and  

E-print Network

) for an intermediate Martian solidus. Core-mantle temperatures cannot exceed $1850°C from geodynamo constraints volcanic degassing to evolving mantle temperatures. Here we use a range of thermal, geophysical, geological-Noachian stagnant lid evolution. We develop a methodology to self-consistently calculate melt extraction from

Jellinek, Mark

254

Melt-Enhanced Rejuvenation of Lithospheric Mantle: Insights from the Colorado Plateau  

E-print Network

The stability of the lithospheric mantle beneath the ancient cratonic cores of continents is primarily a function of chemical modification during the process of melt extraction. Processes by which stable continental lithosphere may be destabilized are not well-understood, although destabilization by thickening and removal of negatively-buoyant lithospheric mantle in "delamination" events has been proposed in a number of tectonic settings. In this paper we explore an alternative process for destabilizing continents, namely, thermal and chemical modification during infiltration of metasomatic fluids and melts into the lithospheric column. We consider observations pertinent to the structure and evolution of the Colorado Plateau within the western United States to argue that the physical and chemical state of the margins of the plateau have been variably modified and destabilized by interaction with melts. In the melt-infiltration process explored here, the primary mechanism for weakening and rejuvenating the pla...

Roy, Mousumi; Holtzman, Ben; Gaherty, James

2012-01-01

255

String melting in a photon bath  

SciTech Connect

We compute the decay rate of a metastable cosmic string in contact with a thermal bath by finding the instanton solution. The new feature is that this decay rate is found in the context of non thermal scalar fields in contact with a thermal bath of photons. In general, to make topologically unstable strings stable, one can couple them to such a bath. The resulting plasma effect creates metastable configurations which can decay from the false vacuum to the true vacuum. In our specific set-up, the instanton computation is realized for the case of two out-of-equilibrium complex scalar fields: one is charged and coupled to the photon field, and the other is neutral. New effects coming from the thermal bath of photons make the radius of the nucleated bubble and most of the relevant physical quantities temperature-dependent. However, the temperature appears in a different way than in the purely thermal case, where all scalar fields are in thermal equilibrium. As a result of the tunneling, the core of the initial string melts while bubbles of true vacuum expand at the speed of light.

Karouby, Johanna, E-mail: karoubyj@mit.edu [Center for Theoretical Physics and Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachussetts 02139 (United States)

2013-10-01

256

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

257

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

258

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

259

Modes of Planetary Reshaping During Core Formation: Numerical Study  

Microsoft Academic Search

The early stages of terrestrial planetary accretion and differentiation related to core formation are largely enigmatic and require extensive realistic numerical modelling efforts especially in 2D(a cross-section of a spherical planet) and 3D geometries. One early stage of terrestrial planets was assumed to have a gravitationally unstable three-layer structure, the innermost undifferentiated solid core, the intermediate metal-melt layer, and the

J. Lin; T. V. Gerya; P. J. Tackley; D. A. Yuen

2007-01-01

260

Late Cretaceous rift-related upwelling and melting of the Trindade starting mantle plume head beneath western Brazil  

NASA Astrophysics Data System (ADS)

High mantle potential temperatures and local extension, associated with the Late-Cretaceous impact of the Trindade mantle plume, produced substantial widespread and voluminous magmatism around the northern half of the Paraná sedimentary basin. Our previous studies have shown that, above the central and eastern portions of the postulated impact zone where lithosphere extension is minimal, heat conducted by the plume caused large-scale melting of the more fusible parts of the subcontinental lithospheric mantle beneath the margin of the São Francisco craton and the surrounding Brasilía mobile belt. Here we combine geochemical data and field evidence from the Poxoreu Igneous Province, western Brazil to show how more intense lithospheric extension above the western margin of the postulated impact zone permitted greater upwelling and melting of the Trindade plume than further east. Laser 40Ar/39Ar age determinations indicate that rift-related basaltic magmas of the Poxoreu Igneous Province were emplaced at 84 Ma. Our detailed geochemical study of the mafic magmas shows that the parental melts underwent polybaric crystal fractionation within the crust prior to final emplacement. Furthermore, some magmas (quartz-normative) appear to have assimilated upper crust whereas others (nepheline- and hypersthene-normative) appear to have been unaffected by open-system crustal magma chamber processes. Incompatible trace element ratios (e.g. chondrite-normalised La/Nb=1) and isotopic ratios (87Sr/86Sr=0.704 and 143Nd/144Nd=0.51274) of the Hy-normative basalts resemble those of oceanic islands (OIB). We therefore propose that these ``OIB-like'' magmas were predominantly derived from convecting-mantle-source melts (i.e. Trindade mantle plume). Inverse modelling of rare-earth element (REE) abundances suggests that the initial melts were predominantly generated within the depth range of 80-100 km, in mantle with a potential temperature of 1500 °C.

Gibson, S. A.; Thompson, R. N.; Weska, R. K.; Dickin, A. P.; Leonardos, O. H.

261

Theory of melting and crystallization  

SciTech Connect

A consistent statistical theory of the crystal-liquid phase transition is developed, being based on a method which takes into account liquidlike fluctuations in crystals and solidlike clusters in liquids. It is shown that degenerate fluidlike droplets have a finite number density at zero temperature, while nondegenerate fluctuations disappear when the temperature goes to zero. The existence of a melting point is proved. This method, which takes into consideration the heterophase fluctuations, provides the possibility of describing metastable states such as a supercooled liquid or an overheated crystal. Conditions for the existence of metastable states are found. The liquid-glass transition can also be described by the method presented here.

Yukalov, V.I.

1985-07-01

262

Nepafenac-associated corneal melt.  

PubMed

We describe a patient with systemic graft-versus-host disease who developed a nonhealing epithelial defect after cataract surgery that healed on cessation of a topical nonsteroidal antiinflammatory drug (NSAID) (ketorolac). The patient developed a central corneal perforation in the fellow eye while on a new NSAID formulation (nepafenac) after routine cataract surgery. Our case suggests that new topical NSAIDs may be similar to older NSAID formulations in promoting corneal melting in patients predisposed to poor epithelialization and corneal wound healing. PMID:17964407

Wolf, Eric Jay; Kleiman, Lynda Z; Schrier, Amilia

2007-11-01

263

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

264

Polymer micelles with crystalline cores for thermally triggered release.  

PubMed

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, M(n) ? 2000. 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 that 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

2012-07-24

265

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

NASA Astrophysics Data System (ADS)

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; Chen, Di; Wang, Jing; Shao, Lin

2014-04-01

266

Melting phase relations in the MgO-MgSiO3 system between 16 and 26 GPa: Implications for melting in Earth's deep interior  

NASA Astrophysics Data System (ADS)

Geochemical and geophysical questions relating to the formation and crystallisation of a global Hadean magma ocean, and present day melting at the core-mantle boundary (CMB), require knowledge of melting temperatures of mantle or bulk Earth compositions at mid- or lower mantle pressures. However, a number of experimental problems complicate precise determination of solidus and liquidus phase relations and temperatures for bulk silicate earth compositions at these pressures. These problems are mainly due to the presence of thermal gradients in high pressure experiments. Here, we present high quality melting experiments in the system MgO-MgSiO3 to study the eutectic melt composition and phase relations between 16 and 26 GPa using a mutlianvil apparatus. By employing a multi-chamber capsule design, several different starting compositions could be run at a single pressure and temperature and internally consistent phase relations and liquidus compositions were obtained. Additional experiments were carried out to determine the effect of FeO on melting relations and temperatures. A simple thermodynamic model is developed to describe the observed melting phase relations and eutectic compositions in the MgO-MgSiO3 binary. The model is based on equations of states from the literature to describe melting curves of end-members and a simple symmetric liquid mixing model. It is shown that melting relations of a natural peridotite composition at high pressure can be well described on the basis of the simple binary, particularly once the effects of FeO on phase relations and melting temperatures are considered. The thermodynamic model, extrapolated to 140 GPa, predicts that the eutectic composition becomes richer in MgO up to about 80 GPa, where it becomes near constant with pressure and has a Mg/Si ratio close to that of a peridotite composition. By applying a correction to account for the effect of FeO on the melting temperatures, the model predicts that the solidus and liquids for a peridotitic composition are never more than 250 K apart. The results can be used to examine a partial melt origin for the existence of localised zones with ultra low shear wave velocities (ULVZ) at the CMB. The solidus temperature of peridotitic mantle at the CMB is estimated to be 4400 K, which would require temperatures at the CMB to be at the very top end of the estimated range for melting to occur. The proximity of the solidus and liquidus temperature implies that large melt fractions could form over small depth intervals as a result of relatively small increases in either temperature or FeO content. This is consistent with a seismically sharp transition in the upper boundary of ULVZ. Given the high temperatures required to melt peridotite at the CMB, a partial melt origin due to raised FeO contents seems more likely. A further application of the data concerns the crystallisation of a magma ocean during early stages of the Earth. The thermodynamic model allows isentropes of a model magma ocean to be calculated, which can be used to estimate depth intervals between the onset of crystallisation and complete solidification as well as liquid fractions in between. Such data may be useful for a more detailed understanding of magma ocean dynamics or the kinetics of element partitioning between core-forming liquids and the silicate Earth.

Liebske, C.; Frost, D. J.

2012-12-01

267

Modelling the Composition of Melts Formed During Continental Breakup of the North Atlantic  

NASA Astrophysics Data System (ADS)

We have developed a generic dynamic model of extension of the lithosphere. Major element composition and volume of melt generated can be predicted from initial extension to steady state seafloor spreading. Stokes equations for non-Newtonian flow are solved, where mantle melts by decompression. Strengthening of the mantle due to dehydration as melting progresses is included. Composition is then empirically related to depletion. Using a fractional crystallisation algorithm, the predicted primitive melt composition was compared with mean North Atlantic mid-ocean ridge basalt (MORB). At steady state, we predict a major element composition that is within the variation in the mean of North Atlantic MORB for half spreading rates from 10 to 20 mm yr-1 and mantle potential temperatures of 1275 to 1350 °C. We then apply the model to the Southeast Greenland margin, which has extensive coverage of seismic and ODP core data. An initial pulse of magmatism on rifting rapidly decayed to leave oceanic crustal thickness of 6 to 7 km. This pattern of melt production can be recreated by introducing a hot layer of asthenosphere beneath the continental lithosphere within the initial condition. The hot layer is convected through the melt region giving a pulse of high magnesian (peak of 18.44 %) and low silica melt (trough of 46.99 %) during the early rifting process. These results are very encouraging as most primitive melts from the Southeast Greenland margin are picritic. Fractional crystallisation of our primitive melt shows a good agreement with slightly altered basalts from the seaward dipping reflector series off Southeast Greenland. These preliminary results lead us to believe that the style of rifting can be well constrained by compositional variations.

Armitage, J. J.; Henstock, T. J.; Minshull, T. A.; Hopper, J. R.

2006-12-01

268

CORE Operations Center  

NASA Technical Reports Server (NTRS)

This report gives an overall view of the CORE program at Goddard Space Flight Center (GSFC). It summarizes the different CORE sessions and gives information about the technical staff. The outlook summarizes the evolution of the different CORE programs.

Thomas, Cynthia; Vandenberg, Nancy

1999-01-01

269

Applications of liquid state physics to the earth's core  

NASA Technical Reports Server (NTRS)

New results derived for application to the earth's outer core using the modern theory of liquids and the hard-sphere model of liquid structure are presented. An expression derived in terms of the incompressibility and pressure is valid for a high-pressure liquid near its melting point, provided that the pressure is derived from a strongly repulsive pair potential; a relation derived between the melting point and density leads to a melting curve law of essentially the same form as Lindemann's law. Finally, it is shown that the 'core paradox' of Higgins and Kennedy (1971) can occur only if the Gruneisen parameter is smaller than 2/3, and this constant is larger than this value in any liquid for which the pair potential is strongly repulsive.

Stevenson, D. J.

1980-01-01

270

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

271

Dynamical Meson Melting in Holography  

E-print Network

We discuss mesons in thermalizing gluon backgrounds in the N=2 supersymmetric QCD using the gravity dual. We numerically compute the dynamics of a probe D7-brane in the Vaidya-AdS geometry that corresponds to a D3-brane background thermalizing from zero to finite temperatures by energy injection. In static backgrounds, it has been known that there are two kinds of brane embeddings where the brane intersects the black hole or not. They correspond to the phases with melted or stable mesons. In our dynamical setup, we obtain three cases depending on final temperatures and injection time scales. The brane stays outside of the black hole horizon when the final temperature is low, while it intersects the horizon and settles down to the static equilibrium state when the final temperature is high. Between these two cases, we find the overeager case where the brane dynamically intersects the horizon although the final temperature is not high enough for a static brane to intersect the horizon. The interpretation of this phenomenon in the dual field theory is meson melting due to non-thermal effects caused by rapid energy injection. In addition, we comment on the late time evolution of the brane and a possibility of its reconnection.

Takaaki Ishii; Shunichiro Kinoshita; Keiju Murata; Norihiro Tanahashi

2014-01-20

272

Dynamical meson melting in holography  

NASA Astrophysics Data System (ADS)

We discuss mesons in thermalizing gluon backgrounds in the = 2 super-symmetric QCD using the gravity dual. We numerically compute the dynamics of a probe D7-brane in the Vaidya-AdS geometry that corresponds to a D3-brane background thermalizing from zero to finite temperatures by energy injection. In static backgrounds, it has been known that there are two kinds of brane embeddings where the brane intersects the black hole or not. They correspond to the phases with melted or stable mesons. In our dynamical setup, we obtain three cases depending on final temperatures and injection time scales. The brane stays outside of the black hole horizon when the final temperature is low, while it intersects the horizon and settles down to the static equilibrium state when the final temperature is high. Between these two cases, we find the overeager case where the brane dynamically intersects the horizon although the final temperature is not high enough for a static brane to intersect the horizon. The interpretation of this phenomenon in the dual field theory is meson melting due to non-thermal effects caused by rapid energy injection. In addition, we comment on the late time evolution of the brane and a possibility of its reconnection.

Ishii, Takaaki; Kinoshita, Shunichiro; Murata, Keiju; Tanahashi, Norihiro

2014-04-01

273

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

274

Intelligent control of cupola melting  

SciTech Connect

The cupola is a furnace used for melting steel scrap, cast iron scrap, and ferroalloys to produce cast iron. Its main energy source is coal coke. It is one of the oldest methods of producing cast iron, and it remains the dominate method because of its simplicity and low fuel cost. Cupolas range in size from 18 inches to 13 feet in diameter, and can produce up to 100 tons per hour of cast iron. Although cupola melting has a long history, automatic control has been elusive because the process has been poorly understood. Most foundries rely on the intuition of experienced operators to make control decisions. The purpose of this work, which has been underway for three years of an anticipated four year program, is to develop a controller for the cupola using intelligent and conventional control methods. The project is a cooperative effort between the Idaho National Engineering and Environmental Laboratory, the Department of Energy Albany Research Center, Idaho State University, and the American Foundrymen`s Society.

Larsen, E.D.; Clark, D.E. [Idaho National Engineering and Environmental Lab., Idaho Falls, ID (United States); Moore, K.L. [Idaho State Univ., Pocatello, ID (United States); King, P.E. [Department of Energy, Albany, OR (United States)

1997-05-01

275

Risk assessment of K basin twelve-inch drain valve failure from a postulated seismic initiating event  

SciTech Connect

The Spent Nuclear Fuel (SNF) Project will transfer metallic SNF from the Hanford 105 K-East and 105 K-West Basins to safe interim storage in the Canister Storage Building in the 200 Area. The initial basis for design, fabrication, installation, and operation of the fuel removal systems was that the basin leak rates which could result from a postulated accident condition would not be excessive relative to reasonable recovery operations. However, an additional potential K Basin water leak path is through the K Basin drain valves. Three twelve-inch drain valves are located in the main basin bays along the north wall. The sumps containing the valves are filled with concrete which covers the drain valve body. Visual observations suggest that only the valve's bonnet and stem are exposed above the basin concrete floor. It was recognized, however, that damage of the drain valve bonnet or stem during a seismic initiating event could provide a potential K Basin water leak path. The objectives of this activity are to: (1) evaluate the risk of damaging the three twelve-inch drain valves located along the north wall of the main basin from a seismic initiating event, and (2) determine the associated potential leak rate from a damaged valve.

MORGAN, R.G.

1999-04-06

276

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

277

Morphology and Melting Behavior of Polypropylenes  

NASA Astrophysics Data System (ADS)

The double melting of isothermally crystallized polypropylenes (metallocenes or Ziegler fractions) of a low defect content, is found to be associated with the presence of dominant (usually thicker) and daughter lamellae. A double population of lamellae thicknesses that adheres to the formulated epitaxial crystallization is seen by TEM even in samples crystallized at temperatures above 160 degC. Mixed and positive spherulites are also observed to grow linearly at these temperatures. During the melting process, positive or mixed spherulites show a well defined change to a negative character at a temperature corresponding to the low temperature endotherm in agreement with the melting of the daughter lamellae at this temperature. It is also found that the melting and stability of the dominant lamellae are influenced by the presence of epitaxial transversal lamellae. The kinetics of the melting process are investigated in relation to the initial morphology. Higher defected polypropylenes with a high concentration of gamma crystals do not show associated melting kinetics.

Alamo, R. G.; Mandelkern, L.

1997-03-01

278

Melt pelletization in high shear mixer using a hydrophobic melt binder: influence of some apparatus and process variables.  

PubMed

The effects of process conditions and the apparatus variables on the granulometric characteristics of a formulation containing a hydrophobic binder (stearic acid), lactose and paracetamol prepared by melt pelletization process were investigated in a 10-litre high shear mixer. The factors under investigation were: impeller speed, massing time, type of impeller blades and presence of the deflector and their reciprocal interactions. Two granule characteristics were analysed: the percentage of aggregates larger than 3000 microm (Y(1)) and the yield of the 2000-microm pellet size fraction (Y(2)). In order to estimate simultaneously the above-mentioned factors, a particular experimental design was adopted, that allowed the reduction of the number of trials from 378 to 35 and took into consideration other uncontrolled factors with the aid of a block variable. Using the postulated model, we found the optimal operating conditions to minimize Y(1) and increase Y(2) by selecting the type of impeller, and by using an impeller speed lower than 300 rpm, a massing time of 8-9 min and by not using the deflector. Finally, the validity of the adopted strategy has been proved with an additional check point. PMID:11677073

Voinovich, D; Moneghini, M; Perissutti, B; Franceschinis, E

2001-11-01

279

Crystal Growth from the Melt: A Review  

Microsoft Academic Search

This paper reviews four aspects of crystal growth theory: the nature of the rate-controlling process, the mechanism controlling molecular attachment onto the growing crystal surface, the nature of the crystal-melt interface, and the stability of planar interfaces relative to cellular interfaces. The rate-controlling process may be diffusion in the melt, heat flow, or the reaction at the crystal-melt interface. Diffusion

R. Jeuss Knrpnrnrcr

280

Certain petrological features of impact melts  

NASA Astrophysics Data System (ADS)

A cluster analysis of impactites and target rocks of the Zhamanshin and Manicouagan astroblemes was carried out. Two types of impact melts were found to exist: (1) highly homogeneous melts resulting from intense mixing during motion in the crater cavity and (2) heterogeneous melts which consist mainly of a single rock and result from ejections of matter that did not have the time to become homogeneous prior to the ejection.

Fel'Dman, V. I.; Riakhovskii, V. M.

281

Surface melting on ice shelves and icebergs  

NASA Astrophysics Data System (ADS)

Disintegration of Larsen Ice Shelf A and B, in 1995 and 2002, respectively, were preceded by two decades of extended summer melt seasons and by surface melt-water accumulation in ponds, surface crevasses and depressions produced by the elastic flexure of the ice. The extraordinary rapidity of ice-shelf fragmentation into large iceberg plumes following the appearance of surface melt water implies that the mechanical effects of surface melt water accumulation may represent an unforeseen process allowing abrupt, large-scale change of Antarctica's ice mass. The present study of surface melting and subsequent movement of melt water, both vertically (i.e., downward percolation into underlying firn) and horizontally (e.g., into crevasses and surface depressions created by ice-shelf flexure in response to both side boundary conditions and the melt-water load itself), is motivated by the need to further describe the energy, mass and momentum balances associated with ice shelves and their surrogates-large tabular icebergs-in the face of unprecedented changes in surface mass balance. The goal of this dissertation is to examine both the thermodynamic and mechanical aspects of surface melting on ice shelves and icebergs subject to sudden changes in climate conditions (e.g ., global warming). Thermodynamic aspects of the study include the development and application of surface energy balance models capable of describing the process of surface melting and subsequent vertical movement of melt water through a porous firn. Mechanical aspects of this study include the analysis of vertical melt-water flow, and more particularly, the elastic flexure response of the ice shelf or iceberg to the melt-water loads. Work presented here involves three methodologies, numerical modeling, field observation, and mathematical analysis (e.g., development of analytic solutions to simple, idealized ice-shelf flexure problems).

Sergienko, Olga V.

282

Seismogenic frictional melting in the magmatic column as the driving force of stick-slip motion  

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 of thermal anomalies, key to unravelling subsurface processes. A combined structural, thermal and magnetic investigation of shear bands from Mount St. Helens (MSH) and Soufrière Hills volcano (SHV) reveal evidence of faulting and frictional melting within the magmatic column. High velocity rotary shear (HVR) experiments demonstrate the propensity for melting of andesitic and dacitic material (from SHV and MSH respectively) at upper conduit stress conditions. Such melting events may be linked to the step-wise extrusion of magma accompanied by repetitive long-period (LP) seismicity. Using a source duration calculated from the waveforms at seismic stations around SHV, and slip distance per drumbeat calculated from extrusion rate, frictional melting of SHV andesite in a high velocity rotary shear apparatus can be achieved at small slip distances (<15cm) in 0.15 s from 800°C magma (at 10MPa). The shear resistance of the slip zone during the experiments is also monitored. Frictional melting induces a higher resistance to sliding than rock on rock, and viscous processes control the slip zone properties. Variable-rate HVR experiments which mimic rapid velocity fluctuations in stick-slip behavior demonstrate velocity-weakening behavior of melt, with a tendency for unstable slip. We postulate that pseudotachylyte generation could be the underlying cause of stick-slip motion and associated seismic 'drumbeats', which are so commonly observed at dome-building volcanoes, allowing for a fixed spatial locus and the occurrence of 'families' of similar seismic events. We conclude that, given the ease with which melting is achieved in volcanic rocks, and considering the high ambient temperatures in volcanic conduits, frictional melting is a highly probable consequence of viscous magma ascent.

Kendrick, J. E.; Lavallee, Y.; Hirose, T.; Di Toro, G.; Hornby, A.; De Angelis, S.; Henton De Angelis, S.; Ferk, A.; Hess, K.; Leonhardt, R.; Dingwell, D. B.

2013-12-01

283

High-pressure melting of molybdenum.  

PubMed

The melting curve of the body-centered cubic (bcc) phase of Mo has been determined for a wide pressure range using both direct ab initio molecular dynamics simulations of melting as well as a phenomenological theory of melting. These two methods show very good agreement. The simulations are based on density functional theory within the generalized gradient approximation. Our calculated equation of state of bcc Mo is in excellent agreement with experimental data. However, our melting curve is substantially higher than the one determined in diamond anvil cell experiments up to a pressure of 100 GPa. An explanation is suggested for this discrepancy. PMID:15169417

Belonoshko, A B; Simak, S I; Kochetov, A E; Johansson, B; Burakovsky, L; Preston, D L

2004-05-14

284

Low-Degree Partial Melting Experiments of CR and H Chondrite Compositions: Implications for Asteroidal Magmatism Recorded in GRA 06128 and GRA 06129 T  

NASA Technical Reports Server (NTRS)

Studies of differentiated meteorites have revealed a diversity of differentiation processes on their parental asteroids; these differentiation mechanisms range from whole-scale melting to partial melting without the core formation [e.g., 1]. Recently discovered paired achondrites GRA 06128 and GRA 06129 (hereafter referred to as GRA) represent unique asteroidal magmatic processes. These meteorites are characterized by high abundances of sodic plagioclase and alkali-rich whole-rock compositions, implying that they could originate from a low-degree partial melt from a volatile-rich oxidized asteroid [e.g., 2, 3, 4]. These conditions are consistent with the high abundances of highly siderophile elements, suggesting that their parent asteroid did not segregate a metallic core [2]. In this study, we test the hypothesis that low-degree partial melts of chondritic precursors under oxidizing conditions can explain the whole-rock and mineral chemistry of GRA based on melting experiments of synthesized CR- and H-chondrite compositions.

Usui, T.; Jones, John H.; Mittlefehldt, D. W.

2010-01-01

285

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

286

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

287

Metal-Silicate Segregation in Deforming Dunitic Rocks: Applications to Core Formation in Europa and Ganymede  

NASA Technical Reports Server (NTRS)

Core formation is an important event in the evolution of a planetary body, affecting both the geochemical and geophysical properties of the body. Metal-silicate segregation could have proceeded either by settling of liquid metal through a magma ocean or by percolation of liquid metal through a solid silicate mantle. Percolation of metallic melt had previously been excluded as a viable segregation mechanism because metallic melts do not form an interconnected network under hydrostatic conditions, except at high melt fraction (>5 vol%), due to the high dihedral angle between metals and silicates (>60 ). Without an interconnected network, porous flow of metallic melt is impossible, leaving the magma ocean scenario as the only mechanism to form the core. Moment-of-inertia measurements of Europa and Ganymede from the Galileo probe indicate that they are differentiated. This evidence suggests that a method for segregating metals and silicates at temperatures low enough to retain volatile compounds must exist. We have investigated the effect of deformation on the distribution of metallic melts in silicates. We have deformed samples of olivine + 5-9 vol% Fe-S to strains of 2.5 in simple shear and find that the metallic melt segregates into melt-rich planes oriented at 20 to the shear plane. These metallic melt-rich bands are similar in structure to the silicate melt-rich bands reported by Holtzman, indicating that deformation can interconnect isolated metallic melt pockets and allow porous flow of non-wetting melts. Such a core formation process could have occurred in the jovian satellites.

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

2004-01-01

288

Heterogeneity and Anisotropy of Earth's Inner Core  

NASA Astrophysics Data System (ADS)

Seismic observations provide strong evidence that Earth's inner core is anisotropic, with larger velocity in the polar than in the equatorial direction. The top 60-80 km of the inner core is isotropic; evidence for an innermost inner core is less compelling. The anisotropy is most likely due to alignment of hcp (hexagonal close-packed) iron crystals, aligned either during solidification or by deformation afterward. The existence of hemispherical variations used to be controversial, but there is now strong evidence from both seismic body wave and normal mode observations, showing stronger anisotropy, less attenuation, and a lower isotropic velocity in the western hemisphere. Two mechanisms have been proposed to explain the hemispherical pattern: either (a) inner core translation, wherein one hemisphere is melting and the other is solidifying, or (b) thermochemical convection in the outer core, leading to different solidification conditions at the inner core boundary. Neither is (yet) able to explain all seismically observed features, and a combination of different mechanisms is probably required.

Deuss, Arwen

2014-05-01

289

Tomographic location of potential melt-bearing phenocrysts in lunar glass spherules  

SciTech Connect

Apollo 17 orange glass spherules contain olivine phenocrysts with melt inclusions from depth. Tomography (<2micron/pxl) of >200 spherules located 1 phenocryst. We will try to find melt inclusions and obtain original magma volatiles and compositions. In 1971, Apollo 17 astronauts collected a 10 cm soil sample (74220) comprised almost entirely of orange glass spherules. Below this, a double drive-tube core sampled a 68 cm thick horizon comprised of orange glass and black beads (crystallized equivalents of orange glass). Primitive lunar glass spherules (e.g.-A17 orange glasses) are thought to represent ejecta from lunar mare fire fountains. The fire-fountains were apparently driven by a combination of C-O gas exsolution from orange glass melt and the oxidation of graphite. Upon eruption, magmas lost their volatiles (e.g., S, CO, CO{sub 2}) to space. Evidence for volatile escape remains as volatile-rich coatings on the exteriors of many spherules. Moreover, it showed that Type I and II Fe-Ni-rich metal particles found within orange glass olivine phenocrysts, or free-floating in the glass itself, are powerful evidence for the volatile driving force for lunar fire fountains. More direct evidence for the volatile mechanism has yet to be uncovered. Issues remaining include: the exact composition of magmatic volatiles; the hypothesized existence of graphite in the magma; the oxygen fugacity of the magma and of the lunar interior. In 1996 reported a single {approx}450 micron, equant olivine phenocryst, containing four glassy melt inclusions (or inclusion cores), the largest {approx}30micron in size, in a thin section of the 74001/2 drill core. The melt is assumed to sample the parent magma of the lunar basalts at depth, evidenced by the S content of the inclusion (600 ppm) which is 400 ppm greater than that of the orange glass host. Such melts potentially contain a full complement of the volatile components of the parent magma, which can be analyzed by infrared spectroscopy. Although the A17 orange glass magma is thought to derive from {approx} 400 km depth, the calculations imply a 4 km depth of graphite oxidation (and melt saturation in C-O volatiles) during ascent. We have imaged several hundred similar orange glass spherules, from sample 74220,764, using synchrotron x-ray computer-aided microtomography (XRCMT). Our goals: (1) locate similar phenocrysts containing melt inclusions; (2) analyze phenocrysts to understand the evolution of the magma; (3) analyze melt and fluid inclusions using EPMA and FTIR to obtain direct evidence of magmatic volatiles and pristine bulk compositions.

Ebel, D.S.; Fogel, R.A.; Rivers, M.L. (AMNH); (UC)

2005-02-04

290

Superalloy Melting in an ac Electroslag Remelt Furnace with Automatic Melt Control and rms Current Regulation  

Microsoft Academic Search

A stationary mold-ingot bottom withdrawal ac consumable electrode electroslag furnace with electrode change capability has been installed for melting superalloys at Teledyne-Allvac. The furnace, which utilizes melt voltage and rms current regulation for automatic melt control and its operation are described. The stationary mold-ingot bottom withdrawal and auto-melt control concepts have proven successful and solution hardening superalloys are in routine

Frank Elliott; Eugene L. Danjou; Raymond C. Blackmond

1976-01-01

291

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

292

Molecular dynamics simulation of melting of fcc Lennard-Jones nanoparticles  

NASA Astrophysics Data System (ADS)

Melting of fcc Lennard-Jones (LJ) nanoparticles is studied by heating up models from low temperature toward liquid phase using molecular dynamics (MD) simulation. Atomic mechanism of melting is analyzed via temperature dependence of potential energy, heat capacity, analysis of the spatio-temporal arrangements of liquidlike atoms occurred during the heating process. Moreover, radial distribution function (RDF), mean-squared displacement (MSD) of atoms and radial density profile are also used for deeper analyzing melting. Surface melting is under much attention. We also analyze the evolution of structure of nanoparticles upon heating via the global order parameter Q6 and Honeycutt-Andersen (HA) analysis. We find previously unreported information as follows. At temperature far below a melting point, a quasi-liquid layer containing both liquidlike and solidlike atoms occurs in the surface shell of nanoparticles unlike that thought in the past. Further heating leads to the formation of a purely liquid layer at the surface and homogeneous occurrence/growth of liquidlike atoms throughout the interior of nanoparticles. Melting proceeds further via two different mechanisms: homogeneous one in the interior and propagation of liquid front from the surface into the core leading to fast collapse of crystalline matrix.

Van Sang, Le; Van Hoang, Vo; Thi Thuy Hang, Nguyen

2013-03-01

293

Theory of pressure-dependent melting of the DNA double helix: Role of strained hydrogen bonds  

NASA Astrophysics Data System (ADS)

In this paper we study the effect of hydrostatic pressure on the thermal stability of DNA base pairs. The thermal stability of a base pair is predominantly determined by the fluctuational motion of the interbase hydrogen bonds in the base pair. We postulate that the pressure exerted on the surface of DNA creates a compressive stress in the interbase hydrogen bonds. This stress in turn induces a strain in these hydrogen bonds. The effect of this compressive stress on the thermal fluctuational motion of the strained interbase hydrogen bonds in DNA can be analyzed by the modified self-consistent phonon approximation theory. We calculate individual hydrogen bond disruption probabilities and base pair opening probabilities of two B-conformation DNA polymers, an adenine-thymine copolymer and a guanine-cytosine homopolymer, at various pressures and at temperatures both in the premelting region and in the helix-coil transition region. Our calculated pressure dependence of the melting temperature for both polymers is in fair agreement with experimental observations. Our values for the melting temperatures are also in agreement with observation and our theory is successful as a theory of cooperative melting.

Chen, Y. Z.; Prohofsky, E. W.

1993-03-01

294

A new deep ice core from Akademii Nauk ice cap, Severnaya Zemlya, Eurasian Arctic: first results  

Microsoft Academic Search

The paper presents first results from the upper 54 m of a 723.91 m ice core drilled on Akademii Nauk ice cap, Severnaya Zemlya, Eurasian Artctic, in 1999-2001, supplemented by data from shallow ice cores. The glacier's peculiarity is the infiltration and refreezing of melting water, which changes the original isotopic and chemical signals. Therefore, stratigraphical observations in these ice

Diedrich Fritzsche; Frank Wilhelms; Lev M. Savatyugin; Jean Francis Pinglot; Hanno Meyer; Hans-Wolfgang Hubberten; Heinz Miller

2002-01-01

295

M551 metals melting experiment  

NASA Technical Reports Server (NTRS)

Electron beam welding studies were conducted in the Skylab M551 metals melting experiment, on three different materials; namely 2219-T87 aluminum alloy, 304L stainless steel, and commercially pure tantalum (0.5 wt % columbium). Welds were made in both one gravity and zero gravity (Skylab) environments. Segments from each of the welds were investigated by microhardness, optical microscopy, scanning microscopy, and electron probe techniques. In the 2219-T87 aluminum alloy samples, macroscopic banding and the presence of an eutectic phase in the grain boundaries of the heat affected zone were observed. The stainless steel samples exhibited a sharp weld interface and macroscopic bands. The primary microstructural features found in the tantalum were the presence of either columnar grains (ground base) or equiaxed grains (Skylab). The factors contributing to these effects are discussed and the role of reduced gravity in welding is considered.

Busch, G.

1977-01-01

296

Surface melting of electronic order.  

SciTech Connect

We report temperature-dependent surface x-ray scattering studies of the orbital ordered surface in La{sub 0.5}Sr{sub 1.5}MnO{sub 4}. We find that as the bulk ordering temperature is approached from below the thickness of the interface between the electronically ordered and electronically disordered regions at the surface grows, though the bulk correlation length remains unchanged. Close to the transition, the surface is so rough that there is no well-defined electronic surface, despite the presence of bulk electronic order. That is, the electronic ordering at the surface has melted. Above the bulk transition, long-range ordering in the bulk is destroyed but finite-sized isotropic fluctuations persist, with a correlation length roughly equal to that of the low-temperature in-plane surface correlation length.

Wilkins, S. B.; Liu, X.; Wakabayashi, Y.; Kim, J.-W.; Ryan, P. J.; Mitchell, J. F.; Hill, J. P. (Materials Science Division); ( XSD); (BNL); (Osaka Univ.)

2011-01-01

297

Do Melt Inclusions Answer Big Questions?  

NASA Astrophysics Data System (ADS)

In a pioneering paper, Sobolev and Shimizu (1993) demonstrated the existence of ultra-depleted melt inclusions in olivine phenocrysts in MORB. They interpreted these as evidence for the preservation of parental melts formed by progressive near-fractional melting. Subsequently many cases have been described where melt inclusions from single basalt samples display enormous chemical and isotopic heterogeneity. The interpretation of these observations hinges critically on whether such melt inclusions can faithfully preserve primary or parental melt composition. If they do, melt inclusion data can truly answer big questions from small-scale observations. If they do not, they answer rather small questions. Favoring the second possibility, Danyushevsky et al. (2004) have suggested that much of the observed variability of highly incompatible trace elements in melt inclusions “may not represent geologically significant melts, but instead reflect localized, grain-scale reaction processes within the magmatic plumbing system.” We disagree and show that this mechanism cannot, for example, explain isotopic heterogeneity measured in several suites of melt inclusions, nor does it not account for the presence of ultra-depleted melts and "ghost" plagioclase signatures in other inclusions. More recently, Spandler et al. (2007) have suggested on the basis of experimental evidence that diffusion rates for REE in olivine are so rapid that parental melt compositions in melt inclusions are rapidly falsified by diffusional exchange with (evolved) host lava. We show that the very fact that extreme chemical and isotopic heterogeneities are routinely preserved in melt inclusions demonstrates that this conclusion is unwarranted, either because residence times of the olivine phenocrysts are much shorter than assumed by Spandler et al. or because the high experimental diffusion rates are caused by an unknown experimental artifact. Although there is no obvious flaw in design and execution of their experiments, geologically relevant diffusion rates are notoriously difficult to determine and may depend on factors not incorporated in the laboratory experiments. More recent diffusion experiments by Remmert et al. (2008) and by Cherniak (2009) have yielded diffusion coefficients three order of magnitude lower than those measured by Spandler. The heavy REE represent a possible exception to the above conclusions. We present data from olivine melt inclusions from Iceland basalts, which show unusual HREE patterns possibly caused by diffusional exchange with the host lava. Sobolev, A.V. & Shimizu, N. (1993) Nature 363, 151-154. Danyushevskii, L.V. et al. (2004) J. Petrol. 45, 2531-2553. Spandler, G., O’Neill, H.St.C., Kamenetsky, V.S. (2007) Nature, 447, 303-306. Remmert, P. Dohmen, R., Chakraborty, S. (2008) EOS Trans. AGU abs. MR331-1844. Cherniak, D.J. (2009) Am. Mineral. Ms. subm.

Hofmann, A. W.; Sobolev, A. V.

2009-12-01

298

Water loss from olivine hosted melt inclusions  

NASA Astrophysics Data System (ADS)

Water content in melt inclusions has long been used as an important index for the water content of the hosting magma. However, many studies have shown that post-entrapment diffusive re-equilibration can affect the water content of melt inclusions. This process must be considered when using melt inclusions to infer water content of the hosting magma. Theoretical model on the diffusive re-equilibration between melt inclusions and external melts showed that the re-equilibration rate depends on the diffusivity of the re-equilibrating species in the host mineral, the partition coefficient of this species between the host mineral and melt, and the geometry of the melt inclusion and host mineral. The water diffusivity in olivine and water partition coefficient between melt and olivine have been measured by recent studies, therefore the diffusive re-equilibration model can be tested by experiments. In this study, we carried out in-situ Fourier transform infrared spectroscopy (FTIR) measurements on the water content of olivine hosted melt inclusions at high temperatures. Initial water content of the melt inclusions is about 4 wt%. A heating stage system is combined with a microscope FTIR and the absorption spectrum through the olivine and melt inclusion is repeatedly measured. Although the absorption band at around 3540 cm-1 has not be calibrated at high temperatures, it is assumed that the absorbance is linearly related to the total water concentration in the melt inclusion, and the relative water content can be inferred. Cautions have been exercised to maintain a consistent measurement spot such that the thickness of the melt inclusion within the beam path did not change significantly during each experiment. Oxygen fugacity in the heating stage is controlled by Zr purified Ar gas to be about 7 logarithm units below the QFM buffer and about 1 logarithm unit above the QIF buffer at 1473 K. Preliminary results showed that at 1430 and 1581 K, the total water content of the melt inclusion decreased by 80% within about 7 and 1 hours, respectively. This rapid decrease of water content agrees with previous observations. Applying the model and water partition coefficient between olivine and melt by a previous study yields water diffusivities in olivine as 5E-12 and 3E-11 m2/s at 1430 and 1581 K, respectively. These numbers are consistent with the diffusivities measured by a previous study. Due to some experimental difficulties, it is unclear whether bubble existed during the experiments and affected the apparent water content change. Oxygen fugacity may also play a role in water re-equilibration. Further efforts will be made to investigate these aspects and better understand the water re-equilibration process.

Chen, Y.; Provost, A.; Schiano, P.; Cluzel, N.

2009-12-01

299

Olivine-hosted melt inclusions and melting processes beneath the FAMOUS zone (Mid-Atlantic Ridge)  

E-print Network

important information about the processes of melt generation beneath mid-ocean ridges. They contain near; Olivine; Mid-ocean ridge basalts; Mantle melting 1. Introduction Melt generation at mid-ocean ridges-element systematics of MORB (mid- ocean ridge basalts) have been explained in terms of variation of the potential

Laubier, Muriel

300

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

301

Core formation, evolution, and convection: A geophysical model  

NASA Technical Reports Server (NTRS)

A model is proposed for the formation and evolution of the Earth's core which provides an adequate energy source for maintaining the geodynamo. 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. 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.

1978-01-01

302

TMI-2 core damage: a summary of present knowledge  

SciTech Connect

Extensive fuel damage (oxidation and fragmentation) has occurred and the top approx. 1.5 m of the center portion of the TMI-2 core has relocated. The fuel fragmentation extends outward to slightly beyond one-half the core radius in the direction examined by the CCTV camera. While the radial extent of core fragmentation in other directions was not directly observed, control and spider drop data and in-core instrument data suggest that the core void is roughly symmetrical, although there are a few indications of severe fuel damage extending to the core periphery. The core material fragmented into a broad range of particle sizes, extending down to a few microns. APSR movement data, the observation of damaged fuel assemblies hanging unsupported from the bottom of the reactor upper plenum structure, and the observation of once-molten stainless steel immediately above the active core indicate high temperatures (up to at least 1720 K) extended to the very top of the core. The relative lack of damage to the underside of the plenum structure implies a sharp temperature demarcation at the core/plenum interface. Filter debris and leadscrew deposit analyses indicate extensive high temperature core materials interaction, melting of the Ag-In-Cd control material, and transport of particulate control material to the plenum and out of the vessel.

Owen, D.E.; Mason, R.E.; Meininger, R.D.; Franz, W.A.

1983-01-01

303

Shock-induced melting and rapid solidification  

SciTech Connect

Model calculations are presented to estimate that approx.50 GPa is required to completely shock melt metal powders with quenching at rates up to 10/sup 8/ K/s. Experiments are discussed for powders of a Cu-Zr alloy compacted in the usual way at 16 GPa and melted by shocking to 60 GPa. 12 refs.

Nellis, W.J.; Gourdin, W.H.; Maple, M.B.

1987-08-01

304

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

305

Melt dumping in string stabilized ribbon growth  

DOEpatents

A method and apparatus for stabilizing the edge positions of a ribbon drawn from a melt includes the use of wettable strings drawn in parallel up through the melt surface, the ribbon being grown between the strings. A furnace and various features of the crucible used therein permit continuous automatic growth of flat ribbons without close temperature control or the need for visual inspection.

Sachs, Emanuel M. (42 Old Middlesex Rd., Belmont, MA 02178)

1986-12-09

306

Segregation of Partly Melted DNA Molecules  

Microsoft Academic Search

Segregation of partly melted DNA molecules is a convenient and efficient method to isolate DNA fragments associated with CpG islands. The method stands on the observation that the electrophoretic mobility of partly melted DNA fragments in a denaturing gradient gel is low and that they persist in the gel so long as the remaining helical part is sufficiently resistant to

Masahiko Shiraishi; Takao Sekiya

2006-01-01

307

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

308

Condensation of saturated vapor on melting surfaces  

Microsoft Academic Search

Melting of vertical and horizontal surfaces as a result of condensation of saturated vapor was studied. For the vertical wall, employing similarity transformation, full boundary layer equations governing laminar films of melt and condensate were obtained. Depending on the magnitude of the Prandtl number, different scaling parameters are needed such that Pr appears in the momentum or energy equation. Numerical

Taghavi-Tafreshi

1982-01-01

309

Recent Changes in the Arctic Melt Season  

NASA Technical Reports Server (NTRS)

Melt-season duration, melt-onset and freeze-up dates are derived from satellite passive microwave data and analyzed from 1979 to 2005 over Arctic sea ice. Results indicate a shift towards a longer melt season, particularly north of Alaska and Siberia, corresponding to large retreats of sea ice observed in these regions. Although there is large interannual and regional variability in the length of the melt season, the Arctic is experiencing an overall lengthening of the melt season at a rate of about 2 weeks decade(sup -1). In fact, all regions in the Arctic (except for the central Arctic) have statistically significant (at the 99% level or higher) longer melt seasons by greater than 1 week decade(sup -1). The central Arctic shows a statistically significant trend (at the 98% level) of 5.4 days decade(sup -1). In 2005 the Arctic experienced its longest melt season, corresponding with the least amount of sea ice since 1979 and the warmest temperatures since the 1880s. Overall, the length of the melt season is inversely correlated with the lack of sea ice seen in September north of Alaska and Siberia, with a mean correlation of -0.8.

Stroeve, Julienne; Markus, Thorsten; Meier, Walter N.; Miller, Jeff

2007-01-01

310

Frictional Melting Processes in Planetary Materials  

E-print Network

lubrication, shock veins Abstract Frictional melting is the result of the conversion of mechanical deforma surfaces can lubricate earthquake faults, facilitate the post-shock modification of impact craters articles rehensive search FurtherANNUAL REVIEWS #12;1. INTRODUCTION Frictional melting is an everyday

Jellinek, Mark

311

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

312

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

313

Mechanical relaxations and melting in semicrystalline polymers  

Microsoft Academic Search

It has long been known that there are relationships between glass temperatures and melting points in semicrystalline polymers. Boyer [1] and Beaman [2] observed that the glass temperature is usually ½ to ? of the melting point in degrees absolute. More recently, Boyer [3] has reviewed what is known about the dependence of these properties on molecular structure.

Howard W. Starkweather Jr

1968-01-01

314

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

315

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

316

Geochemistry of the impact-generated melt sheet at Manicouagan: Evidence for fractional crystallization  

NASA Astrophysics Data System (ADS)

Recent exploration drilling of the Manicouagan impact structure has revealed local developments of impact melt that are substantially thicker than the previously accepted average of ˜300 m and a more complex melt sheet-basement interface showing considerable "topography." The thickest section (1045 m of clast-free to clast-poor impact melt overlying 425 m of clast-laden impact melt) is associated with a centrally located, fault-bounded graben that was in place prior to melt crystallization. Here we report the results of a geochemical investigation of 115 samples obtained from nine drill holes and a set of field samples. The results reveal that most of the drill core comprises an undifferentiated unit, showing minimal geochemical variation. This is typically ˜300 m thick and equates with previous studies performed on samples from exposed rock. In contrast, the deeper section exhibits differentiation and is divided into three layers based on chemical, mineralogical, and textural variations: a quartz monzonite to quartz monzodiorite upper zone (276 m), a quartz monzodioritic middle zone (244 m), and a mainly monzodioritic lower zone (525 m). The mineralogy is defined by plagioclase > orthoclase > clinopyroxene > orthopyroxene, with ubiquitous amphibole and biotite and olivine locally developed in the lower zone and below. Our results reveal that the thicker section of the impact melt sheet has undergone fractional crystallization. Differentiation of parts of the Manicouagan impact melt indicates that lunar impact melt samples possessing different chemistries, previously considered to be derived from distinct impact basins, may be related via the fractionation of common, much smaller diameter impact structures.

O'Connell-Cooper, Catherine D.; Spray, John G.

2011-06-01

317

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

318

Kinetic Limit of Heterogeneous Melting in Metals  

SciTech Connect

The velocity and nanoscale shape of the melting front are investigated in a model that combines the molecular dynamics method with a continuum description of the electron heat conduction and electron-phonon coupling. The velocity of the melting front is strongly affected by the local drop of the lattice temperature, defined by the kinetic balance between the transfer of thermal energy to the latent heat of melting, the electron heat conduction from the overheated solid, and the electron-phonon coupling. The maximum velocity of the melting front is found to be below 3% of the room temperature speed of sound in the crystal, suggesting a limited contribution of heterogeneous melting under conditions of fast heating.

Ivanov, Dmitriy S.; Zhigilei, Leonid V. [Department of Materials Science and Engineering, University of Virginia, 395 McCormick Road, Charlottesville, Virginia 22904-4745 (United States)

2007-05-11

319

Kinetic limit of heterogeneous melting in metals.  

PubMed

The velocity and nanoscale shape of the melting front are investigated in a model that combines the molecular dynamics method with a continuum description of the electron heat conduction and electron-phonon coupling. The velocity of the melting front is strongly affected by the local drop of the lattice temperature, defined by the kinetic balance between the transfer of thermal energy to the latent heat of melting, the electron heat conduction from the overheated solid, and the electron-phonon coupling. The maximum velocity of the melting front is found to be below 3% of the room temperature speed of sound in the crystal, suggesting a limited contribution of heterogeneous melting under conditions of fast heating. PMID:17677632

Ivanov, Dmitriy S; Zhigilei, Leonid V

2007-05-11

320

Nanotexturing of surfaces to reduce melting point.  

SciTech Connect

This investigation examined the use of nano-patterned structures on Silicon-on-Insulator (SOI) material to reduce the bulk material melting point (1414 C). It has been found that sharp-tipped and other similar structures have a propensity to move to the lower energy states of spherical structures and as a result exhibit lower melting points than the bulk material. Such a reduction of the melting point would offer a number of interesting opportunities for bonding in microsystems packaging applications. Nano patterning process capabilities were developed to create the required structures for the investigation. One of the technical challenges of the project was understanding and creating the specialized conditions required to observe the melting and reshaping phenomena. Through systematic experimentation and review of the literature these conditions were determined and used to conduct phase change experiments. Melting temperatures as low as 1030 C were observed.

Garcia, Ernest J.; Zubia, David (University of Texas at El Paso El Paso, TX); Mireles, Jose (Universidad Aut%C3%94onoma de Ciudad Ju%C3%94arez Ciudad Ju%C3%94arez, Mexico); Marquez, Noel (University of Texas at El Paso El Paso, TX); Quinones, Stella (University of Texas at El Paso El Paso, TX)

2011-11-01

321

Simulating the melt blowing of viscoelastic materials  

NASA Astrophysics Data System (ADS)

This work is motivated by recent experimental developments in melt blowing that enable the production of nanofibers. In contrast to electrospinning, which is another method for producing nanofibers, melt blowing is potentially faster and environmentally friendlier. Using a slender-jet approximation, we obtain a set of one-dimensional equations governing the fiber area, centerline velocity, and temperature. The upper convected Maxwell (UCM) model and the Phan-Thien and Tanner (PTT) model are used to describe the viscoelastic rheology of the melts. Key to melt blowing is the shear stress on the fiber surface from the external air flow that attenuates the fiber to small diameter. Larger shear stresses or higher air flowrates produce fibers with smaller diameter. Our results show a significant influence of viscoelasticity on melt blowing, especially on fiber diameter. The fiber diameter is found to increase with polymer elasticity, which agrees qualitatively with experimental observations.

Zhou, Chunfeng; Tan, Dawud H.; Kumar, Satish; Macosko, Christopher W.; Bates, Frank S.

2010-11-01

322

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

323

Passive containment cooling system (PCCS) response with Drywell Gas Recirculation System (DGRS) activated during a postulated Loss of Coolant Accident (LOCA)  

Microsoft Academic Search

Passive Containment Cooling Systems (PCCS) are characterizing the design of several advanced LWR such as SBWR, ESBWR, ABWR-II, etc. These systems should ensure the mitigation of postulated accidents both under Design Basic Accident (DBA) and Beyond DBA (BDBA) conditions. Some ALWR designs integrated in the PCCS a system called Drywell Gas Recirculation System (DGRS). The DGRS works like a fan,

Domenico Paladino; Joerg Dreier

2011-01-01

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

Supplementary documentation for an Environmental Impact Statement regarding the Pantex Plant: radiological consequences of immediate inhalation of plutonium dispersed by postulated accidents  

Microsoft Academic Search

This report documents work performed in support of preparation of an Environmental Impact Statement (EIS) regarding the Department of Energy's (DOE) Pantex Plant near Amarillo, Texas. It describes methods used to estimate potential health consequences offsite resulting from inhalation of plutonium dispersed by each of several postulated accidents. The primary topic of this report is the delayed health effects of

J. C. Elder; R. H. Olsher; J. M. Graf

1982-01-01

326

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

327

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

328

Rheology of Melt-bearing Crustal Rocks  

NASA Astrophysics Data System (ADS)

A review and reinterpretation of previous experimental data on the deformation of melt-bearing crustal rocks (Rosenberg and Handy, 2005) revealed that the relationship of aggregate strength to melt fraction is non-linear, even if plotted on a linear ordinate and abscissa. At melt fractions, ? 0.07, the dependence of aggregate strength on ? is significantly greater than at ? > 0.07. This melt fraction (?= 0.07) marks the transition from a significant increase in the proportion of melt-bearing grain boundaries up to this point to a minor increase thereafter. Therefore, we suggest that the increase of melt-interconnectivity causes the dramatic strength drop between the solidus and a melt fraction of 0.07. A second strength drop occurs at higher melt fractions and corresponds to the breakdown of the solid (crystal) framework, corresponding to the well-known "rheologically critical melt percentage" (RCMP; Arzi, 1978). Although the strength drop at the RCMP is about 4 orders of magnitude, the absolute value of this drop is small compared to the absolute strength of the unmelted aggregate, rendering the RCMP invisible in a linear aggregate strength vs. melt fraction diagram. Predicting the rheological properties and thresholds of melt-bearing crust on the basis of the results and interpretations above is very difficult, because the rheological data base was obtained from experiments performed at undrained conditions in the brittle field. These conditions are unlikely to represent the flow of partially melted crust. The measured strength of most of the experimentally deformed, partially-melted samples corresponds to their maximum differential stress, before the onset of brittle failure, not to their viscous strength during "ductile" (viscous) flow. To overcome these problems, we extrapolated a theoretically-derived flow law for partially melted granite deforming by diffusion-accommodated grain-boundary sliding (Paterson, 2001) and an experimentally-derived flow law for quartz deforming in the dislocation creep regime in the presence of 1-2 % of melt (Gleason and Tullis, 1995). In addition, we compared these data with deformation experiments on olivine plus basalt melt, also conducted in the ductile (viscous) field (Hirth and Kohlstedt, 2003). All these data show a dramatic decrease in viscosity for melt fractions < 0.06. Therefore, they are consistent with the aforementioned results of experimentally deformed granite in the brittle field. Extrapolation of these results to natural conditions suggests that localisation of deformation should effectively coincide with the onset of melting, or with very small melt fractions (0.06-0.07), which may not always be detected in the field. References: Arzi, A. 1978. Tectonophysics, 44: 173-184. Hirth, G. and D. Kohlstedt. 2003. Geophysical Monograph, 138: 83-105. Gleason, G.C. and Tullis, J., 1995. Tectonophysics, 247: 1-23. Paterson, M.S. 2001. Tectonophysics, 335: 51-61. Rosenberg, C.L., and M.R. Handy. 2005. Journal of Metamorphic Geology, 23:19-28.

Rosenberg, C. L.; Medvedev, S.; Handy, M. R.

2006-12-01

329

Melting in two-dimensional Yukawa systems: A Brownian dynamics simulation  

NASA Astrophysics Data System (ADS)

We studied the melting behavior of two-dimensional colloidal crystals with a Yukawa pair potential by Brownian dynamics simulations. The melting follows the Kosterlitz-Thouless-Halperin-Nelson-Young (KTHNY) scenario with two continuous phase transitions and a middle hexatic phase. The two phase-transition points were accurately identified from the divergence of the translational and orientational susceptibilities. Configurational temperatures were employed to monitor the equilibrium of the overdamped system and the strongest temperature fluctuation was observed in the hexatic phase. The inherent structure obtained by rapid quenching exhibits three different behaviors in the solid, hexatic, and liquid phases. The measured core energy of the free dislocations, Ec = 7.81 +/- 0.91 kBT, is larger than the critical value of 2.84 kBT, which consistently supports the KTHNY melting scenario.

Qi, Wei-Kai; Wang, Ziren; Han, Yilong; Chen, Yong

2010-12-01

330

Academic Rigor: The Core of the Core  

ERIC Educational Resources Information Center

Some educators see the Common Core State Standards as reason for stress, most recognize the positive possibilities associated with them and are willing to make the professional commitment to implementing them so that academic rigor for all students will increase. But business leaders, parents, and the authors of the Common Core are not the only…

Brunner, Judy

2013-01-01

331

Descriptions and preliminary interpretations of cores recovered from the Manson Impact Structure (Iowa)  

NASA Technical Reports Server (NTRS)

A core drilling program initiated by the Iowa Geological Survey Bureau and U.S. Geological Survey in 1991 and 1992 collected 12 cores totalling over 1200 m from the Manson Impact Structure, a probable K-T boundary structure located in north-central Iowa. Cores were recovered from each of the major structural terranes, with 2 cores (M-3 and M-4) from the Terrace Terrane, 4 cores (M-2, M-2A, M-6, and M-9) from the Crater Moat, and 6 cores (M-1, M-5, M-7, M-8, M-10, and M-11) from the Central Peak. These supplemented 2 central peak cores (1-A and 2-A) drilled in 1953. The cores penetrated five major impact lithologies: (1) sedimentary clast breccia; (2) impact ejecta; (3) central peak crystallite rocks; (4) crystalline clast breccia with sandy matrix; and (5) crystallite clast breccia with a melt matrix. Descriptions and preliminary interpretations of these cores are presented.

Anderson, R. R.; Witzke, B. J.; Hartung, J. B.; Shoemaker, E. M.; Roddy, D. J.

1993-01-01

332

Structural, petro-geochemical and modelling constraints on melt migration by porosity waves in sub-arc mantle  

NASA Astrophysics Data System (ADS)

Petrographic and structural observations in the mantle lithospheres provided evidence for two end-member processes of melt migration in natural rocks: (1) impregnation features indicate pervasive flow and (2) dykes denote fully segregated flow. Replacive dunite represents an intermediate mode in which porous flow has been channelized. Because the retrograde thermal regime in the upper portion of the mantle wedge is hostile to melt transport, the dominant mechanism by which melts ascend from their source through the mantle remains uncertain. We studied the petro-structural features of melt percolation in a exhumed sub-arc mantle section of the Sapat area in the Kohistan Paleo-Island Arc (NE Pakistan). Our observations indicate a continuum of transport mechanisms ranging from pervasive to fully segregated melt flow: The dominantly harzburgitic mantle section of Sapat exposes tens to hundred of meters size dunitic domains, which comprises clinopyroxene-rich cores associated with gabbroic lenses. The clinopyroxene zones show isolated Cpx blasts, aligned Cpx “trails” and Cpx bands. Gabbro lenses are 3-dimensional lenses terminated horizontally and vertically by clinopyroxene proto-lenses. Proto-lenses refer to Cpx bands prior to plagioclase appearance. Based on bulk and mineral composition, dunite zones formed by orthopyroxene dissolution and olivine crystallization via the peritectic reaction opx + melt = ol; and clinopyroxene-rich parts and gabbros were recognized to have formed from the same melt as dunite. The melt forming gabbros and cpx-rich parts were in near-equilibrium with dunite, but not with the surrounding harzburgite. The structural relationships (i.e parallelism of gabbroic lenses and cpx-trails, and 3D evolution of trails into gabbroic lenses) strengthen the co-genetic origin of the lithologies. Isolated clinopyroxene porphyroblasts evolve into trails that turn into bands in which plagioclase appears. From these observations we infer that the percolation of melt into dunite formed a succession of structures, with increasing melt flux: Isolated clinopyroxene porphyroblasts -> clinopyroxene trails -> clinopyroxene bands -> gabbroic lenses. From the sub-vertically oriented lens-like geometry of the gabbroic lenses and magmatic foliation and lineation we concluded that isolated lenses represent a dynamic mode of melt transport, similar to a self-propagating dyke or porosity wave that has been frozen in place. Indeed, the petrographic-structural features are consistent with numerical two-phase thermo-mechanical model of melt flow, which shows that pervasively distributed melt is channelized by melt-filled waves of porosity. Also, high precision U-Pb ages and Hf isotopic datas on zircons, coupled with bulk rock isotopic analyses, show decoupled isotopic systems, which may be due to this mode of melt transport.

Bouilhol, P.; Connolly, J. A.; Schaltegger, U.; Burg, J.; Chiaradia, M.

2009-12-01

333

Dynamical Meson Melting in Holography  

E-print Network

We discuss mesons in thermalizing gluon backgrounds in the N=2 supersymmetric QCD using the gravity dual. We numerically compute the dynamics of a probe D7-brane in the Vaidya-AdS geometry that corresponds to a D3-brane background thermalizing from zero to finite temperatures by energy injection. In static backgrounds, it has been known that there are two kinds of brane embeddings where the brane intersects the black hole or not. They correspond to the phases with melted or stable mesons. In our dynamical setup, we obtain three cases depending on final temperatures and injection time scales. The brane stays outside of the black hole horizon when the final temperature is low, while it intersects the horizon and settles down to the static equilibrium state when the final temperature is high. Between these two cases, we find the overeager case where the brane dynamically intersects the horizon although the final temperature is not high enough for a static brane to intersect the horizon. The interpretation of thi...

Ishii, Takaaki; Murata, Keiju; Tanahashi, Norihiro

2014-01-01

334

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

335

OECD MCCI project Melt Eruption Test (MET) design report, Rev. 2. April 15, 2003.  

SciTech Connect

The Melt Attack and Coolability Experiments (MACE) program at Argonne National Laboratory addressed the issue of the ability of water to cool and thermally stabilize a molten core-concrete interaction when the reactants are flooded from above. These tests provided data regarding the nature of corium interactions with concrete, the heat transfer rates from the melt to the overlying water pool, and the role of noncondensable gases in the mixing processes that contribute to melt quenching. The Melt Coolability and Concrete Interaction (MCCI) program is pursuing separate effect tests to examine the viability of the melt coolability mechanisms identified as part of the MACE program. These mechanisms include bulk cooling, water ingression, volcanic eruptions, and crust breach. At the second PRG meeting held at ANL on 22-23 October 2002, a preliminary design1 for a separate effects test to investigate the melt eruption cooling mechanism was presented for PRG review. At this meeting, NUPEC made several recommendations on the experiment approach aimed at optimizing the chances of achieving a floating crust boundary condition in this test. The principal recommendation was to incorporate a mortar sidewall liner into the test design, since data from the COTELS experiment program indicates that corium does not form a strong mechanical bond with this material. Other recommendations included: (i) reduction of the electrode elevation to well below the melt upper surface elevation (since the crust may bond to these solid surfaces), and (ii) favorably taper the mortar liner to facilitate crust detachment and relocation during the experiment. Finally, as a precursor to implementing these modifications, the PRG recommended the development of a design for a small-scale scoping test intended to verify the ability of the mortar liner to preclude formation of an anchored bridge crust under core-concrete interaction conditions. This revised Melt Eruption Test (MET) plan is intended to satisfy these PRG recommendations. Specifically, the revised plan focuses on providing data on the extent of crust growth and melt eruptions as a function of gas sparging rate under well-controlled experiment conditions, including a floating crust boundary condition. The overall objective of MET is to determine to what extent core debris is rendered coolable by eruptive-type processes that breach the crust that rests upon the melt. The specific objectives of this test are as follows: (1) Evaluate the augmentation in surface heat flux during periods of melt eruption; (2) Evaluate the melt entrainment coefficient from the heat flux and gas flow rate data for input into models that calculate ex-vessel debris coolability; (3) Characterize the morphology and coolability of debris resulting from eruptive processes that transport melt into overlying water; and (4) Discriminate between periods when eruptions take the form of particle ejections into overlying water, leading to a porous particle bed, and single-phase extrusions, which lead to volcano-type structures.

Farmer, M. T.; Lomperski, S.; Kilsdonk, D. J.; Aeschlimann, R. W.; Basu, S. (Nuclear Engineering Division); (NRC)

2011-05-23

336

Melt segregation in plagioclase-poikilitic mesosiderites  

NASA Technical Reports Server (NTRS)

The Budalan and Mincy mesosiderites contain a poikilitic-plagioclase matrix with orthopyroxene chadacrysts and interstitial-subophitic inverted pigeonite. Orthopyroxene chadacrysts in both mesosiderites are uniformly more aluminous than orthopyroxene clasts, suggesting that they were not derived from clasts by metamorphism. Interstitial inverted pigeonite is more ferroan than adjacent orthopyroxene in the matrix, consistent with the crystallization of a melt with the sequence orthopyroxene followed by pigeonite. The magnesium chadcrysts in Mincy could not have formed from a melt in equilibrium with the clasts but could have crystallized from impact melt. The most Mg chadacrysts are enclosed in large reversely zoned plagioclase crystals as a result of the undercooling in melt-lacking plagioclase clasts and associated nuclei. Mincy contains both plagioclase-poor and plagioclase-rich regions, explained by a separation of silicate melt into pools. Reckling Peak A80258, a plagioclase-poikilitic mesosiderite with a very high chadacryst/plagioclase ratio, resembles Mincy material from which melt has been extracted. It is suggested that the origin of the plagioclase-poikilitic mesosiderites is impact melting of a metal-silicate mixture.

Hewins, R. H.; Harriott, T. A.

1986-01-01

337

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

338

Physics of deep plume melting: komatiitic melt accumulation and segregation in the transition zone  

NASA Astrophysics Data System (ADS)

Komatiites are assumed to be produced in very hot mantle upwellings or plumes. Under such conditions, melting will take place deep within the upper mantle or even within or below the mantle transition zone. Due to its compressibility at such pressures, melt has a higher density than olivine. Whether it would remain buoyant with respect to a peridotitic mantle both above and below the olivine-wadsleyite phase boundary because of the presence of denser garnet remains an open issue, particularly in view of recent X-ray refraction data on molten basalts by Sanloup et al. (2013). We studied the physics of melting and melt segregation within hot upwelling mantle passing through the transition zone, with particular emphasis on the effect of depth-dependent density contrasts between melt and the ambient mantle. Assuming a 1D plume, we solved the two-phase flow equations of the melt-matrix system accounting for matrix compaction and porosity-dependent shear and bulk viscosity. We assumed a constant ascent velocity leading to a constant rate of melt generation. In a first model series, the level of neutral buoyancy zneutral is assumed to lie above the depth of onset of melting, i.e. there exists a region where dense melt may lag behind the solid phases within the rising plume. Depending on two non-dimensional numbers (accumulation number Ac, compaction resistance number Cr) we find four regimes: 1) time-dependent melt accumulation in standing and broadening porosity waves that scale with the compaction length, 2) steady-state weak melt accumulation near zneutral, 3) no melt accumulation due to small density contrast, 4) no melt accumulation due to high matrix viscosity. In regime 4 the high mantle viscosity prevents the opening of pore space and the accumulation of melt. In a second series, the rising mantle crosses the olivine-wadsleyite phase boundary, which imposes a jump in density contrast between melt and ambient mantle. In this case, a sharp melt fraction contrast develops and a large melt fraction accumulates immediately above the phase boundary. In a third set of models, a hot 1D plume head is assumed to move through the transition zone. The top of the plume head remains below the solidus temperature and the melt density is always less than that of the ambient mantle. In this case melt percolates upwards and accumulates near the top of the plume head within a very thin layer, reaching up to 100% melt fraction. These models show 1) that not only melt density, but also porosity dependent matrix viscosity controls the melt ascent or accumulation, 2) that there are parameter ranges and physical conditions which may lead to the accumulation of very large melt fractions (> degree of melting), 3) that in spite of melt being denser than olivine at some depths, in general these melts escape these regions and continue to percolate upward faster than the rising mantle.

Schmeling, Harro; Arndt, Nick; Kohl, Svenja

2014-05-01

339

Generation of liquid water on Mars through the melting of a dusty snowpack  

USGS Publications Warehouse

The possibility that snowmelt could have provided liquid water for valley network formation early in the history of Mars is investigated using an optical-thermal model developed for dusty snowpacks at temperate latitudes. The heating of the postulated snow is assumed to be driven primarily by the absorption of solar radiation during clear sky conditions. Radiative heating rates are predicted as a function of depth and shown to be sensitive to the dust concentration and the size of the ice grains while the thermal conductivity is controlled by temperature, atmospheric pressure, and bulk density. Rates of metamorphism indicate that fresh fine-grained snow on Mars would evolve into moderately coarse snow during a single summer season. Results from global climate models are used to constrain the mean-annual surface temperatures for snow and the atmospheric exchange terms in the surface energy balance. Mean-annual temperatures within Martian snowpacks fail to reach the melting point for all atmospheric pressures below 1000 mbar despite a predicted temperature enhancement beneath the surface of the snowpacks. When seasonal and diurnal variations in the incident solar flux are included in the model, melting occurs at midday during the summer for a wide range of snow types and atmospheric pressures if the dust levels in the snow exceed 100 ppmw (parts per million by weight). The optimum dust concentration appears to be about 1000 ppmw. With this dust load, melting can occur in the upper few centimeters of a dense coarse-grained snow at atmospheric pressures as low as 7 mbar. Snowpack thickness and the thermal conductivity of the underlying substrate determine whether the generated snow-melt can penetrate to the snowpack base, survive basal ice formation, and subsequently become available for runoff. Under favorable conditions, liquid water becomes available for runoff at atmospheric pressures as low as 30 to 100 mbar if the substrate is composed of regolith, as is expected in the ancient cratered terrain of Mars. ?? 1987.

Clow, G. D.

1987-01-01

340

Comparison of CORCON-MOD1 predictions with experimental melt temperature histories  

SciTech Connect

The interaction between molten core materials and the concrete substructure has been identified as a significant phenomenon in Light Water Reactor (LWR) fuel meltdown accidents. High temperature melt/contrete interactions are being studied both experimentally and analytically at Sandia National Laboratories. As part of this program, the CORCON (core/concrete interaction) computer model is being developed to provide quantitative estimates of pertinent phenomena suitable for risk assessment of LWR's. The first version of this program, CORCON-MOD1, has been completed. As an initial code assessment effort, prediction clculations have been performed for the Sandia Code Comparison tests. This paper compares the measured and calculated melt temperature histories and examines their differences.

Muir, J.F.; Corradini, M.L.; Cole, R.K. Jr.

1981-01-06

341

Melt Segregation and Tidal Heating at Io  

NASA Astrophysics Data System (ADS)

Recent evidence of melt beneath Io's surface (Khurana et al., 2010) and repeated observation of volcanic activity and features consistent with volcanic activity at the surface (e.g. Veeder et al, 1994; Rathbun et al., 2004; Lopes-Gautier et al., 1999; Smith et al., 1979) has raised further questions about the structure of the Galilean moon and the processes that shape it. In this study we examine the thermal state, melt fraction, and multiphase dynamics of melt segregation within Io's interior. Using a coupled multiphase dynamics and tidal heating model we explore the location, spatial extent, and temporal residence times of melt in Io's subsurface, as well as response to orbital parameters. In a thermally evolving body subject to tidal forcing, in which melt production and migration takes place, feedback can occur with respect to the physical and thermal properties. We explore this feedback to produce a thermal model of Io, taking into account the rate of tidal heating and fluid motion within the interior. First, a layered model of the internal structure is assumed. The equations of motion for forced oscillations in a layered spherical body are then solved using the propagator matrix method (Sabadini and Vermeesen, 2004) to obtain the displacements and strains due to tidal motion (Roberts and Nimmo, 2008). From this, the radial distribution of tidal heat generation within Io is calculated. This radial heating profile is then used as input for a multi-phase fluid model in order to obtain an estimate of the radial temperature distribution and thus the material properties and melt fractions. In the multiphase model individual phases (melt and solid residue) separately conserve mass, momentum and enthalpy (Dufek and Bachmann, 2010) allowing us to explore melt segregation phenomena. Enthalpy closure is provided by the MELTS (Ghiorso and Sack, 1995) thermodynamics algorithm, which is called at each point in space. This accounts for the partitioning between latent and sensible heat, and updates the physical properties of the melt and solid phase such as density and heat capacity. With this approach we explore the sensitivity of melt generation and the time between melt production and eruption (the residence time) to mantle chemistry and the layered structure of the moon.

Rajendar, A.; Dufek, J.; Roberts, J. H.; Paty, C. S.

2011-12-01

342

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

343

Rapidly solidified titanium alloys by melt overflow  

NASA Technical Reports Server (NTRS)

A pilot plant scale furnace was designed and constructed for casting titanium alloy strips. The furnace combines plasma arc skull melting techniques with melt overflow rapid solidification technology. A mathematical model of the melting and casting process was developed. The furnace cast strip of a suitable length and width for use with honeycomb structures. Titanium alloys Ti-6Al-4V and Ti-14Al-21 Nb were successfully cast into strips. The strips were evaluated by optical metallography, microhardness measurements, chemical analysis, and cold rolling.

Gaspar, Thomas A.; Bruce, Thomas J., Jr.; Hackman, Lloyd E.; Brasmer, Susan E.; Dantzig, Jonathan A.; Baeslack, William A., III

1989-01-01

344

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

345

Local ice melting by an antifreeze protein.  

PubMed

Antifreeze proteins, AFP, impede freezing of bodily fluids and damaging of cellular tissues by low temperatures. Adsorption-inhibition mechanisms have been developed to explain their functioning. Using in silico Molecular Dynamics, we show that type I AFP can also induce melting of the local ice surface. Simulations of antifreeze-positive and antifreeze-negative mutants show a clear correlation between melting induction and antifreeze activity. The presence of local melting adds a function to type I AFPs that is unique to these proteins. It may also explain some apparently conflicting experimental results where binding to ice appears both quasipermanent and reversible. PMID:22657839

Calvaresi, Matteo; Höfinger, Siegfried; Zerbetto, Francesco

2012-07-01

346

Interaction of uranium with nitrate melts  

SciTech Connect

Interaction of metallic uranium with a eutectic mixture of KNO/sub 3/-NaNO/sub 3/ melt at 234-510/sup 0/C in an inert atmosphere is studied. It is shown that the degree of uranium oxidation depends on the melt temperature. At 236-367/sup 0/C uranium dioxide is formed; the latter undergoes oxidation to diuranate at a higher temperature. The interaction is accompanied by accumulation of alkali metal nitrates in a nitrate melt and by NO/sub 2/ evolution.

Denisov, V.P.; Korobeinikov, I.V.; Kutyrev, K.N.; Pyatkov, V.I.; Raspopin, S.P.

1987-07-01

347

Force induced melting of the constrained DNA  

E-print Network

We develop a simple model to study the effects of an applied force on the melting of a double stranded DNA (dsDNA). Using this model, we could study the stretching, unzipping, rupture and slippage like transition in a dsDNA. We show that in absence of an applied force, the melting temperature and the melting profile of dsDNA strongly depend on the constrained imposed on the ends of dsDNA. The nature of the phase boundary which separates the zipped and the open state for the shearing like transition is remarkably different than the DNA unzipping

Amit Raj Singh; D. Giri; S. Kumar

2009-12-12

348

Melting of a finite-sized two-dimensional colloidal crystal  

NASA Astrophysics Data System (ADS)

We have studied the melting process of a finite-sized two-dimensional colloidal crystal by video microscopy. The local area fraction ? and the local hexatic orientational order parameter ?6 have been evaluated for respective Voronoi cells in the crystal. The histogram of ? exhibits a peak and the peak ? continuously decreases with the time elapsed. The histogram of |?6| shows an abrupt broadening for ? <0.65. This critical value of ? is the transition point between the hexatic and dense liquid phases in finite crystal. We have also evaluated ? and |?6| as a function of the distance from the center of the crystal r. ? (r) is almost constant within the crystal and monotonously decreases with the time elapsed. |?6(r)| gradually decreases with r but there is the core with |?6|=1 at earlier time stage. The temporal change of the average ? within the crystal is qualitatively explained by the slow diffusion of the particles situated at the crystal edge. The steric repulsion between the particles within the crystal enhances the expansion rate of the crystal edge. Overall melting behavior is same in the crystals with different sizes. We have also studied the melting of a finite-sized crystal composed of soft-core particles by Brownian dynamics simulation and verified the finite-size effect on the melting process. The simulated behavior is qualitatively in good agreement with the experimental results.

Tanaka, Sayuri; Oki, Yuma; Kimura, Yasuyuki

2014-05-01

349

Experimental alteration of artificial and natural impact melt rock from the Chesapeake Bay impact structure  

USGS Publications Warehouse

The alteration or transformation of impact melt rock to clay minerals, particularly smectite, has been recognized in several impact structures (e.g., Ries, Chicxulub, Mj??lnir). We studied the experimental alteration of two natural impact melt rocks from suevite clasts that were recovered from drill cores into the Chesapeake Bay impact structure and two synthetic glasses. These experiments were conducted at hydrothermal temperature (265 ??C) in order to reproduce conditions found in meltbearing deposits in the first thousand years after deposition. The experimental results were compared to geochemical modeling (PHREEQC) of the same alteration and to original mineral assemblages in the natural melt rock samples. In the alteration experiments, clay minerals formed on the surfaces of the melt particles and as fine-grained suspended material. Authigenic expanding clay minerals (saponite and Ca-smectite) and vermiculite/chlorite (clinochlore) were identified in addition to analcime. Ferripyrophyllite was formed in three of four experiments. Comparable minerals were predicted in the PHREEQC modeling. A comparison between the phases formed in our experiments and those in the cores suggests that the natural alteration occurred under hydrothermal conditions similar to those reproduced in the experiment. ?? 2009 The Geological Society of America.

Declercq, J.; Dypvik, H.; Aagaard, P.; Jahren, J.; Ferrell, Jr. , R. E.; Wright, Horton, Jr. , J.

2009-01-01

350

Modification of Melt-Spun Isotactic Polypropylene and Poly(lactic acid) Bicomponent Filaments with a Premade Block Copolymer  

E-print Network

Modification of Melt-Spun Isotactic Polypropylene and Poly(lactic acid) Bicomponent Filaments copoly- mer to core-sheath filaments consisting of isotactic poly- propylene (iPP) and poly(lactic acid. Polylactide, or poly(lactic acid), (PLA) is produced from lactide monomer, which is obtained from agricultural

Khan, Saad A.

351

On the influence of coil design and electromagnetic configuration on the efficiency of an induction melting furnace  

Microsoft Academic Search

An investigation is done on a novel configuration for an induction melting furnace which is a combination of conventional channel and coreless induction furnaces. The efficiency of the furnace is determined for various coil and magnetic core designs, and these designs are compared with one another. A finite-element simulation of the furnace is done and compared with the results from

Pieter Dorland; Jacobus D. van Wyk; Oskar H. Stielau

2000-01-01

352

On the influence of coil design and electromagnetic configuration on the efficiency of an induction melting furnace  

Microsoft Academic Search

An investigation is done on a novel configuration for an induction melting furnace which is a combination of conventional channel and coreless induction furnaces. The efficiency of the furnace is determined for various coil and magnetic core designs, and these designs are compared with one another. A finite element simulation of the furnace is done and compared with the results

Pieter Dorland; Jacobus D. van Wyk; Oskar H. Stielau

1999-01-01

353

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

354

Characterization of selectively laser melted Ti6Al4 V micro-lattice struts  

Microsoft Academic Search

This paper presents a characterization study of titanium alloy (Ti-6Al-4V) micro-struts manufactured using selective laser melting (SLM). Previous test results from sandwich structures with titanium alloy micro-lattice cores showed that the material experienced brittle fracture failure, although it had a reasonable specific strength. Therefore, the microstructure present in the struts has been investigated in order to understand its influence on

Rafidah Hasan; Robert Mines; Peter Fox

2011-01-01

355

Thermal Modeling of Direct Digital Melt-Deposition Processes  

NASA Astrophysics Data System (ADS)

Additive manufacturing involves creating three-dimensional (3D) objects by depositing materials layer-by-layer. The freeform nature of the method permits the production of components with complex geometry. Deposition processes provide one more capability, which is the addition of multiple materials in a discrete manner to create "heterogeneous" objects with locally controlled composition and microstructure. The result is direct digital manufacturing (DDM) by which dissimilar materials are added voxel-by-voxel (a voxel is volumetric pixel) following a predetermined tool-path. A typical example is functionally gradient material such as a gear with a tough core and a wear-resistant surface. The inherent complexity of DDM processes is such that process modeling based on direct physics-based theory is difficult, especially due to a lack of temperature-dependent thermophysical properties and particularly when dealing with melt-deposition processes. In order to overcome this difficulty, an inverse problem approach is proposed for the development of thermal models that can represent multi-material, direct digital melt deposition. This approach is based on the construction of a numerical-algorithmic framework for modeling anisotropic diffusivity such as that which would occur during energy deposition within a heterogeneous workpiece. This framework consists of path-weighted integral formulations of heat diffusion according to spatial variations in material composition and requires consideration of parameter sensitivity issues.

Cooper, K. P.; Lambrakos, S. G.

2011-02-01

356

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

357

Properties of iron under core conditions  

NASA Astrophysics Data System (ADS)

Underlying an understanding of the geodynamo and evolution of the core is knowledge of the physical and chemical properties of iron and iron mixtures under high pressure and temperature conditions. Key properties include the viscosity of the fluid outer core, thermal diffusivity, equations-of-state, elastic properties of solid phases, and phase equilibria for iron and iron-dominated mixtures. As is expected for work that continues to tax technological and intellectual limits, controversy has followed both experimental and theoretical progress in this field. However, estimates for the melting temperature of the inner core show convergence and the equation-of-state for iron as determined in independent experiments and theories are in remarkable accord. Furthermore, although the structure and elastic properties of the solid inner-core phase remains uncertain, theoretical and experimental underpinnings are better understood and substantial progress is likely in the near future. This talk will focus on an identification of properties that are reasonably well known and those that merit further detailed study. In particular, both theoretical and experimental (static and shock wave) determinations of the density of iron under extreme conditions are in agreement at the 1% or better level. The behavior of the Gruneisen parameter (which determines the geothermal gradient and controls much of the outer core heat flux) is constrained by experiment and theory under core conditions for both solid and liquid phases. Recent experiments and theory are suggestive of structure or structures other than the high-pressure hexagonal close-packed (HCP) phase. Various theories and experiments for the elasticity of HCP iron remain in poor accord. Uncontroversial constraints on core chemistry will likely never be possible. However, reasonable bounds are possible on the basis of seismic profiles, geochemical arguments, and determinations of sound velocities and densities at high pressure and temperature.

Brown, J. M.

2003-04-01

358

Distribution of Siderophile Elements between Mantle and Core in Multistage Core Formation Processes  

NASA Astrophysics Data System (ADS)

The existence of iron meteorites indicates that core formation began in bodies as small as several kilometers due to low pressure melting from heat supplied by the decay of radioactive isotopes. Therefore, the terrestrial planets would be accreted from previously differentiated material. Much of this material could have moved to the center of the planet at the embryo-planet formation stage to form a growing core through percolation and compaction without losing its low-pressure partitioning signature. It is generally thought that the core formation of terrestrial planets such as the Earth involved a magma ocean where metal-silicate equilibration occurred at high pressure in order to explain the observed siderophile element depletions in the Earth's upper mantle. This indicates that the cores of terrestrial planets may be formed from a combination of material: earlier material that equilibrated at low pressures along with later material that equilibrated in deep magma oceans at high pressure. Such core formation process would lead to distinct geochemical signatures dependent on the size of the embryo-planet core formed by the low-pressure process and the pressure dependence of metal-silicate partition coefficients. We have developed models to examine how the overall partitioning signature seen in the modern terrestrial planetary mantles would be affected by this type of multistage partitioning process.

Hier-Majumder, C. A.; Fei, Y.

2006-05-01

359

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

360

Coring Sample Acquisition Tool  

NASA Technical Reports Server (NTRS)

A sample acquisition tool (SAT) has been developed that can be used autonomously to sample drill and capture rock cores. The tool is designed to accommodate core transfer using a sample tube to the IMSAH (integrated Mars sample acquisition and handling) SHEC (sample handling, encapsulation, and containerization) without ever touching the pristine core sample in the transfer process.

Haddad, Nicolas E.; Murray, Saben D.; Walkemeyer, Phillip E.; Badescu, Mircea; Sherrit, Stewart; Bao, Xiaoqi; Kriechbaum, Kristopher L.; Richardson, Megan; Klein, Kerry J.

2012-01-01

361

Sidewall core gun  

Microsoft Academic Search

An apparatus is described for taking core samples from the sidewall of a borehole in a well, the apparatus comprising: a string of drill pipe; at least one gun housing connected to the downhole end of the drill string; at least one coring bullet radially disposed within the gun housing, the coring bullet arranged for securing formation samples from the

E. A. Jr. Colle; D. N. Jr. Yates; E. F. Brieger

1986-01-01

362

Melting of monatomic glass with free surfaces.  

PubMed

Melting of monatomic glass with free surfaces has been studied by molecular dynamics simulations in models with Lennard-Jones-Gauss interatomic potential. Models have been heated up from a glassy state toward a normal liquid state. Atomic mechanism of melting has been analyzed via monitoring spatio-temporal arrangements of liquid-like atoms occurred during heating process. Liquid-like atoms are detected via the Lindemann criterion of melting. It is clear that the transition from glass into supercooled liquid of our "ordinary" glass with free surfaces exhibits a non-heterogeneous behavior, i.e., although liquid-like atoms initiate/grow mainly in the surface shell, significant amount of liquid-like atoms also initiates/grows simultaneously in the interior during heating process. We found three characteristic temperatures of melting of glass with a free surface. Temperature dependence of structure and various thermodynamic quantities of the system upon heating is also presented and discussed. PMID:22423847

Hoang, Vo Van; Dong, To Quy

2012-03-14

363

ESR melting under constant voltage conditions  

SciTech Connect

Typical industrial ESR melting practice includes operation at a constant current. This constant current operation is achieved through the use of a power supply whose output provides this constant current characteristic. Analysis of this melting mode indicates that the ESR process under conditions of constant current is inherently unstable. Analysis also indicates that ESR melting under the condition of a constant applied voltage yields a process which is inherently stable. This paper reviews the process stability arguments for both constant current and constant voltage operation. Explanations are given as to why there is a difference between the two modes of operation. Finally, constant voltage process considerations such as melt rate control, response to electrode anomalies and impact on solidification will be discussed.

Schlienger, M.E.

1997-02-01

364

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

365

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

366

The beginnings of hydrous mantle wedge melting  

NASA Astrophysics Data System (ADS)

This study presents new phase equilibrium data on primitive mantle peridotite (0.33 wt% Na2O, 0.03 wt% K2O) in the presence of excess H2O (14.5 wt% H2O) from 740 to 1,200°C at 3.2-6 GPa. Based on textural and chemical evidence, we find that the H2O-saturated peridotite solidus remains isothermal between 800 and 820°C at 3-6 GPa. We identify both quenched solute from the H2O-rich fluid phase and quenched silicate melt in supersolidus experiments. Chlorite is stable on and above the H2O-saturated solidus from 2 to 3.6 GPa, and chlorite peridotite melting experiments (containing ~6 wt% chlorite) show that melting occurs at the chlorite-out boundary over this pressure range, which is within 20°C of the H2O-saturated melting curve. Chlorite can therefore provide sufficient H2O upon breakdown to trigger dehydration melting in the mantle wedge or perpetuate ongoing H2O-saturated melting. Constraints from recent geodynamic models of hot subduction zones like Cascadia suggest that significantly more H2O is fluxed from the subducting slab near 100 km depth than can be bound in a layer of chloritized peridotite ~ 1 km thick at the base of the mantle wedge. Therefore, the dehydration of serpentinized mantle in the subducted lithosphere supplies free H2O to trigger melting at the H2O-saturated solidus in the lowermost mantle wedge. Alternatively, in cool subduction zones like the Northern Marianas, a layer of chloritized peridotite up to 1.5 km thick could contain all the H2O fluxed from the slab every million years near 100 km depth, which suggests that the dominant form of melting below arcs in cool subduction zones is chlorite dehydration melting. Slab P- T paths from recent geodynamic models also allow for melts of subducted sediment, oceanic crust, and/or sediment diapirs to interact with hydrous mantle melts within the mantle wedge at intermediate to hot subduction zones.

Till, Christy B.; Grove, Timothy L.; Withers, Anthony C.

2012-04-01

367

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

368

PURIFICATION OF IRIDIUM BY ELECTRON BEAM MELTING  

SciTech Connect

The purification of iridium metal by electron beam melting has been characterized for 48 impurity elements. Chemical analysis was performed by glow discharge mass spectrographic (GDMS) analysis for all elements except carbon, which was analyzed by combustion. The average levels of individual elemental impurities in the starting powder varied from 37 g/g to 0.02 g/g. The impurity elements Li, Na, Mg, P, S, Cl, K, Ca, Mn, Co, Ni, Cu, Zn, As, Pd, Ag, Cd, Sn, Sb, Te, Ba, Ce, Tl, Pb, and Bi were not detectable following the purification. No significant change in concentration of the elements Ti, V, Zr, Nb, Mo, and Re was found. The elements B, C, Al, Si, Cr, Fe, Ru, Rh, and Pt were partially removed by vaporization during electron beam melting. Langmuir's equation for ideal vaporization into a vacuum was used to calculate for each impurity element the expected ratio of impurity content after melting to that before melting. Equilibrium vapor pressures were calculated using Henry's law, with activity coefficients obtained from published data for the elements Fe, Ti, and Pt. Activity coefficients were estimated from enthalpy data for Al, Si, V, Cr, Mn, Co, Ni, Zr, Nb, Mo, and Hf and an ideal solution model was used for the remaining elements. The melt temperature was determined from measured iridium weight loss. Excellent agreement was found between measured and calculated impurity ratios for all impurity elements. The results are consistent with some localized heating of the melt pool due to rastering of the electron beam, with an average vaporization temperature of 3100 K as compared to a temperature of 2965 K calculated for uniform heating of the melt pool. The results are also consistent with ideal mixing in the melt pool.

Ohriner, Evan Keith [ORNL

2008-01-01

369

New model better estimates mantle melt percentage  

NASA Astrophysics Data System (ADS)

Studying structures on Earth that arise because of mantle melt—hot spots, mid-ocean ridges, and continental rifts—helps scientists understand the evolution and dynamics of the planet. To quantify the fraction of mantle melting, scientists analyze seismic waves that travel through the mantle and crust, or they conduct a magnetotelluric (MT) survey, which measures the natural variations of the mantle's electrical and magnetic fields.

Wendel, JoAnna

2014-09-01

370

Microstructure devices generation by selective laser melting  

Microsoft Academic Search

Selective Laser Melting (SLM) is a generative manufacturing procedure mainly known for the application with metal powders. From these, metallic structures are produced in a layer-by-layer way. This layer-related procedure is comparable to the stereolithographic manufacturing of polymer devices. On a base plate, a thin layer of metal powder is spread. The powder is locally completely melted by the application

Juergen J. Brandner; Edgar Hansjosten; Eugen Anurjew; Wilhelm Pfleging; Klaus Schubert

2007-01-01

371

Sulfur Contents of Planetary and Protoplanetary Cores  

NASA Astrophysics Data System (ADS)

Sulfur is an important component of protoplanetary cores, as indicated by the presence of sulfides in iron meteorites, as well as the trace element distributions within iron groups that indicate a fractional crystallization process between metal and coexisting sulfide melt. However, sulfur in the Earth’s core is expected to be limited to 2 percent or lower, as indicated by the volatility trend of elements in the bulk Earth (Dreibus and Palme, 1996; McDonough, 2003). This follows an assumption that the order of element volatilities determined in condensation calculations for the solar nebula is also appropriate to the devolatilization of planetary bodies such as the Earth, although planets may have devolatilized by non-nebular processes. The assumption can be evaluated by applying the same logic to the iron meteorites as has been applied to the Earth; the irons exhibit volatility depletions among trace siderophile elements that are similar or greater than the volatile depletions in Earth. Estimates of S content in parent metallic melts have been reported for the IIAB, IID, IIIAB, IVA, and IVB iron meteorite groups (e.g., Chabot, 2004; Wasson and Huber, 2006). Although there are discrepancies between some models, in most cases one finds that the cosmochemical estimates of S abundance in these protoplanetary cores are significantly higher than would be expected on the basis of their volatility trends. For example, CI-normalized S/Ge ratios exceed 100 in some cases. Unless the crystallization models applied to the iron meteorite groups are inaccurate, the assumptions behind the construction of the volatility trends appear to be violated for S in protoplanets (and by extension larger planets, including Earth). Hence, it remains plausible on cosmochemical grounds that Earth’s core is S-rich. Gas speciation and partial pressures in the impact plumes produced during planet formation are very different than those in the low-density, hydrogen-rich solar nebula, and should generate a different volatilization-condensation sequence.

Campbell, A. J.

2009-12-01

372

Planetary cores: a geodynamic perspective (Invited)  

NASA Astrophysics Data System (ADS)

How can measurements of planetary core materials improve our understanding of their geodynamical behaviour? Here I will focus on three aspects of this questions: 1) core formation; 2) the growth and rheology of solid cores; 3) dynamo activity. Core formation occurs either due to the heat generated by short-lived nuclides (for small bodies) or due to gravitational energy released during impacts (for large bodies) [1]. Core formation results in elemental fractionation; such fractionation depends on P,T and oxygen fugacity [2], and for Earth-mass bodies occurs as a succession of discrete events. Experimental measurements of siderophile element partition coefficients are necessary to infer conditions during accretion, though these inferences are non-unique [3]. Core formation may also lead to isotopic fractionation of elements such as Si [4] and Fe [5], although the latter in particular is currently uncertain and merits further experimental investigation. Core solidification depends on the slopes of the adiabat and melting curve, and on the concentration and nature of the light element(s) present [6,7]. Solidification may proceed from outside in (for small bodies) or from inside out (for larger bodies); the solid may be either lighter or heavier than the fluid, depending on the core composition. Thus, core solidification is complex and poorly understood; for instance, Ganymede and Mercury’s cores may be in a completely different solidification regime to that of the Earth [8,9]. Solidification can also vary spatially, giving rise to inner core seismological structure [10,11]. The viscosity of a solid inner core is an important and poorly constrained parameter [12] which controls core deformation, core-mantle coupling and tidal heating. Super-Earths probably lack solid inner cores [13], though further high-P experimental data are needed. Core dynamos are usually thought to be driven by compositional or thermal buoyancy [14] , with the former effect dominant for small bodies. However, forcing driven by tidal or precessional effects may also be important [e.g. 15]. As noted above, the complexities of core solidification can lead to a rich range of potential dynamo styles [e.g. 16]. The long-term evolution of dynamos is governed primarily by the mantle's ability to extract heat from the core. For the Earth, a factor of 2 uncertainty in the thermal conductivity of liquid iron is a current impediment to a better understanding of the dynamo's evolution [14]. [1] Rubie et al. Treat. Geophys. 2007 [2] Righter 2003 [3] Rudge et al. 2010 [4] Ziegler et al. 2010 [5] Polyakov 2009 [6] Chen et al. 2008 [7] Morard et al. 2007 [8] Nimmo & Alfe 2007 [9] Hauck et al. 2006 [10] Monnereau et al. 2010 [11] Alboussiere et al. 2010 [12] Mound & Buffett 2006 [13] Gaidos et al. 2010 [14] Nimmo Treat. Geophys. 2007 [15] Tilgner 2005 [16] Vilim et al. in press

Nimmo, F.

2010-12-01

373

Melting temperature of diamond at ultrahigh pressure  

NASA Astrophysics Data System (ADS)

Since Ross proposed that there might be `diamonds in the sky' in 1981 (ref. 1), the idea of significant quantities of pure carbon existing in giant planets such as Uranus and Neptune has gained both experimental and theoretical support. It is now accepted that the high-pressure, high-temperature behaviour of carbon is essential to predicting the evolution and structure of such planets. Still, one of the most defining of thermal properties for diamond, the melting temperature, has never been directly measured. This is perhaps understandable, given that diamond is thermodynamically unstable, converting to graphite before melting at ambient pressure, and tightly bonded, being the strongest bulk material known. Shock-compression experiments on diamond reported here reveal the melting temperature of carbon at pressures of 0.6-1.1TPa (6-11Mbar), and show that crystalline diamond can be stable deep inside giant planets such as Uranus and Neptune. The data indicate that diamond melts to a denser, metallic fluid-with the melting curve showing a negative Clapeyron slope-between 0.60 and 1.05TPa, in good agreement with predictions of first-principles calculations. Temperature data at still higher pressures suggest diamond melts to a complex fluid state, which dissociates at shock pressures between 1.1 and 2.5TPa (11-25Mbar) as the temperatures increase above 50,000K.

Eggert, J. H.; Hicks, D. G.; Celliers, P. M.; Bradley, D. K.; McWilliams, R. S.; Jeanloz, R.; Miller, J. E.; Boehly, T. R.; Collins, G. W.

2010-01-01

374

Determination of melt influence on divalent element partitioning between anorthite and CMAS melts  

NASA Astrophysics Data System (ADS)

We propose a theory for crystal-melt trace element partitioning that considers the energetic consequences of crystal-lattice strain, of multi-component major-element silicate liquid mixing, and of trace-element activity coefficients in melts. We demonstrate application of the theory using newly determined partition coefficients for Ca, Mg, Sr, and Ba between pure anorthite and seven CMAS liquid compositions at 1330 °C and 1 atm. By selecting a range of melt compositions in equilibrium with a common crystal composition at equal liquidus temperature and pressure, we have isolated the contribution of melt composition to divalent trace element partitioning in this simple system. The partitioning data are fit to Onuma curves with parameterizations that can be thermodynamically rationalized in terms of the melt major element activity product (aO)(a)2 and lattice strain theory modeling. Residuals between observed partition coefficients and the lattice strain plus major oxide melt activity model are then attributed to non-ideality of trace constituents in the liquids. The activity coefficients of the trace species in the melt are found to vary systematically with composition. Accounting for the major and trace element thermodynamics in the melt allows a good fit in which the parameters of the crystal-lattice strain model are independent of melt composition.

Miller, Sarah A.; Asimow, P. D.; Burnett, D. S.

2006-08-01

375

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

376

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

377

Wet melting along the Tonga Volcanic Arc  

NASA Astrophysics Data System (ADS)

Melting in the mantle at convergent margins is driven by water from the subducting slab. Previous work has found a strong role for water-fluxed melting from correlations between the concentration of water in the mantle source, (H2O)o, and the extent of melting beneath backarcs, Fba. Here we explore how wet melting beneath the Lau Backarc Basin relates to that beneath the Tonga Arc, Farc, by providing the first systematic study of water contents in Tonga arc magmas. We have measured volatiles and major and trace elements in melt inclusions, glasses, and whole rocks obtained from recently sampled submarine and subaerial Tonga arc volcanoes. The compositions are varied and range mostly between andesite and basalt/boninite, and least-degassed water contents range from 2 to 5 wt%. We estimate (H2O)o and Farc independently by combining pressure (P) and temperature (T) estimates from an olivine-orthopyroxene-melt thermobarometer with a wet melting productivity model. When P, T, and (H2O)o are known, Farc is uniquely constrained. Results for the volcanoes in the Tonga Arc are bimodal with respect to T: volcanoes located near active backarc spreading centers reflect cooler melting (~1275°C) than those located far from active spreading centers (~1365°C). The cooler primary T’s may result from removal of the heat of fusion during prior melting beneath the Lau backarc, Fba. In the northern portion of the arc, the warmest primary T’s may be due to proximity to the Samoan mantle plume. Farc varies non-systematically along-strike, indicating that Fba is the primary driver of along-arc variability in primary melt compositions. Farc can also be used to calculate the TiO2 concentration of the arc mantle source, (TiO2)o (a proxy for source depletion), which varies monotonically along the Tonga Arc. Arc volcanoes adjacent to the Southern Lau Rifts and Valu Fa Ridge melt mantle with a fertile N-MORB TiO2, while those adjacent to the northern extent of the Eastern Lau Spreading Center (ELSC) reflect more depleted compositions. This variation coincides with a change in primary melt composition from basaltic to boninitic in the middle portion of the ELSC. The depletion trend appears to be related to the relative duration and location of backarc spreading, where the arc in the north entrains mantle that already melted under the backarc. (H2O)o also varies along-strike, peaking at the center of the arc at ~21°S, and may be related to variations in slab fluid composition. This trend is surprising given that the flux of water from the down-going plate must increase to the north, due to the factor of 3 increase in convergence rate along the Tonga Trench. Lastly, (H2O)o and Farc appear to be unrelated in the Tonga Arc, likely due to the impact of other parameters that vary along-strike (e.g., source depletion and mantle T). Only when these other parameters are relatively constant will Farc and (H2O)o vary together. We conclude that the primary driver of the systematic variations observed along the strike of the Tonga Arc is the history of prior melting in the Lau Backarc Basin, which affects source depletion, the melting T, and the magma type erupted.

Cooper, L. B.; Plank, T.; Arculus, R. J.; Hauri, E. H.; Hall, P.

2010-12-01

378

Percolation threshold of Fe-S melt in olivine matrix deduced from in situ electrical conductivity measurement  

NASA Astrophysics Data System (ADS)

The formation a metallic core in a terrestrial planet requires a mechanism for separating and mobilizing Fe-alloy. Measured dihedral angles of well over 60° for molten Fe-alloy in a solid, olivine-rich matrix have apparently precluded metal segregation by grain boundary percolation. However, excess melt over a percolation threshold can create permeability even though the dihedral angle is above the critical value of 60° and some liquid-metal can segregate from the silicate matrix. To determine the percolation threshold for iron alloy melt in crystalline silicate matrix, we performed in situ electrical conductivity measurements on mixtures of olivine and molten FeS compounds with variable volume ratios at high pressure and temperature. Electrical conductivity measurements throughout heating-cooling cycles were conducted at 3GPa using a cubic pressure cell in a DIA-type apparatus. The samples were held at 1473-1573K for over 20 hours to achieve textural equilibrium, which is above the eutectic melting point in the Fe-FeS binary system but below the melting point of Fo90 olivine. After heating at the maximum temperature in runs with metal proportions of 6 vol.% and above, the conductivity was high, nearly constant, and independent of temperature. At lower temperature conditions below the eutectic, preservation of the high conductivity values suggests that the Fe-FeS melt was well connected. In the runs with lower metal proportion (~3 vol.%), conductivities were low and nearly constant up to 873K, but increased considerably as temperature was raised to the maximum temperature. Temperature-conductivity paths in these runs are essentially the same as that without Fe-FeS eutectic melt so we consider that melt was not connected. The percolation threshold of liquid Fe-S compound is approximately 5 vol.%. Dihedral angles determined from these runs were large (95°), consistent with that for pinch-off boundaries predicted by von Bargen and Waff (1986). This suggests that core formation due to the grain boundary percolation can occur when the temperature exceeds the Fe-S melting point. Planetesimals can heat to the FeS melting point within about 3 million years due to radioactive decay of Al26 and Fe60, causing considerable amounts of Fe-alloy to segregate to form a core. This explains the early formation of cores in planetesimals as predicted from Hf-W chronometry, and also provides a mechanism for potential energy release in large proto-planets to form a magma ocean.

Yoshino, T.; Walter, M. J.; Katsura, T.

2002-12-01

379

23. CORE WORKER OPERATING A COREBLOWER THAT PNEUMATICALLY FILLED CORE ...  

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

23. CORE WORKER OPERATING A CORE-BLOWER THAT PNEUMATICALLY FILLED CORE BOXES WITH RESIGN IMPREGNATED SAND AND CREATED A CORE THAT THEN REQUIRED BAKING, CA. 1950. - Stockham Pipe & Fittings Company, 4000 Tenth Avenue North, Birmingham, Jefferson County, AL

380

Express Letter Radial variations of melt viscosity around growing bubbles  

E-print Network

strain rates of the £ow [5,6], the bubble-bearing magma fragments and erupts explosively [7,8]. The gas variations of melt viscosity on the growth of bub- bles. We analyze the hydrodynamic equations of the melt-viscosity rind that forms at the bubble^melt interface. 2. The hydrodynamics of the melt around a growing bubble

Lyakhovsky, Vladimir

381

Elongational viscosity of monodisperse and bidisperse polystyrene melts  

E-print Network

Elongational viscosity of monodisperse and bidisperse polystyrene melts Jens Kromann Nielsen have been measured for two monodisperse polystyrene melts with molecular weights of 52 and 103 kg/mole, and for three bidisperse polystyrene melts. The monodisperse melts show a maximum in the steady elongational

382

Strain localization and melt segregation in deforming metapelites  

Microsoft Academic Search

Crustal rocks commonly experience partial melting in deep parts of orogenic belts. Present concepts predict that the melt generation is directly related to shear localization, which also provides paths for the melt to migrate. Existing experimental studies, however, are insufficient to directly relate melt generation to deformation. We present the results of a series of laboratory experiments on synthetic pelites

Santanu Misra; Luigi Burlini; Jean-Pierre Burg

2009-01-01

383

Density Effects of Melt Extraction from a Mantle Plum Pudding  

Microsoft Academic Search

Both ocean island (plume) and mid ocean ridge melting are thought to tap a lithologically heterogeneous source with both peridotites and `eclogite' recycled basaltic material. We explore how melting of both components effect the density of the upwelling and melting assemblage. Using the thermodynamic modeling program Perplex, two potential mantle sources are put through adiabatic batch and fractional melting to

G. Kirkpatrick; J. Phipps Morgan

2006-01-01

384

Melting relations in the iron-sulfur system at ultra-high pressures - Implications for the thermal state of the earth  

Microsoft Academic Search

The melting temperatures of FeS-troilite and of a 10-wt-pct sulfur iron alloy have been measured to pressures of 120 and 90 GPa, respectively. The results document that FeS melts at a temperature of 4100 (+ or - 300) K at the pressure of the core-mantle boundary. Eutecticlike behavior persists in the iron-sulfur system to the highest pressures of measurements, in

Quentin Williams; Raymond Jeanloz

1990-01-01

385

Core-mantle boundary heat flow  

NASA Astrophysics Data System (ADS)

The Earth can be viewed as a massive heat engine, with various energy sources and sinks. Insights into its evolution can be obtained by quantifying the various energy contributions in the context of the overall energy budget. Over the past decade, estimates of the heat flow across the core-mantle boundary, or across a chemical boundary layer above it, have generally increased by a factor of 2 to 3. The current total heat flow at the Earth's surface - 46 +/- 3 terawatts (1012 J s-1) - involves contributions from heat entering the mantle from the core, as well as mantle cooling, radiogenic heating of the mantle from the decay of radioactive elements, and various minor processes such as tidal deformation, chemical segregation and thermal contraction gravitational heating. The increased estimates of deep-mantle heat flow indicate a more prominent role for thermal plumes in mantle dynamics, more extensive partial melting of the lowermost mantle in the past, and a more rapidly growing and younger inner core and/or presence of significant radiogenic material in the outer core or lowermost mantle as compared with previous estimates.

Lay, Thorne; Hernlund, John; Buffett, Bruce A.

2008-01-01

386

MORECA: A computer code for simulating modular high-temperature gas-cooled reactor core heatup accidents  

SciTech Connect

The design features of the modular high-temperature gas-cooled reactor (MHTGR) have the potential to make it essentially invulnerable to damage from postulated core heatup accidents. This report describes the ORNL MORECA code, which was developed for analyzing postulated long-term core heatup scenarios for which active cooling systems used to remove afterheat following the accidents can be assumed to the unavailable. Simulations of long-term loss-of-forced-convection accidents, both with and without depressurization of the primary coolant, have shown that maximum core temperatures stay below the point at which any significant fuel failures and fission product releases are expected. Sensitivity studies also have been done to determine the effects of errors in the predictions due both to uncertainties in the modeling and to the assumptions about operational parameters. MORECA models the US Department of Energy reference design of a standard MHTGR.

Ball, S.J. (Oak Ridge National Lab., TN (United States))

1991-10-01

387

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

388

PHYSICAL REVIEW B VOLUME 20, NUMBER 1 I JULY 1979 Duality relations for the Gaussian core model  

E-print Network

of the Gaussian core model at absolute-zero temperature exhibits duality relations, In the cases of one and two-density limit, and they suggest (but do not prove) an asymptotic scaling for melting and freezing temperatures in the same limit ~ I. INTRODUCTION II. ONE DIMENSION The "Gaussian core model" consists of a set of point

Stillinger, Frank

389

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

NASA Astrophysics Data System (ADS)

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