The gallium melting-point standard: its role in our temperature measurement system.

PubMed

Mangum, B W

1977-01-01

The latest internationally-adopted temperature scale, the International Practical Temperature Scale of 1968 (amended edition of 1975), is discussed in some detail and a brief description is given of its evolution. The melting point of high-purity gallium (stated to be at least 99.99999% pure) as a secondary temperature reference point is evaluated. I believe that this melting-point temperature of gallium should be adopted by the various medical professional societies and voluntary standards groups as the reaction temperature for enzyme reference methods in clinical enzymology. Gallium melting-point cells are available at the National Bureau of Standards as Standard Reference Material No. 1968.

Melting Point Depression and Fast Diffusion in Nanostructured Brazing Fillers Confined Between Barrier Nanolayers

NASA Astrophysics Data System (ADS)

Kaptay, G.; Janczak-Rusch, J.; Jeurgens, L. P. H.

2016-08-01

Successful brazing using Cu-based nanostructured brazing fillers at temperatures much below the bulk melting temperature of Cu was recently demonstrated (Lehmert et al. in, Mater Trans 56:1015-1018, 2015). The Cu-based nano-fillers are composed of alternating nanolayers of Cu and a permeable, non-wetted AlN barrier. In this study, a thermodynamic model is derived to estimate the melting point depression (MPD) in such Cu/AlN nano-multilayers (NMLs) as function of the Cu nanolayer thickness. Depending on the melting route, the model predicts a MPD range of 238-609 K for Cu10nm/AlN10nm NMLs, which suggests a heterogeneous pre-melting temperature range of 750-1147 K (476-874 °C), which is consistent with experimental observations. As suggested by basic kinetic considerations, the observed Cu outflow to the NML surface at the temperatures of 723-1023 K (450-750 °C) can also be partially rationalized by fast solid-state diffusion of Cu along internal interfaces, especially for the higher temperatures.

Low-melting point heat transfer fluid

DOEpatents

Cordaro, Joseph Gabriel; Bradshaw, Robert W.

2010-11-09

A low-melting point, heat transfer fluid made of a mixture of five inorganic salts including about 29.1-33.5 mol % LiNO.sub.3, 0-3.9 mol % NaNO.sub.3, 2.4-8.2 mol % KNO.sub.3, 18.6-19.9 mol % NaNO.sub.2, and 40-45.6 mol % KNO.sub.2. These compositions can have liquidus temperatures below 80.degree. C. for some compositions.

Thermal diffusivity of UO2 up to the melting point

NASA Astrophysics Data System (ADS)

Vlahovic, L.; Staicu, D.; Küst, A.; Konings, R. J. M.

2018-02-01

The thermal diffusivity of uranium dioxide was measured from 500 to 3060 K with two different set-ups, both based on the laser-flash technique. Above 1600 K the measurements were performed with an advanced laser-flash technique, which was slightly improved in comparison with a former work. In the temperature range 500-2000 K the thermal diffusivity is decreasing, then relatively constant up to 2700 K, and tends to increase by approaching the melting point. The measurements of the thermal diffusivity in the vicinity of the melting point are possible under certain conditions, and are discussed in this paper.

A density functional theory based approach for predicting melting points of ionic liquids

DOE PAGES

Chen, Lihua; Bryantsev, Vyacheslav S.

2017-01-17

Accurate prediction of melting points of ILs is important both from the fundamental point of view and from the practical perspective for screening ILs with low melting points and broadening their utilization in a wider temperature range. In this work, we present an ab initio approach to calculating melting points of ILs with known crystal structures and illustrate its application for a series of 11 ILs containing imidazolium/pyrrolidinium cations and halide/polyatomic fluoro-containing anions. The melting point is determined as a temperature at which the Gibbs free energy of fusion is zero. The Gibbs free energy of fusion can be expressedmore » through the use of the Born-Fajans-Haber cycle via the lattice free energy of forming a solid IL from gaseous phase ions and the sum of the solvation free energies of ions comprising IL. Dispersion-corrected density functional theory (DFT) involving (semi)local (PBE-D3) and hybrid exchange-correlation (HSE06-D3) functionals is applied to estimate the lattice enthalpy, entropy, and free energy. The ions solvation free energies are calculated with the SMD-generic-IL solvation model at the M06-2X/6-31+G(d) level of theory under standard conditions. The melting points of ILs computed with the HSE06-D3 functional are in good agreement with the experimental data, with a mean absolute error of 30.5 K and a mean relative error of 8.5%. The model is capable of accurately reproducing the trends in melting points upon variation of alkyl substituents in organic cations and replacement one anion by another. The results verify that the lattice energies of ILs containing polyatomic fluoro-containing anions can be approximated reasonably well using the volume-based thermodynamic approach. However, there is no correlation of the computed lattice energies with molecular volume for ILs containing halide anions. Moreover, entropies of solid ILs follow two different linear relationships with molecular volume for halides and polyatomic fluoro

A density functional theory based approach for predicting melting points of ionic liquids

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

Chen, Lihua; Bryantsev, Vyacheslav S.

Accurate prediction of melting points of ILs is important both from the fundamental point of view and from the practical perspective for screening ILs with low melting points and broadening their utilization in a wider temperature range. In this work, we present an ab initio approach to calculating melting points of ILs with known crystal structures and illustrate its application for a series of 11 ILs containing imidazolium/pyrrolidinium cations and halide/polyatomic fluoro-containing anions. The melting point is determined as a temperature at which the Gibbs free energy of fusion is zero. The Gibbs free energy of fusion can be expressedmore » through the use of the Born-Fajans-Haber cycle via the lattice free energy of forming a solid IL from gaseous phase ions and the sum of the solvation free energies of ions comprising IL. Dispersion-corrected density functional theory (DFT) involving (semi)local (PBE-D3) and hybrid exchange-correlation (HSE06-D3) functionals is applied to estimate the lattice enthalpy, entropy, and free energy. The ions solvation free energies are calculated with the SMD-generic-IL solvation model at the M06-2X/6-31+G(d) level of theory under standard conditions. The melting points of ILs computed with the HSE06-D3 functional are in good agreement with the experimental data, with a mean absolute error of 30.5 K and a mean relative error of 8.5%. The model is capable of accurately reproducing the trends in melting points upon variation of alkyl substituents in organic cations and replacement one anion by another. The results verify that the lattice energies of ILs containing polyatomic fluoro-containing anions can be approximated reasonably well using the volume-based thermodynamic approach. However, there is no correlation of the computed lattice energies with molecular volume for ILs containing halide anions. Moreover, entropies of solid ILs follow two different linear relationships with molecular volume for halides and polyatomic fluoro

Theoretical Understanding the Relations of Melting-point Determination Methods from Gibbs Thermodynamic Surface and Applications on Melting Curves of Lower Mantle Minerals

NASA Astrophysics Data System (ADS)

Yin, K.; Belonoshko, A. B.; Zhou, H.; Lu, X.

2016-12-01

The melting temperatures of materials in the interior of the Earth has significant implications in many areas of geophysics. The direct calculations of the melting point by atomic simulations would face substantial hysteresis problem. To overcome the hysteresis encountered in the atomic simulations there are a few different melting-point determination methods available nowadays, which are founded independently, such as the free energy method, the two-phase or coexistence method, and the Z method, etc. In this study, we provide a theoretical understanding the relations of these methods from a geometrical perspective based on a quantitative construction of the volume-entropy-energy thermodynamic surface, a model first proposed by J. Willard Gibbs in 1873. Then combining with an experimental data and/or a previous melting-point determination method, we apply this model to derive the high-pressure melting curves for several lower mantle minerals with less computational efforts relative to using previous methods only. Through this way, some polyatomic minerals at extreme pressures which are almost unsolvable before are calculated fully from first principles now.

The melting point of lithium: an orbital-free first-principles molecular dynamics study

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

Chen, Mohan; Hung, Linda; Huang, Chen

2013-08-25

The melting point of liquid lithium near zero pressure is studied with large-scale orbital-free first-principles molecular dynamics (OF-FPMD) in the isobaric-isothermal ensemble. Here, we adopt the Wang-Govind-Carter (WGC) functional as our kinetic energy density functional (KEDF) and construct a bulk-derived local pseudopotential (BLPS) for Li. Our simulations employ both the ‘heat-until-melts’ method and the coexistence method. We predict 465 K as an upper bound of the melting point of Li from the ‘heat-until-melts’ method, while we predict 434 K as the melting point of Li from the coexistence method. These values compare well with an experimental melting point of 453more » K at zero pressure. Furthermore, we calculate a few important properties of liquid Li including the diffusion coefficients, pair distribution functions, static structure factors, and compressibilities of Li at 470 K and 725 K in the canonical ensemble. This theoretically-obtained results show good agreement with known experimental results, suggesting that OF-FPMD using a non-local KEDF and a BLPS is capable of accurately describing liquid metals.« less

Hydrogenation and interesterification effects on the oxidative stability and melting point of soybean oil.

PubMed

Daniels, Roger L; Kim, Hyun Jung; Min, David B

2006-08-09

Soybean oil with an iodine value of 136 was hydrogenated to have iodine values of 126 and 117. The soybean oils with iodine values of 136, 126, and 117 were randomly interesterified using sodium methoxide. The oxidative stabilities of the hydrogenated and/or interesterified soybean oils were evaluated by measuring the headspace oxygen content by gas chromatography, and the induction time was measured using Rancimat. The melting points of the oils were evaluated by differential scanning calorimetry. Duncan's multiple range test of the headspace oxygen and induction time showed that hydrogenation increased the headspace oxygen content and induction time at alpha = 0.05. Interesterification decreased the headspace oxygen and the induction time for the soybean oils with iodine values of 136, 126, and 117 at alpha = 0.05. Hydrogenation increased the melting points as the iodine value decreased from 136 and 126 to 117 at alpha = 0.05. The random interesterification increased the melting points of soybean oils with iodine values of 136, 126, and 117 at alpha = 0.05. The combined effects of hydrogenation and interesterification increased the oxidative stability of soybean oil at alpha = 0.05 and the melting point at alpha = 0.01. The optimum combination of hydrogenation and random interesterification can improve the oxidative stability and increase the melting point to expand the application of soybean oil in foods.

Effect of Melting Point on the Physical Properties of Anhydrous Milk Fat

NASA Astrophysics Data System (ADS)

Wang, Yunna; Li, Yang; Han, Jie; Li, Yan; Zhang, Liebing

2017-12-01

The effect of melting point on the physical properties of anhydrous milk fat were investigated. The results showed that high melting fractions (HMF) (S30,S35) were enriched in long-chain fatty acids, whereas low melting fractions (LMF)(S5,S10,S15) were enriched in short-chain and unsaturated fatty acids. From S5 to S35, enthalpy value was gradually increased on both crystallization and melting condition, so as SFC on different temperature. The mixture and chemical interesterification allowed obtaining fats with various degrees of plasticity, increasing the possibilities for the commercial use of different fraction of AMF.

Palm-Based Standard Reference Materials for Iodine Value and Slip Melting Point

PubMed Central

Tarmizi, Azmil Haizam Ahmad; Lin, Siew Wai; Kuntom, Ainie

2008-01-01

This work described study protocols on the production of Palm-Based Standard Reference Materials for iodine value and slip melting point. Thirty-three laboratories collaborated in the inter-laboratory proficiency tests for characterization of iodine value, while thirty-two laboratories for characterization of slip melting point. The iodine value and slip melting point of palm oil, palm olein and palm stearin were determined in accordance to MPOB Test Methods p3.2:2004 and p4.2:2004, respectively. The consensus values and their uncertainties were based on the acceptability of statistical agreement of results obtained from collaborating laboratories. The consensus values and uncertainties for iodine values were 52.63 ± 0.14 Wijs in palm oil, 56.77 ± 0.12 Wijs in palm olein and 33.76 ± 0.18 Wijs in palm stearin. For the slip melting points, the consensus values and uncertainties were 35.6 ± 0.3 °C in palm oil, 22.7 ± 0.4 °C in palm olein and 53.4 ± 0.2 °C in palm stearin. Repeatability and reproducibility relative standard deviations were found to be good and acceptable, with values much lower than that of 10%. Stability of Palm-Based Standard Reference Materials remained stable at temperatures of −20 °C, 0 °C, 6 °C and 24 °C upon storage for one year. PMID:19609396

Low-melting point heat transfer fluid

DOEpatents

Cordaro, Joseph G [Oakland, CA; Bradshaw, Robert W [Livermore, CA

2011-04-12

A low-melting point, heat transfer fluid comprising a mixture of LiNO.sub.3, NaNO.sub.3, KNO.sub.3, NaNO.sub.2 and KNO.sub.2 salts where the Li, Na and K cations are present in amounts of about 20-33.5 mol % Li, about 18.6-40 mol % Na, and about 40-50.3 mol % K and where the nitrate and nitrite anions are present in amounts of about 36-50 mol % NO.sub.3, and about 50-62.5 mol % NO.sub.2. These compositions can have liquidus temperatures between 70.degree. C. and 80.degree. C. for some compositions.

46 CFR 153.908 - Cargo viscosity and melting point information; measuring cargo temperature during discharge...

Code of Federal Regulations, 2014 CFR

2014-10-01

... 46 Shipping 5 2014-10-01 2014-10-01 false Cargo viscosity and melting point information; measuring... Cargo viscosity and melting point information; measuring cargo temperature during discharge: Categories... lading, a written statement of the following: (1) For Category A or B NLS, the cargo's viscosity at 20 °C...

46 CFR 153.908 - Cargo viscosity and melting point information; measuring cargo temperature during discharge...

Code of Federal Regulations, 2013 CFR

2013-10-01

... 46 Shipping 5 2013-10-01 2013-10-01 false Cargo viscosity and melting point information; measuring... Cargo viscosity and melting point information; measuring cargo temperature during discharge: Categories... lading, a written statement of the following: (1) For Category A or B NLS, the cargo's viscosity at 20 °C...

46 CFR 153.908 - Cargo viscosity and melting point information; measuring cargo temperature during discharge...

Code of Federal Regulations, 2012 CFR

2012-10-01

... 46 Shipping 5 2012-10-01 2012-10-01 false Cargo viscosity and melting point information; measuring... Cargo viscosity and melting point information; measuring cargo temperature during discharge: Categories... lading, a written statement of the following: (1) For Category A or B NLS, the cargo's viscosity at 20 °C...

Heat transfer in melt ponds with convection and radiative heating: observationally-inspired modelling

NASA Astrophysics Data System (ADS)

Wells, A.; Langton, T.; Rees Jones, D. W.; Moon, W.; Kim, J. H.; Wilkinson, J.

2016-12-01

Melt ponds have key impacts on the evolution of Arctic sea ice and summer ice melt. Small changes to the energy budget can have significant consequences, with a net heat-flux perturbation of only a few Watts per square metre sufficient to explain the thinning of sea ice over recent decades. Whilst parameterisations of melt-pond thermodynamics often assume that pond temperatures remain close to the freezing point, recent in-situ observations show more complex thermal structure with significant diurnal and synoptic variability. We here consider the energy budget of melt ponds and explore the role of internal convective heat transfer in determining the thermal structure within the pond in relatively calm conditions with low winds. We quantify the energy fluxes and temperature variability using two-dimensional direct numerical simulations of convective turbulence within a melt pond, driven by internal radiative heating and surface fluxes. Our results show that the convective flow dynamics are modulated by changes to the incoming radiative flux and sensible heat flux at the pond surface. The evolving pond surface temperature controls the outgoing longwave emissions from the pond. Hence the convective flow modifies the net energy balance of a melt pond, modulating the relative fractions of the incoming heat flux that is re-emitted to the atmosphere or transferred downward into the sea ice to drive melt.

Estimating the physicochemical properties of polyhalogenated aromatic and aliphatic compounds using UPPER: part 1. Boiling point and melting point.

PubMed

Admire, Brittany; Lian, Bo; Yalkowsky, Samuel H

2015-01-01

The UPPER (Unified Physicochemical Property Estimation Relationships) model uses enthalpic and entropic parameters to estimate 20 biologically relevant properties of organic compounds. The model has been validated by Lian and Yalkowsky on a data set of 700 hydrocarbons. The aim of this work is to expand the UPPER model to estimate the boiling and melting points of polyhalogenated compounds. In this work, 19 new group descriptors are defined and used to predict the transition temperatures of an additional 1288 compounds. The boiling points of 808 and the melting points of 742 polyhalogenated compounds are predicted with average absolute errors of 13.56 K and 25.85 K, respectively. Copyright © 2014 Elsevier Ltd. All rights reserved.

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

NASA Astrophysics Data System (ADS)

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

2017-02-01

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

SHORT COMMUNICATION: Correlation between the Resistance Ratios of Platinum Resistance Thermometers at the Melting Point of Gallium and the Triple Point of Mercury

NASA Astrophysics Data System (ADS)

Singh, Y. P.; Maas, H.; Edler, F.; Zaidi, Z. H.

1994-01-01

A set of resistance ratios (W) for platinum resistance thermometers was obtained at the triple point of Hg and the melting point of Ga in order to study their relationship. It was found that using measured values for one of the fixed points, a linear equation will predict the value of the other. These measurements also indicate that the fixed points of Hg and of Ga are inconsistent by about 1,5 mK in the sense that either the melting point of Ga or the triple point of Hg was assigned too high a value on the ITS-90.

Evaluation of methods for characterizing the melting curves of a high temperature cobalt-carbon fixed point to define and determine its melting temperature

NASA Astrophysics Data System (ADS)

Lowe, David; Machin, Graham

2012-06-01

The future mise en pratique for the realization of the kelvin will be founded on the melting temperatures of particular metal-carbon eutectic alloys as thermodynamic temperature references. However, at the moment there is no consensus on what should be taken as the melting temperature. An ideal melting or freezing curve should be a completely flat plateau at a specific temperature. Any departure from the ideal is due to shortcomings in the realization and should be accommodated within the uncertainty budget. However, for the proposed alloy-based fixed points, melting takes place over typically some hundreds of millikelvins. Including the entire melting range within the uncertainties would lead to an unnecessarily pessimistic view of the utility of these as reference standards. Therefore, detailed analysis of the shape of the melting curve is needed to give a value associated with some identifiable aspect of the phase transition. A range of approaches are or could be used; some purely practical, determining the point of inflection (POI) of the melting curve, some attempting to extrapolate to the liquidus temperature just at the end of melting, and a method that claims to give the liquidus temperature and an impurity correction based on the analytical Scheil model of solidification that has not previously been applied to eutectic melting. The different methods have been applied to cobalt-carbon melting curves that were obtained under conditions for which the Scheil model might be valid. In the light of the findings of this study it is recommended that the POI continue to be used as a pragmatic measure of temperature but where required a specified limits approach should be used to define and determine the melting temperature.

An observational and thermodynamic investigation of carbonate partial melting

NASA Astrophysics Data System (ADS)

Floess, David; Baumgartner, Lukas P.; Vonlanthen, Pierre

2015-01-01

Melting experiments available in the literature show that carbonates and pelites melt at similar conditions in the crust. While partial melting of pelitic rocks is common and well-documented, reports of partial melting in carbonates are rare and ambiguous, mainly because of intensive recrystallization and the resulting lack of criteria for unequivocal identification of melting. Here we present microstructural, textural, and geochemical evidence for partial melting of calcareous dolomite marbles in the contact aureole of the Tertiary Adamello Batholith. Petrographic observations and X-ray micro-computed tomography (X-ray μCT) show that calcite crystallized either in cm- to dm-scale melt pockets, or as an interstitial phase forming an interconnected network between dolomite grains. Calcite-dolomite thermometry yields a temperature of at least 670 °C, which is well above the minimum melting temperature of ∼600 °C reported for the CaO-MgO-CO2-H2O system. Rare-earth element (REE) partition coefficients (KDcc/do) range between 9-35 for adjacent calcite-dolomite pairs. These KD values are 3-10 times higher than equilibrium values between dolomite and calcite reported in the literature. They suggest partitioning of incompatible elements into a melt phase. The δ18O and δ13C isotopic values of calcite and dolomite support this interpretation. Crystallographic orientations measured by electron backscattered diffraction (EBSD) show a clustering of c-axes for dolomite and interstitial calcite normal to the foliation plane, a typical feature for compressional deformation, whereas calcite crystallized in pockets shows a strong clustering of c-axes parallel to the pocket walls, suggesting that it crystallized after deformation had stopped. All this together suggests the formation of partial melts in these carbonates. A Schreinemaker analysis of the experimental data for a CO2-H2O fluid-saturated system indeed predicts formation of calcite-rich melt between 650-880 °C, in

Multi-platform observations on melt pond in Arctic summer 2010

NASA Astrophysics Data System (ADS)

Wang, Y.; Huang, W.; Lu, P.; Li, Z.

2011-12-01

Melt ponds play an important role in sea ice surface albedo and further affect the heat budget between ice-air interface. The overall reductions of Arctic sea ice extend and thickness especially in recent years is considered to be enhanced partly by the melt ponds, and understanding of melt ponds on how they change the heat and mass balance of sea ice through the ice surface albedo decrease is urgently required. Although satellite remote sensing is a general tool to observe sea ice surface features on a large scale, the small scale information with higher spatial and temporal resolution is more helpful to understand the physical mechanism in the evolution of melt ponds. Arctic summer in 2010 is special because of an obvious trans-polar melting, during which the multi-year ice in the central Arctic was seriously melted, and formed a trans-polar zone with ice concentration less than 80% stretching from the Chukchi Sea to the Greenland Sea. It provided a fantastic opportunity to observe melt ponds especially at the high latitude. The Fourth Chinese National Arctic Research Expedition in 2010 (CHINARE-2010) was carried out from July 1 to September 20, 2010. As R/V Xuelong sailing in the ice-infested seas, a multi-platform observation was conducted to investigate the evolution of melt ponds on Arctic sea ice. Among which, aerial photography provided a downward-looking snapshot of the ice surface by using the camera installed on a helicopter, and melt pond information on a 100-meter scale can be obtained. Shipboard photography gave an inclined inspection on the ice conditions beside the ship using the camera installed on the vessel, and melt pond information on a 10-meter scale can be determined. Ground-based photography was similar to the shipboard photography, but the camera with tilt angle was installed on the top of a vertical lifting device fixed on the ice, and melt pond information on a 1-meter scale can be observed. Over 10,000 sea ice images from different

In situ observation of melting and crystallization of Si on porous Si3N4 substrate that repels Si melt

NASA Astrophysics Data System (ADS)

Itoh, Hironori; Okamura, Hideyuki; Asanoma, Susumu; Ikemura, Kouhei; Nakayama, Masaharu; Komatsu, Ryuichi

2014-09-01

High temperature in situ observation of melting and crystallization of spherical Si droplets on a substrate with a porous surface was carried out for the first time using an original in situ observation apparatus. The contact angle between the Si melt and the substrate was measured to be 160°, with the Si melt forming spherical droplets on the substrate. During crystallization, a ring-like pattern was observed on the surface of the spherical Si melt droplets due to crystal growth at low levels of supercooling. The solidified spherical Si crystals consisted of single or twin grains. This demonstrates that high-quality spherical Si crystals can be prepared easily and stably by using a Si melt-repelling substrate.

Models for mean bonding length, melting point and lattice thermal expansion of nanoparticle materials

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

Omar, M.S., E-mail: dr_m_s_omar@yahoo.com

2012-11-15

Graphical abstract: Three models are derived to explain the nanoparticles size dependence of mean bonding length, melting temperature and lattice thermal expansion applied on Sn, Si and Au. The following figures are shown as an example for Sn nanoparticles indicates hilly applicable models for nanoparticles radius larger than 3 nm. Highlights: ► A model for a size dependent mean bonding length is derived. ► The size dependent melting point of nanoparticles is modified. ► The bulk model for lattice thermal expansion is successfully used on nanoparticles. -- Abstract: A model, based on the ratio number of surface atoms to thatmore » of its internal, is derived to calculate the size dependence of lattice volume of nanoscaled materials. The model is applied to Si, Sn and Au nanoparticles. For Si, that the lattice volume is increases from 20 Å{sup 3} for bulk to 57 Å{sup 3} for a 2 nm size nanocrystals. A model, for calculating melting point of nanoscaled materials, is modified by considering the effect of lattice volume. A good approach of calculating size-dependent melting point begins from the bulk state down to about 2 nm diameter nanoparticle. Both values of lattice volume and melting point obtained for nanosized materials are used to calculate lattice thermal expansion by using a formula applicable for tetrahedral semiconductors. Results for Si, change from 3.7 × 10{sup −6} K{sup −1} for a bulk crystal down to a minimum value of 0.1 × 10{sup −6} K{sup −1} for a 6 nm diameter nanoparticle.« less

Improvement of gel strength and melting point of fish gelatin by addition of coenhancers using response surface methodology.

PubMed

Koli, Jayappa M; Basu, Subrata; Nayak, Binay B; Kannuchamy, Nagalakshmi; Gudipati, Venkateshwarlu

2011-08-01

Fish gelatin is a potential alternative to mammalian gelatin. However, poor gel strength and low melting point limit its applications. The study was aimed at improving these properties by adding coenhancers in the range obtained from response surface methodology (RSM) by using Box-Behnken design. Three different coenhancers, MgSO₄, sucrose, and transglutaminase were used as the independent variables for improving the gel strength and melting point of gelatin extracted from Tiger-toothed croaker (Otolithes ruber). Addition of coenhancers at different combinations resulted gel strength and melting point in the range of 150.5 to 240.5 g and 19.5 to 22.5 °C, respectively. The optimal concentrations of coenhancers for predicted maximum gel strength (242.8 g) obtained by RSM were 0.23 M MgSO₄, 12.60% sucrose (w/v), and 5.92 mg/g transglutaminase and for predicted maximum melting point (22.57 °C), the values were 0.24 M MgSO₄, 10.44% sucrose (w/v), and 5.72 mg/g transglutaminase. By addition of coenhancers at these optimal concentrations in verification experiments, the gel strength and melting point were improved from 170 to 240.89 g and 20.3 to 22.7 °C, respectively. These experimental values agreed well with the predicted values demonstrating the fitness of the models. Results from the present study clearly revealed that the addition of coenhancers at a particular combination can improve the gel strength and melting point of fish gelatin to enhance its range of applications. There is a growing interest in the use of fish gelatin as an alternative to mammalian gelatin. However, poor gel strength and low melting point of fish gelatin have limited its commercial applications. The gel strength and melting point of fish gelatin can be increased by incorporation of coenhancers such as magnesium sulphate, sucrose, and transglutaminase. Results of this work help to produce the fish gelatin suitable for wide range of applications in the food industry. © 2011 Institute

Models and observations of Arctic melt ponds

NASA Astrophysics Data System (ADS)

Golden, K. M.

2016-12-01

During the Arctic melt season, the sea ice surface undergoes a striking transformation from vast expanses of snow covered ice to complex mosaics of ice and melt ponds. Sea ice albedo, a key parameter in climate modeling, is largely determined by the complex evolution of melt pond configurations. In fact, ice-albedo feedback has played a significant role in the recent declines of the summer Arctic sea ice pack. However, understanding melt pond evolution remains a challenge to improving climate projections. It has been found that as the ponds grow and coalesce, the fractal dimension of their boundaries undergoes a transition from 1 to about 2, around a critical length scale of 100 square meters in area. As the ponds evolve they take complex, self-similar shapes with boundaries resembling space-filling curves. I will outline how mathematical models of composite materials and statistical physics, such as percolation and Ising models, are being used to describe this evolution and predict key geometrical parameters that agree very closely with observations.

Estimating the melting point, entropy of fusion, and enthalpy of fusion of organic compounds via SPARC.

PubMed

Whiteside, T S; Hilal, S H; Brenner, A; Carreira, L A

2016-08-01

The entropy of fusion, enthalpy of fusion, and melting point of organic compounds can be estimated through three models developed using the SPARC (SPARC Performs Automated Reasoning in Chemistry) platform. The entropy of fusion is modelled through a combination of interaction terms and physical descriptors. The enthalpy of fusion is modelled as a function of the entropy of fusion, boiling point, and flexibility of the molecule. The melting point model is the enthalpy of fusion divided by the entropy of fusion. These models were developed in part to improve SPARC's vapour pressure and solubility models. These models have been tested on 904 unique compounds. The entropy model has a RMS of 12.5 J mol(-1) K(-1). The enthalpy model has a RMS of 4.87 kJ mol(-1). The melting point model has a RMS of 54.4°C.

Greenland iceberg melt variability from high-resolution satellite observations

NASA Astrophysics Data System (ADS)

Enderlin, Ellyn M.; Carrigan, Caroline J.; Kochtitzky, William H.; Cuadros, Alexandra; Moon, Twila; Hamilton, Gordon S.

2018-02-01

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

[Fine stereo structure for natural organic molecules, a preliminary study. II. Melting point influenced by structure factors].

PubMed

Lu, Y; Zheng, Q; Lu, D; Ma, P; Chen, Y

1995-06-01

Crystal structures of two compounds from Tripterygium wilfordii Hook f. have been determined by X-ray diffraction method. Structure factors influencing melting point of solid state have been analysed. Crystal class (or space group), recrystallization solvent, force between molecules and fine changes of molecular structures will all cause melting point changes of crystal substance.

Ice shelf basal melt rates around Antarctica from simulations and observations

NASA Astrophysics Data System (ADS)

Schodlok, M. P.; Menemenlis, D.; Rignot, E. J.

2016-02-01

We introduce an explicit representation of Antarctic ice shelf cavities in the Estimating the Circulation and Climate of the Ocean, Phase II (ECCO2) ocean retrospective analysis; and compare resulting basal melt rates and patterns to independent estimates from satellite observations. Two simulations are carried out: the first is based on the original ECCO2 vertical discretization; the second has higher vertical resolution particularly at the depth range of ice shelf cavities. The original ECCO2 vertical discretization produces higher than observed melt rates and leads to a misrepresentation of Southern Ocean water mass properties and transports. In general, thicker levels at the base of the ice shelves lead to increased melting because of their larger heat capacity. This strengthens horizontal gradients and circulation within and outside the cavities and, in turn, warm water transports from the shelf break to the ice shelves. The simulation with more vertical levels produces basal melt rates (1735 ± 164 Gt/a) and patterns that are in better agreement with observations. Thinner levels in the sub-ice-shelf cavities improve the representation of a fresh/cold layer at the ice shelf base and of warm/salty water near the bottom, leading to a sharper pycnocline and reduced vertical mixing underneath the ice shelf. Improved water column properties lead to more accurate melt rates and patterns, especially for melt/freeze patterns under large cold-water ice shelves. At the 18 km grid spacing of the ECCO2 model configuration, the smaller, warm-water ice shelves cannot be properly represented, with higher than observed melt rates in both simulations.

Shifting of the melting point for semi-crystalline polymer nanofibers

NASA Astrophysics Data System (ADS)

Arinstein, A.; Liu, Y.; Rafailovich, M.; Zussman, E.

2011-02-01

The depression of melting temperature as a function of the diameter of electrospun semi-crystalline polymer nanofibers is discussed. Due to fast solvent evaporation during nanofiber electrospinning, there occurs the fixation of topological structure of the polymer matrix corresponding to chain entanglement of the initial concentration of the semi-dilute solution. The resulting level of chain entanglement is lower than that in polymer bulk at equilibrium. This difference results in an addition to the entropy jump corresponding to the polymer's melting, and accounts for the observed shift in melting temperature in as-spun fibers. The proposed concept is found to be in good agreement with experimental results obtained for as-spun poly(ethylene-co-vinyl acetate) (PEVA) and low-density polyethylene (LDPE) fibers.

Improvements in the realization of the ITS-90 over the temperature range from the melting point of gallium to the freezing point of silver at NIM

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

Sun, J.; Zhang, J. T.; Ping, Q.

2013-09-11

The temperature primary standard over the range from the melting point of gallium to the freezing point of silver in National institute of Metrology (NIM), China, was established in the early 1990s. The performance of all of fixed-point furnaces degraded and needs to be updated due to many years of use. Nowadays, the satisfactory fixed point materials can be available with the development of the modern purification techniques. NIM plans to use a group of three cells for each defining fixed point temperature. In this way the eventual drift of individual cells can be evidenced by periodic intercomparison and thismore » will increase the reliability in disseminating the ITS-90 in China. This article describes the recent improvements in realization of ITS-90 over temperature range from the melting point of gallium to the freezing point of silver at NIM. Taking advantages of the technological advances in the design and manufacture of furnaces, the new three-zone furnaces and the open-type fixed points were developed from the freezing point of indium to the freezing point of silver, and a furnace with the three-zone semiconductor cooling was designed to automatically realize the melting point of gallium. The reproducibility of the new melting point of gallium and the new open-type freezing points of In, Sn, Zn. Al and Ag is improved, especially the freezing points of Al and Ag with the reproducibility of 0.2mK and 0.5mK respectively. The expanded uncertainty in the realization of these defining fixed point temperatures is 0.34mK, 0.44mK, 0.54mK, 0.60mK, 1.30mK and 1.88mK respectively.« less

Abnormal Winter Melting of the Arctic Sea Ice Cap Observed by the Spaceborne Passive Microwave Sensors

NASA Astrophysics Data System (ADS)

Lee, Seongsuk; Yi, Yu

2016-12-01

The spatial size and variation of Arctic sea ice play an important role in Earth’s climate system. These are affected by conditions in the polar atmosphere and Arctic sea temperatures. The Arctic sea ice concentration is calculated from brightness temperature data derived from the Defense Meteorological Satellite program (DMSP) F13 Special Sensor Microwave/Imagers (SSMI) and the DMSP F17 Special Sensor Microwave Imager/Sounder (SSMIS) sensors. Many previous studies point to significant reductions in sea ice and their causes. We investigated the variability of Arctic sea ice using the daily sea ice concentration data from passive microwave observations to identify the sea ice melting regions near the Arctic polar ice cap. We discovered the abnormal melting of the Arctic sea ice near the North Pole during the summer and the winter. This phenomenon is hard to explain only surface air temperature or solar heating as suggested by recent studies. We propose a hypothesis explaining this phenomenon. The heat from the deep sea in Arctic Ocean ridges and/ or the hydrothermal vents might be contributing to the melting of Arctic sea ice. This hypothesis could be verified by the observation of warm water column structure below the melting or thinning arctic sea ice through the project such as Coriolis dataset for reanalysis (CORA).

The gallium melting-point standard: a determination of the liquid-solid equilibrium temperature of pure gallium on the International Practical Temperature Scale of 1968.

PubMed

Thornton, D D

1977-01-01

The sharpness and reproducibility of the gallium melting point were studied and the melting temperature of gallium in terms of IPTS-68 was determined. Small melting-point cells designed for use with thermistors are described. Nine gallium cells including three levels of purity were used in 68 separate determinations fo the melting point. The melting point of 99.99999% pure gallium in terms of IPTS-68 is found to be 29.771(4) +/- 0.001(4) degree C; the melting range is less than 0.0005 degree C and is reproducible to +/- 0.0004 degree C.

Melting line of polymeric nitrogen

NASA Astrophysics Data System (ADS)

Yakub, L. N.

2013-05-01

We made an attempt to predict location of the melting line of polymeric nitrogen using two equations for Helmholtz free energy: proposed earlier for cubic gauche-structure and developed recently for liquid polymerized nitrogen. The P-T relation, orthobaric densities and latent heat of melting were determined using a standard double tangent construction. The estimated melting temperature decreases with increasing pressure, alike the temperature of molecular-nonmolecular transition in solid. We discuss the possibility of a triple point (solid-molecular fluid-polymeric fluid) at ˜80 GPa and observed maximum of melting temperature of nitrogen.

Low-melting point inorganic nitrate salt heat transfer fluid

DOEpatents

Bradshaw, Robert W [Livermore, CA; Brosseau, Douglas A [Albuquerque, NM

2009-09-15

A low-melting point, heat transfer fluid made of a mixture of four inorganic nitrate salts: 9-18 wt % NaNO.sub.3, 40-52 wt % KNO.sub.3, 13-21 wt % LiNO.sub.3, and 20-27 wt % Ca(NO.sub.3).sub.2. These compositions can have liquidus temperatures less than 100 C; thermal stability limits greater than 500 C; and viscosity in the range of 5-6 cP at 300 C; and 2-3 cP at 400 C.

New Approach in Filling of Fixed-Point Cells: Case Study of the Melting Point of Gallium

NASA Astrophysics Data System (ADS)

Bojkovski, J.; Hiti, M.; Batagelj, V.; Drnovšek, J.

2008-02-01

The typical way of constructing fixed-point cells is very well described in the literature. The crucible is loaded with shot, or any other shape of pure metal, inside an argon-filled glove box. Then, the crucible is carefully slid into a fused-silica tube that is closed at the top with an appropriate cap. After that, the cell is removed from the argon glove box and melted inside a furnace while under vacuum or filled with an inert gas like argon. Since the metal comes as shot, or in some other shape such as rods of various sizes, and takes more volume than the melted material, it is necessary to repeat the procedure until a sufficient amount of material is introduced into the crucible. With such a procedure, there is the possibility of introducing additional impurities into the pure metal with each cycle of melting the material and putting it back into the glove box to fill the cell. Our new approach includes the use of a special, so-called dry-box system, which is well known in chemistry. The atmosphere inside the dry box contains less than 20 ppm of water and less than 3 ppm of oxygen. Also, the size of the dry box allows it to contain a furnace for melting materials, not only for gallium but for higher-temperature materials as well. With such an approach, the cell and all its parts (pure metal, graphite, fused-silica tube, and cap) are constantly inside the controlled atmosphere, even while melting the material and filling the crucible. With such a method, the possibility of contaminating the cell during the filling process is minimized.

Dissolution Mechanism for High Melting Point Transition Elements in Aluminum Melt

NASA Astrophysics Data System (ADS)

Lee, Young E.; Houser, Stephen L.

When added cold in aluminum melt, the alloying process for compacts of transition metal elements such as Mn, Fe, Cr, Ni, Ti, Cu, and Zn takes a sequence of incubation, exothermic reactions to form intermetallic compounds, and dispersion of the alloying elements into aluminum melt. The experiments with Cr compacts show that the incubation period is affected by the content of ingredient Al and size of compacts and by size of Cr particles. Incubation period becomes longer as the content of ingredient aluminum in compact decreases, and this prolonged incubation period negatively impacts the dissolution of the alloying elements in aluminum. Once liquid aluminum forms at reaction sites, the exothermic reaction takes place quickly and significantly raises the temperature of the compacts. As the result of it, the compacts swell in volume with a sponge like structure. Such porous structure encourages the penetration of liquid aluminum from the melt. The compacts become weak mechanically, and the alloying elements are dispersed and entrained in aluminum melt as discrete and small sized units. When Cr compacts are deficient in aluminum, the unreacted Cr particles are encased by the intermetallic compounds in the dispersed particles. They are carried in the melt flow and continue the dissolution reaction in aluminum. The entire dissolution process of Cr compacts completes within 10 to 15 minutes with a full recovery when the aluminum content is 10 to 20% in compacts.

Experimental study and numerical simulation of the salinity effect on water-freezing point and ice-melting rate

NASA Astrophysics Data System (ADS)

Qin, N.; Wu, Y.; Wang, H. W.; Wang, Y. Y.

2017-12-01

In this paper, based on the background of snowmelt de-icing tools, we studied the effect of salt on freezing point and melting rate of ice through laboratory test and FLUENT numerical simulation analysis. It was confirmed that the freezing point is inversely proportional to the salt solid content, and with the salt solid content increasing, the freezing process of salt water gradually accepts the curing rule of non-crystal solids. At the same temperature, an increase in the salt solid content, the ice melting rate increase by the empirical formula linking the melting time with temperature and salt content. The theoretical aspects of solid/fluid transformation are discussed in detail.

Observations of brine plumes below melting Arctic sea ice

NASA Astrophysics Data System (ADS)

Peterson, Algot K.

2018-02-01

In sea ice, interconnected pockets and channels of brine are surrounded by fresh ice. Over time, brine is lost by gravity drainage and flushing. The timing of salt release and its interaction with the underlying water can impact subsequent sea ice melt. Turbulence measurements 1 m below melting sea ice north of Svalbard reveal anticorrelated heat and salt fluxes. From the observations, 131 salty plumes descending from the warm sea ice are identified, confirming previous observations from a Svalbard fjord. The plumes are likely triggered by oceanic heat through bottom melt. Calculated over a composite plume, oceanic heat and salt fluxes during the plumes account for 6 and 9 % of the total fluxes, respectively, while only lasting in total 0.5 % of the time. The observed salt flux accumulates to 7.6 kg m-2, indicating nearly full desalination of the ice. Bulk salinity reduction between two nearby ice cores agrees with accumulated salt fluxes to within a factor of 2. The increasing fraction of younger, more saline ice in the Arctic suggests an increase in desalination processes with the transition to the new Arctic.

Genome-Wide Association Study in Arabidopsis thaliana of Natural Variation in Seed Oil Melting Point: A Widespread Adaptive Trait in Plants.

PubMed

Branham, Sandra E; Wright, Sara J; Reba, Aaron; Morrison, Ginnie D; Linder, C Randal

2016-05-01

Seed oil melting point is an adaptive, quantitative trait determined by the relative proportions of the fatty acids that compose the oil. Micro- and macro-evolutionary evidence suggests selection has changed the melting point of seed oils to covary with germination temperatures because of a trade-off between total energy stores and the rate of energy acquisition during germination under competition. The seed oil compositions of 391 natural accessions of Arabidopsis thaliana, grown under common-garden conditions, were used to assess whether seed oil melting point within a species varied with germination temperature. In support of the adaptive explanation, long-term monthly spring and fall field temperatures of the accession collection sites significantly predicted their seed oil melting points. In addition, a genome-wide association study (GWAS) was performed to determine which genes were most likely responsible for the natural variation in seed oil melting point. The GWAS found a single highly significant association within the coding region of FAD2, which encodes a fatty acid desaturase central to the oil biosynthesis pathway. In a separate analysis of 15 a priori oil synthesis candidate genes, 2 (FAD2 and FATB) were located near significant SNPs associated with seed oil melting point. These results comport with others' molecular work showing that lines with alterations in these genes affect seed oil melting point as expected. Our results suggest natural selection has acted on a small number of loci to alter a quantitative trait in response to local environmental conditions. © The American Genetic Association. 2016. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

A noise thermometry investigation of the melting point of gallium at the NIM

NASA Astrophysics Data System (ADS)

Zhang, J. T.; Xue, S.

2006-06-01

This paper describes a study of the melting point of gallium with the new NIM Johnson noise thermometer (JNT). The new thermometer adopts the structure of switching correlator and commutator with the reference resistor maintained at the triple point of water. The electronic system of the new thermometer is basically the same as the current JNT, but the preamplifiers have been improved slightly. This study demonstrates that examining the characteristics of the noise signals in the frequency domain is of critical importance in constructing an improved new thermometer, where a power spectral analysis is found to be critical in establishing appropriate grounding for the new thermometer. The new JNT is tested on measurements of the thermodynamic temperature of the melting point of gallium, which give the thermodynamic temperature of 302.9160 K, with an overall integration time of 190 h and a combined standard uncertainty of 9.4 mK. The uncertainty analysis indicates that a standard combined uncertainty of 3 mK could be achieved with the new thermometer over an integration period of 1750 h.

The effect of coconut oil and palm oil as substituted oils to cocoa butter on chocolate bar texture and melting point

NASA Astrophysics Data System (ADS)

Limbardo, Rebecca Putri; Santoso, Herry; Witono, Judy Retti

2017-05-01

Cocoa butter has responsibility for dispersion medium to create a stable chocolate bar. Due to the economic reason, cocoa butter is partially or wholly substituted by edible oils e.g palm oil and coconut oil. The objective of the research was to observe the effect of oil substitution in the chocolate bar towards its melting point and texture. The research were divided in three steps which were preliminary research started with fat content analysis in cocoa powder, melting point analysis of substituted oils anc cocoa butter, and iodine number analysis in vegetable fats (cocoa butter, coconut oil, and palm oil), chocolate bar production with substitution 0%, 20%, 40%, 60%, 80%, and 100%wt of cocoa butter with each of substituted oils, and analysis process to determine the chocolate bar melting point with DSC and chocolate bar hardness with texture analyser. The increasement of substituted oils during substitution in chocolate bar would reduce the melting point of chocolate bar from 33.5°C to 31.6°C in palm oil substitution with cocoa butter and 33.5°C to 30.75°C in coconut oil substitution. The hardness of chocolate with palm oil were around 88.5 to 139 g on the 1st cycle and 22.75 to 132 g on the 2nd cycle. The hardness of chocolate with coconut oil were around 74.75 to 152.5 g on the 1st cycle and 53.25 to 132 g on the 2nd cycle. Maximum amount of fats substitution to produce a stable texture chocolate bar is 60% wt.

Experimental determination of the thermal conductivity of liquid UO2 near the melting point

NASA Astrophysics Data System (ADS)

Sheindlin, M.; Staicu, D.; Ronchi, C.; Game-Arnaud, L.; Remy, B.; Degiovanni, A.

2007-05-01

The article gives an account of measurements of the thermal conductivity of liquid UO2. The sample was heated up to above the melting point by a laser pulse of a controlled shape, and the produced thermogram of temperature history was measured by a fast and accurate pyrometer with a time resolution of 10 μs. The experiment shows that the rate of temperature increase during the ascending part of the pulse changes moderately across the melting point. Due to the high power input, this effect cannot be explained in terms of the sole intake of latent heat of fusion. By solving the related heat transfer equation with a 2D-axisymmetric numerical model, it is demonstrated that this feature depends principally on heat conduction in the sample, and proves that the thermal conductivities of solid and liquid are not very different. A theoretical sensitivity study assessing the influence of the liquid thermal conductivity on the pulse temperature evolution showed that the conductivity of the liquid can be deduced from the fitting of the thermograms with a numerical precision of the order of 1%. The analysis reveals that the thermal conductivity is weakly correlated with the effective heat losses during the pulse and to the melting enthalpy, so that the uncertainty in its evaluation by fitting the experimental thermograms with model predictions is satisfactory. The value of the thermal conductivity of liquid UO2 near the melting point resulted to be 2.6±0.35 W m-1 K-1, where the magnitude of the uncertainty is much lower than the scatter of the previously published, discordant measurements.

The thermal expansion of gold: point defect concentrations and pre-melting in a face-centred cubic metal.

PubMed

Pamato, Martha G; Wood, Ian G; Dobson, David P; Hunt, Simon A; Vočadlo, Lidunka

2018-04-01

On the basis of ab initio computer simulations, pre-melting phenomena have been suggested to occur in the elastic properties of hexagonal close-packed iron under the conditions of the Earth's inner core just before melting. The extent to which these pre-melting effects might also occur in the physical properties of face-centred cubic metals has been investigated here under more experimentally accessible conditions for gold, allowing for comparison with future computer simulations of this material. The thermal expansion of gold has been determined by X-ray powder diffraction from 40 K up to the melting point (1337 K). For the entire temperature range investigated, the unit-cell volume can be represented in the following way: a second-order Grüneisen approximation to the zero-pressure volumetric equation of state, with the internal energy calculated via a Debye model, is used to represent the thermal expansion of the 'perfect crystal'. Gold shows a nonlinear increase in thermal expansion that departs from this Grüneisen-Debye model prior to melting, which is probably a result of the generation of point defects over a large range of temperatures, beginning at T / T m > 0.75 (a similar homologous T to where softening has been observed in the elastic moduli of Au). Therefore, the thermodynamic theory of point defects was used to include the additional volume of the vacancies at high temperatures ('real crystal'), resulting in the following fitted parameters: Q = ( V 0 K 0 )/γ = 4.04 (1) × 10 -18  J, V 0 = 67.1671 (3) Å 3 , b = ( K 0 ' - 1)/2 = 3.84 (9), θ D = 182 (2) K, ( v f /Ω)exp( s f / k B ) = 1.8 (23) and h f = 0.9 (2) eV, where V 0 is the unit-cell volume at 0 K, K 0 and K 0 ' are the isothermal incompressibility and its first derivative with respect to pressure (evaluated at zero pressure), γ is a Grüneisen parameter, θ D is the Debye temperature, v f , h f and s f are the vacancy formation volume, enthalpy and entropy

Melt production in large-scale impact events: Implications and observations at terrestrial craters

NASA Technical Reports Server (NTRS)

Grieve, Richard A. F.; Cintala, Mark J.

1992-01-01

The volume of impact melt relative to the volume of the transient cavity increases with the size of the impact event. Here, we use the impact of chondrite into granite at 15, 25, and 50 km s(sup -1) to model impact-melt volumes at terrestrial craters in crystalline targets and explore the implications for terrestrial craters. Figures are presented that illustrate the relationships between melt volume and final crater diameter D(sub R) for observed terrestrial craters in crystalline targets; also included are model curves for the three different impact velocities. One implication of the increase in melt volumes with increasing crater size is that the depth of melting will also increase. This requires that shock effects occurring at the base of the cavity in simple craters and in the uplifted peaks of central structures at complex craters record progressively higher pressures with increasing crater size, up to a maximum of partial melting (approx. 45 GPa). Higher pressures cannot be recorded in the parautochthonous rocks of the cavity floor as they will be represented by impact melt, which will not remain in place. We have estimated maximum recorded pressures from a review of the literature, using such observations as planar features in quartz and feldspar, diaplectic glasses of feldspar and quartz, and partial fusion and vesiculation, as calibrated with estimates of the pressures required for their formation. Erosion complicates the picture by removing the surficial (most highly shocked) rocks in uplifted structures, thereby reducing the maximum shock pressures observed. In addition, the range of pressures that can be recorded is limited. Nevertheless, the data define a trend to higher recorded pressures with crater diameter, which is consistent with the implications of the model. A second implication is that, as the limit of melting intersects the base of the cavity, central topographic peaks will be modified in appearance and ultimately will not occur. That is

Comparison between the liquidus temperature and triple-point temperature of tin realized by heat pulse-based melting

NASA Astrophysics Data System (ADS)

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

2018-06-01

In this work, the consistency of the heat pulse-based melting technique, which was used to determine the liquidus temperature of tin, was examined by comparing the liquidus temperatures of tin at 101 325 Pa and at the vapour pressure of tin (i.e. the triple-point temperature), both of which were realized by heat pulse-based melting. Periodic square wave-type temperature steps with an amplitude of 0.7 °C were generated in the isothermal region of the pressure-controlled loop heat pipe, and the tin sample, having a segregated impurity distribution established by the prior outward slow freezing, was melted by application of the temperature step-based heat pulses. The triple-point temperature was found to be lower than the liquidus temperature of tin at 101 325 Pa by 3.23 mK with an expanded measurement uncertainty of 0.24 mK (i.e. a coverage factor of k  =  2), while the ideal temperature difference calculated from the ITS-90 given pressure coefficient (i.e. 3.3  ×  10‑8 K Pa‑1) is about 3.34 mK. The difference between the measured temperature difference and ideal temperature difference was attributed to the incomplete removal of the gases in the tin triple-point cell. Overall, these results further corroborated the notion that the heat pulse-based melting technique was shown to yield results consistent with the prescription of the ITS-90, and to be a reliable method in terms of the realization of the fixed-point temperatures.

Melting behavior of nanometer sized gold isomers

NASA Astrophysics Data System (ADS)

Liu, H. B.; Ascencio, J. A.; Perez-Alvarez, M.; Yacaman, M. J.

2001-09-01

In the present work, the melting behavior of nanometer sized gold isomers was studied using a tight-binding potential with a second momentum approximation. The cases of cuboctahedra, icosahedra, Bagley decahedra, Marks decahedra and star-like decahedra were considered. We calculated the temperature dependence of the total energy and volume during melting and the melting point for different types and sizes of clusters. In addition, the structural evolutions of the nanosized clusters during the melting transition were monitored and revealed. It is found that the melting process has three characteristic time periods for the intermediate nanosized clusters. The whole process includes surface disordering and reordering, followed by surface melting and a final rapid overall melting. This is a new observation, which it is in contrast with previous reports where surface melting is the dominant step.

Solidification observations and sliding wear behavior of vacuum arc melting processed Ni-Al-TiC composites

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

Karantzalis, A.E., E-mail: akarantz@cc.uoi.gr; Lekatou, A.; Tsirka, K.

2012-07-15

Monolithic Ni{sub 3}Al and Ni-25 at.%Al intermetallic matrix TiC-reinforced composites were successfully produced by vacuum arc melting. TiC crystals were formed through a dissolution-reprecipitation mechanism and their final morphology is explained by means of a) Jackson's classical nucleation and growth phenomena and b) solidification rate considerations. The TiC presence altered the matrix microconstituents most likely due to specific melt-particle interactions and crystal plane epitaxial matching. TiC particles caused a significant decrease on the specific wear rate of the monolithic Ni{sub 3}Al alloy and the possible wear mechanisms are approached by means of a) surface oxidation, b) crack/flaws formation, c) materialmore » detachment and d) debris-counter surfaces interactions. - Highlights: Black-Right-Pointing-Pointer Vacuum arc melting (VAM) of Ni-Al based intermetallic matrix composite materials. Black-Right-Pointing-Pointer Solidification phenomena examination. Black-Right-Pointing-Pointer TiC crystal formation and growth mechanisms. Black-Right-Pointing-Pointer Sliding wear examination.« less

Explaining Melting and Evaporation below Boiling Point. Can Software Help with Particle Ideas?

ERIC Educational Resources Information Center

Papageorgiou, George; Johnson, Philip; Fotiades, Fotis

2008-01-01

This paper reports the findings of a study exploring the use of a software package to help pupils understand particulate explanations for melting and evaporation below boiling point. Two matched classes in a primary school in Greece (ages 11-12, n = 16 and 19) were involved in a short intervention of six one hour lessons. Covering the same…

Observation of Weyl points

Science.gov Websites

copolymers, liquid crystals. Experimental observation of Weyl points First public annoucement on 11 Feburary Vishwanath from University of California, Berkeley. "Experimental Observation of Weyl Semimetals" ; Published by Science on 16 July, 2015. "Experimental observation of Weyl points" Featured on the

Why do gallium clusters have a higher melting point than the bulk?

PubMed

Chacko, S; Joshi, Kavita; Kanhere, D G; Blundell, S A

2004-04-02

Density functional molecular dynamical simulations have been performed on Ga17 and Ga13 clusters to understand the recently observed higher-than-bulk melting temperatures in small gallium clusters [Phys. Rev. Lett. 91, 215508 (2003)

Laser-Induced Melting of Co-C Eutectic Cells as a New Research Tool

NASA Astrophysics Data System (ADS)

van der Ham, E.; Ballico, M.; Jahan, F.

2015-08-01

A new laser-based technique to examine heat transfer and energetics of phase transitions in metal-carbon fixed points and potentially to improve the quality of phase transitions in furnaces with poor uniformity is reported. Being reproducible below 0.1 K, metal-carbon fixed points are increasingly used as reference standards for the calibration of thermocouples and radiation thermometers. At NMIA, the Co-C eutectic point is used for the calibration of thermocouples, with the fixed point traceable to the International Temperature Scale (ITS-90) using radiation thermometry. For thermocouple use, these cells are deep inside a high-uniformity furnace, easily obtaining excellent melting plateaus. However, when used with radiation thermometers, the essential large viewing cone to the crucible restricts the furnace depth and introduces large heat losses from the front furnace zone, affecting the quality of the phase transition. Short laser bursts have been used to illuminate the cavity of a conventional Co-C fixed-point cell during various points in its melting phase transition. The laser is employed to partially melt the metal at the rear of the crucible providing a liquid-solid interface close to the region being observed by the reference pyrometer. As the laser power is known, a quantitative estimate of can be made for the Co-C latent heat of fusion. Using a single laser pulse during a furnace-induced melt, a plateau up to 8 min is observed before the crucible resumes a characteristic conventional melt curve. Although this plateau is satisfyingly flat, well within 100 mK, it is observed that the plateau is laser energy dependent and elevates from the conventional melt "inflection-point" value.

Frictional melting of clayey gouge during seismic fault slip: Experimental observation and implications

NASA Astrophysics Data System (ADS)

Han, Raehee; Hirose, Takehiro; Jeong, Gi Young; Ando, Jun-ichi; Mukoyoshi, Hideki

2014-08-01

Clayey gouges are common in fault slip zones at shallow depths. Thus, the fault zone processes and frictional behaviors of the gouges are critical to understanding seismic slip at these depths. We conducted rotary shear tests on clayey gouge (~41 wt % clay minerals) at a seismic slip rate of 1.3 m/s. Here we report that the gouge was melted at 5 MPa of normal stress and room humidity conditions. The initial local melting was followed by melt layer formation. Clay minerals (e.g., smectite and illite) and plagioclase were melted and quenched to glass with numerous vesicles. Both flash heating and bulk temperature increases appear to be responsible for the melting. This observation of clayey gouge melting is comparable to that of natural faults (e.g., Chelungpu fault, Taiwan). Due to heterogeneous fault zone properties (e.g., permeability), frictional melting may be one of the important processes in clayey slip zones at shallow depths.

A molecular dynamics study of melting and dissociation of tungsten nanoparticles

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

Li, Min; Wang, Jun; Fu, Baoqin

2015-12-15

Molecular dynamics simulations were conducted to study the melting and dissociation of free tungsten nanoparticles. For the various interatomic potentials applied, the melting points of the tungsten nanoparticles increased with increasing nanoparticle diameter. Combining these results with the melting point of bulk tungsten in the experiment, the melting point of nanoparticles with diameters ranging from 4 to 12 nm could be determined. As the temperature increases, free nanoparticles are subject to dissociation phenomena. The dissociation rate was observed to follow Arrhenius behavior, and the Meyer–Neldel rule was obeyed. These results are useful in understanding the behavior of tungsten dust generatedmore » in nuclear fusion devices as well as for the preparation, formation, and application of tungsten powders.« less

A novel method of measuring the melting point of animal fats.

PubMed

Lloyd, S S; Dawkins, S T; Dawkins, R L

2014-10-01

The melting point (TM) of fat is relevant to health, but available methods of determining TM are cumbersome. One of the standard methods of measuring TM for animal and vegetable fats is the slip point, also known as the open capillary method. This method is imprecise and not amenable to automation or mass testing. We have developed a technique for measuring TM of animal fat using the Rotor-Gene Q (Qiagen, Hilden, Germany). The assay has an intra-assay SD of 0.08°C. A single operator can extract and assay up to 250 samples of animal fat in 24 h, including the time to extract the fat from the adipose tissue. This technique will improve the quality of research into genetic and environmental contributions to fat composition of meat.

Initial Observations of Lunar Impact Melts and Ejecta Flows with the Mini-RF Radar

NASA Technical Reports Server (NTRS)

Carter, Lynn M.; Neish, Catherine D.; Bussey, D. B. J.; Spudis, Paul D.; Patterson, G. Wesley; Cahill, Joshua T.; Raney, R. Keith

2011-01-01

The Mini-RF radar on the Lunar Reconnaissance Orbiter's spacecraft has revealed a great variety of crater ejecta flow and impact melt deposits, some of which were not observed in prior radar imaging. The craters Tycho and Glushko have long melt flows that exhibit variations in radar backscatter and circular polarization ratio along the flow. Comparison with optical imaging reveals that these changes are caused by features commonly seen in terrestrial lava flows, such as rafted plates, pressure ridges, and ponding. Small (less than 20 km) sized craters also show a large variety of features, including melt flows and ponds. Two craters have flow features that may be ejecta flows caused by entrained debris flowing across the surface rather than by melted rock. The circular polarization ratios (CPRs) of the impact melt flows are typically very high; even ponded areas have CPR values between 0.7-1.0. This high CPR suggests that deposits that appear smooth in optical imagery may be rough at centimeter- and decimeter- scales. In some places, ponds and flows are visible with no easily discernable source crater. These melt deposits may have come from oblique impacts that are capable of ejecting melted material farther downrange. They may also be associated with older, nearby craters that no longer have a radar-bright proximal ejecta blanket. The observed morphology of the lunar crater flows has implications for similar features observed on Venus. In particular, changes in backscatter along many of the ejecta flows are probably caused by features typical of lava flows.

Double Bright Band Observations with High-Resolution Vertically Pointing Radar, Lidar, and Profiles

NASA Technical Reports Server (NTRS)

Emory, Amber E.; Demoz, Belay; Vermeesch, Kevin; Hicks, Michael

2014-01-01

On 11 May 2010, an elevated temperature inversion associated with an approaching warm front produced two melting layers simultaneously, which resulted in two distinct bright bands as viewed from the ER-2 Doppler radar system, a vertically pointing, coherent X band radar located in Greenbelt, MD. Due to the high temporal resolution of this radar system, an increase in altitude of the melting layer of approximately 1.2 km in the time span of 4 min was captured. The double bright band feature remained evident for approximately 17 min, until the lower atmosphere warmed enough to dissipate the lower melting layer. This case shows the relatively rapid evolution of freezing levels in response to an advancing warm front over a 2 h time period and the descent of an elevated warm air mass with time. Although observations of double bright bands are somewhat rare, the ability to identify this phenomenon is important for rainfall estimation from spaceborne sensors because algorithms employing the restriction of a radar bright band to a constant height, especially when sampling across frontal systems, will limit the ability to accurately estimate rainfall.

Double bright band observations with high-resolution vertically pointing radar, lidar, and profilers

NASA Astrophysics Data System (ADS)

Emory, Amber E.; Demoz, Belay; Vermeesch, Kevin; Hicks, Micheal

2014-07-01

On 11 May 2010, an elevated temperature inversion associated with an approaching warm front produced two melting layers simultaneously, which resulted in two distinct bright bands as viewed from the ER-2 Doppler radar system, a vertically pointing, coherent X band radar located in Greenbelt, MD. Due to the high temporal resolution of this radar system, an increase in altitude of the melting layer of approximately 1.2 km in the time span of 4 min was captured. The double bright band feature remained evident for approximately 17 min, until the lower atmosphere warmed enough to dissipate the lower melting layer. This case shows the relatively rapid evolution of freezing levels in response to an advancing warm front over a 2 h time period and the descent of an elevated warm air mass with time. Although observations of double bright bands are somewhat rare, the ability to identify this phenomenon is important for rainfall estimation from spaceborne sensors because algorithms employing the restriction of a radar bright band to a constant height, especially when sampling across frontal systems, will limit the ability to accurately estimate rainfall.

A Two-Dimensional Liquid Structure Explains the Elevated Melting Temperatures of Gallium Nanoclusters.

PubMed

Steenbergen, Krista G; Gaston, Nicola

2016-01-13

Melting in finite-sized materials differs in two ways from the solid-liquid phase transition in bulk systems. First, there is an inherent scaling of the melting temperature below that of the bulk, known as melting point depression. Second, at small sizes changes in melting temperature become nonmonotonic and show a size-dependence that is sensitive to the structure of the particle. Melting temperatures that exceed those of the bulk material have been shown to occur for a very limited range of nanoclusters, including gallium, but have still never been ascribed a convincing physical explanation. Here, we analyze the structure of the liquid phase in gallium clusters based on molecular dynamics simulations that reproduce the greater-than-bulk melting behavior observed in experiments. We observe persistent nonspherical shape distortion indicating a stabilization of the surface, which invalidates the paradigm of melting point depression. This shape distortion suggests that the surface acts as a constraint on the liquid state that lowers its entropy relative to that of the bulk liquid and thus raises the melting temperature.

Control of Low Melting Point Mno-Sio2-Al2o3 Inclusions in Low Carbon Thin-Strip Continuous Casting Steel

NASA Astrophysics Data System (ADS)

Chen, Jing; Zhu, Qing; Huang, Di; Zheng, Shaobo; Zhang, Jieyu; Li, Huigai

2017-09-01

There is a significant difference in the demand for molten steel quality between thin-strip continuous casting and traditional continuous casting. In order to make sure the better surface quality of the thin strips, to generate an oxidation film on the surface of cooling roller is required. This will require that the higher oxygen potential in molten steel and inclusions with low melting point. In this article, the possibility of producing low-melting inclusions which is mainly consisted of SiO2 and MnO is studied by controlling the initial oxygen potential and addition order of deoxidizing alloys. The interaction activity between each component in the ternary system of Al2O3-SiO2-MnO is obtained by Action Concentration model. The equal [Mn], [Si], [O], [Al] curve under the temperature of 1823K and equilibrium condition in ternary system of Al2O3-SiO2-MnO is obtained by relative thermodynamic calculation as well. The control method for getting the low-melting point inclusion is as below. While the weight percentage of Si is 0.35% and the one of Mn is 0.90%, in order to maintain the melting point of inclusion around 1200°C, the free oxygen potential in melted steel F[O] should be maintained between 0.002% ∼ 0.004%. On the contrary, the requirement for acid dissolved [Al] content in melted steel is as low as 0.0001% ∼ 0.0005%.

Effect of low-melting point phases on the microstructure and properties of spark plasma sintered and hot deformed Nd-Fe-B alloys

NASA Astrophysics Data System (ADS)

Zhang, Li; Wang, Meiyu; Yan, Xueliang; Lin, Ye; Shield, Jeffrey

2018-04-01

The effect of adding a low melting point Pr-Cu-Al alloy during spark plasma sintering of melt-spun Nd-Fe-B ribbons is investigated. Regions of coarse grains were reduced and overall grain refinement was observed after the addition of Pr68Cu25Al7, leading to an enhancement of coercivity from 12.7 kOe to 20.4 kOe. Hot deformation of the samples in the spark plasma sintering system resulted in the formation of platelet-like grains, producing crystallographic alignment and magnetic anisotropy. The hot deformation process improved the remanence and energy product but reduced the coercivity. The decrease of coercivity resulted from grain growth and aggregation of Pr and Nd elements at triple-junction phases.

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

ERIC Educational Resources Information Center

Talbot, Christopher; Yap, Lydia

2013-01-01

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…

Estimating the melting point, entropy of fusion, and enthalpy of fusion of organic compounds via SPARC

EPA Science Inventory

The entropies of fusion, enthalies of fusion, and melting points of organic compounds can be estimated through three models developed using the SPARC (SPARC Performs Automated Reasoning in Chemistry) platform. The entropy of fusion is modeled through a combination of interaction ...

A metastable liquid melted from a crystalline solid under decompression

NASA Astrophysics Data System (ADS)

Lin, Chuanlong; Smith, Jesse S.; Sinogeikin, Stanislav V.; Kono, Yoshio; Park, Changyong; Kenney-Benson, Curtis; Shen, Guoyin

2017-01-01

A metastable liquid may exist under supercooling, sustaining the liquid below the melting point such as supercooled water and silicon. It may also exist as a transient state in solid-solid transitions, as demonstrated in recent studies of colloidal particles and glass-forming metallic systems. One important question is whether a crystalline solid may directly melt into a sustainable metastable liquid. By thermal heating, a crystalline solid will always melt into a liquid above the melting point. Here we report that a high-pressure crystalline phase of bismuth can melt into a metastable liquid below the melting line through a decompression process. The decompression-induced metastable liquid can be maintained for hours in static conditions, and transform to crystalline phases when external perturbations, such as heating and cooling, are applied. It occurs in the pressure-temperature region similar to where the supercooled liquid Bi is observed. Akin to supercooled liquid, the pressure-induced metastable liquid may be more ubiquitous than we thought.

A metastable liquid melted from a crystalline solid under decompression

PubMed Central

Lin, Chuanlong; Smith, Jesse S.; Sinogeikin, Stanislav V.; Kono, Yoshio; Park, Changyong; Kenney-Benson, Curtis; Shen, Guoyin

2017-01-01

A metastable liquid may exist under supercooling, sustaining the liquid below the melting point such as supercooled water and silicon. It may also exist as a transient state in solid–solid transitions, as demonstrated in recent studies of colloidal particles and glass-forming metallic systems. One important question is whether a crystalline solid may directly melt into a sustainable metastable liquid. By thermal heating, a crystalline solid will always melt into a liquid above the melting point. Here we report that a high-pressure crystalline phase of bismuth can melt into a metastable liquid below the melting line through a decompression process. The decompression-induced metastable liquid can be maintained for hours in static conditions, and transform to crystalline phases when external perturbations, such as heating and cooling, are applied. It occurs in the pressure–temperature region similar to where the supercooled liquid Bi is observed. Akin to supercooled liquid, the pressure-induced metastable liquid may be more ubiquitous than we thought. PMID:28112152

Interpreting Continental Break-Up From Surface Observations: Analysis of 1D Partial Melting Using Synthetic Waveform Propagation

NASA Astrophysics Data System (ADS)

Franken, T.; Armitage, J. J.; Fuji, N.; Fournier, A.

2017-12-01

Low shear-wave velocity zones underneath margins of continental break-up are believed to be related to the presence of melt. Many models attempt to model the process of melt production and transportation during mantle upwelling, yet there is a disconnect between geodynamic models, seismic observations, and petrological studies of melt flow velocities. Geodynamic models that emulate melt retention of 2 %, suggested by shear-wave velocity anomalies (Forsyth & MELT Seismic Team, 1998), fail to adequately reproduce the seismic signal as seen in receiver functions (Rychert, 2012; Armitage et al., 2015). Furthermore, numerical models of melt migration conclude mean melt flow velocities up to 1,3 m yr-1(Weatherley & Katz, 2015), whereas Uranium isotope migration rates advocate velocities up to two orders of magnitude higher. This study aims to reconcile the diverting assertions on the partial melting process by analysing the effect of melt presence on the coda of the seismic signal. A 1D forward model has been created to emulate melt production and transportation in an upwelling mantle environment. Scenarios have been modelled for variable upwelling velocities v (1 - 100 mm yr-1), initial temperatures T0 (1200 - 1800 °C) and permeabilities k0 (10-9 - 10-5 m2). The 1D model parameters are converted to anharmonic seismic parameters using look-up tables from phase diagrams (Goes et al., 2012) to generate synthetic seismograms with the Direct Solution Method. The maximum frequency content of the synthetics is 1,25 Hz, sampled at 20 Hz with a low-pass filter of 0,1 Hz. A comparison between the synthetics and seismic observations of the La Reunion mantle plume from the RER Geoscope receiver is performed using a Monte-Carlo approach. The synthetic seismograms show highest sensitivity to the presence of melt in S-waves within epicentral distances of 0-20 degrees. In the 0-10 degree range only a time-shift is observed proportional to the melt fraction at the onset of melting

Removal of oxides from alkali metal melts by reductive titration to electrical resistance-change end points

DOEpatents

Tsang, Floris Y.

1980-01-01

Alkali metal oxides dissolved in alkali metal melts are reduced with soluble metals which are converted to insoluble oxides. The end points of the reduction is detected as an increase in electrical resistance across an alkali metal ion-conductive membrane interposed between the oxide-containing melt and a material capable of accepting the alkali metal ions from the membrane when a difference in electrical potential, of the appropriate polarity, is established across it. The resistance increase results from blocking of the membrane face by ions of the excess reductant metal, to which the membrane is essentially non-conductive.

Monte Carlo Study of Melting of a Model Bulk Ice.

NASA Astrophysics Data System (ADS)

Han, Kyu-Kwang

The methods of NVT (constant number, volume and temperature) and NPT (constant number, pressure and temperature) Monte Carlo computer simulations are used to examine the melting of a periodic hexagonal ice (ice Ih) sample with a unit cell of 192 (rigid) water molecules interacting via the revised central force potentials of Stillinger and Rahman (RSL2). In NVT Monte Carlo simulation of P-T plot for a constant density (0.904g/cm^3) is used to locate onset of the liquid-solid coexistence region (where the slope of the pressure changes sign) and estimate the (constant density) melting point. The slope reversal is a natural consequence of the constant density condition for substances which expand upon freezing and it is pointed out that this analysis is extremely useful for substances such as water. In this study, a sign reversal of the pressure slope is observed near 280 K, indicating that the RSL2 potentials reproduce the freezing expansion expected for water and support a bulk ice Ih system which melts <280 K. The internal energy, specific heat, and two dimensional structure factors for the constant density H_2O system are also examined at a range of temperatures between 100 and 370 K and support the P-T analysis for location of the melting point. This P-T analysis might likewise be useful for determining a (constant density) freezing point, or, with multiple simulations at appropriate densities, the triple point. For NPT Monte Carlo simulations preliminary results are presented. In this study the density, enthalpy, specific heat, and structure factor dependences on temperature are monitored during a sequential heating of the system from 100 to 370 K at a constant pressure (1 atm.). A jump in density upon melting is observed and indicates that the RSL2 potentials reproduce the melting contraction of ice. From the dependences of monitored physical properties on temperature an upper bound on the melting temperature is estimated. In this study we made the first

Erythritol: crystal growth from the melt.

PubMed

Lopes Jesus, A J; Nunes, Sandra C C; Ramos Silva, M; Matos Beja, A; Redinha, J S

2010-03-30

The structural changes occurring on erythritol as it is cooled from the melt to low temperature, and then heated up to the melting point have been investigated by differential scanning calorimetry (DSC), polarized light thermal microscopy (PLTM), X-ray powder diffraction (PXRD) and Fourier transform infrared spectroscopy (FTIR). By DSC, it was possible to set up the conditions to obtain an amorphous solid, a crystalline solid, or a mixture of both materials in different proportions. Two crystalline forms have been identified: a stable and a metastable one with melting points of 117 and 104 degrees C, respectively. The fusion curve decomposition of the stable form revealed the existence of three conformational structures. The main paths of the crystallization from the melt were followed by PLTM. The texture and colour changes allowed the characterization of the different phases and transitions in which they are involved on cooling as well as on heating processes. The type of crystallization front and its velocity were also followed by microscopic observation. These observations, together with the data provided by PXRD, allowed elucidating the transition of the metastable form into the stable one. The structural changes occurring upon the cooling and subsequent heating processes, namely those arising from intermolecular hydrogen bonds, were also accompanied by infrared spectroscopy. Particular attention was given to the spectral changes occurring in the OH stretching region. Copyright (c) 2009 Elsevier B.V. All rights reserved.

The melting mechanism in binary Pd0.25Ni0.75 nanoparticles: molecular dynamics simulations

NASA Astrophysics Data System (ADS)

Domekeli, U.; Sengul, S.; Celtek, M.; Canan, C.

2018-02-01

The melting mechanism for Pd0.25Ni0.75 alloy nanoparticles (NPs) was investigated using molecular dynamics (MD) simulations with quantum Sutton-Chen many-body potentials. NPs of six different sizes ranging from 682 to 22,242 atoms were studied to observe the effect of size on the melting point. The melting temperatures of the NPs were estimated by following the changes in both the thermodynamic and structural quantities such as the total energy, heat capacity and Lindemann index. We also used a thermodynamics model to better estimate the melting point and to check the accuracy of MD simulations. We observed that the melting points of the NPs decreased as their sizes decreased. Although the MD simulations for the bulk system yielded higher melting temperatures because of the lack of a seed for the liquid phase, the melting temperatures determined for both the bulk material and the NPs are in good agreement with those predicted from the thermodynamics model. The melting mechanism proceeds in two steps: firstly, a liquid-like shell is formed in the outer regions of the NP with increasing temperature. The thickness of the liquid-like shell increases with increasing temperature until the shell reaches a critical thickness. Then, the entire Pd-Ni NP including core-related solid-like regions melts at once.

A metastable liquid melted from a crystalline solid under decompression

DOE PAGES

Lin, Chuanlong; Smith, Jesse S.; Sinogeikin, Stanislav V.; ...

2017-01-23

A metastable liquid may exist under supercooling, sustaining the liquid below the melting point such as supercooled water and silicon. It may also exist as a transient state in solid–solid transitions, as demonstrated in recent studies of colloidal particles and glass-forming metallic systems. One important question is whether a crystalline solid may directly melt into a sustainable metastable liquid. By thermal heating, a crystalline solid will always melt into a liquid above the melting point. Here we report that a high-pressure crystalline phase of bismuth can melt into a metastable liquid below the melting line through a decompression process. Themore » decompression-induced metastable liquid can be maintained for hours in static conditions, and transform to crystalline phases when external perturbations, such as heating and cooling, are applied. It occurs in the pressure–temperature region similar to where the supercooled liquid Bi is observed. Finally, akin to supercooled liquid, the pressure-induced metastable liquid may be more ubiquitous than we thought.« less

Hydrous partial melting in the sheeted dike complex at fast spreading ridges: experimental and natural observations

NASA Astrophysics Data System (ADS)

France, Lydéric; Koepke, Juergen; Ildefonse, Benoit; Cichy, Sarah B.; Deschamps, Fabien

2010-11-01

In ophiolites and in present-day oceanic crust formed at fast spreading ridges, oceanic plagiogranites are commonly observed at, or close to the base of the sheeted dike complex. They can be produced either by differentiation of mafic melts, or by hydrous partial melting of the hydrothermally altered sheeted dikes. In addition, the hydrothermally altered base of the sheeted dike complex, which is often infiltrated by plagiogranitic veins, is usually recrystallized into granoblastic dikes that are commonly interpreted as a result of prograde granulitic metamorphism. To test the anatectic origin of oceanic plagiogranites, we performed melting experiments on a natural hydrothermally altered dike, under conditions that match those prevailing at the base of the sheeted dike complex. All generated melts are water saturated, transitional between tholeiitic and calc-alkaline, and match the compositions of oceanic plagiogranites observed close to the base of the sheeted dike complex. Newly crystallized clinopyroxene and plagioclase have compositions that are characteristic of the same minerals in granoblastic dikes. Published silicic melt compositions obtained in classical MORB fractionation experiments also broadly match the compositions of oceanic plagiogranites; however, the compositions of the coexisting experimental minerals significantly deviate from those of the granoblastic dikes. Our results demonstrate that hydrous partial melting is a likely common process in the root zone of the sheeted dike complex, starting at temperatures exceeding 850°C. The newly formed melt can either crystallize to form oceanic plagiogranites or may be recycled within the melt lens resulting in hybridized and contaminated MORB melts. It represents the main MORB crustal contamination process. The residue after the partial melting event is represented by the granoblastic dikes. Our results support a model with a dynamic melt lens that has the potential to trigger hydrous partial melting

Microneedle pretreatment enhances the percutaneous permeation of hydrophilic compounds with high melting points

PubMed Central

2012-01-01

Background Two commercially available microneedle rollers with a needle length of 200 μm and 300 μm were selected to examine the influence of microneedle pretreatment on the percutaneous permeation of four non-steroidal anti-inflammatory drugs (diclofenac, ibuprofen, ketoprofen, paracetamol) with different physicochemical drug characteristics in Franz-type diffusion cells. Samples of the receptor fluids were taken at predefined times over 6 hours and were analysed by UV–VIS high-performance liquid-chromatography. Histological examinations after methylene blue application were additionally performed to gather information about barrier disruption. Results Despite no visible pores in the stratum corneum, the microneedle pretreatment resulted in a twofold (200 μm) and threefold higher (300 μm) flux through the pretreated skin samples compared to untreated skin samples for ibuprofen and ketoprofen (LogKow > 3, melting point < 100°C). The flux of the hydrophilic compounds diclofenac and paracetamol (logKow < 1, melting point > 100°C) increased their amount by four (200 μm) to eight (300 μm), respectively. Conclusion Commercially available microneedle rollers with 200–300 μm long needles enhance the drug delivery of topically applied non-steroidal anti-inflammatory drugs and represent a valuable tool for percutaneous permeation enhancement particularly for substances with poor permeability due to a hydrophilic nature and high melting points. PMID:22947102

Melting in Superheated Silicon Films Under Pulsed-Laser Irradiation

NASA Astrophysics Data System (ADS)

Wang, Jin Jimmy

This thesis examines melting in superheated silicon films in contact with SiO2 under pulsed laser irradiation. An excimer-laser pulse was employed to induce heating of the film by irradiating the film through the transparent fused-quartz substrate such that most of the beam energy was deposited near the bottom Si-SiO2 interface. Melting dynamics were probed via in situ transient reflectance measurements. The temperature profile was estimated computationally by incorporating temperature- and phase-dependent physical parameters and the time-dependent intensity profile of the incident excimer-laser beam obtained from the experiments. The results indicate that a significant degree of superheating occurred in the subsurface region of the film. Surface-initiated melting was observed in spite of the internal heating scheme, which resulted in the film being substantially hotter at and near the bottom Si-SiO2 interface. By considering that the surface melts at the equilibrium melting point, the solid-phase-only heat-flow analysis estimates that the bottom Si-SiO2 interface can be superheated by at least 220 K during excimer-laser irradiation. It was found that at higher laser fluences (i.e., at higher temperatures), melting can be triggered internally. At heating rates of 1010 K/s, melting was observed to initiate at or near the (100)-oriented Si-SiO2 interface at temperatures estimated to be over 300 K above the equilibrium melting point. Based on theoretical considerations, it was deduced that melting in the superheated solid initiated via a nucleation and growth process. Nucleation rates were estimated from the experimental data using Johnson-Mehl-Avrami-Kolmogorov (JMAK) analysis. Interpretation of the results using classical nucleation theory suggests that nucleation of the liquid phase occurred via the heterogeneous mechanism along the Si-SiO2 interface.

Hot and solid gallium clusters: too small to melt.

PubMed

Breaux, Gary A; Benirschke, Robert C; Sugai, Toshiki; Kinnear, Brian S; Jarrold, Martin F

2003-11-21

A novel multicollision induced dissociation scheme is employed to determine the energy content for mass-selected gallium cluster ions as a function of their temperature. Measurements were performed for Ga(+)(n) (n=17 39, and 40) over a 90-720 K temperature range. For Ga+39 and Ga+40 a broad maximum in the heat capacity-a signature of a melting transition for a small cluster-occurs at around 550 K. Thus small gallium clusters melt at substantially above the 302.9 K melting point of bulk gallium, in conflict with expectations that they will remain liquid to below 150 K. No melting transition is observed for Ga+17.

46 CFR 153.488 - Design and equipment for tanks carrying high melting point NLSs: Category B.

Code of Federal Regulations, 2010 CFR

2010-10-01

... HAZARDOUS MATERIALS Design and Equipment Design and Equipment for Pollution Control § 153.488 Design and... 46 Shipping 5 2010-10-01 2010-10-01 false Design and equipment for tanks carrying high melting point NLSs: Category B. 153.488 Section 153.488 Shipping COAST GUARD, DEPARTMENT OF HOMELAND SECURITY...

46 CFR 153.488 - Design and equipment for tanks carrying high melting point NLSs: Category B.

Code of Federal Regulations, 2014 CFR

2014-10-01

... HAZARDOUS MATERIALS Design and Equipment Design and Equipment for Pollution Control § 153.488 Design and... 46 Shipping 5 2014-10-01 2014-10-01 false Design and equipment for tanks carrying high melting point NLSs: Category B. 153.488 Section 153.488 Shipping COAST GUARD, DEPARTMENT OF HOMELAND SECURITY...

46 CFR 153.488 - Design and equipment for tanks carrying high melting point NLSs: Category B.

Code of Federal Regulations, 2013 CFR

2013-10-01

... HAZARDOUS MATERIALS Design and Equipment Design and Equipment for Pollution Control § 153.488 Design and... 46 Shipping 5 2013-10-01 2013-10-01 false Design and equipment for tanks carrying high melting point NLSs: Category B. 153.488 Section 153.488 Shipping COAST GUARD, DEPARTMENT OF HOMELAND SECURITY...

46 CFR 153.488 - Design and equipment for tanks carrying high melting point NLSs: Category B.

Code of Federal Regulations, 2012 CFR

2012-10-01

... HAZARDOUS MATERIALS Design and Equipment Design and Equipment for Pollution Control § 153.488 Design and... 46 Shipping 5 2012-10-01 2012-10-01 false Design and equipment for tanks carrying high melting point NLSs: Category B. 153.488 Section 153.488 Shipping COAST GUARD, DEPARTMENT OF HOMELAND SECURITY...

46 CFR 153.488 - Design and equipment for tanks carrying high melting point NLSs: Category B.

Code of Federal Regulations, 2011 CFR

2011-10-01

... HAZARDOUS MATERIALS Design and Equipment Design and Equipment for Pollution Control § 153.488 Design and... 46 Shipping 5 2011-10-01 2011-10-01 false Design and equipment for tanks carrying high melting point NLSs: Category B. 153.488 Section 153.488 Shipping COAST GUARD, DEPARTMENT OF HOMELAND SECURITY...

(abstract) The Design of a Benign Fail-safe Mechanism Using a Low-melting-point Metal Alloy Coupler

NASA Technical Reports Server (NTRS)

Blomquist, Richard S.

1995-01-01

Because the alpha proton X ray spectrometer (APXS) sensor head on the Mars Pathfinder rover, Sojourner, is placed on Martian soil by the deployment mechanism (ADM), the rover would be crippled if the actuator fails when the mechanism is in its deployed position, as rover ground clearance is then reduced to zero. This paper describes the unique fail-safe mounted on the ADM, especially the use of a low-temperature-melting alloy as a coupler device. The final form of the design is a low-melting-point metal pellet coupler, made from Cerrobend, in parallel with a Negator spring pack. In its solid state, the metal rigidly connects the driver (the actuator) and the driven part (the mechanism). When commanded, a strip heater wrapped around the coupler melts the metal pellet (at 60(deg)C), allowing the driven part to turn independent of the driver. The Negator spring retracts the mechanism to its fully stowed position. This concept meets all the design criteria, and provides an added benefit. When the metal hardens the coupler once again rigidly connects the actuator and the mechanism. The concept presented here can easily be applied to other applications. Anywhere release devices are needed, low-melting-point couplers can be considered. The issues to be concerned with are thermal isolation, proper setting of the parts before actuation, and possible outgassing concerns. However, when these issues are overcome, the resulting release mechanism can promise to be the most light, simple, power conserving alternative available.

Free-energy calculations using classical molecular simulation: application to the determination of the melting point and chemical potential of a flexible RDX model.

PubMed

Sellers, Michael S; Lísal, Martin; Brennan, John K

2016-03-21

We present an extension of various free-energy methodologies to determine the chemical potential of the solid and liquid phases of a fully-flexible molecule using classical simulation. The methods are applied to the Smith-Bharadwaj atomistic potential representation of cyclotrimethylene trinitramine (RDX), a well-studied energetic material, to accurately determine the solid and liquid phase Gibbs free energies, and the melting point (Tm). We outline an efficient technique to find the absolute chemical potential and melting point of a fully-flexible molecule using one set of simulations to compute the solid absolute chemical potential and one set of simulations to compute the solid-liquid free energy difference. With this combination, only a handful of simulations are needed, whereby the absolute quantities of the chemical potentials are obtained, for use in other property calculations, such as the characterization of crystal polymorphs or the determination of the entropy. Using the LAMMPS molecular simulator, the Frenkel and Ladd and pseudo-supercritical path techniques are adapted to generate 3rd order fits of the solid and liquid chemical potentials. Results yield the thermodynamic melting point Tm = 488.75 K at 1.0 atm. We also validate these calculations and compare this melting point to one obtained from a typical superheated simulation technique.

Melting point suppression in new lanthanoid(III) ionic liquids by trapping of kinetic polymorphs: an in situ synchrotron powder diffraction study.

PubMed

Chesman, Anthony S R; Yang, Mei; Mallick, Bert; Ross, Tamsyn M; Gass, Ian A; Deacon, Glen B; Batten, Stuart R; Mudring, Anja-Verena

2012-01-04

The complexes (N(4444))(3)[Ln(dcnm)(6)] (Ln = La-Nd, Sm; N(4444) = tetrabutylammonium) display a decrease in the melting point upon fast cooling from a melt, which is shown by in situ synchrotron based X-ray powder diffraction to be due to the formation of a second, less thermodynamically stable, polymorph. This journal is © The Royal Society of Chemistry 2012

Quasi-equilibrium melting of quartzite upon extreme friction

NASA Astrophysics Data System (ADS)

Lee, Sung Keun; Han, Raehee; Kim, Eun Jeong; Jeong, Gi Young; Khim, Hoon; Hirose, Takehiro

2017-06-01

The friction on fault planes that controls how rocks slide during earthquakes decreases significantly as a result of complex fault-lubrication processes involving frictional melting. Fault friction has been characterized in terms of the preferential melting of minerals with low melting points--so-called disequilibrium melting. Quartz, which has a high melting temperature of about 1,726 °C and is a major component of crustal rocks, is not expected to melt often during seismic slip. Here we use high-velocity friction experiments on quartzite to show that quartz can melt at temperatures of 1,350 to 1,500 °C. This implies that quartz within a fault plane undergoing rapid friction sliding could melt at substantially lower temperatures than expected. We suggest that depression of the melting temperature is caused by the preferential melting of ultra-fine particles and metastable melting of β-quartz at about 1,400 °C during extreme frictional slip. The results for quartzite are applicable to complex rocks because of the observed prevalence of dynamic grain fragmentation, the preferential melting of smaller grains and the kinetic preference of β-quartz formation during frictional sliding. We postulate that frictional melting of quartz on a fault plane at temperatures substantially below the melting temperature could facilitate slip-weakening and lead to large earthquakes.

High precision determination of the melting points of water TIP4P/2005 and water TIP4P/Ice models by the direct coexistence technique

NASA Astrophysics Data System (ADS)

Conde, M. M.; Rovere, M.; Gallo, P.

2017-12-01

An exhaustive study by molecular dynamics has been performed to analyze the factors that enhance the precision of the technique of direct coexistence for a system of ice and liquid water. The factors analyzed are the stochastic nature of the method, the finite size effects, and the influence of the initial ice configuration used. The results obtained show that the precision of estimates obtained through the technique of direct coexistence is markedly affected by the effects of finite size, requiring systems with a large number of molecules to reduce the error bar of the melting point. This increase in size causes an increase in the simulation time, but the estimate of the melting point with a great accuracy is important, for example, in studies on the ice surface. We also verified that the choice of the initial ice Ih configuration with different proton arrangements does not significantly affect the estimate of the melting point. Importantly this study leads us to estimate the melting point at ambient pressure of two of the most popular models of water, TIP4P/2005 and TIP4P/Ice, with the greatest precision to date.

Melting temperatures of MgO under high pressure determined by micro-texture observation

NASA Astrophysics Data System (ADS)

Kimura, T.; Ohfuji, H.; Nishi, M.; Irifune, T.

2016-12-01

Periclase (MgO) is the second abundant mineral after bridgmanite in the Earth's lower mantle, and its melting temperature (Tm) under pressure is important to constrain the chemical composition of ultra-deep magma formed near the mantle-core boundary. However, the melting behavior is highly controversial among previous studies: a laser-heated diamond anvil cell (LHDAC) study reported a melting curve with a dTm/dP of 30 K/GPa at zero pressure [1], while several theoretical computations gave substantially higher dTm/dP of 90 100 K/GPa [2,3]. We performed a series of LHDAC experiments for measurements of Tm of MgO under high pressure, using single crystal MgO as the starting material. The melting was detected by using micro-texture observations of the quenched samples. We found that the laser-heated area of the sample quenched from the Tm in previous LHDAC experiments [1] showed randomly aggregated granular crystals, which was not caused by melting, but by plastic deformation of the sample. This suggests that the Tms of their study were substantially underestimated. On the other hand, the sample recovered from the temperature higher by 1500-1700 K than the Tms in previous LHDAC experiments showed a characteristic internal texture comparable to the solidification texture typically shown in metal casting. We determined the Tms based on the observation of this texture up to 32 GPa. Fitting our Tms to the Simon equation yields dTm/dP of 82 K/GPa at zero pressure, which is consistent with those of the theoretical predictions (90 100 K/GPa) [2,3]. Extrapolation of the present melting curve of MgO to the pressure of the CMB (135 GPa) gives a melting temperature of 8900 K. The present steep melting slope offers the eutectic composition close to peridotite (in terms of Mg/Si ratio) throughout the lower mantle conditions. According to the model for sink/float relationship between the solid mantle and the magma [4], a considerable amount of iron (Fe/(Mg+Fe) > 0.24) is expected

Subaqueous melting in Zachariae Isstrom, Northeast Greenland combining observations and an ocean general circulation model

NASA Astrophysics Data System (ADS)

Cai, C.; Rignot, E. J.; Menemenlis, D.; Nakayama, Y.

2016-12-01

Zachariae Isstrom, a major ice stream in northeast Greenland, has lost its entire ice shelf in the past decade. Here, we study the evolution of subaqueous melting of its floating section during the transition. Observations show that the rate of ice shelf melting has doubled during 1999-2010 and is twice higher than that maintaining the ice shelf in a steady state. The ice shelf melt rate depends on the thermal forcing from warm, saline, subsurface ocean water of Atlantic origin (AW), and on the mixing of AW with fresh buoyant subglacial discharge. Subglacial discharge has increased as result of enhanced ice sheet runoff driven by warmer air temperature; ocean thermal forcing has increased due to enhanced advection of AW. Here, we employ the Massachusetts Institute of Technology general circulation model (MITgcm) at a high spatial resolution to simulate the melting process in 3-D. The model is constrained by ice thickness from mass conservation, oceanic bathymetry inverted from gravity data by NASA Operation IceBridge and NASA Ocean Melting Greenland missions, in-situ ocean temperature/salinity data, ocean tide height and current from the Arctic Ocean Tidal Inverse Model (AOTIM-5) and reconstructed seasonal subglacial discharge from the Regional Atmospheric Climate Model (RACMO2). We compare the results in winter (small runoff but not negligible) with summer (maximum runoff) at two different stages with (prior to 2012) and without the ice shelf (after 2012) to subaqueous melt rates deduced from remote sensing observations. We show that ice melting by the ocean has increased by one order of magnitude as a result of the transition from ice shelf terminating to near-vertical calving front terminating. We also find that subglacial discharge has a significant impact on ice shelf melt rates in Greenland. We conclude on the impact of ocean warming and air temperature warming on the melting regime of the ice margin of Zachariae Isstrom, Greenland. This work was performed

Process observation in fiber laser-based selective laser melting

NASA Astrophysics Data System (ADS)

Thombansen, Ulrich; Gatej, Alexander; Pereira, Milton

2015-01-01

The process observation in selective laser melting (SLM) focuses on observing the interaction point where the powder is processed. To provide process relevant information, signals have to be acquired that are resolved in both time and space. Especially in high-power SLM, where more than 1 kW of laser power is used, processing speeds of several meters per second are required for a high-quality processing results. Therefore, an implementation of a suitable process observation system has to acquire a large amount of spatially resolved data at low sampling speeds or it has to restrict the acquisition to a predefined area at a high sampling speed. In any case, it is vitally important to synchronously record the laser beam position and the acquired signal. This is a prerequisite that allows the recorded data become information. Today, most SLM systems employ f-theta lenses to focus the processing laser beam onto the powder bed. This report describes the drawbacks that result for process observation and suggests a variable retro-focus system which solves these issues. The beam quality of fiber lasers delivers the processing laser beam to the powder bed at relevant focus diameters, which is a key prerequisite for this solution to be viable. The optical train we present here couples the processing laser beam and the process observation coaxially, ensuring consistent alignment of interaction zone and observed area. With respect to signal processing, we have developed a solution that synchronously acquires signals from a pyrometer and the position of the laser beam by sampling the data with a field programmable gate array. The relevance of the acquired signals has been validated by the scanning of a sample filament. Experiments with grooved samples show a correlation between different powder thicknesses and the acquired signals at relevant processing parameters. This basic work takes a first step toward self-optimization of the manufacturing process in SLM. It enables the

A conceptual model for the asthenosphere: redox melting in the C-O-H-bearing mantle vs. geophysical observations

NASA Astrophysics Data System (ADS)

Gaillard, Fabrice; Tarits, Pascal; Massuyeau, Malcolm; David, Sifre; Leila, Hashim; Emmanuel, Gardes

2013-04-01

The asthenosphere has classically been considered as a convective layer, with its viscosity decreased by the presence of 100's ppm water in olivine, and being overtopped by a rigid and dry lithosphere. It, however, needs a new conceptual definition as the presence of water seems not able to affect the rheology of olivine; furthermore, properties such as electrical conductivity and seismic wave's velocity are not sensibly affected by water content in olivine, leaving the geophysical features of the asthenosphere unexplained. An asthenosphere impregnated by low melt fractions is consistent with constraints on melting behavior of C-O-H-bearing peridotites and may also better explain electrical conductivity and seismic features. The challenge is therefore to confront and reconcile the complexity of mantle melting in the C-O-H system with geophysical observations. This work reviews and discusses several key properties of the asthenosphere and relates their vertical and lateral heterogeneities to geodynamic processes. The first discussion is about the top of the Lithosphere-Asthenosphere boundary in the oceanic mantle. The discontinuity identified by seismic and electrical surveys is located at an average depth of 65km and is weakly influenced by the age, and therefore, the temperature of the lithosphere. This puzzling observation is shown here to be in perfect line the onset of peridotite melting in presence of both H2O and CO2. Mantle melting is therefore expected at 65 km depth, where the melt is essentially carbonatitic, inducing weakening and imposing transition in the regime of thermal transfer. Deeper, the melt evolve to silica-richer compositions. Twenty years of petrological investigations on processes that control mantle redox state unanimously concur on an increasingly reduced mantle with increasing depth. The conventional wisdom defines garnet as being increasingly abundant and increasingly able to concentrate ferric iron with increasing depth. Such oxygen

Diameter-Dependent Modulus and Melting Behavior in Electrospun Semicrystalline Polymer Fibers

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

Y Liu; S Chen; E Zussman

2011-12-31

Confinement of the semicrystalline polymers, poly(ethylene-co-vinyl acetate) (PEVA) and low-density polyethylene (LDPE), produced by electrospinning has been observed to produce fibers with large protrusions, which have not been previously observed in fibers of comparable diameters produced by other methods. SAXS spectra confirmed the crystalline structure and determined that the lamellar spacing was almost unchanged from the bulk. Measurement of the mechanical properties of these fibers, by both shear modulation force microscopy (SMFM) and atomic force acoustic microscopy (AFAM), indicates that the modulii of these fibers increases with decreasing diameter, with the onset at {approx}10 {micro}m, which is an order ofmore » magnitude larger than previously reported. Melting point measurements indicate a decrease of more than 7% in T{sub m}/T{sub 0} (where T{sub m} is the melting point of semicrystalline polymer fibers and T{sub 0} is the melting point of the bulk polymer) for fibers ranging from 4 to 10 {micro}m in diameter. The functional form of the decrease followed a universal curve for PEVA, when scaled with T{sub 0}.« less

Thermodynamic temperature assignment to the point of inflection of the melting curve of high-temperature fixed points.

PubMed

Woolliams, E R; Anhalt, K; Ballico, M; Bloembergen, P; Bourson, F; Briaudeau, S; Campos, J; Cox, M G; del Campo, D; Dong, W; Dury, M R; Gavrilov, V; Grigoryeva, I; Hernanz, M L; Jahan, F; Khlevnoy, B; Khromchenko, V; Lowe, D H; Lu, X; Machin, G; Mantilla, J M; Martin, M J; McEvoy, H C; Rougié, B; Sadli, M; Salim, S G R; Sasajima, N; Taubert, D R; Todd, A D W; Van den Bossche, R; van der Ham, E; Wang, T; Whittam, A; Wilthan, B; Woods, D J; Woodward, J T; Yamada, Y; Yamaguchi, Y; Yoon, H W; Yuan, Z

2016-03-28

The thermodynamic temperature of the point of inflection of the melting transition of Re-C, Pt-C and Co-C eutectics has been determined to be 2747.84 ± 0.35 K, 2011.43 ± 0.18 K and 1597.39 ± 0.13 K, respectively, and the thermodynamic temperature of the freezing transition of Cu has been determined to be 1357.80 ± 0.08 K, where the ± symbol represents 95% coverage. These results are the best consensus estimates obtained from measurements made using various spectroradiometric primary thermometry techniques by nine different national metrology institutes. The good agreement between the institutes suggests that spectroradiometric thermometry techniques are sufficiently mature (at least in those institutes) to allow the direct realization of thermodynamic temperature above 1234 K (rather than the use of a temperature scale) and that metal-carbon eutectics can be used as high-temperature fixed points for thermodynamic temperature dissemination. The results directly support the developing mise en pratique for the definition of the kelvin to include direct measurement of thermodynamic temperature. © 2016 The Author(s).

Microstructural Evolution of the Interface Between Pure Titanium and Low Melting Point Zr-Ti-Ni(Cu) Filler Metals

NASA Astrophysics Data System (ADS)

Lee, Dongmyoung; Sun, Juhyun; Kang, Donghan; Shin, Seungyoung; Hong, Juhwa

2014-12-01

Low melting point Zr-based filler metals with melting point depressants (MPDs) such as Cu and Ni elements are used for titanium brazing. However, the phase transition of the filler metals in the titanium joint needs to be explained, since the main element of Zr in the filler metals differs from that of the parent titanium alloys. In addition, since the MPDs easily form brittle intermetallics, that deteriorate joint properties, the phase evolution they cause needs to be studied. Zr-based filler metals having Cu content from 0 to 12 at. pct and Ni content from 12 to 24 at. pct with a melting temperature range of 1062 K to 1082 K (789 °C to 809 °C) were wetting-tested on a titanium plate to investigate the phase transformation and evolution at the interface between the titanium plate and the filler metals. In the interface, the alloys system with Zr, Zr2Ni, and (Ti,Zr)2Ni phases was easily changed to a Ti-based alloy system with Ti, Ti2Ni, and (Ti,Zr)2Ni phases, by the local melting of parent titanium. The dissolution depths of the parent metal were increased with increasing Ni content in the filler metals because Ni has a faster diffusion rate than Cu. Instead, slow diffusion of Cu into titanium substrate leads to the accumulation of Cu at the molten zone of the interface, which could form undesirable Ti x Cu y intermetallics. This study confirmed that Zr-based filler metals are compatible with the parent titanium metal with the minimum content of MPDs.

Pre-melting Behaviour in fcc Metals

NASA Astrophysics Data System (ADS)

Pamato, M. G.; Wood, I. G.; Dobson, D. P.; Hunt, S.; Vocadlo, L.

2016-12-01

Although the Earth's core is accepted to be made of an iron-nickel alloy with a few percent of light elements, its exact structure and composition are still unknown. Seismological and mineralogical models in the Earth's inner core do not agree, with mineralogical models derived from ab initiocalculations predicting shear-wave velocities up to 30% greater than seismically observed values. Recent computer simulations revealed that such difference may be explained by a dramatic, non-linear, softening of the elastic constants of Fe prior to melting. Up to date, computer calculations are the only result on pre-melting of direct applicability to the Earth's core and it is essential to systematically investigate such phenomena at inner core pressures and temperatures. Measuring the pressure dependence of pre-melting effects at such conditions and to the required precision is however extremely challenging. Also, pre-melting effects have been observed or suggested to occur in other materials, particularly noble metals, which exhibit large departures from linearity (modulus defects) at elevated temperatures. The aim of this study is to investigate to what extent pre-melting behaviour occurs in the physical properties of other metals at more experimentally tractable conditions. In particular, we report measurements of density and thermal expansion coefficients of both pure and alloyed gold (Au) up to their melting points. Au is an ideal test material since it crystallises in a simple monatomic face-centred structure and has a relatively low melting temperature. Precise measurements of unit cell lattice parameters were performed using a PANalytical X'Pert Pro powder diffractometer, equipped with an incident beam monochromator (giving very high resolution diffraction patterns) and with environmental stages covering the range from 40 K to 1373 K, with a readily achievable temperature resolution of 1K. We will discuss the circumstances under which pre-melting occurs, its

Microstructures and microhardness evolutions of melt-spun Al-8Ni-5Nd-4Si alloy

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

Karakoese, Ercan, E-mail: ekarakose@karatekin.edu.tr; Keskin, Mustafa

2012-03-15

Al-Ni-Nd-Si alloy with nominal composition of Al-8 wt.%Ni-5 wt.%Nd-4 wt.%Si was rapidly solidified by using melt-spinning technique to examine the influence of the cooling rate/conditions on microstructure and mechanical properties. The resulting conventional cast (ingot) and melt-spun ribbons were characterized by X-ray diffraction, optical microscopy, scanning electron microscopy together with energy dispersive spectroscopy, differential scanning calorimetry, differential thermal analysis and Vickers microhardness tester. The ingot alloys consists of four phases namely {alpha}-Al, intermetallic Al{sub 3}Ni, Al{sub 11}Nd{sub 3} and fcc Si. Melt-spun ribbons are completely composed of {alpha}-Al phase. The optical microscopy and scanning electron microscopy results show that themore » microstructures of rapidly solidified ribbons are clearly different from their ingot alloy. The change in microhardness is discussed based on the microstructural observations. - Highlights: Black-Right-Pointing-Pointer Rapid solidification allows a reduction in grain size, extended solid solution ranges. Black-Right-Pointing-Pointer We observed the matrix lattice parameter increases with increasing wheel speed. Black-Right-Pointing-Pointer Melt-spun ribbons consist of partly amorphous phases embedded in crystalline phases. Black-Right-Pointing-Pointer The solidification rate is high enough to retain most of alloying elements in the Al matrix. Black-Right-Pointing-Pointer The rapid solidification has effect on the phase constitution.« less

Observations and modeling of ocean-induced melt beneath Petermann Glacier Ice Shelf in northwestern Greenland

NASA Astrophysics Data System (ADS)

Cai, Cilan; Rignot, Eric; Menemenlis, Dimitris; Nakayama, Yoshihiro

2017-08-01

We update observationally based estimates of subaqueous melt, Qm, beneath Petermann Glacier Ice Shelf (PGIS), Greenland, and model its sensitivity to oceanic thermal forcing, TF, and subglacial runoff, Qsg, using the Massachusetts Institute of Technology general circulation model (MITgcm), in a two-dimensional domain, with 20 m vertical and 40 m horizontal resolution at the grounding line. We adjust the drag coefficient to match the observationally based Qm. With the inclusion of Qsg, the maximum melt rate (Qmmax) is 2 times larger in summer and 1/3 larger annually than in winter. Qmmax increases above linear with TF and below linear with Qsg. We estimate that Qmmax increased by 24% (+8.1 m/yr) beneath PGIS from the 1990s to the 2000s from a 0.21°C warming in ocean temperature and a doubling in Qsg, hence contributing to its thinning. If the PGIS is removed, we estimate that the modeled melt rate near the grounding line will increase 13-16 times.

Subaqueous melting in Zachariae Isstrom, Northeast Greenland combining observations and an ocean general circulation model

NASA Astrophysics Data System (ADS)

Cai, C.; Rignot, E. J.; Menemenlis, D.

2015-12-01

Zachariae Isstrom, a major ice stream in northeast Greenland, has lost its entire ice shelf in the past decade. Here, we study the evolution of subaqueous melting of its floating section during the transition. Observations show that the rate of ice shelf melting has doubled during 1999-2010 and is twice higher than that maintaining the ice shelf in a state of mass equilibrium. The ice shelf melt rate depends on the thermal forcing from warm, salty, subsurface ocean water of Atlantic origin (AW), and - in contrast with Antarctic ice shelves - on the mixing of AW with fresh buoyant subglacial discharge. Subglacial discharge has increased as result of enhanced ice sheet runoff driven by warmer air temperature; ocean thermal forcing has increased due enhanced advection of AW. Here, we employ the Massassuchetts Institute of Technology general circulation model (MITgcm) at a high spatial resolution (1 m horizontal and 1 m vertical spacing near the grounding line) to simulate the melting process in 3-D. The model is constrained by ice thickness from mass conservation, oceanic bathymetry from NASA Operation IceBridge gravity data, in-situ ocean temperature/salinity data, ocean tide height and current from the Arctic Ocean Tidal Inverse Model (AOTIM-5) and subglacial discharge from output products of the Regional Atmospheric Climate Model (RACMO). We compare the results in winter (no runoff) with summer (maximum runoff) at two different stages with (prior to 2012) and without the ice shelf (after 2012) to subaqueous melt rates deduced from remote sensing observations. We show that ice melting by the ocean has increased by one order of magnitude as a result of the transition from ice shelf terminating to near-vertical calving front terminating. We also find that subglacial discharge has a significant impact on the ice shelf melt rates in Greenland. We conclude on the impact of ocean warming and air temperature warming on the melting regime of the ice margin of Zachariae

Stabilizing Crystal Oscillators With Melting Metals

NASA Technical Reports Server (NTRS)

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

1984-01-01

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

Laboratory Experiments Investigating Glacier Submarine Melt Rates and Circulation in an East Greenland Fjord

NASA Astrophysics Data System (ADS)

Cenedese, C.

2014-12-01

Idealized laboratory experiments investigate the glacier-ocean boundary dynamics near a vertical 'glacier' (i.e. no floating ice tongue) in a two-layer stratified fluid, similar to Sermilik Fjord where Helheim Glacier terminates. In summer, the discharge of surface runoff at the base of the glacier (subglacial discharge) intensifies the circulation near the glacier and increases the melt rate with respect to that in winter. In the laboratory, the effect of subglacial discharge is simulated by introducing fresh water at melting temperatures from either point or line sources at the base of an ice block representing the glacier. The circulation pattern observed both with and without subglacial discharge resembles those observed in previous studies. The buoyant plume of cold meltwater and subglacial discharge water entrains ambient water and rises vertically until it finds either the interface between the two layers or the free surface. The results suggest that the meltwater deposits within the interior of the water column and not entirely at the free surface, as confirmed by field observations. The submarine melt rate increases with the subglacial discharge rate. Furthermore, the same subglacial discharge causes greater submarine melting if it exits from a point source rather than from a line source. When the subglacial discharge exits from two point sources, two buoyant plumes are formed which rise vertically and interact. The results suggest that the distance between the two subglacial discharges influences the entrainment in the plumes and consequently the amount of submarine melting and the final location of the meltwater within the water column. Hence, the distribution and number of sources of subglacial discharge may play an important role in glacial melt rates and fjord stratification and circulation. Support was given by NSF project OCE-113008.

Liquid structure and temperature invariance of sound velocity in supercooled Bi melt

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

Emuna, M.; Mayo, M.; Makov, G.

2014-03-07

Structural rearrangement of liquid Bi in the vicinity of the melting point has been proposed due to the unique temperature invariant sound velocity observed above the melting temperature, the low symmetry of Bi in the solid phase and the necessity of overheating to achieve supercooling. The existence of this structural rearrangement is examined by measurements on supercooled Bi. The sound velocity of liquid Bi was measured into the supercooled region to high accuracy and it was found to be invariant over a temperature range of ∼60°, from 35° above the melting point to ∼25° into the supercooled region. The structuralmore » origin of this phenomenon was explored by neutron diffraction structural measurements in the supercooled temperature range. These measurements indicate a continuous modification of the short range order in the melt. The structure of the liquid is analyzed within a quasi-crystalline model and is found to evolve continuously, similar to other known liquid pnictide systems. The results are discussed in the context of two competing hypotheses proposed to explain properties of liquid Bi near the melting: (i) liquid bismuth undergoes a structural rearrangement slightly above melting and (ii) liquid Bi exhibits a broad maximum in the sound velocity located incidentally at the melting temperature.« less

Observation of melt onset on multiyear Arctic sea ice using the ERS 1 synthetic aperture radar

NASA Technical Reports Server (NTRS)

Winebrenner, D. P.; Nelson, E. D.; Colony, R.; West, R. D.

1994-01-01

We present nearly coincident observations of backscattering from the Earth Remote-Sensing Satellite (ERS) 1 synthetic aperture radar (SAR) and of near-surface temperature from six drifting buoys in the Beaufort Sea, showing that the onset of melting in snow on multiyear sea ice is clearly detectable in the SAR data. Melt onset is marked by a clean, steep decrease in the backscattering cross section of multiyear ice at 5.3 GHz and VV polarization. We investigate the scattering physics responsible for the signature change and find that the cross section decrease is due solely to the appearance of liquid water in the snow cover overlying the ice. A thin layer of moist snow is sufficient to cause the observed decrease. We present a prototype algorithm to estimate the date of melt onset using the ERS 1 SAR and apply the algorithm first to the SAR data for which we have corresponding buoy temperatures. The melt onset dates estimated by the SAR algorithm agree with those obtained independently from the temperature data to within 4 days or less, with the exception of one case in which temperatures oscillated about 0 C for several weeks. Lastly, we apply the algorithm to the entire ERS 1 SAR data record acquired by the Alaska SAR Facility for the Beaufort Sea north of 73 deg N during the spring of 1992, to produce a map of the dates of melt onset over an area roughly 1000 km on a side. The progression of melt onset is primarily poleward but shows a weak meridional dependence at latitudes of approximately 76 deg-77 deg N. Melting begins in the southern part of the study region on June 13 and by June 20 has progressed to the northermost part of the region.

Induction heating pure vapor source of high temperature melting point materials on electron cyclotron resonance ion source.

PubMed

Kutsumi, Osamu; Kato, Yushi; Matsui, Yuuki; Kitagawa, Atsushi; Muramatsu, Masayuki; Uchida, Takashi; Yoshida, Yoshikazu; Sato, Fuminobu; Iida, Toshiyuki

2010-02-01

Multicharged ions that are needed are produced from solid pure material with high melting point in an electron cyclotron resonance ion source. We develop an evaporator by using induction heating (IH) with multilayer induction coil, which is made from bare molybdenum or tungsten wire without water cooling and surrounding the pure vaporized material. We optimize the shapes of induction coil and vaporized materials and operation of rf power supply. We conduct experiment to investigate the reproducibility and stability in the operation and heating efficiency. IH evaporator produces pure material vapor because materials directly heated by eddy currents have no contact with insulated materials, which are usually impurity gas sources. The power and the frequency of the induction currents range from 100 to 900 W and from 48 to 23 kHz, respectively. The working pressure is about 10(-4)-10(-3) Pa. We measure the temperature of the vaporized materials with different shapes, and compare them with the result of modeling. We estimate the efficiency of the IH vapor source. We are aiming at the evaporator's higher melting point material than that of iron.

Induction heating pure vapor source of high temperature melting point materials on electron cyclotron resonance ion sourcea)

NASA Astrophysics Data System (ADS)

Kutsumi, Osamu; Kato, Yushi; Matsui, Yuuki; Kitagawa, Atsushi; Muramatsu, Masayuki; Uchida, Takashi; Yoshida, Yoshikazu; Sato, Fuminobu; Iida, Toshiyuki

2010-02-01

Multicharged ions that are needed are produced from solid pure material with high melting point in an electron cyclotron resonance ion source. We develop an evaporator by using induction heating (IH) with multilayer induction coil, which is made from bare molybdenum or tungsten wire without water cooling and surrounding the pure vaporized material. We optimize the shapes of induction coil and vaporized materials and operation of rf power supply. We conduct experiment to investigate the reproducibility and stability in the operation and heating efficiency. IH evaporator produces pure material vapor because materials directly heated by eddy currents have no contact with insulated materials, which are usually impurity gas sources. The power and the frequency of the induction currents range from 100to900W and from 48to23kHz, respectively. The working pressure is about 10-4-10-3Pa. We measure the temperature of the vaporized materials with different shapes, and compare them with the result of modeling. We estimate the efficiency of the IH vapor source. We are aiming at the evaporator's higher melting point material than that of iron.

Acyl-gelatins for cell-hybrid biomaterials: preparation of gelatins with high melting point and affinity for hydrophobic surfaces.

PubMed

Miyamoto, Keiichi; Chinzei, Hiroko; Komai, Takashi

2002-12-01

In the development of cell-hybrid biomaterials, the functional activity of cells depends on the selective binding of cells to artificial ligands on the biomaterials. The extracellular matrix (ECM) is the most important ligand for cell activity. ECM is known to contain collagen, one of whose constituents is gelatin. Although natural gelatin has good cell attachment properties, the melting point of gelatin hydrogel is lower than body temperature. Thus, non-chemically cross-linked gelatin hydrogel is not a biomaterial that is used for prostheses. In the present study, we report the preparation of acyl-gelatin hydrogels with high melting point (>37 degrees C) and high affinity for hydrophobic surfaces for easy handling for transportation and adhesion activities on the hydrophobic surfaces. In addition, the doubling time of endothelial cells on the coated cell culture plate was faster than that of natural gelatin owing to the higher adhesion activity of acyl-gelatin. The results clearly demonstrated that the acyl-gelatin acted as an interface that enabled cell adhesion to artificial materials surfaces.

Optically induced melting of colloidal crystals and their recrystallization.

PubMed

Harada, Masashi; Ishii, Masahiko; Nakamura, Hiroshi

2007-04-15

Colloidal crystals melt by applying focused light of optical tweezers and recrystallize after removing it. The disturbed zone by the light grows radially from the focus point and the ordering starts from the interface with the crystal. Although the larger disturbed zone is observed for the higher power optical tweezers, a master curve is extracted by normalization of the disturbed zone. The temporal changes of the normalized disturbed zone are well described with exponential functions, indicating that the melting and recrystallization process is governed by a simple relaxation mechanism.

Pitted rock surfaces on Mars: A mechanism of formation by transient melting of snow and ice

NASA Astrophysics Data System (ADS)

Head, James W.; Kreslavsky, Mikhail A.; Marchant, David R.

2011-09-01

Pits in rocks on the surface of Mars have been observed at several locations. Similar pits are observed in rocks in the Mars-like hyperarid, hypothermal stable upland zone of the Antarctic Dry Valleys; these form by very localized chemical weathering due to transient melting of small amounts of snow on dark dolerite boulders preferentially heated above the melting point of water by sunlight. We examine the conditions under which a similar process might explain the pitted rocks seen on the surface of Mars (rock surface temperatures above the melting point; atmospheric pressure exceeding the triple point pressure of H2O; an available source of solid water to melt). We find that on Mars today each of these conditions is met locally and regionally, but that they do not occur together in such a way as to meet the stringent requirements for this process to operate. In the geological past, however, conditions favoring this process are highly likely to have been met. For example, increases in atmospheric water vapor content (due, for example, to the loss of the south perennial polar CO2 cap) could favor the deposition of snow, which if collected on rocks heated to above the melting temperature during favorable conditions (e.g., perihelion), could cause melting and the type of locally enhanced chemical weathering that can cause pits. Even when these conditions are met, however, the variation in heating of different rock facets under Martian conditions means that different parts of the rock may weather at different times, consistent with the very low weathering rates observed on Mars. Furthermore, as is the case in the stable upland zone of the Antarctic Dry Valleys, pit formation by transient melting of small amounts of snow readily occurs in the absence of subsurface active layer cryoturbation.

Structure and thermal expansion of Lu 2O 3 and Yb 2O 3 up to the melting points

DOE PAGES

Pavlik, Alfred; Ushakov, Sergey V.; Navrotsky, Alexandra; ...

2017-08-24

Knowledge of thermal expansion and high temperature phase transformations is essential for prediction and interpretation of materials behavior under the extreme conditions of high temperature and intense radiation encountered in nuclear reactors. We studied the structure and thermal expansion of Lu 2O 3 and Yb 2O 3 were studied in oxygen and argon atmospheres up to their melting temperatures using synchrotron X-ray diffraction on laser heated levitated samples. Both oxides retained the cubic bixbyite C-type structure in oxygen and argon to melting. In contrast to fluorite-type structures, the increase in the unit cell parameter of Yb 2O 3 and Lumore » 2O 33 with temperature is linear within experimental error from room temperature to the melting point, with mean thermal expansion coefficients (8.5 ± 0.6) · 10 -6 K -1 and (7.7 ± 0.6) · 10 -6 K -1, respectively. There is no indication of a superionic (Bredig) transition in the C-type structure or of a previously suggested Yb 2O 3 phase transformation to hexagonal phase prior to melting.« less

Structure and thermal expansion of Lu 2O 3 and Yb 2O 3 up to the melting points

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

Pavlik, Alfred; Ushakov, Sergey V.; Navrotsky, Alexandra

Knowledge of thermal expansion and high temperature phase transformations is essential for prediction and interpretation of materials behavior under the extreme conditions of high temperature and intense radiation encountered in nuclear reactors. We studied the structure and thermal expansion of Lu 2O 3 and Yb 2O 3 were studied in oxygen and argon atmospheres up to their melting temperatures using synchrotron X-ray diffraction on laser heated levitated samples. Both oxides retained the cubic bixbyite C-type structure in oxygen and argon to melting. In contrast to fluorite-type structures, the increase in the unit cell parameter of Yb 2O 3 and Lumore » 2O 33 with temperature is linear within experimental error from room temperature to the melting point, with mean thermal expansion coefficients (8.5 ± 0.6) · 10 -6 K -1 and (7.7 ± 0.6) · 10 -6 K -1, respectively. There is no indication of a superionic (Bredig) transition in the C-type structure or of a previously suggested Yb 2O 3 phase transformation to hexagonal phase prior to melting.« less

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

NASA Astrophysics Data System (ADS)

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

2013-12-01

Bubble growth strongly affects the physical properties of degassing magmas and their eruption dynamics. Natural samples and products from quench experiments provide only a snapshot of the final state of volatile exsolution, leaving the processes occurring during its early stages unconstrained. In order to fill this gap, we present in-situ high-temperature observations of bubble growth in magmas of different compositions (basalt, andesite and rhyodacite) at 1100 to 1240 °C and 1 bar, obtained using a moissanite cell apparatus. The data show that nucleation occurs at very small degrees of supersaturaturation (<20 MPa in basalt and andesite, ca. 100 MPa in rhyodacite), probably due to heterogeneous nucleation of bubbles occurring simultaneously with the nucleation of crystals. During the early stages of exsolution, melt degassing is the driving mechanism of bubble growth, with coalescence becoming increasingly important as exsolution progresses. Ostwald ripening occurs only at the end of the process and only in basaltic melt. The average bubble growth rate (GR) ranges from 3.4*10-6 to 5.2*10-7 mm/s, with basalt and andesite showing faster growth rates than rhyodacite. The bubble number density (NB) at nucleation ranges from 1.8*108 to 7.9*107 cm-3 and decreases exponentially over time. While the rhyodacite melt maintained a well-sorted bubble-size distribution (BSD) through time, the BSD's of basalt and andesite are much more inhomogeneous. Our experimental observations demonstrate that bubble growth cannot be ascribed to a single mechanism but is rather a combination of many processes, which depend on the physical properties of the melt. Depending on coalescence rate, annealing of bubbles following a single nucleation event can produce complex bubble size distributions. In natural samples, such BSD's may be misinterpreted as resulting from several separate nucleation events. Incipient crystallization upon cooling of a magma may allow bubble nucleation already at

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

NASA Astrophysics Data System (ADS)

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

2014-02-01

Bubble growth strongly affects the physical properties of degassing magmas and their eruption dynamics. Natural samples and products from quench experiments provide only a snapshot of the final state of volatile exsolution, leaving the processes occurring during its early stages unconstrained. In order to fill this gap, we present in situ high-temperature observations of bubble growth in magmas of different compositions (basalt, andesite and rhyodacite) at 1,100 to 1,240 °C and 0.1 MPa (1 bar), obtained using a moissanite cell apparatus. The data show that nucleation occurs at very small degrees of supersaturaturation (<60 MPa in basalt and andesite, 200 MPa in rhyodacite), probably due to heterogeneous nucleation of bubbles occurring simultaneously with the nucleation of crystals. During the early stages of exsolution, melt degassing is the driving mechanism of bubble growth, with coalescence becoming increasingly important as exsolution progresses. Ostwald ripening occurs only at the end of the process and only in basaltic melt. The average bubble growth rate ( G R) ranges from 3.4 × 10-6 to 5.2 × 10-7 mm/s, with basalt and andesite showing faster growth rates than rhyodacite. The bubble number density ( N B) at nucleation ranges from 7.9 × 104 mm-3 to 1.8 × 105 mm-3 and decreases exponentially over time. While the rhyodacite melt maintained a well-sorted bubble size distribution (BSD) through time, the BSDs of basalt and andesite are much more inhomogeneous. Our experimental observations demonstrate that bubble growth cannot be ascribed to a single mechanism but is rather a combination of many processes, which depend on the physical properties of the melt. Depending on coalescence rate, annealing of bubbles following a single nucleation event can produce complex bubble size distributions. In natural samples, such BSDs may be misinterpreted as resulting from several separate nucleation events. Incipient crystallization upon cooling of a magma may allow

On high-pressure melting of tantalum

NASA Astrophysics Data System (ADS)

Luo, Sheng-Nian; Swift, Damian C.

2007-01-01

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

Mixing and electronic entropy contributions to thermal energy storage in low melting point alloys

NASA Astrophysics Data System (ADS)

Shamberger, Patrick J.; Mizuno, Yasushi; Talapatra, Anjana A.

2017-07-01

Melting of crystalline solids is associated with an increase in entropy due to an increase in configurational, rotational, and other degrees of freedom of a system. However, the magnitude of chemical mixing and electronic degrees of freedom, two significant contributions to the entropy of fusion, remain poorly constrained, even in simple 2 and 3 component systems. Here, we present experimentally measured entropies of fusion in the Sn-Pb-Bi and In-Sn-Bi ternary systems, and decouple mixing and electronic contributions. We demonstrate that electronic effects remain the dominant contribution to the entropy of fusion in multi-component post-transition metal and metalloid systems, and that excess entropy of mixing terms can be equal in magnitude to ideal mixing terms, causing regular solution approximations to be inadequate in the general case. Finally, we explore binary eutectic systems using mature thermodynamic databases, identifying eutectics containing at least one semiconducting intermetallic phase as promising candidates to exceed the entropy of fusion of monatomic endmembers, while simultaneously maintaining low melting points. These results have significant implications for engineering high-thermal conductivity metallic phase change materials to store thermal energy.

Towards Estimate of Present Day Ice Melting in Polar Regions From Altimetry, Gravity, Ocean Bottom Pressure and GPS Observations

NASA Astrophysics Data System (ADS)

Jiang, Y.; Wu, X.; van den Broeke, M. R.; Munneke, P. K.; Simonsen, S. B.; van der Wal, W.; Vermeersen, B. L.

2013-12-01

The ice sheet in Polar Regions stores the largest freshwater bodies on Earth, sufficient to elevate global sea level by more than 65 meters if melted. The earth may have entered an intensive ice-melting episode, possibly due to anthropogenic global warming rather than natural orbit variations. Determining present-day ice mass balance, however, is complicated by the fact that most observations contain both present day ice melting signal and residual signals from past glacier melting. Despite decades of progress in geodynamic modeling and new observations, significant uncertainties remain in both. The key to separate present-day ice mass change and signals from past melting is to include data of different physical characteristics. We conducted a new global kinematic inversion scheme to estimate both present-day ice melting and past glacier signatures simultaneously and assess their contribution to current and future global mean sea level change. Our approach is designed to invert and separate present-day melting signal in the spherical harmonic domain using a globally distributed interdisciplinary data with distinct physical information. Interesting results with unprecedented precisions have been achieved so far. We will present our results of the estimated present-day ice mass balance trend in both Greenland and Antarctica ice sheet as well as other regions where significant mass change occurs.

The melting curve of Ni to 1 Mbar

NASA Astrophysics Data System (ADS)

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

2014-12-01

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 σ), 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.

Melting Processes at the Base of the Mantle Wedge: Melt Compositions and Melting Reactions for the First Melts of Vapor-Saturated Lherzolite

NASA Astrophysics Data System (ADS)

Grove, T. L.; Till, C. B.

2014-12-01

Vapor-saturated melting experiments have been performed at pressures near the base of the mantle wedge (3.2 GPa). The starting composition is a metasomatized lherzolite containing 3 wt. % H2O. Near-solidus melts and coexisting mineral phases have been characterized in experiments that span 925 to 1100 oC with melt % varying from 6 to 9 wt. %. Olivine, orthopyroxene, clinopyroxene and garnet coexist with melt over the entire interval and rutile is also present at < 1000 oC. Melt is andesitic in composition and varies from 60 wt. % SiO2 at 950 oC to 52 wt. % at 1075 oC. The Al2O3 contents of the melt are 13 to 14 wt. %, and CaO contents range from 1 and 4 wt. %. Melting is peritectic with orthopyroxene + liquid produced by melting of garnet + olivine + high-Ca pyroxene. In addition to quenched melt, we observe a quenched silicate component that is rhyolitic (>72 % SiO2) that we interpret as a precipitate from the coexisting supercritical H2O-rich vapor. Extrapolation of the measured compositional variation toward the solidus suggests that the first melt may be very SiO2 rich (i.e., granitic). We suggest that these granitic melts are the first melts of the mantle near the slab-wedge interface. As these SiO2-rich melts ascend into shallower, hotter overlying mantle, they continue to interact with the surrounding mantle and evolve in composition. These first melts may elucidate the geochemical and physical processes that accompany the beginnings of H2O flux melting.

Tungsten migration in Alcator C-Mod: sputtering and melting

NASA Astrophysics Data System (ADS)

Wright, G. M.; Barnard, H.; Lipschultz, B.; Whyte, D. G.

2010-11-01

A row of bulk tungsten (W) tiles were installed near the typical outer strike-point location in the Alcator C-Mod divertor in 2007. In the 2009/2010 campaign, one of the W tiles mechanically failed resulting in significant W melting at that location. Post-campaign PIXE surface analysis has been used to observe tungsten (W) deposition and migration patterns in the divertor for the typical operations (sputtering only) and operation with melted components. For sputtering conditions, W deposition of up to 20 nm equivalent thickness is observed at various divertor surfaces indicating prompt re-deposition at the outer divertor, neutral and ion transport through the private-flux region and ion transport in the scrape off layer. For melting conditions, W deposition of up to 400 nm equivalent thickness is observed at some locations at the outer divertor. However, the toroidal distribution of W on the outer divertor is strongly non-uniform. There is no W deposition measured on the inner wall limiter. These results indicate that impurity migration is affected by the erosion mechanism and source, with the migration from melting being less predictable and uniform than from the sputtering case. Supported by USDoE award DE-SC00-02060.

Melting curve of compressed barium carbonate from in situ ionic conductivity measurements: Implications for the melting behavior of alkaline earth carbonates in Earth's deep carbon cycle

NASA Astrophysics Data System (ADS)

Dong, J.; Li, J.; Zhu, F.; Li, Z.; Farawi, R.

2017-12-01

The whereabouts of subducted carbonates place a major constraint on the Earth's deep carbon cycle, but the fraction of carbon retained in the slab and transported into the deep mantle, compared to that released from the slab and recycled to the surface, is still under debate. Knowledge of the stability of carbonated mantle rocks is pivotal for assessing the ability of slabs to carry carbonates into the deep mantle. Determination and systematic comparison of the melting curves of alkali and alkaline earth carbonates at high pressure can help construct thermodynamic models to predict the melting behavior of complex carbonated mantle rocks. Among alkaline earth carbonates, the melting behavior of barium carbonate (BaCO3) has not been adequately understood. The reported melting point of BaCO3at 1 bar differ by nearly 800 °C and constraints on the melting curve of BaCO3 at high pressure are not available. In this study, the melting temperatures of BaCO3 were determined up to 11 GPa from in situ ionic conductivity measurements using the multi-anvil apparatus at the University of Michigan. The solid-liquid boundary at high pressure was detected on the basis of a steep rise in conductivity through the sample upon melting. The melting point of BaCO3 was found to drop from 1797 °C at 3.3 GPa to 1600 °C at 5.5 GPa and then rise with pressure to 2180 °C at 11 GPa. The observed melting depression point at 5.5 GPa corresponds to the phase transition of BaCO3 from the aragonite structure (Pmcn) to post-aragonite structure (Pmmn) at 6.3 GPa, 877 °C and 8.0 GPa, 727 °C, determined from synchrotron X-ray diffraction measurements using laser-heated DAC experiments at the Advanced Photon Source, Argonne National Laboratory. These results are also compared with ex situ falling marker experiments, and the three methods together place tight constraints on the melting curve of BaCO3 and elucidates the effect of structural phase transitions on its melting behavior.

Melting and glass transition for Ni clusters.

PubMed

Teng, Yuyong; Zeng, Xianghua; Zhang, Haiyan; Sun, Deyan

2007-03-08

The melting of NiN clusters (N = 29, 50-150) has been investigated by using molecular dynamics (MD) simulations with a quantum corrected Sutton-Chen (Q-SC) many-body potential. Surface melting for Ni147, direct melting for Ni79, and the glass transition for Ni29 have been found, and those melting points are equal to 540, 680, and 940 K, respectively. It shows that the melting temperatures are not only size-dependent but also a symmetrical structure effect; in the neighborhood of the clusters, the cluster with higher symmetry has a higher melting point. From the reciprocal slopes of the caloric curves, the specific heats are obtained as 4.1 kB per atom for the liquid and 3.1 kB per atom for the solid; these values are not influenced by the cluster size apart in the transition region. The calculated results also show that latent heat of fusion is the dominant effect on the melting temperatures (Tm), and the relationship between S and L is given.

Melt electrospinning of poly(ε-caprolactone) scaffolds: phenomenological observations associated with collection and direct writing.

PubMed

Brown, Toby D; Edin, Fredrik; Detta, Nicola; Skelton, Anthony D; Hutmacher, Dietmar W; Dalton, Paul D

2014-12-01

Melt electrospinning and its additive manufacturing analogue, melt electrospinning writing (MEW), are two processes which can produce porous materials for applications where solvent toxicity and accumulation in solution electrospinning are problematic. This study explores the melt electrospinning of poly(ε-caprolactone) (PCL) scaffolds, specifically for applications in tissue engineering. The research described here aims to inform researchers interested in melt electrospinning about technical aspects of the process. This includes rapid fiber characterization using glass microscope slides, allowing influential processing parameters on fiber morphology to be assessed, as well as observed fiber collection phenomena on different collector substrates. The distribution and alignment of melt electrospun PCL fibers can be controlled to a certain degree using patterned collectors to create large numbers of scaffolds with shaped macroporous architectures. However, the buildup of residual charge in the collected fibers limits the achievable thickness of the porous template through such scaffolds. One challenge identified for MEW is the ability to control charge buildup so that fibers can be placed accurately in close proximity, and in many centimeter heights. The scale and size of scaffolds produced using MEW, however, indicate that this emerging process will fill a technological niche in biofabrication. Copyright © 2014 Elsevier B.V. All rights reserved.

Viscosity of Hg(0.84)Zn(0.16)Te Pseudobinary Melt

NASA Technical Reports Server (NTRS)

Mazuruk, K.; Su, Ching-Hua; Sha, Yi-Gao; Lehoczky, S. L.

1996-01-01

An oscillating-cup viscometer was developed to measure viscosity of molten HgZnTe ternary semiconductor alloys. Data were collected for the pseudobinary Hg(0.84)Zn(0.16)Te melt between 770 and 850 C. The kinematic viscosity was found to vary from approximately 1.1 to 1.4 x 10(sup -3)sq cm/s. A slow relaxation phenomena was also observed for temperatures from the melting point of 770 to approx. 800 C. Possible mechanisms for this effect are discussed.

Some physical aspects of fluid-fluxed melting

NASA Astrophysics Data System (ADS)

Patiño Douce, A.

2012-04-01

Fluid-fluxed melting is thought to play a crucial role in the origin of many terrestrial magmas. We can visualize the fundamental physics of the process as follows. An infinitesimal amount of fluid infiltrates dry rock at the temperature of its dry solidus. In order to restore equilibrium the temperature must drop, so that enthalpy is released and immediately reabsorbed as enthalpy of melting. The amount of melt produced must be such that the energy balance and thermodynamic equilibrium conditions are simultaneously satisfied. We wish to understand how an initially dry rock melts in response to progressive fluid infiltration, under both batch and fractional melting constraints. The simplest physical model for this process is a binary system in which one of the components makes up a pure solid phase and the other component a pure fluid phase, and in which a binary melt phase exists over certain temperature range. Melting point depression is calculated under the assumption of ideal mixing. The equations of energy balance and thermodynamic equilibrium are solved simultaneously for temperature and melt fraction, using an iterative procedure that allows addition of fluid in infinitesimal increments. Batch melting and fractional melting are simulated by allowing successive melt increments to remain in the system (batch) or not (fractional). Despite their simplified nature, these calculations reveal some important aspects of fluid-fluxed melting. The model confirms that, if the solubility of the fluid in the melt is sufficiently high, fluid fluxed melting is an efficient mechanism of magma generation. One might expect that the temperature of the infiltrating fluid would have a significant effect on melt productivity, but the results of the calculations show this not to be the case, because a relatively small mass of low molecular weight fluid has a strong effect on the melting point of minerals with much higher molecular weights. The calculations reveal the somewhat

Observational Evidence for Enhanced Greenhouse Effect Reinforcing Wintertime Arctic Amplification and Sea Ice Melting Onset

NASA Astrophysics Data System (ADS)

Cao, Y.; Liang, S.

2017-12-01

Despite an apparent hiatus in global warming, the Arctic climate continues to experience unprecedented changes. Summer sea ice is retreating at an accelerated rate, and surface temperatures in this region are rising at a rate double that of the global average, a phenomenon known as Arctic amplification. Although a lot of efforts have been made, the causes this unprecedented phenomenon remain unclear and are subjects of considerable debate. In this study, we report strong observational evidence, for the first time from long-term (1984-2014) spatially complete satellite records, that increased cloudiness and atmospheric water vapor in winter and spring have caused an extraordinary downward longwave radiative flux to the ice surface, which may then amplify the Arctic wintertime ice-surface warming. In addition, we also provide observed evidence that it is quite likely the enhancement of the wintertime greenhouse effect caused by water vapor and cloudiness has advanced the time of onset of ice melting in mid-May through inhibiting sea-ice refreezing in the winter and accelerating the pre-melting process in the spring, and in turn triggered the positive sea-ice albedo feedback process and accelerated the sea ice melting in the summer.

Thermal processing of a poorly water-soluble drug substance exhibiting a high melting point: the utility of KinetiSol® Dispersing.

PubMed

Hughey, Justin R; Keen, Justin M; Brough, Chris; Saeger, Sophie; McGinity, James W

2011-10-31

Poorly water-soluble drug substances that exhibit high melting points are often difficult to successfully process by fusion-based techniques. The purpose of this study was to identify a suitable polymer system for meloxicam (MLX), a high melting point class II BCS compound, and investigate thermal processing techniques for the preparation of chemically stable single phase solid dispersions. Thermal and solution based screening techniques were utilized to screen hydrophilic polymers suitable for immediate release formulations. Results of the screening studies demonstrated that Soluplus(®)(SOL) provided the highest degree of miscibility and solubility enhancement. A hot-melt extrusion feasibility study demonstrated that high temperatures and extended residence times were required in order to render compositions amorphous, causing significant degradation of MLX. A design of experiments (DOE) was conducted on the KinetiSol(®) Dispersing (KSD) process to evaluate the effect of processing conditions on the chemical stability and amorphous character of MLX. The study demonstrated that ejection temperature significantly impacted MLX stability. All samples prepared by KSD were substantially amorphous. Dissolution analysis of the KSD processed solid dispersions showed increased dissolution rates and extent of supersaturation over the marketed generic MLX tablets. Copyright © 2011 Elsevier B.V. All rights reserved.

Secondary Confinement of Water Observed in Eutectic Melting of Aqueous Salt Systems in Nanopores.

PubMed

Meissner, Jens; Prause, Albert; Findenegg, Gerhard H

2016-05-19

Freezing and melting of aqueous solutions of alkali halides confined in the cylindrical nanopores of MCM-41 and SBA-15 silica was probed by differential scanning calorimetry (DSC). We find that the confinement-induced shift of the eutectic temperature in the pores can be significantly greater than the shift of the melting temperature of pure water. Greatest shifts of the eutectic temperature are found for salts that crystallize as oligohydrates at the eutectic point. This behavior is explained by the larger fraction of pore volume occupied by salt hydrates as compared to anhydrous salts, on the assumption that precipitated salt constitutes an additional confinement for ice/water in the pores. A model based on this secondary confinement effect gives a good representation of the experimental data. Salt-specific secondary confinement may play a role in a variety of fields, from salt-impregnated advanced adsorbents and catalysts to the thermal weathering of building materials.

Methods for Melting Temperature Calculation

NASA Astrophysics Data System (ADS)

Hong, Qi-Jun

Melting temperature calculation has important applications in the theoretical study of phase diagrams and computational materials screenings. In this thesis, we present two new methods, i.e., the improved Widom's particle insertion method and the small-cell coexistence method, which we developed in order to capture melting temperatures both accurately and quickly. We propose a scheme that drastically improves the efficiency of Widom's particle insertion method by efficiently sampling cavities while calculating the integrals providing the chemical potentials of a physical system. This idea enables us to calculate chemical potentials of liquids directly from first-principles without the help of any reference system, which is necessary in the commonly used thermodynamic integration method. As an example, we apply our scheme, combined with the density functional formalism, to the calculation of the chemical potential of liquid copper. The calculated chemical potential is further used to locate the melting temperature. The calculated results closely agree with experiments. We propose the small-cell coexistence method based on the statistical analysis of small-size coexistence MD simulations. It eliminates the risk of a metastable superheated solid in the fast-heating method, while also significantly reducing the computer cost relative to the traditional large-scale coexistence method. Using empirical potentials, we validate the method and systematically study the finite-size effect on the calculated melting points. The method converges to the exact result in the limit of a large system size. An accuracy within 100 K in melting temperature is usually achieved when the simulation contains more than 100 atoms. DFT examples of Tantalum, high-pressure Sodium, and ionic material NaCl are shown to demonstrate the accuracy and flexibility of the method in its practical applications. The method serves as a promising approach for large-scale automated material screening in which

Empirical equation for predicting the surface tension of some liquid metals at their melting point

NASA Astrophysics Data System (ADS)

Ceotto, D.

2014-07-01

A new empirical equation is proposed for predicting the surface tension of some pure metals at their melting point. The investigation has been conducted adopting a statistical approach using some of the most accredited data available in literature. It is found that for Ag, Al, Au, Co, Cu, Fe, Ni, and Pb the surface tension can be conveniently expressed in function of the latent heat of fusion and of the geometrical parameters of an ideal liquid spherical drop. The equation proposed has been compared also with the model proposed by Lu and Jiang giving satisfactory agreement for the metals considered.

Stretching and smearing of chemical heterogeneity by melting and melt migration beneath mid-ocean ridges

NASA Astrophysics Data System (ADS)

Liu, B.; Liang, Y.

2017-12-01

The size of mantle source heterogeneity is important to the interpretation of isotopic signals observed in residual peridotites and basalts. During concurrent melting and melt migration beneath a mid-ocean ridge, both porosity and melt velocity increase upward, resulting in an upward increase in the effective transport velocity for a trace element. Hence a chemical heterogeneity of finite size will be stretched during its transport in the upwelling mantle. This melt migration induced chemical deformation can be quantified by a simple stretching factor. During equilibrium melting, the isotope signals of Sr, Nd and Hf in a 1 km size enriched mantle will be stretched to 2 6 km at the top of the melting column, depending on the style of melt migration. A finite rate of diffusive exchange between residual minerals and partial melt will result in smearing of chemical heterogeneity during its transport in the upwelling melting column. A Gaussian-shaped enriched source in depleted background mantle would be gradually deformed its transit through the melting column. The width of the enriched signal spreads out between the fronts of melt and solid while its amplitude decreases. This melt migration induced smearing also cause mixing of nearby heterogeneities or absorption of enriched heterogeneity by the ambient mantle. Smaller heterogeneities in the solid is more efficiently mixed or aborted by the background mantle than larger ones. Mixing of heterogeneities in the melt depends on the size in the same sense although the erupted melt is more homogenized due to melt accumulation and magma chamber process. The mapping of chemical heterogeneities observed in residual peridotites and basalts into their source region is therefore highly nonlinear. We will show that the observed variations in Nd and Hf isotopes in the global MORB and abyssal peridotites are consistent with kilometer-scale enriched heterogeneities embedded in depleted MORB mantle.

String-like cooperative motion in homogeneous melting

PubMed Central

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

2013-01-01

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

String-like cooperative motion in homogeneous melting.

PubMed

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

2013-03-28

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

Characterization of Low-Melting-Point Sn-Bi-In Lead-Free Solders

NASA Astrophysics Data System (ADS)

Li, Qin; Ma, Ninshu; Lei, YongPing; Lin, Jian; Fu, HanGuang; Gu, Jian

2016-11-01

Development of lead-free solders with low melting temperature is important for substitution of Pb-based solders to reduce direct risks to human health and the environment. In the present work, Sn-Bi-In solders were studied for different ratios of Bi and Sn to obtain solders with low melting temperature. The microstructure, thermal properties, wettability, mechanical properties, and reliability of joints with Cu have been investigated. The results show that the microstructures of the Sn-Bi-In solders were composed of β-Sn, Bi, and InBi phases. The intermetallic compound (IMC) layer was mainly composed of Cu6Sn5, and its thickness increased slightly as the Bi content was increased. The melting temperature of the solders was around 100°C to 104°C. However, when the Sn content exceeded 50 wt.%, the melting range became larger and the wettability became worse. The tensile strength of the solder alloys and solder joints declined with increasing Bi content. Two fracture modes (IMC layer fracture and solder/IMC mixed fracture) were found in solder joints. The fracture mechanism of solder joints was brittle fracture. In addition, cleavage steps on the fracture surface and coarse grains in the fracture structure were comparatively apparent for higher Bi content, resulting in decreased elongation for both solder alloys and solder joints.

Melting of Iron to 290 Gigapascals

NASA Astrophysics Data System (ADS)

Sinmyo, R.; Hirose, K.; Ohishi, Y.

2017-12-01

The Earth's core is composed mainly of iron. Since liquid core coexists with solid core at the inner core boundary (ICB), the melting point of iron at 330 gigapascals offers a key constraint on core temperatures. However, previous results using a laser-heated diamond-anvil cell (DAC) have been largely inconsistent with each other, likely because of an intrinsic large temperature gradient and its temporal fluctuation. Here we employed an internal-resistance-heated DAC and determined the melting temperature of pure iron up to 290 gigapascals, the highest ever in static compression experiments. A small extrapolation indicates a melting point of 5500 ± 80 kelvin at the ICB, about 500-1000 degrees lower than earlier shock-compression data. It suggests a relatively low temperature for the core-mantle boundary, which avoids global melting of the lowermost mantle in the last more than 1.5 billion years.

Computing the melting point and thermodynamic stability of the orthorhombic and monoclinic crystalline polymorphs of the ionic liquid 1-n-butyl-3-methylimidazolium chloride

NASA Astrophysics Data System (ADS)

Jayaraman, Saivenkataraman; Maginn, Edward J.

2007-12-01

The melting point, enthalpy of fusion, and thermodynamic stability of two crystal polymorphs of the ionic liquid 1-n-butyl-3-methylimidazolium chloride are calculated using a thermodynamic integration-based atomistic simulation method. The computed melting point of the orthorhombic phase ranges from 365 to 369 K, depending on the classical force field used. This compares reasonably well with the experimental values, which range from 337 to 339 K. The computed enthalpy of fusion ranges from 19 to 29 kJ/mol, compared to the experimental values of 18.5-21.5 kJ/mol. Only one of the two force fields evaluated in this work yielded a stable monoclinic phase, despite the fact that both give accurate liquid state densities. The computed melting point of the monoclinic polymorph was found to be 373 K, which is somewhat higher than the experimental range of 318-340 K. The computed enthalpy of fusion was 23 kJ/mol, which is also higher than the experimental value of 9.3-14.5 kJ/mol. The simulations predict that the monoclinic form is more stable than the orthorhombic form at low temperature, in agreement with one set of experiments but in conflict with another. The difference in free energy between the two polymorphs is very small, due to the fact that a single trans-gauche conformational difference in an alkyl sidechain distinguishes the two structures. As a result, it is very difficult to construct simple classical force fields that are accurate enough to definitively predict which polymorph is most stable. A liquid phase analysis of the probability distribution of the dihedral angles in the alkyl chain indicates that less than half of the dihedral angles are in the gauche-trans configuration that is adopted in the orthorhombic crystal. The low melting point and glass forming tendency of this ionic liquid is likely due to the energy barrier for conversion of the remaining dihedral angles into the gauche-trans state. The simulation procedure used to perform the melting point

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

NASA Technical Reports Server (NTRS)

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

2000-01-01

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.

Simulation on Melting Process of Water Using Molecular Dynamics Method

NASA Astrophysics Data System (ADS)

Okawa, Seiji; Saito, Akio; Kang, Chaedong

Simulation on phase change from ice to water was presented using molecular dynamics method. 576molecules were placed in a cell at ice forming arrangement. The volume of the cell was fixed so that the density of ice was kept at 923 kg/m3. Periodic boundary condition was used. According to the phase diagram of water, melting point of ice at the density of 923 kg/m3 is about 400 K. In order to perform melting process from surface, only the molecules near the boundary were scaled at each time step to keep its average temperature at 420 K, and the average temperature of other molecules were set to 350 K as initial condition. By observing time variation of the change in molecular arrangement, it was found that the hydrogen bond network near the boundary surface started to break its configuration and the melting surface moved towards the center until no more ice forming configuration was observed. This phenomenon was also discussed in a form of temperature and energy variation. The total energy increased and reached to a steady state at the time around 6.5 ps. This increment was due to the energy supplied from the boundary at a constant temperature. The temperature in the cell kept almost constant at 380 K during the period between 0.6 and 5.5 ps. This period coincides with melting process observed in molecular arrangement. Hence, it can be said that 380 K corresponds to the melting point. The total energy stored in the cell consisted of sensible and latent heat. Specific heat of water and ice were calculated, and they were found to be 5.6 kJ/kg·K and 3.7 kJ/kg·K, respectively. Hence, latent heat was found to be 316kJ/kg. These values agreed quite well to the physical properties of water.

CATALYST-FREE REACTIONS UNDER SOLVENT-FEE CONDITIONS: MICROWAVE-ASSISTED SYNTHESIS OF HETEROCYCLIC HYDRAZONES BELOW THE MELTING POINT OF NEAT REACTANTS: JOURNAL ARTICLE

EPA Science Inventory

NRMRL-CIN-1437 Jeselnik, M., Varma*, R.S., Polanc, S., and Kocevar, M. Catalyst-free Reactions under Solvent-fee Conditions: Microwave-assisted Synthesis of Heterocyclic Hydrazones below the Melting Point of Neat Reactants. Published in: Chemical Communications 18:1716-1717 (200...

Melt fracture revisited

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

Greenberg, J. M.

2003-07-16

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 referredmore » 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.« less

Simulation on the Effects of Surfactants and Observed Thermocapillary Motion for Laser Melting Physics

NASA Astrophysics Data System (ADS)

Nourgaliev, Robert; Barney, Rebecca; Weston, Brian; Delplanque, Jean-Pierre; McCallen, Rose

2017-11-01

A newly developed, robust, high-order in space and time, Newton-Krylov based reconstructed discontinuous Galerkin (rDG) method is used to model and analyze thermocapillary convection in melt pools. The application of interest is selective laser melting (SLM) which is an Additive Manufacturing (AM, 3D metal laser printing) process. These surface tension driven flows are influenced by temperature gradients and surfactants (impurities), and are known as the Marangoni flow. They have been experimentally observed in melt pools for welding applications, and are thought to influence the microstructure of the re-solidified material. We study the effects of the laser source configuration (power, beam size and scanning speed), as well as surfactant concentrations. Results indicate that the surfactant concentration influences the critical temperature, which governs the direction of the surface thermocapillary traction. When the surface tension traction changes sign, very complex flow patterns emerge, inducing hydrodynamic instability under certain conditions. These in turn would affect the melt pool size (depth) and shape, influencing the resulting microstructure, properties, and performance of a finished product part produced using 3D metal laser printing technologies. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. Information management release number LLNL-ABS-735908.

In situ study on atomic mechanism of melting and freezing of single bismuth nanoparticles

NASA Astrophysics Data System (ADS)

Li, Yingxuan; Zang, Ling; Jacobs, Daniel L.; Zhao, Jie; Yue, Xiu; Wang, Chuanyi

2017-02-01

Experimental study of the atomic mechanism in melting and freezing processes remains a formidable challenge. We report herein on a unique material system that allows for in situ growth of bismuth nanoparticles from the precursor compound SrBi2Ta2O9 under an electron beam within a high-resolution transmission electron microscope (HRTEM). Simultaneously, the melting and freezing processes within the nanoparticles are triggered and imaged in real time by the HRTEM. The images show atomic-scale evidence for point defect induced melting, and a freezing mechanism mediated by crystallization of an intermediate ordered liquid. During the melting and freezing, the formation of nucleation precursors, nucleation and growth, and the relaxation of the system, are directly observed. Based on these observations, an interaction-relaxation model is developed towards understanding the microscopic mechanism of the phase transitions, highlighting the importance of cooperative multiscale processes.

In situ study on atomic mechanism of melting and freezing of single bismuth nanoparticles.

PubMed

Li, Yingxuan; Zang, Ling; Jacobs, Daniel L; Zhao, Jie; Yue, Xiu; Wang, Chuanyi

2017-02-13

Experimental study of the atomic mechanism in melting and freezing processes remains a formidable challenge. We report herein on a unique material system that allows for in situ growth of bismuth nanoparticles from the precursor compound SrBi 2 Ta 2 O 9 under an electron beam within a high-resolution transmission electron microscope (HRTEM). Simultaneously, the melting and freezing processes within the nanoparticles are triggered and imaged in real time by the HRTEM. The images show atomic-scale evidence for point defect induced melting, and a freezing mechanism mediated by crystallization of an intermediate ordered liquid. During the melting and freezing, the formation of nucleation precursors, nucleation and growth, and the relaxation of the system, are directly observed. Based on these observations, an interaction-relaxation model is developed towards understanding the microscopic mechanism of the phase transitions, highlighting the importance of cooperative multiscale processes.

In situ study on atomic mechanism of melting and freezing of single bismuth nanoparticles

PubMed Central

Li, Yingxuan; Zang, Ling; Jacobs, Daniel L.; Zhao, Jie; Yue, Xiu; Wang, Chuanyi

2017-01-01

Experimental study of the atomic mechanism in melting and freezing processes remains a formidable challenge. We report herein on a unique material system that allows for in situ growth of bismuth nanoparticles from the precursor compound SrBi2Ta2O9 under an electron beam within a high-resolution transmission electron microscope (HRTEM). Simultaneously, the melting and freezing processes within the nanoparticles are triggered and imaged in real time by the HRTEM. The images show atomic-scale evidence for point defect induced melting, and a freezing mechanism mediated by crystallization of an intermediate ordered liquid. During the melting and freezing, the formation of nucleation precursors, nucleation and growth, and the relaxation of the system, are directly observed. Based on these observations, an interaction–relaxation model is developed towards understanding the microscopic mechanism of the phase transitions, highlighting the importance of cooperative multiscale processes. PMID:28194017

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

NASA Astrophysics Data System (ADS)

Currier, R. M.

2017-12-01

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

On the Melting Curve of Sulfur Hexafluoride

NASA Astrophysics Data System (ADS)

Harvey, Allan H.

2017-12-01

A previous correlation for the melting curve of sulfur hexafluoride (SF6) is inconsistent with the thermodynamic slope at the triple point derived from the Clapeyron equation. It is shown that this is probably due to the previous authors combining an accurate measurement of the triple point with melting-curve data that were distorted by impurities. A new equation is proposed that is consistent with the Clapeyron slope.

Vitrification of waste with conitnuous filling and sequential melting

DOEpatents

Powell, James R.; Reich, Morris

2001-09-04

A method of filling a canister with vitrified waste starting with a waste, such as high-level radioactive waste, that is cooler than its melting point. Waste is added incrementally to a canister forming a column of waste capable of being separated into an upper zone and a lower zone. The minimum height of the column is defined such that the waste in the lower zone can be dried and melted while maintaining the waste in the upper zone below its melting point. The maximum height of the column is such that the upper zone remains porous enough to permit evolved gases from the lower zone to flow through the upper zone and out of the canister. Heat is applied to the waste in the lower zone to first dry then to raise and maintain its temperature to a target temperature above the melting point of the waste. Then the heat is applied to a new lower zone above the melted waste and the process of adding, drying and melting the waste continues upward in the canister until the entire canister is filled and the entire contents are melted and maintained at the target temperature for the desired period. Cooling of the melted waste takes place incrementally from the bottom of the canister to the top, or across the entire canister surface area, forming a vitrified product.

Dynamic melting of metals in the diamond cell: Clues for melt viscosity?

NASA Astrophysics Data System (ADS)

Boehler, R.; Karandikar, A.; Yang, L.

2011-12-01

From the observed decreasing mobility of liquid iron at high pressure in the laser-heated diamond cell and the gradual decrease in the shear modulus in shock experiments, one may derive high viscosity in the liquid outer core of the Earth. A possible explanation could be the presence of local structures in the liquid as has been observed for several transition metals. In order to bridge the large gap in the timescales between static and dynamic melting experiments, we have developed new experimental techniques to solve the large discrepancies in the melting curves of transition metals (Fe, W, Ta, Mo) measured statically in the laser-heated diamond cell and in shock experiments. The new methods employ "single-shot" laser heating in order to reduce problems associated with mechanical instabilities and chemical reactions of the samples subjected to several thousand degrees at megabar pressures. For melt detection, both synchrotron X-ray diffraction and Scanning Electron Microscopy (SEM) on recovered samples are used. A third approach is the measurement of latent heat effects associated with melting or freezing. This method employs simultaneous CW and pulse laser heating and monitoring the temperature-time history with fast photomultipliers. Using the SEM recovery method, we measured first melting temperatures of rhenium, which at high pressure may be one of the most refractory materials. From the melt textures of Re, we did not observe a significant pressure dependence of viscosity.

Revisiting the Potential of Melt Pond Fraction as a Predictor for the Seasonal Arctic Sea Ice Extent Minimum

NASA Technical Reports Server (NTRS)

Liu, Jiping; Song, Mirong; Horton, Radley M.; Hu, Yongyun

2015-01-01

The rapid change in Arctic sea ice in recent decades has led to a rising demand for seasonal sea ice prediction. A recent modeling study that employed a prognostic melt pond model in a stand-alone sea ice model found that September Arctic sea ice extent can be accurately predicted from the melt pond fraction in May. Here we show that satellite observations show no evidence of predictive skill in May. However, we find that a significantly strong relationship (high predictability) first emerges as the melt pond fraction is integrated from early May to late June, with a persistent strong relationship only occurring after late July. Our results highlight that late spring to mid summer melt pond information is required to improve the prediction skill of the seasonal sea ice minimum. Furthermore, satellite observations indicate a much higher percentage of melt pond formation in May than does the aforementioned model simulation, which points to the need to reconcile model simulations and observations, in order to better understand key mechanisms of melt pond formation and evolution and their influence on sea ice state.

Observed Melt Season Seismicity of Taylor Glacier, Antarctica

NASA Astrophysics Data System (ADS)

Carmichael, J. D.; Pettit, E. C.; Creager, K. C.

2006-12-01

Sufficient evidence exists to suggest that interaction of crevasses and meltwater accelerates ice cliff disintegration of tidewater glaciers. It is not clear what role meltwater plays in calving characteristics from dry- based polar glaciers. We have obtained seismic data from a six-sensor seismic array deployed in October of 2004 near the terminus cliffs of Taylor Glacier, West Antarctica, to analyze near-cliff seismicity throughout a melt season. Discharge data from the adjacent Lawson stream suggests that dramatic increases in meltwater volume temporally correlate with changes in seismic character near ice cliffs. We calculated source-locations for ice-quake during hours of melting and re-freezing and found most large energy events to be located near the ice cliffs. The associated spectra and waveform characteristics are indicative of literature descriptions of crevassing events.

Melt Segregation and Tidal Heating at Io

NASA Astrophysics Data System (ADS)

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

2011-12-01

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

Melting Inside the Tibetan Crust? Constraint From Electrical Conductivity of Peraluminous Granitic Melt

NASA Astrophysics Data System (ADS)

Guo, Xuan; Zhang, Li; Su, Xue; Mao, Zhu; Gao, Xiao-Ying; Yang, Xiaozhi; Ni, Huaiwei

2018-05-01

Magnetotelluric and seismological studies suggested the presence of partial melts in the middle to lower Himalaya-Tibetan crust. However, the melt fractions inferred by previous work were based on presumed electrical conductivity of melts. We performed measurements on the electrical conductivity of peraluminous granitic melts with 0.16-8.4 wt % H2O (the expected compositions in the Tibetan crust) at 600-1,300°C and 0.5-1.0 GPa. Peraluminous melt exhibits lower electrical conductivity than peralkaline melt at dry condition, but this difference diminishes at H2O > 2 wt %. With our data, the observed electrical anomalies in the Tibetan crust could be explained by 2-33 vol % of peraluminous granitic melts with H2O > 6 wt %. Possible reasons for our inferred melt fractions being higher than seismological constraints include the following: (1) The real melts are more Na and H2O rich, (2) the effect of melt reducing seismic velocities was overestimated, and (3) the anomalies at some locations are due to fluids.

Anisotropic surface melting in lyotropic cubic crystals: part 2: facet-by-facet melting at Ia3d/vapor interfaces.

PubMed

Leroy, S; Grenier, J; Rohe, D; Even, C; Pieranski, P

2006-05-01

From experiments with metal crystals, in the vicinity of their crystal/liquid/vapor triple points, it is known that melting of crystals starts on their surfaces and is anisotropic. Recently, we have shown that anisotropic surface melting occurs also in lyotropic systems. In our previous paper (Eur. Phys. J. E 19, 223 (2006)), we have focused on the case of poor faceting at the Pn3m/L1 interface in C12EO2/water binary mixtures. There anisotropic melting occurs in the vicinity of a Pn3m/L3/L1 triple point. In the present paper, we focus on the opposite case of a rich devil's-staircase-type faceting at Ia3d/vapor interfaces in monoolein/water and phytantriol/water mixtures. We show that anisotropic surface melting takes place in these systems in a narrow humidity range close to the Ia3d-L2 transition. As whole (hkl) sets of facets disappear one after another when the transition is approached, surface melting occurs in a facet-by-facet type.

Solid Lipid Nanoparticle Formulations of Docetaxel Prepared with High Melting Point Triglycerides: In Vitro and in Vivo Evaluation

PubMed Central

2015-01-01

Docetaxel (DCX) is a second generation taxane. It is approved by the U.S. Food and Drug Administration for the treatment of various types of cancer, including breast, non-small cell lung, and head and neck cancers. However, side effects, including those related to Tween 80, an excipient in current DCX formulations, can be severe. In the present study, we developed a novel solid lipid nanoparticle (SLN) composition of DCX. Trimyristin was selected from a list of high melting point triglycerides as the core lipid component of the SLNs, based on the rate at which the DCX was released from the SLNs and the stability of the SLNs. The trimyristin-based, PEGylated DCX-incorporated SLNs (DCX-SLNs) showed significantly higher cytotoxicity against various human and murine cancer cells in culture, as compared to DCX solubilized in a Tween 80/ethanol solution. Moreover, in a mouse model with pre-established tumors, the new DCX-SLNs were significantly more effective than DCX solubilized in a Tween 80/ethanol solution in inhibiting tumor growth without toxicity, likely because the DCX-SLNs increased the concentration of DCX in tumor tissues, but decreased the levels of DCX in major organs such as liver, spleen, heart, lung, and kidney. DCX-incorporated SLNs prepared with one or more high-melting point triglycerides may represent an improved DCX formulation. PMID:24621456

Construction of a Cr3C2-C Peritectic Point Cell for Thermocouple Calibration

NASA Astrophysics Data System (ADS)

Ogura, Hideki; Deuze, Thierry; Morice, Ronan; Ridoux, Pascal; Filtz, Jean-Remy

The melting points of Cr3C2-C peritectic (1826°C) and Cr7C3-Cr3C2 eutectic (1742°C) alloys as materials for high-temperature fixed point cells are investigated for the use of thermocouple calibration. Pretests are performed to establish a suitable procedure for constructing contact thermometry cells based on such chromium-carbon mixtures. Two cells are constructed following two different possible procedures. The above two melting points are successfully observed for one of these cells using tungsten-rhenium alloy thermocouples.

Consistent estimate of ocean warming, land ice melt and sea level rise from Observations

NASA Astrophysics Data System (ADS)

Blazquez, Alejandro; Meyssignac, Benoît; Lemoine, Jean Michel

2016-04-01

Based on the sea level budget closure approach, this study investigates the consistency of observed Global Mean Sea Level (GMSL) estimates from satellite altimetry, observed Ocean Thermal Expansion (OTE) estimates from in-situ hydrographic data (based on Argo for depth above 2000m and oceanic cruises below) and GRACE observations of land water storage and land ice melt for the period January 2004 to December 2014. The consistency between these datasets is a key issue if we want to constrain missing contributions to sea level rise such as the deep ocean contribution. Numerous previous studies have addressed this question by summing up the different contributions to sea level rise and comparing it to satellite altimetry observations (see for example Llovel et al. 2015, Dieng et al. 2015). Here we propose a novel approach which consists in correcting GRACE solutions over the ocean (essentially corrections of stripes and leakage from ice caps) with mass observations deduced from the difference between satellite altimetry GMSL and in-situ hydrographic data OTE estimates. We check that the resulting GRACE corrected solutions are consistent with original GRACE estimates of the geoid spherical harmonic coefficients within error bars and we compare the resulting GRACE estimates of land water storage and land ice melt with independent results from the literature. This method provides a new mass redistribution from GRACE consistent with observations from Altimetry and OTE. We test the sensibility of this method to the deep ocean contribution and the GIA models and propose best estimates.

Printing low-melting-point alloy ink to directly make a solidified circuit or functional device with a heating pen

PubMed Central

Wang, Lei; Liu, Jing

2014-01-01

A new method to directly print out a solidified electronic circuit through low-melting-point metal ink is proposed. A functional pen with heating capability was fabricated. Several typical thermal properties of the alloy ink Bi35In48.6Sn16Zn0.4 were measured and evaluated. Owing to the specifically selected melting point of the ink, which is slightly higher than room temperature, various electronic devices, graphics or circuits can be manufactured in a short period of time and then rapidly solidified by cooling in the surrounding air. The liquid–solid phase change mechanism of the written lines was experimentally characterized using a scanning electron microscope. In order to determine the matching substrate, wettability between the metal ink Bi35In48.6Sn16Zn0.4 and several materials, including mica plate and silicone rubber, was investigated. The resistance–temperature curve of a printed resistor indicated its potential as a temperature control switch. Furthermore, the measured reflection coefficient of a printed double-diamond antenna accords well with the simulated result. With unique merits such as no pollution, no requirement for encapsulation and easy recycling, the present printing approach is an important supplement to current printed electronics and has enormous practical value in the future. PMID:25484611

Printing low-melting-point alloy ink to directly make a solidified circuit or functional device with a heating pen.

PubMed

Wang, Lei; Liu, Jing

2014-12-08

A new method to directly print out a solidified electronic circuit through low-melting-point metal ink is proposed. A functional pen with heating capability was fabricated. Several typical thermal properties of the alloy ink Bi 35 In 48.6 Sn 16 Zn 0.4 were measured and evaluated. Owing to the specifically selected melting point of the ink, which is slightly higher than room temperature, various electronic devices, graphics or circuits can be manufactured in a short period of time and then rapidly solidified by cooling in the surrounding air. The liquid-solid phase change mechanism of the written lines was experimentally characterized using a scanning electron microscope. In order to determine the matching substrate, wettability between the metal ink Bi 35 In 48.6 Sn 16 Zn 0.4 and several materials, including mica plate and silicone rubber, was investigated. The resistance-temperature curve of a printed resistor indicated its potential as a temperature control switch. Furthermore, the measured reflection coefficient of a printed double-diamond antenna accords well with the simulated result. With unique merits such as no pollution, no requirement for encapsulation and easy recycling, the present printing approach is an important supplement to current printed electronics and has enormous practical value in the future.

The effect of salt on the melting of ice: A molecular dynamics simulation study.

PubMed

Kim, Jun Soo; Yethiraj, Arun

2008-09-28

The effect of added salt (NaCl) on the melting of ice is studied using molecular dynamics simulations. The equilibrium freezing point depression observed in the simulations is in good agreement with experimental data. The kinetic aspects of melting are investigated in terms of the exchange of water molecules between ice and the liquid phase. The ice/liquid equilibrium is a highly dynamic process with frequent exchange of water molecules between ice and the liquid phase. The balance is disturbed when ice melts and the melting proceeds in two stages; the inhibition of the association of water molecules to the ice surface at short times, followed by the increased dissociation of water molecules from the ice surface at longer times. We also find that Cl(-) ions penetrate more deeply into the interfacial region than Na(+) ions during melting. This study provides an understanding of the kinetic aspects of melting that could be useful in other processes such as the inhibition of ice growth by antifreeze proteins.

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

NASA Technical Reports Server (NTRS)

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

2013-01-01

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

Ab-initio calculations on melting of thorium

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

Mukherjee, D., E-mail: debojyoti@barc.gov.in; Sahoo, B. D.; Joshi, K. D.

2016-05-23

Ab-initio molecular dynamics study has been performed on face centered cubic structured thorium to determine its melting temperature at room pressure. The ion-electron interaction potential energy calculated as a function of temperature for three volumes (a{sub 0}){sup 3} and (1.02a{sub 0}){sup 3} and (1.04a{sub 0}){sup 3} increases gradually with temperature and undergoes a sharp jump at ~2200 K, ~2100 K and ~1800 K, respectively. Here, a{sub 0} = 5.043 Å is the equilibrium lattice parameter at 0 K obtained from ab-initio calculations. These jumps in interaction energy are treated as due to the onset of melting and corresponding temperatures asmore » melting point. The melting point of 2100 K is close to the experimental value of 2023 K. Further, the same has been verified by plotting the atomic arrangement evolved at various temperatures and corresponding pair correlation functions.« less

Molecular dynamics simulations of the melting curve of NiAl alloy under pressure

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

Zhang, Wenjin; Peng, Yufeng; Liu, Zhongli, E-mail: zhongliliu@yeah.net

2014-05-15

The melting curve of B2-NiAl alloy under pressure has been investigated using molecular dynamics technique and the embedded atom method (EAM) potential. The melting temperatures were determined with two approaches, the one-phase and the two-phase methods. The first one simulates a homogeneous melting, while the second one involves a heterogeneous melting of materials. Both approaches reduce the superheating effectively and their results are close to each other at the applied pressures. By fitting the well-known Simon equation to our melting data, we yielded the melting curves for NiAl: 1783(1 + P/9.801){sup 0.298} (one-phase approach), 1850(1 + P/12.806){sup 0.357} (two-phase approach).more » The good agreement of the resulting equation of states and the zero-pressure melting point (calc., 1850 ± 25 K, exp., 1911 K) with experiment proved the correctness of these results. These melting data complemented the absence of experimental high-pressure melting of NiAl. To check the transferability of this EAM potential, we have also predicted the melting curves of pure nickel and pure aluminum. Results show the calculated melting point of Nickel agrees well with experiment at zero pressure, while the melting point of aluminum is slightly higher than experiment.« less

Polarimetric C-/X-band Synthetic Aperture Radar Observations of Melting Sea Ice in the Canadian Arctic Archipelago

NASA Astrophysics Data System (ADS)

Casey, J. A.; Beckers, J. F.; Brossier, E.; Haas, C.

2013-12-01

Operational ice information services rely heavily on space-borne synthetic aperture radar (SAR) data for the production of ice charts to meet their mandate of providing timely and accurate sea ice information to support safe and efficient marine operations. During the summer melt period, the usefulness of SAR data for sea ice monitoring is limited by the presence of wet snow and melt ponds on the ice surface, which can mask the signature of the underlying ice. This is a critical concern for ice services whose clients (e.g. commercial shipping, cruise tourism, resource exploration and extraction) are most active at this time of year when sea ice is at its minimum extent, concentration and thickness. As a result, there is a need to further quantify the loss of ice information in SAR data during the melt season and to identify what information can still be retrieved about ice surface conditions and melt pond evolution at this time of year. To date the majority of studies have been limited to analysis of single-polarization C-band SAR data. This study will investigate the potential complimentary and unique sea ice information that polarimetric C- and X-band SAR data can provide to supplement the information available from traditional single co-polarized C-band SAR data. A time-series of polarimetric C- and X-band SAR data was acquired over Jones Sound in the Canadian Arctic Archipelago, in the vicinity of the Grise Fiord, Nunavut. Five RADARSAT-2 Wide Fine Quad-pol images and 11 TerraSAR-X StripMap dual-pol (HH/VV) images were acquired. The time-series begins at the onset of melt in early June and extends through advanced melt conditions in late July. Over this period several ponding and drainage events and two snowfall events occurred. Field observations of sea ice properties were collected using an Ice Mass Balance (IMB) buoy, hourly photos from a time-lapse camera deployed on a coastal cliff, and manual in situ measurements of snow thickness and melt pond depth

Seeing Your Error Alters My Pointing: Observing Systematic Pointing Errors Induces Sensori-Motor After-Effects

PubMed Central

Ronchi, Roberta; Revol, Patrice; Katayama, Masahiro; Rossetti, Yves; Farnè, Alessandro

2011-01-01

During the procedure of prism adaptation, subjects execute pointing movements to visual targets under a lateral optical displacement: As consequence of the discrepancy between visual and proprioceptive inputs, their visuo-motor activity is characterized by pointing errors. The perception of such final errors triggers error-correction processes that eventually result into sensori-motor compensation, opposite to the prismatic displacement (i.e., after-effects). Here we tested whether the mere observation of erroneous pointing movements, similar to those executed during prism adaptation, is sufficient to produce adaptation-like after-effects. Neurotypical participants observed, from a first-person perspective, the examiner's arm making incorrect pointing movements that systematically overshot visual targets location to the right, thus simulating a rightward optical deviation. Three classical after-effect measures (proprioceptive, visual and visual-proprioceptive shift) were recorded before and after first-person's perspective observation of pointing errors. Results showed that mere visual exposure to an arm that systematically points on the right-side of a target (i.e., without error correction) produces a leftward after-effect, which mostly affects the observer's proprioceptive estimation of her body midline. In addition, being exposed to such a constant visual error induced in the observer the illusion “to feel” the seen movement. These findings indicate that it is possible to elicit sensori-motor after-effects by mere observation of movement errors. PMID:21731649

Solubility of NaCl in water and its melting point by molecular dynamics in the slab geometry and a new BK3-compatible force field

NASA Astrophysics Data System (ADS)

Kolafa, Jiří

2016-11-01

Saturated concentration of rock salt in water is determined by a simulation of brine in contact with a crystal in the slab geometry. The NaCl crystals are rotated to expose facets with higher Miller indices than [001] to brine. The rock salt melting point is obtained by both the standard and adiabatic simulations in the slab geometry with attention paid to finite size effects as well as to a possible influence of facets with higher Miller indices and applied stress. Two force fields are used, the Lennard-Jones-based model by Young and Cheatham with SPC/E water and the Kiss and Baranyai polarizable model with BK3 water. The latter model is refitted to thermomechanical properties of crystal NaCl leading to better values of solubility and the melting point.

Solubility of NaCl in water and its melting point by molecular dynamics in the slab geometry and a new BK3-compatible force field.

PubMed

Kolafa, Jiří

2016-11-28

Saturated concentration of rock salt in water is determined by a simulation of brine in contact with a crystal in the slab geometry. The NaCl crystals are rotated to expose facets with higher Miller indices than [001] to brine. The rock salt melting point is obtained by both the standard and adiabatic simulations in the slab geometry with attention paid to finite size effects as well as to a possible influence of facets with higher Miller indices and applied stress. Two force fields are used, the Lennard-Jones-based model by Young and Cheatham with SPC/E water and the Kiss and Baranyai polarizable model with BK3 water. The latter model is refitted to thermomechanical properties of crystal NaCl leading to better values of solubility and the melting point.

A Reevaluation of Impact Melt Production

NASA Astrophysics Data System (ADS)

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

1997-06-01

The production of melt and vapor is an important process in impact cratering events. Because significant melting and vaporization do not occur in impacts at velocities currently achievable in the laboratory, a detailed study of the production of melt and vapor in planetary impact events is carried out with hydrocode simulations. Sandia's two-dimensional axisymmetric hydrocode CSQ was used to estimate the amount of melt and vapor produced for widely varying initial conditions: 10 to 80 km/sec for impact velocity, 0.2 to 10 km for the projectile radius. Runs with different materials demonstrate the material dependency of the final result. These results should apply to any size projectile (for given impact velocity and material), since the results can be dynamically scaled so long as gravity is unimportant in affecting the early-time flow. In contrast with the assumptions of previous analytical models, a clear difference in shape, impact-size dependence, and depth of burial has been found between the melt regions and the isobaric core. In particular, the depth of the isobaric core is not a good representation of the depth of the melt regions, which form deeper in the target. While near-surface effects cause the computed melt region shapes to look like “squashed spheres” the spherical shape is still a good analytical analog. One of the goals of melt production studies is to find proper scaling laws to infer melt production for any impact event of interest. We tested the point source limit scaling law for melt volumes (μ = 0.55-0.6) proposed by M. D. Bjorkman and K. A. Holsapple (1987,Int. J. Impact Eng.5, 155-163). Our results indicate that the point source limit concept does not apply to melt and vapor production. Rather, melt and vapor production follows an energy scaling law (μ = 0.67), in good agreement with previous results of T. J. Ahrens and J. D. O'Keefe [1977, inImpact and Explosion Cratering(D. J. Roddy, R. O. Pepin, and R. B. Merrill, Eds.), pp. 639

Arctic melt ponds and bifurcations in the climate system

NASA Astrophysics Data System (ADS)

Sudakov, I.; Vakulenko, S. A.; Golden, K. M.

2015-05-01

Understanding how sea ice melts is critical to climate projections. In the Arctic, melt ponds that develop on the surface of sea ice floes during the late spring and summer largely determine their albedo - a key parameter in climate modeling. Here we explore the possibility of a conceptual sea ice climate model passing through a bifurcation point - an irreversible critical threshold as the system warms, by incorporating geometric information about melt pond evolution. This study is based on a bifurcation analysis of the energy balance climate model with ice-albedo feedback as the key mechanism driving the system to bifurcation points.

July 2012 Greenland melt extent enhanced by low-level liquid clouds.

PubMed

Bennartz, R; Shupe, M D; Turner, D D; Walden, V P; Steffen, K; Cox, C J; Kulie, M S; Miller, N B; Pettersen, C

2013-04-04

Melting of the world's major ice sheets can affect human and environmental conditions by contributing to sea-level rise. In July 2012, an historically rare period of extended surface melting was observed across almost the entire Greenland ice sheet, raising questions about the frequency and spatial extent of such events. Here we show that low-level clouds consisting of liquid water droplets ('liquid clouds'), via their radiative effects, played a key part in this melt event by increasing near-surface temperatures. We used a suite of surface-based observations, remote sensing data, and a surface energy-balance model. At the critical surface melt time, the clouds were optically thick enough and low enough to enhance the downwelling infrared flux at the surface. At the same time they were optically thin enough to allow sufficient solar radiation to penetrate through them and raise surface temperatures above the melting point. Outside this narrow range in cloud optical thickness, the radiative contribution to the surface energy budget would have been diminished, and the spatial extent of this melting event would have been smaller. We further show that these thin, low-level liquid clouds occur frequently, both over Greenland and across the Arctic, being present around 30-50 per cent of the time. Our results may help to explain the difficulties that global climate models have in simulating the Arctic surface energy budget, particularly as models tend to under-predict the formation of optically thin liquid clouds at supercooled temperatures--a process potentially necessary to account fully for temperature feedbacks in a warming Arctic climate.

Melting-solidification transition of Zn nanoparticles embedded in SiO2: Observation by synchrotron x-ray and ultraviolet-visible-near-infrared light

NASA Astrophysics Data System (ADS)

Amekura, H.; Tanaka, M.; Katsuya, Y.; Yoshikawa, H.; Ohnuma, M.; Matsushita, Y.; Kobayashi, K.; Kishimoto, N.

2010-11-01

Melting-solidification transition of Zn nanoparticles (NPs) with the mean diameter of 11.5 nm, embedded in silica glass, was investigated by glancing incident x-ray diffraction (GIXRD) at high temperatures using synchrotron radiation (SR). With increasing temperature, 101Zn diffraction peak gradually decreases up to ˜360 °C and then steeply decreases. This is due to the melting of Zn NPs, which completes around 420 °C. With decreasing temperature, the solidification of the NPs begins around ˜310 °C. The temperature hysteresis with a width of ˜110 °C was observed. With temperature, the diffraction angle shows a shift without hysteresis, which is ascribed to thermal expansion of Zn NP lattice. Thermal expansion coefficient of Zn NPs was determined as 24.4×10-6 K-1 along the ⟨101⟩ direction. Optical absorption spectroscopy shows a broad ultraviolet (UV) peak which was observed at even higher temperatures than the melting temperature but shifts to the low-energy side with the melting. The energy shift in the UV peak also shows the temperature hysteresis which resembles with the melting-solidification hysteresis recorded by SR-GIXRD. The melting-solidification transition is also detectable by the optical absorption spectroscopy in the UV-visible-near-infrared region.

X-ray characterization of indium during melting

NASA Astrophysics Data System (ADS)

Gondi, P.; Montanari, R.; Costanza, G.

During melting of Indium the structure of solid and liquid phases have been investigated by X-ray diffractometry (XRD) in 1-g conditions. At the melting point T M a re-orientation of crystalline grains occurs in the solid phase. The texture change, unusually rapid for a thermally activated process, is attributed to an abnormal increase of vacancy concentration. This explanation is in agreement with the observed shifts of XRD peaks towards lower angles. As a consequence of the texture change, the lattice planes facing the first formed liquid are (002) and (101) planes, i.e. those planes allocating 1st and 2nd neighbours around a given atom with shell radii very close to the mean distance of nearest neighbours in liquid as obtained from the radial distribution function (RDF). Convective motions in the liquid can be eliminated by repeating the same XRD measurements in μ-g. To get the best experimental conditions it is discussed the possibility to use thin oxide films grown on the external surface of samples as containers during melting. This technique was already successfully tested by present investigators in the experiment ES 311 A-B carried out during the mission SPACELAB-1.

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

NASA Astrophysics Data System (ADS)

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

2008-07-01

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

Melting of size-selected gallium clusters with 60-183 atoms.

PubMed

Pyfer, Katheryne L; Kafader, Jared O; Yalamanchali, Anirudh; Jarrold, Martin F

2014-07-10

Heat capacities have been measured as a function of temperature for size-selected gallium cluster cations with between 60 and 183 atoms. Almost all clusters studied show a single peak in the heat capacity that is attributed to a melting transition. The peaks can be fit by a two-state model incorporating only fully solid-like and fully liquid-like species, and hence no partially melted intermediates. The exceptions are Ga90(+), which does not show a peak, and Ga80(+) and Ga81(+), which show two peaks. For the clusters with two peaks, the lower temperature peak is attributed to a structural transition. The melting temperatures for clusters with less than 50 atoms have previously been shown to be hundreds of degrees above the bulk melting point. For clusters with more than 60 atoms the melting temperatures decrease, approaching the bulk value (303 K) at around 95 atoms, and then show several small upward excursions with increasing cluster size. A plot of the latent heat against the entropy change for melting reveals two groups of clusters: the latent heats and entropy changes for clusters with less than 94 atoms are distinct from those for clusters with more than 93 atoms. This observation suggests that a significant change in the nature of the bonding or the structure of the clusters occurs at 93-94 atoms. Even though the melting temperatures are close to the bulk value for the larger clusters studied here, the latent heats and entropies of melting are still far from the bulk values.

A Melting Layer Model for Passive/Active Microwave Remote Sensing Applications. Part 1; Model Formulation and Comparison with Observations

NASA Technical Reports Server (NTRS)

Olson, William S.; Bauer, Peter; Viltard, Nicolas F.; Johnson, Daniel E.; Tao, Wei-Kuo

2000-01-01

that do not contain mixed-phase precipitation particles yield optical depths that are systematically lower than those observed. Therefore, the use of the melting layer model to extend 3-D CRM simulations appears justified, at least until more realistic spectral methods for describing melting precipitation in high-resolution, 3-D CRM's are implemented.

Melting of isolated tin nanoparticles

PubMed

Bachels; Guntherodt; Schafer

2000-08-07

The melting of isolated neutral tin cluster distributions with mean sizes of about 500 atoms has been investigated in a molecular beam experiment by calorimetrically measuring the clusters' formation energies as a function of their internal temperature. For this purpose the possibility to adjust the temperature of the clusters' internal degrees of freedom by means of the temperature of the cluster source's nozzle was exploited. The melting point of the investigated tin clusters was found to be lowered by 125 K and the latent heat of fusion per atom is reduced by 35% compared to bulk tin. The melting behavior of the isolated tin clusters is discussed with respect to the occurrence of surface premelting.

Our Educational Melting Pot: Have We Reached the Boiling Point?

ERIC Educational Resources Information Center

Lauderdale, Katherine Lynn, Ed.; Bonilla, Carlos A., Ed.

The articles and excerpts in this collection illustrate the complexity of the melting pot concept. Multiculturalism has become a watchword in American life and education, but it may be that in trying to atone for past transgressions educators and others are simply going too far. These essays illustrate some of the problems of a multicultural…

Petrogenesis of melt rocks, Manicouagan impact structure, Quebec

NASA Technical Reports Server (NTRS)

Simonds, C. H.; Floran, R. J.; Mcgee, P. E.; Phinney, W. C.; Warner, J. L.

1978-01-01

It is suggested, on the basis of previous theoretical studies of shock waves, that the Manicouagan melt formed in 1 or 2 s in a 5-km-radius hemisphere near the point of impact. The melt and the less shocked debris surrounding it flowed downward and outward for a few minutes until the melt formed a lining of a 5- to 8-km deep, 15- to 22-km-radius cavity. Extremely turbulent flow thoroughly homogenized the melt and promoted the incorporation and progressive digestion of debris that had been finely fragmented (but not melted) to grain sizes of less than one mm by the passage of the shock waves. The equilibration of clasts and melt, plagioclase nucleation, and readjustment of the crater floor are discussed.

Experiments with the low melting indium-bismuth alloy system

NASA Technical Reports Server (NTRS)

Krepski, Richard P.

1992-01-01

The following is a laboratory experiment designed to create an interest in and to further understanding of materials science. The primary audience for this material is the junior high school or middle school science student having no previous familiarity with the material, other than some knowledge of temperature and the concepts of atoms, elements, compounds, and chemical reactions. The objective of the experiment is to investigate the indium-bismuth alloy system. Near the eutectic composition, the liquidus is well below the boiling point of water, allowing simple, minimal hazard casting experiments. Such phenomena as metal oxidation, formation of intermetallic compound crystals, and an unusual volume increase during solidification could all be directly observed. A key concept for students to absorb is that properties of an alloy (melting point, mechanical behavior) may not correlate with simple interpolation of properties of the pure components. Discussion of other low melting metals and alloys leads to consideration of environmental and toxicity issues, as well as providing some historical context. Wetting behavior can also be explored.

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

PubMed

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

2018-01-23

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

Olivine-hosted melt inclusions record efficient mixing of mantle melts in continental flood basalt provinces

NASA Astrophysics Data System (ADS)

Jennings, E. S.; Gibson, S. A.; Maclennan, J.; Heinonen, J. S.

2017-12-01

Primitive melt inclusions trapped in various minerals found in global ridge settings have been shown to record highly variable magmatic compositions. Mantle melting is expected to be near-fractional, producing a wide range of melt compositions that must accumulate and mix in crustal magma chambers. In primitive rocks, the melt inclusion variability observed in major, trace and isotope geochemistry is consistent to the first order with partial melting of variably depleted mantle, and indicate that the host phases began to crystallise prior to the completion of melt aggregation and mixing. We present new major and trace element data from a large number of rehomogenised olivine-hosted melt inclusions from the Cretaceous Paraná-Etendeka and Jurassic Karoo continental flood basalt (CFB) provinces [1]. We show that the major element chemistry of the melt inclusions can be severely disrupted by the rehomogenisation process and, as a consequence, their initial compositions cannot easily be back-calculated. However, despite the age of the samples, the trace element geochemistry of the melt inclusions is well-preserved. Despite coming from near-liquidus olivines from primitive picrites and ferropicrites, the inclusions are remarkably homogeneous; none of the anticipated variability in incompatible trace element compositions is observed. When considered alongside literature data, it appears that variability in primitive melts - as recorded by melt inclusions - is low in CFBs and OIBs relative to ridge settings, e.g. Iceland. We suggest that the tectonic setting imposes a control on the mixing of mantle melts: hot, plume-derived melts generated beneath relatively thick lithosphere may be prone to efficient mixing, perhaps due to their low viscosity, long transport pathways, and/or a superliquidus emplacement temperature [1]. This interpretation is supported by the almost non-existent variability of olivine-hosted inclusions from ferropicrite samples: these magmas represents

Melting phenomena: effect of composition for 55-atom Ag-Pd bimetallic clusters.

PubMed

Cheng, Daojian; Wang, Wenchuan; Huang, Shiping

2008-05-14

Understanding the composition effect on the melting processes of bimetallic clusters is important for their applications. Here, we report the relationship between the melting point and the metal composition for the 55-atom icosahedral Ag-Pd bimetallic clusters by canonical Monte Carlo simulations, using the second-moment approximation of the tight-binding potentials (TB-SMA) for the metal-metal interactions. Abnormal melting phenomena for the systems of interest are found. Our simulation results reveal that the dependence of the melting point on the composition is not a monotonic change, but experiences three different stages. The melting temperatures of the Ag-Pd bimetallic clusters increase monotonically with the concentration of the Ag atoms first. Then, they reach a plateau presenting almost a constant value. Finally, they decrease sharply at a specific composition. The main reason for this change can be explained in terms of the relative stability of the Ag-Pd bimetallic clusters at different compositions. The results suggest that the more stable the cluster, the higher the melting point for the 55-atom icosahedral Ag-Pd bimetallic clusters at different compositions.

Observable consequences of zero-point energy

NASA Astrophysics Data System (ADS)

Sen, Siddhartha; Gupta, Kumar S.

2017-12-01

Spectral line widths, the Lamb shift and the Casimir effect are generally accepted to be observable consequences of the zero-point electromagnetic (ZPEM) fields. A new class of observable consequences of ZPEM field at the mesoscopic scale were recently proposed and observed. Here, we extend this class of observable effects and predict that mesoscopic water layers should have a high value for its solid-liquid phase transition temperature, as illustrated by water inside a single-walled carbon nanotube (CNT). For this case, our analysis predicts that the phase transition temperature scales inversely with the square of the effective radius available for the water flow within the CNT.

Nonlinear Response of Iceberg Melting to Ocean Currents

NASA Astrophysics Data System (ADS)

Cenedese, C.; FitzMaurice, A.; Straneo, F.

2017-12-01

Icebergs calving into Greenlandic Fjords frequently experience strongly sheared flows over their draft, but the impact of this flow past the iceberg on the melt plumes generated along the iceberg sides is not fully captured by existing parameterizations. We present a series of novel laboratory experiments to determine the dependence of side submarine melt rates on a background flow. We show, for the first time, that two distinct regimes of melting exist depending on the melt plume behavior (side-attached or side-detached). These two regimes produce a nonlinear dependence of melt rate on velocity, and different distributions of meltwater in the water column. Iceberg meltwater may either be confined to a thin surface layer, when the melt plumes are side-attached, or mixed down to the iceberg draft, when the melt plumes are side-detached. In a two-layer vertically sheared flow the average flow speed in existing melt parameterizations gives an underestimate of the submarine melt rate, in part due to the nonlinearity of the dependence of melt rate on flow speed, but also because vertical shear in the velocity profile fundamentally changes the flow splitting around the ice block and consequently the velocity felt by the ice surface. Including this nonlinear velocity dependence in melting parameterizations applied to observed icebergs increases iceberg side melt in the attached regime, improving agreement with observations of iceberg submarine melt rates. We show that both attached and detached plume regimes are relevant to icebergs observed in a Greenland fjord.

Biomass Burning and the 2012 Greenland Ice Sheet (GrIS) melt

NASA Astrophysics Data System (ADS)

Choi, H. D.; Soja, A. J.; Polashenski, C.; Fairlie, T. D.; Winker, D. M.; Trepte, C. R.

2017-12-01

This study is the part of the Sunlight Absorption on the Greenland ice sheet Experiment (SAGE) project investigating the impact of light absorbing impurities (e.g., aerosols) on the Greenland Ice Sheet (GrIS). Satellite observations, [e.g. Oceansat-2 (OS2) and the Moderate-resolution Imaging Spectroradionmeter (MODIS)] discovered an unusually large melt event in July 2012. NASA sensors showed that nearly 98.6% of the GrIS experienced melting at or near surface [Nghiem et al., 2012]. In this study, we question the extent to which biomass burning derived aerosols enhanced melting across the GrIS. Random points [59 total, 13 coincident with snow pit sites and 46 gridded] are selected across the entire extent of the GrIS from April 1st to August 31st 2012, and then the NASA Langley Trajectory Model (LaTM) is used to simulate the transport of potentially smoke-filled air parcels backwards for 5 days form these points, evaluation the back trajectory for coincidence with active fire detections. The trajectory model is initialized for 24-hour sustained injection from each site, and air parcels are released from the surface to 2 km at 200m intervals. With the trajectory model outputs, we are able to identify trajectories that have coincidences with fires. We focus on events in April through July when the GrIS albedo was dramatically decreased. We also utilize Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) data to verify smoke-aerosol signatures in boreal regions based on the NASA LaTM results. The results of this study will help us better understand the transport of biomass burning plumes and black carbon deposition that could lead to enhanced GrIS melting.

CADASTER QSPR Models for Predictions of Melting and Boiling Points of Perfluorinated Chemicals.

PubMed

Bhhatarai, Barun; Teetz, Wolfram; Liu, Tao; Öberg, Tomas; Jeliazkova, Nina; Kochev, Nikolay; Pukalov, Ognyan; Tetko, Igor V; Kovarich, Simona; Papa, Ester; Gramatica, Paola

2011-03-14

Quantitative structure property relationship (QSPR) studies on per- and polyfluorinated chemicals (PFCs) on melting point (MP) and boiling point (BP) are presented. The training and prediction chemicals used for developing and validating the models were selected from Syracuse PhysProp database and literatures. The available experimental data sets were split in two different ways: a) random selection on response value, and b) structural similarity verified by self-organizing-map (SOM), in order to propose reliable predictive models, developed only on the training sets and externally verified on the prediction sets. Individual linear and non-linear approaches based models developed by different CADASTER partners on 0D-2D Dragon descriptors, E-state descriptors and fragment based descriptors as well as consensus model and their predictions are presented. In addition, the predictive performance of the developed models was verified on a blind external validation set (EV-set) prepared using PERFORCE database on 15 MP and 25 BP data respectively. This database contains only long chain perfluoro-alkylated chemicals, particularly monitored by regulatory agencies like US-EPA and EU-REACH. QSPR models with internal and external validation on two different external prediction/validation sets and study of applicability-domain highlighting the robustness and high accuracy of the models are discussed. Finally, MPs for additional 303 PFCs and BPs for 271 PFCs were predicted for which experimental measurements are unknown. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Molecular dynamics for near melting temperatures simulations of metals using modified embedded-atom method

NASA Astrophysics Data System (ADS)

Etesami, S. Alireza; Asadi, Ebrahim

2018-01-01

Availability of a reliable interatomic potential is one of the major challenges in utilizing molecular dynamics (MD) for simulations of metals at near the melting temperatures and melting point (MP). Here, we propose a novel approach to address this challenge in the concept of modified-embedded-atom (MEAM) interatomic potential; also, we apply the approach on iron, nickel, copper, and aluminum as case studies. We propose adding experimentally available high temperature elastic constants and MP of the element to the list of typical low temperature properties used for the development of MD interatomic potential parameters. We show that the proposed approach results in a reasonable agreement between the MD calculations of melting properties such as latent heat, expansion in melting, liquid structure factor, and solid-liquid interface stiffness and their experimental/computational counterparts. Then, we present the physical properties of mentioned elements near melting temperatures using the new MEAM parameters. We observe that the behavior of elastic constants, heat capacity and thermal linear expansion coefficient at room temperature compared to MP follows an empirical linear relation (α±β × MP) for transition metals. Furthermore, a linear relation between the tetragonal shear modulus and the enthalpy change from room temperature to MP is observed for face-centered cubic materials.

When Is Melting Not Really Melting?

ERIC Educational Resources Information Center

Mangiaracina, Mike

2017-01-01

This 5E cycle of lessons takes students through a fun and thorough study of Silly Putty's properties, progressing from an initial observation of a "melting snowman" toy in the Engage phase to making and "marketing" their own homemade putty in the Evaluate phase. Along the way, students use evidence to construct their own…

The gallium melting-point standard: its application and evaluation for temperature measurements in the clinical laboratory.

PubMed

Bowers, G N; Inman, S R

1977-01-01

We are impressed with the ease and certainty of calibration electronic thermometers with thermistor probes to +/- 0.01 degree C at the gallium melting point, 29.771(4) degrees C. The IFCC reference method for measuring aspartate aminotransferase activity in serum was run at the reaction temperature of 29.771(4) degrees C. By constantly referencing to gallium as an integral part of the assay procedure, we determined the absolute reaction temperature to IPTS-68 (International Practical Temperature Scale of 1968) to +/- 0.02 degrees C. This unique temperature calibration standard near the center of the range of temperatures commonly used in the clinical laboratory is a valuable addition and can be expected to improve the accuracy of measurements, especially in clinical enzymology.

Melt spinning study

NASA Technical Reports Server (NTRS)

Workman, Gary L.; Rathz, Thomas

1993-01-01

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

NASA's Observes Effects of Summer Melt on Greenland Ice Sheet

NASA Image and Video Library

2017-12-08

NASA's IceBridge, an airborne survey of polar ice, flew over the Helheim/Kangerdlugssuaq region of Greenland on Sept. 11, 2016. This photograph from the flight captures Greenland's Steenstrup Glacier, with the midmorning sun glinting off of the Denmark Strait in the background. IceBridge completed the final flight of the summer campaign to observe the impact of the summer melt season on the ice sheet on Sept. 16. The IceBridge flights, which began on Aug. 27, are mostly repeats of lines that the team flew in early May, so that scientists can observe changes in ice elevation between the spring and late summer. For this short, end-of-summer campaign, the IceBridge scientists flew aboard an HU-25A Guardian aircraft from NASA's Langley Research Center in Hampton, Virginia. Credit: NASA/John Sonntag NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

Pressure-Induced Melting of Confined Ice

PubMed Central

2017-01-01

The classic regelation experiment of Thomson in the 1850s deals with cutting an ice cube, followed by refreezing. The cutting was attributed to pressure-induced melting but has been challenged continuously, and only lately consensus emerged by understanding that compression shortens the O:H nonbond and lengthens the H–O bond simultaneously. This H–O elongation leads to energy loss and lowers the melting point. The hot debate survived well over 150 years, mainly due to a poorly defined heat exchange with the environment in the experiment. In our current experiment, we achieved thermal isolation from the environment and studied the fully reversible ice–liquid water transition for water confined between graphene and muscovite mica. We observe a transition from two-dimensional (2D) ice into a quasi-liquid phase by applying a pressure exerted by an atomic force microscopy tip. At room temperature, the critical pressure amounts to about 6 GPa. The transition is completely reversible: refreezing occurs when the applied pressure is lifted. The critical pressure to melt the 2D ice decreases with temperature, and we measured the phase coexistence line between 293 and 333 K. From a Clausius–Clapeyron analysis, we determine the latent heat of fusion of two-dimensional ice at 0.15 eV/molecule, being twice as large as that of bulk ice. PMID:29112376

Pressure-Induced Melting of Confined Ice.

PubMed

Sotthewes, Kai; Bampoulis, Pantelis; Zandvliet, Harold J W; Lohse, Detlef; Poelsema, Bene

2017-12-26

The classic regelation experiment of Thomson in the 1850s deals with cutting an ice cube, followed by refreezing. The cutting was attributed to pressure-induced melting but has been challenged continuously, and only lately consensus emerged by understanding that compression shortens the O:H nonbond and lengthens the H-O bond simultaneously. This H-O elongation leads to energy loss and lowers the melting point. The hot debate survived well over 150 years, mainly due to a poorly defined heat exchange with the environment in the experiment. In our current experiment, we achieved thermal isolation from the environment and studied the fully reversible ice-liquid water transition for water confined between graphene and muscovite mica. We observe a transition from two-dimensional (2D) ice into a quasi-liquid phase by applying a pressure exerted by an atomic force microscopy tip. At room temperature, the critical pressure amounts to about 6 GPa. The transition is completely reversible: refreezing occurs when the applied pressure is lifted. The critical pressure to melt the 2D ice decreases with temperature, and we measured the phase coexistence line between 293 and 333 K. From a Clausius-Clapeyron analysis, we determine the latent heat of fusion of two-dimensional ice at 0.15 eV/molecule, being twice as large as that of bulk ice.

Solid and liquid heat capacities of n-alkyl para-aminobenzoates near the melting point.

PubMed

Neau, S H; Flynn, G L

1990-11-01

The expression that relates the ideal mole fraction solubility of a crystalline compound to physicochemical properties of the compound includes a term involving the difference in the heat capacities of the solid and liquid forms of the solute, delta Cp. There are two alternate conventions which are employed to eliminate this term. The first assumes that the term involving delta Cp, or delta Cp itself, is zero. The alternate assumption assigns the value of the entropy of fusion to the differential heat capacity. The relative validity of these two assumptions was evaluated using the straight-chain alkyl para-aminobenzoates as test compounds. The heat capacities of the solid and liquid forms of each of the para-aminobenzoates, near the respective melting point, were determined by differential scanning calorimetry. The data lead one to conclude that the assumption that the differential heat capacity is not usually negligible and is better approximated by the entropy of fusion.

A Review of In Situ Observations of Crystallization and Growth in High Temperature Oxide Melts

NASA Astrophysics Data System (ADS)

Wang, Zhanjun; Sohn, Il

2018-05-01

This review summarizes the significant results of high-temperature confocal laser scanning microscopy (CLSM) and single hot thermocouple technology (SHTT) and its application in observing the crystallization and growth in high-temperature oxide melts from iron- and steel-making slags to continuous casting mold fluxes. Using in situ observations of CLSM and SHTT images of high-temperature molten oxides with time, temperature, and composition, the crystallization behavior, including crystal morphology, crystallization temperature, initial nucleation and growth rate, could be obtained. The broad range of applications using in situ observations during crystallization have provided a wealth of opportunities in pyrometallurgy and is provided in this review.

The gallium melting-point standard: its role in manufacture and quality control of electronic thermometers for the clinical laboratory.

PubMed

Sostman, H E

1977-01-01

I discuss the traceability of calibration of electronic thermometers to thermometric constants of nature or to the National Bureau of Standards, form a manufacturer's basic standards through the manufacturing process to the user's laboratory. Useful electrical temperature sensors, their advantages, and means for resolving their disadvantages are described. I summarize our development of a cell for realizing the melting phase equilibrium of pure gallium (at 29.770 degrees C) as a thermometer calibration fixed point, and enumerate its advantages in the routine calibration verification of electrical thermometers in the clinical chemistry laboratory.

Physicochemical properties of film-coated melt-extruded pellets.

PubMed

Young, Chistopher R; Crowley, Michael; Dietzsch, Caroline; McGinity, James W

2007-02-01

The purpose of this study was to investigate the physicochemical properties of poly(ethylene oxide) (PEO) and guaifenesin containing beads prepared by a melt-extrusion process and film-coated with a methacrylic acid copolymer. Solubility parameter calculations, thermal gravimetric analysis (TGA), scanning electron microscopy (SEM), modulated differential scanning calorimetry (MDSC), X-ray powder diffraction (XRPD) and high performance liquid chromatography (HPLC) were used to determine drug/polymer miscibility and/or the thermal processibility of the systems. Powder blends of guaifenesin, PEO and functional excipients were processed using a melt-extrusion and spheronization technique and then film-coated in a fluidized bed apparatus. Solubility parameter calculations were used to predict miscibility between PEO and guaifenesin, and miscibility was confirmed by SEM and observation of a single melting point for extruded drug/polymer blends during MDSC investigations. The drug was stable following melt-extrusion as determined by TGA and HPLC; however, drug release rate from pellets decreased upon storage in sealed HDPE containers with silica desiccants at 40 degrees C/75% RH. The weight loss on drying, porosity and tortuosity determinations were not influenced by storage. Recrystallization of guaifenesin and PEO was confirmed by SEM and XRPD. Additionally, the pellets exhibited a change in adhesion behaviour during dissolution testing. The addition of ethylcellulose to the extruded powder blend decreased and stabilized the drug release rate from the thermally processed pellets. The current study also demonstrated film-coating to be an efficient process for providing melt-extruded beads with pH-dependent drug release properties that were stable upon storage at accelerated conditions.

Studies of thermal dissolution of RDX in TNT melt

NASA Astrophysics Data System (ADS)

Suvorova, N. A.; Hamilton, V. T.; Oschwald, D. M.; Balakirev, F. F.; Smilowitz, L. B.; Henson, B. F.

2017-01-01

The thermal response of energetic materials is studied due to its importance in issues of material safety and surety. Secondary high explosives which melt before they thermally decompose present challenging systems to model due to the addition of material flow. Composition B is a particularly challenging system due to its multiphase nature with a low melt component (TNT) and a high melt component (RDX). The dissolution of RDX crystals in molten TNT at the temperature below RDX melting point has been investigated using hot stage microscopy. In this paper, we present data on the dissolution rate of RDX crystals in molten TNT as a function of temperature above the TNT melt.

Investigation of transient melting of tungsten by ELMs in ASDEX Upgrade

NASA Astrophysics Data System (ADS)

Krieger, K.; Sieglin, B.; Balden, M.; Coenen, J. W.; Göths, B.; Laggner, F.; de Marne, P.; Matthews, G. F.; Nille, D.; Rohde, V.; Dejarnac, R.; Faitsch, M.; Giannone, L.; Herrmann, A.; Horacek, J.; Komm, M.; Pitts, R. A.; Ratynskaia, S.; Thoren, E.; Tolias, P.; ASDEX-Upgrade Team; EUROfusion MST1 Team

2017-12-01

Repetitive melting of tungsten by power transients originating from edge localized modes (ELMs) has been studied in the tokamak experiment ASDEX Upgrade. Tungsten samples were exposed to H-mode discharges at the outer divertor target plate using the Divertor Manipulator II system. The exposed sample was designed with an elevated sloped surface inclined against the incident magnetic field to increase the projected parallel power flux to a level were transient melting by ELMs would occur. Sample exposure was controlled by moving the outer strike point to the sample location. As extension to previous melt studies in the new experiment both the current flow from the sample to vessel potential and the local surface temperature were measured with sufficient time resolution to resolve individual ELMs. The experiment provided for the first time a direct link of current flow and surface temperature during transient ELM events. This allows to further constrain the MEMOS melt motion code predictions and to improve the validation of its underlying model assumptions. Post exposure ex situ analysis of the retrieved samples confirms the decreased melt motion observed at shallower magnetic field line to surface angles compared to that at leading edges exposed to the parallel power flux.

Do Melt Inclusions Answer Big Questions?

NASA Astrophysics Data System (ADS)

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

2009-12-01

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

Understanding Melt-Memory of Commercial Polyolefins

NASA Astrophysics Data System (ADS)

Alamo, Rufina

Self-nucleation (SN) or controlling self-generated seeds in a polymer melt is an avenue to increase the rate of solidification of semicrystalline polymers of commercial relevance. Self-nuclei are remains in the melt of the segmental self-assembly to form polymer crystallites providing a path to enhance primary crystal nucleation. SN has been extensively studied in homopolymers such as iPP. Recently, a strong memory effect of crystallization has been observed in melts of random ethylene copolymers well above the equilibrium melting temperature. The melt memory is associated with clusters or seeds that remain in the melt from the copolymer's sequence length partitioning. Cooling from progressively lower self-seeded melt temperatures, ethylene copolymers with a broad inter-chain comonomer composition (1 - 15 mol%) display first the expected accelerated crystallization, followed by a decrease in the rate in a range of melt temperatures where narrow copolymers show a continuous acceleration of the rate. This unusual inversion of the crystallization rate was postulated to arise from the onset of liquid-liquid phase separation (LLPS) between comonomer-rich and comonomer-poor components of the broad copolymer. The UCST type phase diagram of these commercial copolymers has been documented via SANS using a blend of components, some deuterated, to reproduce the broad distribution. Furthermore, the components that contribute to LLPS have been identified by the crystallization behavior of molar mass fractions. The influence of long chain branching on the topology of copolymer melts has been analyzed using model 3-arm stars hydrogenated polybutadienes. The effect of melt viscosity on strength of melt memory is also evident when SN data of random ethylene copolymers are compared with those of propylene-ethylene copolymers. The strong dependence of melt viscosity on melt memory, and a critical threshold crystallinity level to observe the effect of melt memory on crystallization

Surface-tension-driven flow in a glass melt

NASA Technical Reports Server (NTRS)

Mcneil, Thomas J.; Cole, Robert; Shankar Subramanian, R.

1985-01-01

Motion driven by surface tension gradients was observed in a vertical capillary liquid bridge geometry in a sodium borate melt. The surface tension gradients were introduced by maintaining a temperature gradient on the free melt surface. The flow velocities at the free surface of the melt, which were measured using a tracer technique, were found to be proportional to the applied temperature difference and inversely proportional to the melt viscosity. The experimentally observed velocities were in reasonable accord with predictions from a theoretical model of the system.

Partial melting and melt percolation in the mantle: The message from Fe isotopes

NASA Astrophysics Data System (ADS)

Weyer, Stefan; Ionov, Dmitri A.

2007-07-01

High precision Fe isotope measurements have been performed on various mantle peridotites (fertile lherzolites, harzburgites, metasomatised Fe-enriched peridotites) and volcanic rocks (mainly oceanic basalts) from different localities and tectonic settings. The peridotites yield an average δ 56Fe = 0.01‰ and are significantly lighter than the basalts (average δ 56Fe = 0.11‰). Furthermore, the peridotites display a negative correlation of δ 56Fe with Mg# indicating a link between δ 56Fe and degrees of melt extraction. Taken together, these findings imply that Fe isotopes fractionate during partial melting, with heavy isotopes preferentially entering the melt. The slope of depletion trends (δ 56Fe versus Mg#) of the peridotites was used to model Fe isotope fractionation during partial melting, resulting in αmantle-melt ≈ 1.0001-1.0003 or ln αmantle-melt ≈ 0.1-0.3‰. In contrast to most other peridotites investigated in this study, spinel lherzolites and harzburgites from three localities (Horoman, Kamchatka and Lherz) are virtually unaffected by metasomatism. These three sites display a particularly good correlation and define an isotope fractionation factor of ln αmantle-melt ≈ 0.3‰. This modelled value implies Fe isotope fractionation between residual mantle and mantle-derived melts corresponding to Δ56Fe mantle-basalt ≈ 0.2-0.3‰, i.e. significantly higher than the observed difference between averages for all the peridotites and the basalts in this study (corresponding to Δ56Fe mantle-basalt ≈ 0.1‰). Either disequilibrium melting increased the modelled αmantle-melt for these particular sites or the difference between average peridotite and basalt may be reduced by partial re-equilibration between the isotopically heavy basalts and the isotopically light depleted lithospheric mantle during melt ascent. The slope of the weaker δ 56Fe-Mg# trend defined by the combined set of all mantle peridotites from this study is more consistent with

Melting processes of oligomeric α and β isotactic polypropylene crystals at ultrafast heating rates

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

Ji, Xiaojing; He, Xuehao, E-mail: xhhe@tju.edu.cn, E-mail: scjiang@tju.edu.cn; Jiang, Shichun, E-mail: xhhe@tju.edu.cn, E-mail: scjiang@tju.edu.cn

The melting behaviors of α (stable) and β (metastable) isotactic polypropylene (iPP) crystals at ultrafast heating rates are simulated with atomistic molecular dynamics method. Quantitative information about the melting processes of α- and β-iPP crystals at atomistic level is achieved. The result shows that the melting process starts from the interfaces of lamellar crystal through random dislocation of iPP chains along the perpendicular direction of lamellar crystal structure. In the melting process, the lamellar crystal gradually expands but the corresponding thickness decreases. The analysis shows that the system expansion lags behind the crystallinity decreasing and the lagging extents for α-more » and β-iPP are significantly different. The apparent melting points of α- and β-iPP crystals rise with the increase of the heating rate and lamellar crystal thickness. The apparent melting point of α-iPP crystal is always higher than that of β-iPP at differently heating rates. Applying the Gibbs-Thomson rule and the scaling property of the melting kinetics, the equilibrium melting points of perfect α- and β-iPP crystals are finally predicted and it shows a good agreement with experimental result.« less

Fugacity ratio estimations for high-melting rigid aromatic compounds.

PubMed

Van Noort, Paul C M

2004-07-01

Prediction of the environmental fate of organic compounds requires knowledge of their tendency to stay in the gas and water phase. Vapor pressure and aqueous solubility are commonly used descriptors for these processes. Depending on the type of distribution process, values for either the pure solid state or the (subcooled) liquid state have to be used. Values for the (subcooled) liquid state can be calculated from those for the solid state, and vice versa, using the fugacity ratio. Fugacity ratios are usually calculated from the entropy of fusion and the melting point. For polycyclic aromatic hydrocarbons, chlorobenzenes, chlorodibenzofuranes, and chlorodibenzo(p)dioxins, fugacity ratios calculated using experimental entropies of fusion were systematically less than those obtained from a thermodynamically more rigorous approach using heat capacity data. The deviation was more than 1 order of magnitude at the highest melting point. The use of a universal value for the entropy of fusion of 56 J/molK resulted in either over or underestimation by up to more than 1 order of magnitude. A simple correction factor, based on the melting point only, was derived. This correction factor allowed the fugacity ratios to be estimated from experimental entropies of fusion and melting point with an accuracy better than 0.1-0.2 log units. Copyright 2004 Elsevier Ltd.

Shape evolution of a melting nonspherical particle

NASA Astrophysics Data System (ADS)

Kintea, Daniel M.; Hauk, Tobias; Roisman, Ilia V.; Tropea, Cameron

2015-09-01

In this study melting of irregular ice crystals was observed in an acoustic levitator. The evolution of the particle shape is captured using a high-speed video system. Several typical phenomena have been discovered: change of the particle shape, appearance of a capillary flow of the melted liquid on the particle surface leading to liquid collection at the particle midsection (where the interface curvature is smallest), and appearance of sharp cusps at the particle tips. No such phenomena can be observed during melting of spherical particles. An approximate theoretical model is developed which accounts for the main physical phenomena associated with melting of an irregular particle. The agreement between the theoretical predictions for the melting time, for the evolution of the particle shape, and the corresponding experimental data is rather good.

Zipper model for the melting of thin films

NASA Astrophysics Data System (ADS)

Abdullah, Mikrajuddin; Khairunnisa, Shafira; Akbar, Fathan

2016-01-01

We propose an alternative model to Lindemann’s criterion for melting that explains the melting of thin films on the basis of a molecular zipper-like mechanism. Using this model, a unique criterion for melting is obtained. We compared the results of the proposed model with experimental data of melting points and heat of fusion for many materials and obtained interesting results. The interesting thing reported here is how complex physics problems can sometimes be modeled with simple objects around us that seemed to have no correlation. This kind of approach is sometimes very important in physics education and should always be taught to undergraduate or graduate students.

Thermodynamics of freezing and melting

PubMed Central

Pedersen, Ulf R.; Costigliola, Lorenzo; Bailey, Nicholas P.; Schrøder, Thomas B.; Dyre, Jeppe C.

2016-01-01

Although the freezing of liquids and melting of crystals are fundamental for many areas of the sciences, even simple properties like the temperature–pressure relation along the melting line cannot be predicted today. Here we present a theory in which properties of the coexisting crystal and liquid phases at a single thermodynamic state point provide the basis for calculating the pressure, density and entropy of fusion as functions of temperature along the melting line, as well as the variation along this line of the reduced crystalline vibrational mean-square displacement (the Lindemann ratio), and the liquid's diffusion constant and viscosity. The framework developed, which applies for the sizable class of systems characterized by hidden scale invariance, is validated by computer simulations of the standard 12-6 Lennard-Jones system. PMID:27530064

Construction of Gallium Point at NMIJ

NASA Astrophysics Data System (ADS)

Widiatmo, J. V.; Saito, I.; Yamazawa, K.

2017-03-01

Two open-type gallium point cells were fabricated using ingots whose nominal purities are 7N. Measurement systems for the realization of the melting point of gallium using these cells were built. The melting point of gallium is repeatedly realized by means of the measurement systems for evaluating the repeatability. Measurements for evaluating the effect of hydrostatic pressure coming from the molten gallium existing during the melting process and the effect of gas pressure that fills the cell were also performed. Direct cell comparisons between those cells were conducted. This comparison was aimed to evaluate the consistency of each cell, especially related to the nominal purity. Direct cell comparison between the open-type and the sealed-type gallium point cell was also conducted. Chemical analysis was conducted using samples extracted from ingots used in both the newly built open-type gallium point cells, from which the effect of impurities in the ingot was evaluated.

First observation of the fourth neutral polarization point in the atmosphere

NASA Astrophysics Data System (ADS)

Horvath, Gabor; Bernath, Balazs; Suhai, Bence; Barta, Andras; Wehner, Rudiger

2002-10-01

In the clear sky there are three commonly known loci, the Arago, Babinet, and Brewster neutral points, where the skylight is unpolarized. These peculiar celestial points, bearing the names of their discoverers, have been the subject of many ground-based investigations, because their positions are sensitive indicators of the amount and type of atmospheric turbidity. According to theoretical considerations and computer simulations, there should exist an additional neutral point approximately opposite to the Babinet point, which can be observed only at higher altitudes in the air or space. Until now, this anonymous fourth neutral point has not been observed during air- or space-borne polarimetric experiments and has been forgotten, in spite of the fact that the neutral points were a basic tool in atmospheric research for a century. Here, we report on the first observation of this fourth neutral point from a hot air balloon. Using 180-field-of-view imaging polarimetry, we could observe the fourth neutral point at 450, 550, and 650 nm from different altitudes between 900 and 3500 m during and after sunrise at approximately 2240 below the anti-solar point along the anti-solar meridian, depending on the wavelength and solar elevation. We show that the fourth neutral point exists at the expected location and has characteristics similar to those of the Arago, Babinet, and Brewster points. We discuss why the fourth neutral point has not been observed in previous air- or space-borne polarimetric experiments. 2002 Optical Society of America

Creating Stiff, Tough, and Functional Hydrogel Composites with Low-Melting-Point Alloys.

PubMed

Takahashi, Riku; Sun, Tao Lin; Saruwatari, Yoshiyuki; Kurokawa, Takayuki; King, Daniel R; Gong, Jian Ping

2018-04-01

Reinforcing hydrogels with a rigid scaffold is a promising method to greatly expand the mechanical and physical properties of hydrogels. One of the challenges of creating hydrogel composites is the significant stress that occurs due to swelling mismatch between the water-swollen hydrogel matrix and the rigid skeleton in aqueous media. This stress can cause physical deformation (wrinkling, buckling, or fracture), preventing the fabrication of robust composites. Here, a simple yet versatile method is introduced to create "macroscale" hydrogel composites, by utilizing a rigid reinforcing phase that can relieve stress-induced deformation. A low-melting-point alloy that can transform from a load-bearing solid state to a free-deformable liquid state at relatively low temperature is used as a reinforcing skeleton, which enables the release of any swelling mismatch, regardless of the matrix swelling degree in liquid media. This design can generally provide hydrogels with hybridized functions, including excellent mechanical properties, shape memory, and thermal healing, which are often difficult or impossible to achieve with single-component hydrogel systems. Furthermore, this technique enables controlled electrochemical reactions and channel-structure templating in hydrogel matrices. This work may play an important role in the future design of soft robots, wearable electronics, and biocompatible functional materials. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Greater-than-bulk melting temperatures explained: Gallium melts Gangnam style

NASA Astrophysics Data System (ADS)

Gaston, Nicola; Steenbergen, Krista

2014-03-01

The experimental discovery of superheating in gallium clusters contradicted the clear and well-demonstrated paradigm that the melting temperature of a particle should decrease with its size. However the extremely sensitive dependence of melting temperature on size also goes to the heart of cluster science, and the interplay between the effects of electronic and geometric structure. We have performed extensive first-principles molecular dynamics calculations, incorporating parallel tempering for an efficient exploration of configurational phase space. This is necessary, due to the complicated energy landscape of gallium. In the nanoparticles, melting is preceded by a transitions between phases. A structural feature, referred to here as the Gangnam motif, is found to increase with the latent heat and appears throughout the observed phase changes of this curious metal. We will present our detailed analysis of the solid-state isomers, performed using extensive statistical sampling of the trajectory data for the assignment of cluster structures to known phases of gallium. Finally, we explain the greater-than-bulk melting through analysis of the factors that stabilise the liquid structures.

Molecular dynamical simulations of melting Al nanoparticles using a reaxff reactive force field

NASA Astrophysics Data System (ADS)

Liu, Junpeng; Wang, Mengjun; Liu, Pingan

2018-06-01

Molecular dynamics simulations were performed to study thermal properties and melting points of Al nanoparticles by using a reactive force field under canonical (NVT) ensembles. Al nanoparticles (particle size 2–4 nm) were considered in simulations. A combination of structural and thermodynamic parameters such as the Lindemann index, heat capacities, potential energy and radial-distribution functions was employed to decide melting points. We used annealing technique to obtain the initial Al nanoparticle model. Comparison was made between ReaxFF results and other simulation results. We found that ReaxFF force field is reasonable to describe Al cluster melting behavior. The linear relationship between particle size and melting points was found. After validating the ReaxFF force field, more attention was paid on thermal properties of Al nanoparticles with different defect concentrations. 4 nm Al nanoparticles with different defect concentrations (5%–20%) were considered in this paper. Our results revealed that: the melting points are irrelevant with defect concentration at a certain particle size. The extra storage energy of Al nanoparticles is proportional to nanoparticles’ defect concentration, when defect concentration is 5%–15%. While the particle with 20% defect concentration is similar to the cluster with 10% defect concentration. After melting, the extra energy of all nanoparticles decreases sharply, and the extra storage energy is nearly zero at 600 K. The centro-symmetry parameter analysis shows structure evolution of different models during melting processes.

ELM-induced transient tungsten melting in the JET divertor

NASA Astrophysics Data System (ADS)

Coenen, J. W.; Arnoux, G.; Bazylev, B.; Matthews, G. F.; Autricque, A.; Balboa, I.; Clever, M.; Dejarnac, R.; Coffey, I.; Corre, Y.; Devaux, S.; Frassinetti, L.; Gauthier, E.; Horacek, J.; Jachmich, S.; Komm, M.; Knaup, M.; Krieger, K.; Marsen, S.; Meigs, A.; Mertens, Ph.; Pitts, R. A.; Puetterich, T.; Rack, M.; Stamp, M.; Sergienko, G.; Tamain, P.; Thompson, V.; Contributors, JET-EFDA

2015-02-01

The original goals of the JET ITER-like wall included the study of the impact of an all W divertor on plasma operation (Coenen et al 2013 Nucl. Fusion 53 073043) and fuel retention (Brezinsek et al 2013 Nucl. Fusion 53 083023). ITER has recently decided to install a full-tungsten (W) divertor from the start of operations. One of the key inputs required in support of this decision was the study of the possibility of W melting and melt splashing during transients. Damage of this type can lead to modifications of surface topology which could lead to higher disruption frequency or compromise subsequent plasma operation. Although every effort will be made to avoid leading edges, ITER plasma stored energies are sufficient that transients can drive shallow melting on the top surfaces of components. JET is able to produce ELMs large enough to allow access to transient melting in a regime of relevance to ITER. Transient W melt experiments were performed in JET using a dedicated divertor module and a sequence of IP = 3.0 MA/BT = 2.9 T H-mode pulses with an input power of PIN = 23 MW, a stored energy of ˜6 MJ and regular type I ELMs at ΔWELM = 0.3 MJ and fELM ˜ 30 Hz. By moving the outer strike point onto a dedicated leading edge in the W divertor the base temperature was raised within ˜1 s to a level allowing transient, ELM-driven melting during the subsequent 0.5 s. Such ELMs (δW ˜ 300 kJ per ELM) are comparable to mitigated ELMs expected in ITER (Pitts et al 2011 J. Nucl. Mater. 415 (Suppl.) S957-64). Although significant material losses in terms of ejections into the plasma were not observed, there is indirect evidence that some small droplets (˜80 µm) were released. Almost 1 mm (˜6 mm3) of W was moved by ˜150 ELMs within 7 subsequent discharges. The impact on the main plasma parameters was minor and no disruptions occurred. The W-melt gradually moved along the leading edge towards the high-field side, driven by j × B forces. The evaporation rate determined

A penalized quantitative structure-property relationship study on melting point of energetic carbocyclic nitroaromatic compounds using adaptive bridge penalty.

PubMed

Al-Fakih, A M; Algamal, Z Y; Lee, M H; Aziz, M

2018-05-01

A penalized quantitative structure-property relationship (QSPR) model with adaptive bridge penalty for predicting the melting points of 92 energetic carbocyclic nitroaromatic compounds is proposed. To ensure the consistency of the descriptor selection of the proposed penalized adaptive bridge (PBridge), we proposed a ridge estimator ([Formula: see text]) as an initial weight in the adaptive bridge penalty. The Bayesian information criterion was applied to ensure the accurate selection of the tuning parameter ([Formula: see text]). The PBridge based model was internally and externally validated based on [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], the Y-randomization test, [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text] and the applicability domain. The validation results indicate that the model is robust and not due to chance correlation. The descriptor selection and prediction performance of PBridge for the training dataset outperforms the other methods used. PBridge shows the highest [Formula: see text] of 0.959, [Formula: see text] of 0.953, [Formula: see text] of 0.949 and [Formula: see text] of 0.959, and the lowest [Formula: see text] and [Formula: see text]. For the test dataset, PBridge shows a higher [Formula: see text] of 0.945 and [Formula: see text] of 0.948, and a lower [Formula: see text] and [Formula: see text], indicating its better prediction performance. The results clearly reveal that the proposed PBridge is useful for constructing reliable and robust QSPRs for predicting melting points prior to synthesizing new organic compounds.

Skylab M551 metals melting experiment

NASA Technical Reports Server (NTRS)

Poorman, R. M.

1975-01-01

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

Antifreeze protein-induced superheating of ice inside Antarctic notothenioid fishes inhibits melting during summer warming

PubMed Central

Cziko, Paul A.; DeVries, Arthur L.; Evans, Clive W.; Cheng, Chi-Hing Christina

2014-01-01

Antifreeze proteins (AFPs) of polar marine teleost fishes are widely recognized as an evolutionary innovation of vast adaptive value in that, by adsorbing to and inhibiting the growth of internalized environmental ice crystals, they prevent death by inoculative freezing. Paradoxically, systemic accumulation of AFP-stabilized ice could also be lethal. Whether or how fishes eliminate internal ice is unknown. To investigate if ice inside high-latitude Antarctic notothenioid fishes could melt seasonally, we measured its melting point and obtained a decadal temperature record from a shallow benthic fish habitat in McMurdo Sound, Antarctica. We found that AFP-stabilized ice resists melting at temperatures above the expected equilibrium freezing/melting point (eqFMP), both in vitro and in vivo. Superheated ice was directly observed in notothenioid serum samples and in solutions of purified AFPs, and ice was found to persist inside live fishes at temperatures more than 1 °C above their eqFMP for at least 24 h, and at a lower temperature for at least several days. Field experiments confirmed that superheated ice occurs naturally inside wild fishes. Over the long-term record (1999–2012), seawater temperature surpassed the fish eqFMP in most summers, but never exceeded the highest temperature at which ice persisted inside experimental fishes. Thus, because of the effects of AFP-induced melting inhibition, summer warming may not reliably eliminate internal ice. Our results expose a potentially antagonistic pleiotropic effect of AFPs: beneficial freezing avoidance is accompanied by melting inhibition that may contribute to lifelong accumulation of detrimental internal ice crystals. PMID:25246548

Antifreeze protein-induced superheating of ice inside Antarctic notothenioid fishes inhibits melting during summer warming.

PubMed

Cziko, Paul A; DeVries, Arthur L; Evans, Clive W; Cheng, Chi-Hing Christina

2014-10-07

Antifreeze proteins (AFPs) of polar marine teleost fishes are widely recognized as an evolutionary innovation of vast adaptive value in that, by adsorbing to and inhibiting the growth of internalized environmental ice crystals, they prevent death by inoculative freezing. Paradoxically, systemic accumulation of AFP-stabilized ice could also be lethal. Whether or how fishes eliminate internal ice is unknown. To investigate if ice inside high-latitude Antarctic notothenioid fishes could melt seasonally, we measured its melting point and obtained a decadal temperature record from a shallow benthic fish habitat in McMurdo Sound, Antarctica. We found that AFP-stabilized ice resists melting at temperatures above the expected equilibrium freezing/melting point (eqFMP), both in vitro and in vivo. Superheated ice was directly observed in notothenioid serum samples and in solutions of purified AFPs, and ice was found to persist inside live fishes at temperatures more than 1 °C above their eqFMP for at least 24 h, and at a lower temperature for at least several days. Field experiments confirmed that superheated ice occurs naturally inside wild fishes. Over the long-term record (1999-2012), seawater temperature surpassed the fish eqFMP in most summers, but never exceeded the highest temperature at which ice persisted inside experimental fishes. Thus, because of the effects of AFP-induced melting inhibition, summer warming may not reliably eliminate internal ice. Our results expose a potentially antagonistic pleiotropic effect of AFPs: beneficial freezing avoidance is accompanied by melting inhibition that may contribute to lifelong accumulation of detrimental internal ice crystals.

Icebergs Melting in Uniform and Vertically Sheared Flows

NASA Astrophysics Data System (ADS)

Cenedese, Claudia; Fitzmaurice, Anna; Straneo, Fiammetta

2017-11-01

Icebergs calving into Greenlandic Fjords frequently experience strongly sheared flows over their draft, but the impact of this flow past the iceberg on the melt plumes generated along the iceberg sides is not fully captured by existing melt parameterizations. A series of novel laboratory experiments showed that side melting of icebergs subject to relative velocities is controlled by two distinct regimes, which depend on the melt plume behavior (side-attached or side-detached). These two regimes produce a nonlinear dependence of melt rate on velocity, and different distributions of meltwater in the water column. Iceberg meltwater may either be confined to a thin surface layer, when the melt plumes are side-attached, or mixed down to the iceberg draft, when the melt plumes are side-detached. In a two-layer vertically sheared flow, the average flow speed in existing melt parameterizations gives an underestimate of the submarine melt rate, in part due to the nonlinearity of the dependence of melt rate on flow speed, but also because vertical shear in the velocity profile fundamentally changes the flow splitting around the ice block and consequently the velocity felt by the ice surface. Including this nonlinear velocity dependence in melting parameterizations applied to observed icebergs increases iceberg side melt in the side-attached regime, improving agreement with observations of iceberg submarine melt rates. AF was supported by NA14OAR4320106, CC by NSF OCE-1434041 and OCE-1658079, and FS by NSF PLR-1332911 and OCE-1434041.

Multi-Decadal Averages of Basal Melt for Ross Ice Shelf, Antarctica Using Airborne Observations

NASA Astrophysics Data System (ADS)

Das, I.; Bell, R. E.; Tinto, K. J.; Frearson, N.; Kingslake, J.; Padman, L.; Siddoway, C. S.; Fricker, H. A.

2017-12-01

Changes in ice shelf mass balance are key to the long term stability of the Antarctic Ice Sheet. Although the most extensive ice shelf mass loss currently is occurring in the Amundsen Sea sector of West Antarctica, many other ice shelves experience changes in thickness on time scales from annual to ice age cycles. Here, we focus on the Ross Ice Shelf. An 18-year record (1994-2012) of satellite radar altimetry shows substantial variability in Ross Ice Shelf height on interannual time scales, complicating detection of potential long-term climate-change signals in the mass budget of this ice shelf. Variability of radar signal penetration into the ice-shelf surface snow and firn layers further complicates assessment of mass changes. We investigate Ross Ice Shelf mass balance using aerogeophysical data from the ROSETTA-Ice surveys using IcePod. We use two ice-penetrating radars; a 2 GHz unit that images fine-structure in the upper 400 m of the ice surface and a 360 MHz radar to identify the ice shelf base. We have identified internal layers that are continuous along flow from the grounding line to the ice shelf front. Based on layer continuity, we conclude that these layers must be the horizons between the continental ice of the outlet glaciers and snow accumulation once the ice is afloat. We use the Lagrangian change in thickness of these layers, after correcting for strain rates derived using modern day InSAR velocities, to estimate multidecadal averaged basal melt rates. This method provides a novel way to quantify basal melt, avoiding the confounding impacts of spatial and short-timescale variability in surface accumulation and firn densification processes. Our estimates show elevated basal melt rates (> -1m/yr) around Byrd and Mullock glaciers within 100 km from the ice shelf front. We also compare modern InSAR velocity derived strain rates with estimates from the comprehensive ground-based RIGGS observations during 1973-1978 to estimate the potential magnitude of

Molecular dynamics study of the melting of a supported 887-atom Pd decahedron.

PubMed

Schebarchov, D; Hendy, S C; Polak, W

2009-04-08

We employ classical molecular dynamics simulations to investigate the melting behaviour of a decahedral Pd(887) cluster on a single layer of graphite (graphene). The interaction between Pd atoms is modelled with an embedded-atom potential, while the adhesion of Pd atoms to the substrate is approximated with a Lennard-Jones potential. We find that the decahedral structure persists at temperatures close to the melting point, but that just below the melting transition, the cluster accommodates to the substrate by means of complete melting and then recrystallization into an fcc structure. These structural changes are in qualitative agreement with recently proposed models, and they verify the existence of an energy barrier preventing softly deposited clusters from 'wetting' the substrate at temperatures below the melting point.

Paradise Lost: Uncertainties in melting and melt extraction processes beneath oceanic spreading ridges

NASA Astrophysics Data System (ADS)

Kelemen, P. B.

2014-12-01

In many ways, decompression melting and focused melt transport beneath oceanic spreading ridges is the best understood igneous process on Earth. However, there are remaining - increasing - uncertainties in interpreting residual mantle peridotites. Indicators of degree of melting in residual peridotite are questionable. Yb concentration and spinel Cr# are affected by (a) small scale variations in reactive melt transport, (b) variable extents of melt extraction, and (c) "impregnation", i.e. partial crystallization of cooling melt in pore space. Roughly 75% of abyssal peridotites have undergone major element refertilization. Many may have undergone several melting events. The following three statements are inconsistent: (1) Peridotite melt productivity beyond cpx exhaustion is > 0.1%/GPa. (2) Crustal thickness is independent of spreading rate at rates > 2 cm/yr full rate (excluding ultra-slow spreading ridges). (3) Thermal models predict, and observations confirm, thick thermal boundary layers beneath slow spreading ridges. If (a) melt productivity is << 0.1%/GPa beyond cpx-out, and (b) cpx-out occurs > 15 km below the seafloor beneath most ridges, then the independence of crustal thickness with spreading rate can be understood. Most sampled peridotites from ridges melted beyond cpx-out. Cpx in these rocks formed via impregnation and/or exsolution during cooling. Most peridotites beneath ridges may undergo cpx exhaustion during decompression melting. This would entail an upward modification of potential temperature estimates. Alternatively, perhaps oceanic crustal thickness does vary with spreading rate but this is masked by complicated tectonics and serpentinization at slow-spreading ridges. Dissolution channels (dunites) are predicted to coalesce downstream, but numerical models of these have not shown why > 95% of oceanic crust forms in a zone < 5 km wide. There may be permeability barriers guiding deeper melt toward the ridge, but field studies have not identified

Fe, Co, Ni: Electrical Resistivity Along their Melting Boundaries

NASA Astrophysics Data System (ADS)

Silber, R. E.; Ezenwa, I.; Secco, R.; Yong, W.

2017-12-01

Electrical resistivity of Fe, Co, and Ni was measured at pressures up to 11 GPa and temperatures into their liquid states in multi-anvil and cubic-anvil presses. Two thermocouples placed at opposite ends of the wire sample served as T probes as well as 4-wire resistance electrodes in a switched circuit. A polarity switch was also used to remove any bias associated with current flow and voltage measurement using thermocouple legs. Post experimental examination of recovered and sectioned samples was done using electron microprobe analyses to check for diffusion in our samples. The observed large jumps in resistivity at the high P melting T of each metal is consistent with its known P,T phase diagram and with post-run compositional analyses. The electrical resistivity behavior in these late transition metals as a function of increasing P and T shows expected trends consistent with 1atm data. Within the error of measurement, the resistivity values at the melting T at high P of Co and Ni appear to mimic their 1 atm value suggesting constant resistivity along the melting boundary. For liquid Fe, resistivity decreases along the melting boundary up to the triple point at 5.2 GPa, and then is nearly constant at higher pressures. The results are compared to prediction by Stacey and Loper (PEPI, 2007).

Experimental observation of optical Weyl points and Fermi arcs

NASA Astrophysics Data System (ADS)

Rechtsman, Mikael

We directly observe the presence type-II Weyl points for optical photons in a three-dimensional dielectric structure comprising arrays of evanescently-coupled, single-mode, helical waveguides. We also observe the corresponding Fermi arc surface states emerging from Weyl points (despite the use of the `Fermi arc' terminology, we are referring to bosons rather than fermions). The Weyl points are manifested by the presence of conical diffraction at the Weyl frequency in the photonic band structure, and the Fermi arc states are manifested by the emergence of surface states as we scan in frequency past the Weyl point. We map the Weyl points to Dirac points of the isofrequency surface, and the Fermi arcs to chiral edge states of an anomalous Floquet insulator. In collaboration with: Jiho Noh, Sheng Huang, Daniel Leykam*, Y. D. Chong, Kevin Chen, and Mikael C. Rechtsman M.C.R. acknowledges the National Science Foundation under Award Number ECCS-1509546, the Penn State MRSEC, Center for Nanoscale Science, under Award Number NSF DMR-1420620, and the Alfred P. Sloan Foundation under fellowship number FG-2016-6418.

Melting Curve of Molecular Crystal GeI4

NASA Astrophysics Data System (ADS)

Fuchizaki, Kazuhiro; Hamaya, Nozomu

2014-07-01

In situ synchrotron x-ray diffraction measurements were carried out to determine the melting curve of the molecular crystal GeI4. We found that the melting line rapidly increases with a pressure up to about 3 GPa, at which it abruptly breaks. Such a strong nonlinear shape of the melting curve can be approximately captured by the Kumari-Dass-Kechin equation. The parameters involved in the equation could be determined from the equation of state for the crystalline phase, which was also established in the present study. The melting curve predicted from the equation approaches the actual melting curve as the degree of approximation involved in obtaining the equation is improved. However, the treatment is justifiable only if the slope of the melting curve is everywhere continuous. We believe that this is not the case for GeI4's melting line at the breakpoint, as inferred from the nature of breakdown of the Kraut-Kennedy and the Magalinskii-Zubov relationships.The breakpoint may then be a triple point among the crystalline phase and two possible liquid phases.

Hot-melt extrusion--basic principles and pharmaceutical applications.

PubMed

Lang, Bo; McGinity, James W; Williams, Robert O

2014-09-01

Originally adapted from the plastics industry, the use of hot-melt extrusion has gained favor in drug delivery applications both in academia and the pharmaceutical industry. Several commercial products made by hot-melt extrusion have been approved by the FDA, demonstrating its commercial feasibility for pharmaceutical processing. A significant number of research articles have reported on advances made regarding the pharmaceutical applications of the hot-melt extrusion processing; however, only limited articles have been focused on general principles regarding formulation and process development. This review provides an in-depth analysis and discussion of the formulation and processing aspects of hot-melt extrusion. The impact of physicochemical properties of drug substances and excipients on formulation development using a hot-melt extrusion process is discussed from a material science point of view. Hot-melt extrusion process development, scale-up, and the interplay of formulation and process attributes are also discussed. Finally, recent applications of hot-melt extrusion to a variety of dosage forms and drug substances have also been addressed.

On a possible melting curve of C60 fullerite

NASA Astrophysics Data System (ADS)

Zubov, V. I.; Rodrigues, C. G.; Zubov, I. V.

2003-07-01

We study the thermodynamic properties of the high-temperature modification of fullerites on the basis of the Girifalco intermolecular potential. In the present work, using Lindemann's melting criterion, we estimate a possible melting curve Tm(P) of C60 fullerite. To take into account the lattice anharmonicity, which has a strong effect at T > 700 K, we use the correlative method of unsymmetrized self-consistent field. To check this approach, first we have applied it to solid Ar. In the range between its triple point Tt = 83.807 K and 260 K we obtained the mean square relative deviation from experimental data of about 0.7%. The melting curve for C60 fullerite has been calculated from the melting point at normal pressure estimated at 1500 K up to 15 kbar, which corresponds to Tm = 4000 K, i.e. to the temperature estimated by Kim and Tománek [Phys. Rev. Lett. 72, 2418 (1994)] as that of the decomposition of the C60 molecule itself. The temperature dependence of the melting pressure is approximated very well by the Simon equation (Pm(T)/bar - 1)/b = (T/T0)c with T0 = 1500 K, b = 6643.8, and c = 1.209. The temperature dependence of the molar volume along the melting curve is described by Vs(T) = Vs(T0) - 29.20 ln (T/T0.

String-like collective atomic motion in the melting and freezing of nanoparticles.

PubMed

Zhang, Hao; Kalvapalle, Pranav; Douglas, Jack F

2011-12-08

The melting of a solid represents a transition between a solid state in which atoms are localized about fixed average crystal lattice positions to a fluid state that is characterized by relative atomic disorder and particle mobility so that the atoms wander around the material as a whole, impelled by the random thermal impulses of surrounding atoms. Despite the fundamental nature and practical importance of this particle delocalization transition, there is still no fundamental theory of melting and instead one often relies on the semi-phenomenological Lindemann-Gilvarry criterion to estimate roughly the melting point as an instability of the crystal lattice. Even the earliest simulations of melting in hexagonally packed hard discs by Alder and Wainwright indicated the active role of nonlocal collective atomic motions in the melting process, and here we utilize molecular dynamics (MD) simulation to determine whether the collective particle motion observed in melting has a similar geometrical form as those in recent studies of nanoparticle (NP) interfacial dynamics and the molecular dynamics of metastable glass-forming liquids. We indeed find string-like collective atomic motion in NP melting that is remarkably similar in form to the collective interfacial motions in NPs at equilibrium and to the collective motions found in the molecular dynamics of glass-forming liquids. We also find that the spatial localization and extent of string-like motion in the course of NP melting and freezing evolves with time in distinct ways. Specifically, the collective atomic motion propagates from the NP surface and from within the NP in melting and freezing, respectively, and the average string length varies smoothly with time during melting. In contrast, the string-like cooperative motion peaks in an intermediate stage of the freezing process, reflecting a general asymmetry in the dynamics of NP superheating and supercooling. © 2011 American Chemical Society

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

NASA Technical Reports Server (NTRS)

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

2010-01-01

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

Long-Term Stability of WC-C Peritectic Fixed Point

NASA Astrophysics Data System (ADS)

Khlevnoy, B. B.; Grigoryeva, I. A.

2015-03-01

The tungsten carbide-carbon peritectic (WC-C) melting transition is an attractive high-temperature fixed point with a temperature of . Earlier investigations showed high repeatability, small melting range, low sensitivity to impurities, and robustness of WC-C that makes it a prospective candidate for the highest fixed point of the temperature scale. This paper presents further study of the fixed point, namely the investigation of the long-term stability of the WC-C melting temperature. For this purpose, a new WC-C cell of the blackbody type was built using tungsten powder of 99.999 % purity. The stability of the cell was investigated during the cell aging for 50 h at the cell working temperature that tooks 140 melting/freezing cycles. The method of investigation was based on the comparison of the WC-C tested cell with a reference Re-C fixed-point cell that reduces an influence of the probable instability of a radiation thermometer. It was shown that after the aging period, the deviation of the WC-C cell melting temperature was with an uncertainty of.

Preliminary results of sulfide melt/silicate wetting experiments in a partially melted ordinary chondrite

NASA Technical Reports Server (NTRS)

Jurewicz, Stephen R.; Jones, John H.

1994-01-01

Recently, mechanisms for core formation in planetary bodies have received considerable attention. Most current theories emphasize the need for large degrees of silicate partial melting to facilitate the coalescence and sinking of sulfide-metal liquid blebs through a low strength semi-crystalline silicate mush. This scenario is based upon observations that sulfide-metal liquid tends to form circular blebs in partially molten meteorites during laboratory experiments. However, recent experimental work by Herpfer and Larimer indicates that some sulfide-Fe liquids have wetting angles at and slightly below 60 deg in an olivine aggregate, implying an interconnected melt structure at any melt fraction. Such melt interconnectivity provides a means for gravitational compaction and extraction of the majority of a sulfide liquid phase in small planetary bodies without invoking large degrees of silicate partial melting. Because of the important ramifications of these results, we conducted a series of experiments using H-chondrite starting material in order to evaluate sulfide-liquid/silicate wetting behavior in a more complex natural system.

Shear melting and high temperature embrittlement: theory and application to machining titanium.

PubMed

Healy, Con; Koch, Sascha; Siemers, Carsten; Mukherji, Debashis; Ackland, Graeme J

2015-04-24

We describe a dynamical phase transition occurring within a shear band at high temperature and under extremely high shear rates. With increasing temperature, dislocation deformation and grain boundary sliding are supplanted by amorphization in a highly localized nanoscale band, which allows for massive strain and fracture. The mechanism is similar to shear melting and leads to liquid metal embrittlement at high temperature. From simulation, we find that the necessary conditions are lack of dislocation slip systems, low thermal conduction, and temperature near the melting point. The first two are exhibited by bcc titanium alloys, and we show that the final one can be achieved experimentally by adding low-melting-point elements: specifically, we use insoluble rare earth metals (REMs). Under high shear, the REM becomes mixed with the titanium, lowering the melting point within the shear band and triggering the shear-melting transition. This in turn generates heat which remains localized in the shear band due to poor heat conduction. The material fractures along the shear band. We show how to utilize this transition in the creation of new titanium-based alloys with improved machinability.

Probing the atomic structure of basaltic melts generated by partial melting of upper mantle peridotite (KLB-1): Insights from high-resolution solid-state NMR study

NASA Astrophysics Data System (ADS)

Park, S. Y.; Lee, S. K.

2015-12-01

Probing the structural disorder in multi-component silicate glasses and melts with varying composition is essential to reveal the change of macroscopic properties in natural silicate melts. While a number of NMR studies for the structure of multi-component silicate glasses and melts including basaltic and andesitic glasses have been reported (e.g., Park and Lee, Geochim. Cosmochim. Acta, 2012, 80, 125; Park and Lee, Geochim. Cosmochim. Acta, 2014, 26, 42), many challenges still remain. The composition of multi-component basaltic melts vary with temperature, pressure, and melt fraction (Kushiro, Annu. Rev. Earth Planet. Sci., 2001, 71, 107). Especially, the eutectic point (the composition of first melt) of nepheline-forsterite-quartz (the simplest model of basaltic melts) moves with pressure from silica-saturated to highly undersaturated and alkaline melts. The composition of basaltic melts generated by partial melting of upper mantle peridotite (KLB-1, the xenolith from Kilbourne Hole) also vary with pressure. In this study we report experimental results for the effects of composition on the atomic structure of Na2O-MgO-Al2O3-SiO2 (NMAS) glasses in nepheline (NaAlSiO4)-forsterite (Mg2SiO4)-quartz (SiO2) eutectic composition and basaltic glasses generated by partial melting of upper mantle peridotite (KLB-1) using high-resolution multi-nuclear solid-state NMR. The Al-27 3QMAS (triple quantum magic angle spinning) NMR spectra of NMAS glasses in nepheline-forsterite-quartz eutectic composition show only [4]Al. The Al-27 3QMAS NMR spectra of KLB-1 basaltic glasses show mostly [4]Al and a non-negligible fraction of [5]Al. The fraction of [5]Al, the degree of configurational disorder, increases from 0 at XMgO [MgO/(MgO+Al2O3)]=0.55 to ~3% at XMgO=0.79 in KLB-1 basaltic glasses while only [4]Al are observed in nepheline-forsterite-quartz eutectic composition. The current experimental results provide that the fraction of [5]Al abruptly increases by the effect of

Dynamical Scaling and Phase Coexistence in Topologically Constrained DNA Melting.

PubMed

Fosado, Y A G; Michieletto, D; Marenduzzo, D

2017-09-15

There is a long-standing experimental observation that the melting of topologically constrained DNA, such as circular closed plasmids, is less abrupt than that of linear molecules. This finding points to an important role of topology in the physics of DNA denaturation, which is, however, poorly understood. Here, we shed light on this issue by combining large-scale Brownian dynamics simulations with an analytically solvable phenomenological Landau mean field theory. We find that the competition between melting and supercoiling leads to phase coexistence of denatured and intact phases at the single-molecule level. This coexistence occurs in a wide temperature range, thereby accounting for the broadening of the transition. Finally, our simulations show an intriguing topology-dependent scaling law governing the growth of denaturation bubbles in supercoiled plasmids, which can be understood within the proposed mean field theory.

Evolution of melt-vapor surface tension in silicic volcanic systems: Experiments with hydrous melts

USGS Publications Warehouse

Mangan, M.; Sisson, T.

2005-01-01

We evaluate the melt-vapor surface tension (??) of natural, water-saturated dacite melt at 200 MPa, 950-1055??C, and 4.8-5.7 wt % H2O. We experimentally determine the critical supersaturation pressure for bubble nucleation as a function of dissolved water and then solve for ?? at those conditions using classical nucleation theory. The solutions obtained give dacite melt-vapor surface tensions that vary inversely with dissolved water from 0.042 (??0.003) J m-2 at 5.7 wt% H2O to 0.060 (??0.007) J m-2 at 5.2 wt% H2O to 0.073 (??0.003) J m-2 at 4.8 wt% H2O. Combining our dacite results with data from published hydrous haplogranite and high-silica rhyolite experiments reveals that melt-vapor surface tension also varies inversely with the concentration of mafic melt components (e.g., CaO, FeOtotal, MgO). We develop a thermodynamic context for these observations in which melt-vapor surface tension is represented by a balance of work terms controlled by melt structure. Overall, our results suggest that cooling, crystallization, and vapor exsolution cause systematic changes in ?? that should be considered in dynamic modeling of magmatic processes.

Interface structure and contact melting in AgCu eutectic. A molecular dynamics study

NASA Astrophysics Data System (ADS)

Bystrenko, O.; Kartuzov, V.

2017-12-01

Molecular dynamics simulations of the interface structure in binary AgCu eutectic were performed by using the realistic EAM potential. In simulations, we examined the time dependence of the total energy in the process of equilibration, the probability distributions, the composition profiles for the components, and the component diffusivities within the interface zone. It is shown that the relaxation to the equilibrium in the solid state is accompanied by the formation of the steady disordered diffusion zone at the boundary between the crystalline components. At higher temperatures, closer to the eutectic point, the increase in the width of the steady diffusion zone is observed. The particle diffusivities grow therewith to the numbers typical for the liquid metals. Above the eutectic point, the steady zone does not form, instead, the complete contact melting in the system occurs. The results of simulations indicate that during the temperature increase the phenomenon of contact melting is preceded by the similar process spatially localized in the vicinity of the interface.

Melt electrospinning of biodegradable polyurethane scaffolds

PubMed Central

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

2014-01-01

Electrospinning from the melt, in contrast to from 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 a well-controlled high temperature setup and the difficulty in developing an appropriate polymer. In this paper, a biodegradable and thermally stable polyurethane (PU) is described specifically for use in melt electrospinning. Polymer formulations of aliphatic PUs based on (CH2)4-content diisocyanates, polycaprolactone (PCL), 1,4-butanediamine and 1,4-butanediol (BD) were evaluated for utility in the melt electrospinning process. The final polymer formulation, a catalyst-purified PU based on 1,4-butane diisocyanate, PCL and BD in a 4/1/3 molar ratio with a weight-average molecular weight of about 40 kDa, yielded a nontoxic polymer that could be readily electrospun from the melt. Scaffolds electrospun from this polymer contained point bonds between fibers and mechanical properties analogous to many in vivo soft tissues. PMID:21640853

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

PubMed

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

2018-03-01

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

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

NASA Astrophysics Data System (ADS)

Tirone, Massimiliano

2018-03-01

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

The importance of accurate interaction potentials in the melting of argon nanoclusters

NASA Astrophysics Data System (ADS)

Pahl, E.; Calvo, F.; Schwerdtfeger, P.

The melting temperatures of argon clusters ArN (N = 13, 55, 147, 309, 561, and 923) and of bulk argon have been obtained from exchange Monte Carlo simulations and are compared using different two-body interaction potentials, namely the standard Lennard-Jones (LJ), Aziz and extended Lennard-Jones (ELJ) potentials. The latter potential has many advantages: while maintaining the computational efficiency of the commonly used LJ potential, it is as accurate as the Aziz potential but the computer time scales more favorably with increasing cluster size. By applying the ELJ form and extrapolating the cluster data to the infinite system, we are able to extract the melting point of argon already in good agreement with experimental measurements. By considering the additional Axilrod-Teller three-body contribution as well, we calculate a melting temperature of T meltELJ = 84.7 K compared to the experimental value of T meltexp = 83.85 K, whereas the LJ potential underestimates the melting point by more than 7 K. Thus melting temperatures within 1 K accuracy are now feasible.

Size-Dependent Melting Behavior of Colloidal In, Sn, and Bi Nanocrystals

PubMed Central

Liu, Minglu; Wang, Robert Y.

2015-01-01

Colloidal nanocrystals are a technologically important class of nanostructures whose phase change properties have been largely unexplored. Here we report on the melting behavior of In, Sn, and Bi nanocrystals dispersed in a polymer matrix. This polymer matrix prevents the nanocrystals from coalescing with one another and enables previously unaccessed observations on the melting behavior of colloidal nanocrystals. We measure the melting temperature, melting enthalpy, and melting entropy of colloidal nanocrystals with diameters of approximately 10 to 20 nm. All of these properties decrease as nanocrystal size decreases, although the depression rate for melting temperature is comparatively slower than that of melting enthalpy and melting entropy. We also observe an elevated melting temperature during the initial melt-freeze cycle that we attribute to surface stabilization from the organic ligands on the nanocrystal surface. Broad endothermic melting valleys and very large supercoolings in our calorimetry data suggest that colloidal nanocrystals exhibit a significant amount of surface pre-melting and low heterogeneous nucleation probabilities during freezing. PMID:26573146

Microgravity Studies of Liquid-Liquid Phase Transitions in Alumina-Yttria Melts

NASA Technical Reports Server (NTRS)

Guynes, Buddy (Technical Monitor); Weber, Richard; Nordine, Paul

2004-01-01

The scientific objective of this research is to increase the fundamental knowledge base for liquid- phase processing of technologically important oxide materials. The experimental objective is to define conditions and hardware requirements for microgravity flight experiments to test and expand the experimental hypotheses that: 1. Liquid phase transitions can occur in undercooled melts by a diffusionless process. 2. Onset of the liquid phase transition is accompanied by a large change in the temperature dependence of melt viscosity. Experiments on undercooled YAG (Y3A15012)- and rare earth oxide aluminate composition liquids demonstrated a large departure from an Arrhenian temperature dependence of viscosity. Liquid YAG is nearly inviscid at its 2240 K melting point. Glass fibers were pulled from melts undercooled by ca. 600 K indicating that the viscosity is on the order of 100 Pans (1000 Poise) at 1600 K. This value of viscosity is 500 times greater than that obtained by extrapolation of data for temperatures above the melting point of YAG. These results show that the liquids are extremely fragile and that the onset of the highly non-Arrhenian viscosity-temperature relationship occurs at a temperature considerably below the equilibrium melting point of the solid phases. Further results on undercooled alumina-yttria melts containing 23-42 mole % yttrium oxide indicate that a congruent liquid-liquid phase transition occurs in the undercooled liquids. The rates of transition are inconsistent with a diffusion-limited process. This research is directed to investigation of the scientifically interesting phenomena of polyamorphism and fragility in undercooled rare earth oxide aluminum oxide liquids. The results bear on the technologically important problem of producing high value rare earth-based optical materials.

Melting ice

NASA Astrophysics Data System (ADS)

Benedetto, Elmo

2018-01-01

In this brief frontline, we want to describe the well-known fact that, when freshwater ice melts, the freshwater liquid level does not change. In the Italian Ministerial programs, fluid statics is introduced in the three years of middle school (students of 11-13 years) and during the first two years of high school (14-15 years). The Italian textbooks do not clearly explain why the abovementioned phenomenon occurs. The explanations are qualitative and they may lead to misinterpretation. I have noted that the students are very curious about this phenomenon. They sought a demonstration from books and from the web; and when they do not find it they asked me. Moreover, they have allowed me to observe that there are contradictory statements about the melting of icebergs. Some authors claim that they would not raise the sea-level, others say the opposite. Honestly speaking, I had never thought about this phenomenon and in classroom I tried to give them proof, expressing my opinion about the melting of icebergs.

Comment on 'Water-fluxed melting of the continental crust: A review' by R.F. Weinberg and P. Hasalová

NASA Astrophysics Data System (ADS)

Clemens, J. D.; Stevens, G.

2015-10-01

In this invited 'review' article, the authors come to the conclusion that fluid-present partial melting reactions are of widespread occurrence and critical importance in the processes of high-grade metamorphism and crustal differentiation. In their abstract, the authors correctly restate the conclusions of Clemens and Droop (1998) that it is not necessarily the case that melts formed by fluid-present reactions (even by H2O-saturated melting) cannot leave their sources. This realisation is not actually relevant to the question of formation and ascent of granitic magmas by crustal partial melting. Although they refer to Clemens and Watkins (2001), the authors seem ignore the main point of the argument presented therein, namely that the distribution of temperature and H2O contents in felsic igneous systems is only compatible with derivation of the magmas by fluid-absent partial melting reactions at high-temperature, granulite-facies conditions. Neither fluid-saturated nor fluid-deficient partial melting could have resulted in the observed covariation in temperature and melt H2O content.

Fabrication of a mini multi-fixed-point cell for the calibration of industrial platinum resistance thermometers

NASA Astrophysics Data System (ADS)

Ragay-Enot, Monalisa; Lee, Young Hee; Kim, Yong-Gyoo

2017-07-01

A mini multi-fixed-point cell (length 118 mm, diameter 33 mm) containing three materials (In-Zn eutectic (mass fraction 3.8% Zn), Sn and Pb) in a single crucible was designed and fabricated for the easy and economical fixed-point calibration of industrial platinum resistance thermometers (IPRTs) for use in industrial temperature measurements. The melting and freezing behaviors of the metals were investigated and the phase transition temperatures were determined using a commercial dry-block calibrator. Results showed that the melting plateaus are generally easy to realize and are reproducible, flatter and of longer duration. On the other hand, the freezing process is generally difficult, especially for Sn, due to the high supercooling required to initiate freezing. The observed melting temperatures at optimum set conditions were 143.11 °C (In-Zn), 231.70 °C (Sn) and 327.15 °C (Pb) with expanded uncertainties (k  = 2) of 0.12 °C, 0.10 °C and 0.13 °C, respectively. This multi-fixed-point cell can be treated as a sole reference temperature-generating system. Based on the results, the realization of melting points of the mini multi-fixed-point cell can be recommended for the direct calibration of IPRTs in industrial applications without the need for a reference thermometer.

Lipid melting and cuticular permeability: new insights into an old problem.

PubMed

Gibbs, Allen G.

2002-04-01

The idea that the physical properties of cuticular lipids affect cuticular permeability goes back over 65 years. This proposal has achieved textbook status, despite controversy and the general lack of direct supporting evidence. Recent work supports the standard model, in which lipid melting results in increased cuticular permeability. Surprisingly, although all species studied to date can synthesize lipids that remain in a solid state at environmental temperatures, partial melting often occurs due to the deposition of lipids with low melting points. This will tend to increase water loss; the benefits may include better dispersal of lipids or other compounds across the cuticle or improved communication via cuticular pheromones. In addition, insects with high melting-point lipids are not necessarily less permeable at low temperatures. One likely reason is variation in lipid properties within the cuticle. Surface lipids differ from one region to another, and biophysical studies of model mixtures suggest the occurrence of phase separation between melted and solid lipid fractions. Lipid phase separation may have important implications for insect water balance and chemical communication.

Melting of superheated molecular crystals

NASA Astrophysics Data System (ADS)

Cubeta, Ulyana; Bhattacharya, Deepanjan; Sadtchenko, Vlad

2017-07-01

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

Investigating evaporation of melting ice particles within a bin melting layer model

NASA Astrophysics Data System (ADS)

Neumann, Andrea J.

Single column models have been used to help develop algorithms for remote sensing retrievals. Assumptions in the single-column models may affect the assumptions of the remote sensing retrievals. Studies of the melting layer that use single column models often assume environments that are near or at water saturation. This study investigates the effects of evaporation upon melting particles to determine whether the assumption of negligible mass loss still holds within subsaturated melting layers. A single column, melting layer model is modified to include the effects of sublimation and evaporation upon the particles. Other changes to the model include switching the order in which the model loops over particle sizes and model layers; including a particle sedimentation scheme; adding aggregation, accretion, and collision and coalescence processes; allowing environmental variables such as the water vapor diffusivity and the Schmidt number to vary with the changes in the environment; adding explicitly calculated particle temperature, changing the particle terminal velocity parameterization; and using a newly-derived effective density-dimensional relationship for use in particle mass calculations. Simulations of idealized melting layer environments show that significant mass loss due to evaporation during melting is possible within subsaturated environments. Short melting distances, accelerating particle fall speeds, and short melting times help constrain the amount of mass lost due to evaporation while melting is occurring, even in subsaturated profiles. Sublimation prior to melting can also be a significant source of mass loss. The trends shown on the particle scale also appear in the bulk distribution parameters such as rainfall rate and ice water content. Simulations incorporating observed melting layer environments show that significant mass loss due to evaporation during the melting process is possible under certain environmental conditions. A profile such as the

Dynamics of the Axial Melt Lens/Dike transition at fast spreading ridges: assimilation and hydrous partial melting

NASA Astrophysics Data System (ADS)

France, L.; Ildefonse, B.; Koepke, J.

2009-04-01

Recent detailed field studies performed in the Oman ophiolite on the gabbro/sheeted dike transition, compared to corresponding rocks from the EPR drilled by IODP (Site 1256), constrain a general model for the dynamics of the axial melt lens (AML) present at fast spreading ridges (France et al., 2008). This model implies that the AML/dike transition is a dynamic interface migrating up- and downward, and that the isotropic gabbro horizon on top of the igneous section represents its fossilization. It is also proposed that upward migrations are associated to reheating of the base of the sheeted dike complex and to assimilation processes. Plagiogranitic lithologies are observed close to the truncated base of the dikes and are interpreted to represent frozen melts generated by partial melting of previously hydrothermalized sheeted dikes. Relicts of previously hydrothermalized lithologies are also observed in the fossil melt lens, and are associated to lithologies that have crystallized under high water activities, with clinopyroxene crystallizing before plagioclase, and An-rich plagioclase. To better understand our field data, we performed hydrous partial melting experiments at shallow pressures (0.1 GPa) under slightly oxidizing conditions (NNO oxygen buffer) and water saturated conditions on hydrothermalized sheeted dike sample from the Oman ophiolite. These experiments have been performed between 850°C and 1030°C; two additional experiments in the subsolidus regime were also conducted (750°C and 800°C). Clinopyroxenes formed during incongruent melting at low temperature (<910°C) have compositions that match those from the corresponding natural rocks (reheated base of the sheeted dike and relicts of assimilated lithologies). In particular, the characteristic low TiO2 and Al2O3 contents are reproduced. The experimental melts produced at low temperatures correspond to compositions of typical natural plagiogranites. In natural settings, these silicic liquids would be

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

NASA Astrophysics Data System (ADS)

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

2017-12-01

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

Analysis of the heat capacity for pure CH4 and CH4/CCl4 on graphite near the melting point and calculation of the T-X phase diagram for (CH3)CCl3 + CCl4

NASA Astrophysics Data System (ADS)

Yurtseven, Hamit; Yılmaz, Aygül

2016-06-01

We study the temperature dependence of the heat capacity Cp for the pure CH4 and the coadsorbed CH4/CCl4 on graphite near the melting point. The heat capacity peaks are analyzed using the experimental data from the literature by means of the power-law formula. The critical exponents for the heat capacity are deduced below and above the melting point for CH4 (Tm = 104.8 K) and CH4/CCl4 (Tm = 99.2 K). Our exponent values are larger as compared with the predicted values of some theoretical models exhibiting second order transition. Our analyses indicate that the pure methane shows a nearly second order (weak discontinuity in the heat capacity peak), whereas the transition in coadsorbed CH4/CCl4 is of first order (apparent discontinuity in Cp). We also study the T - X phase diagram of a two-component system of CH3CCl3+CCl4 using the Landau phenomenological model. Phase lines of the R+L (rhombohedral+liquid) and FCC+L (face-centred cubic + liquid) are calculated using the observed T - X phase diagram of this binary mixture. Our results show that the Landau mean field theory describes the observed behavior of CH3CCl3+CCl4 adequately. From the calculated T - X phase diagram, critical behavior of some thermodynamic quantities can be predicted at various temperatures and concentrations (CCl4) for a binary mixture of CH3CCl3+CCl4.

Impact melting early in lunar history

NASA Technical Reports Server (NTRS)

Lange, M. A.; Ahrens, T. J.

1979-01-01

The total amount of impact melt produced during early lunar history is examined in light of theoretically and experimentally determined relations between crater diameter (D) and impact melt volume. The time dependence of the melt production is given by the time dependent impact rate as derived from cratering statistics for two different crater-size classes. Results show that small scale cratering (D less than or equal to 30 km) leads to melt volumes which fit selected observations specifying the amount of impact melt contained in the lunar regolith and in craters with diameters less than 10 km. Larger craters (D greater than 30 km) are capable of forming the abundant impact melt breccias found on the lunar surface. The group of large craters (D greater than 30 km) produces nearly 10 times as much impact melt as all the smaller craters, and thus, the large impacts dominate the modification of the lunar surface. A contradiction between the distribution of radiometric rock ages and a model of exponentially decreasing cratering rate going back to 4.5 b.y. is reflected in uncertainty in the distribution of impact melt as a function of time on the moon.

Radiation from an Accelerated Point Charge and Non-Inertial Observers

ERIC Educational Resources Information Center

Leonov, A. B.

2012-01-01

It is known that observers comoving with a uniformly accelerated point charge detect the electromagnetic field of a charge as a static electric field. We show that one can find a similar family of observers, which detect the field of a charge as a static electric field, in the general case of arbitrary point-charge motion. We find the velocities…

Density Affects the Nature of the Hexatic-Liquid Transition in Two-Dimensional Melting of Soft-Core Systems

NASA Astrophysics Data System (ADS)

Zu, Mengjie; Liu, Jun; Tong, Hua; Xu, Ning

2016-08-01

We find that both continuous and discontinuous hexatic-liquid transitions can happen in the melting of two-dimensional solids of soft-core disks. For three typical model systems, Hertzian, harmonic, and Gaussian-core models, we observe the same scenarios. These systems exhibit reentrant crystallization (melting) with a maximum melting temperature Tm happening at a crossover density ρm. The hexatic-liquid transition at a density smaller than ρm is discontinuous. Liquid and hexatic phases coexist in a density interval, which becomes narrower with increasing temperature and tends to vanish approximately at Tm. Above ρm, the transition is continuous, in agreement with the Kosterlitz-Thouless-Halperin-Nelson-Young theory. For these soft-core systems, the nature of the hexatic-liquid transition depends on density (pressure), with the melting at ρm being a plausible transition point from discontinuous to continuous hexatic-liquid transition.

Occurrence and mechanisms of impact melt emplacement at small lunar craters

NASA Astrophysics Data System (ADS)

Stopar, Julie D.; Hawke, B. Ray; Robinson, Mark S.; Denevi, Brett W.; Giguere, Thomas A.; Koeber, Steven D.

2014-11-01

Using observations from the Lunar Reconnaissance Orbiter Camera (LROC), we assess the frequency and occurrence of impact melt at simple craters less than 5 km in diameter. Nine-hundred-and-fifty fresh, randomly distributed impact craters were identified for study based on their maturity, albedo, and preservation state. The occurrence, frequency, and distribution of impact melt deposits associated with these craters, particularly ponded melt and lobate flows, are diagnostic of melt emplacement mechanisms. Like larger craters, those smaller than a few kilometers in diameter often exhibit ponded melt on the crater floor as well as lobate flows near the crater rim crest. The morphologies of these deposits suggest gravity-driven flow while the melt was molten. Impact melt deposits emplaced as veneers and ;sprays;, thin layers of ejecta that drape other crater materials, indicate deposition late in the cratering process; the deposits of fine sprays are particularly sensitive to degradation. Exterior melt deposits found near the rims of a few dozen craters are distributed asymmetrically around the crater and are rare at craters less than 2 km in diameter. Pre-existing topography plays a role in the occurrence and distribution of these melt deposits, particularly for craters smaller than 1 km in diameter, but does not account for all observed asymmetries in impact melt distribution. The observed relative abundance and frequency of ponded melt and flows in and around simple lunar craters increases with crater diameter, as was previously predicted from models. However, impact melt deposits are found more commonly at simple lunar craters (i.e., those less than a few kilometers in diameter) than previously expected. Ponded melt deposits are observed in roughly 15% of fresh craters smaller than 300 m in diameter and 80% of fresh craters between 600 m and 5 km in diameter. Furthermore, melt deposits are observed at roughly twice as many non-mare craters than at mare craters. We

First-principles melting of gallium clusters down to nine atoms: structural and electronic contributions to melting.

PubMed

Steenbergen, Krista G; Gaston, Nicola

2013-10-07

First-principles Born-Oppenheimer molecular dynamics simulations of small gallium clusters, including parallel tempering, probe the distinction between cluster and molecule in the size range of 7-12 atoms. In contrast to the larger sizes, dynamic measures of structural change at finite temperature demonstrate that Ga7 and Ga8 do not melt, suggesting a size limit to melting in gallium exists at 9 atoms. Analysis of electronic structure further supports this size limit, additionally demonstrating that a covalent nature cannot be identified for clusters larger than the gallium dimer. Ga9, Ga10 and Ga11 melt at greater-than-bulk temperatures, with no evident covalent character. As Ga12 represents the first small gallium cluster to melt at a lower-than-bulk temperature, we examine the structural properties of each cluster at finite temperature in order to probe both the origins of greater-than-bulk melting, as well as the significant differences in melting temperatures induced by a single atom addition. Size-sensitive melting temperatures can be explained by both energetic and entropic differences between the solid and liquid phases for each cluster. We show that the lower-than-bulk melting temperature of the 12-atom cluster can be attributed to persistent pair bonding, reminiscent of the pairing observed in α-gallium. This result supports the attribution of greater-than-bulk melting in gallium clusters to the anomalously low melting temperature of the bulk, due to its dimeric structure.

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

NASA Astrophysics Data System (ADS)

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

2018-01-01

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

Investigating the highest melting temperature materials: A laser melting study of the TaC-HfC system.

PubMed

Cedillos-Barraza, Omar; Manara, Dario; Boboridis, K; Watkins, Tyson; Grasso, Salvatore; Jayaseelan, Daniel D; Konings, Rudy J M; Reece, Michael J; Lee, William E

2016-12-01

TaC, HfC and their solid solutions are promising candidate materials for thermal protection structures in hypersonic vehicles because of their very high melting temperatures (>4000 K) among other properties. The melting temperatures of slightly hypostoichiometric TaC, HfC and three solid solution compositions (Ta 1-x Hf x C, with x = 0.8, 0.5 and 0.2) have long been identified as the highest known. In the current research, they were reassessed, for the first time in the last fifty years, using a laser heating technique. They were found to melt in the range of 4041-4232 K, with HfC having the highest and TaC the lowest. Spectral radiance of the hot samples was measured in situ, showing that the optical emissivity of these compounds plays a fundamental role in their heat balance. Independently, the results show that the melting point for HfC 0.98 , (4232 ± 84) K, is the highest recorded for any compound studied until now.

Investigating the highest melting temperature materials: A laser melting study of the TaC-HfC system

NASA Astrophysics Data System (ADS)

Cedillos-Barraza, Omar; Manara, Dario; Boboridis, K.; Watkins, Tyson; Grasso, Salvatore; Jayaseelan, Daniel D.; Konings, Rudy J. M.; Reece, Michael J.; Lee, William E.

2016-12-01

TaC, HfC and their solid solutions are promising candidate materials for thermal protection structures in hypersonic vehicles because of their very high melting temperatures (>4000 K) among other properties. The melting temperatures of slightly hypostoichiometric TaC, HfC and three solid solution compositions (Ta1-xHfxC, with x = 0.8, 0.5 and 0.2) have long been identified as the highest known. In the current research, they were reassessed, for the first time in the last fifty years, using a laser heating technique. They were found to melt in the range of 4041-4232 K, with HfC having the highest and TaC the lowest. Spectral radiance of the hot samples was measured in situ, showing that the optical emissivity of these compounds plays a fundamental role in their heat balance. Independently, the results show that the melting point for HfC0.98, (4232 ± 84) K, is the highest recorded for any compound studied until now.

Investigating the highest melting temperature materials: A laser melting study of the TaC-HfC system

PubMed Central

Cedillos-Barraza, Omar; Manara, Dario; Boboridis, K.; Watkins, Tyson; Grasso, Salvatore; Jayaseelan, Daniel D.; Konings, Rudy J. M.; Reece, Michael J.; Lee, William E.

2016-01-01

TaC, HfC and their solid solutions are promising candidate materials for thermal protection structures in hypersonic vehicles because of their very high melting temperatures (>4000 K) among other properties. The melting temperatures of slightly hypostoichiometric TaC, HfC and three solid solution compositions (Ta1−xHfxC, with x = 0.8, 0.5 and 0.2) have long been identified as the highest known. In the current research, they were reassessed, for the first time in the last fifty years, using a laser heating technique. They were found to melt in the range of 4041–4232 K, with HfC having the highest and TaC the lowest. Spectral radiance of the hot samples was measured in situ, showing that the optical emissivity of these compounds plays a fundamental role in their heat balance. Independently, the results show that the melting point for HfC0.98, (4232 ± 84) K, is the highest recorded for any compound studied until now. PMID:27905481

Detection and discrimination of members of the family Luteoviridae by real-time PCR and SYBR® GreenER™ melting curve analysis.

PubMed

Chomic, Anastasija; Winder, Louise; Armstrong, Karen F; Pearson, Michael N; Hampton, John G

2011-01-01

This study investigated the suitability of a two step real-time RT-PCR melting curve analysis as a tool for the detection and discrimination of nine species in the plant virus family Luteoviridae, being Soybean dwarf virus [SbDV], Bean leafroll virus [BLRV], Beet chlorosis virus [BChV], Beet mild yellowing virus [BMYV], Beet western yellows virus [BWYV], Cereal yellow dwarf virus-RPV [CYDV-RPV], Cucurbit aphid-borne yellows virus [CABYV], Potato leafroll virus [PLRV] and Turnip yellows virus [TuYV]. Melting temperature and shape of the melting peak were analysed for 68 bp and 148 bp coat protein gene amplicons using SYBR® GreenER™ fluorescent dye. Specific melting peaks with unique melting temperature were observed for the various species of the family Luteoviridae using the 68 bp amplicon, but not with the 148 bp amplicon. Due to the high variability of sequences for some members of this family, different melting temperatures were also observed between different isolates of the species CYDV-RPV and TuYV. Nevertheless, discrimination between species was achieved for SbDV, BLRV, BChV, BMYV, CABYV and either PLRV or BWYV. Melting curve analysis, in this study, is a faster and more discriminatory alternative to gel electrophoresis of end-point PCR products for the detection of Luteoviridae infection. Copyright © 2010 Elsevier B.V. All rights reserved.

Eutectic melting temperature of the lowermost Earth's mantle

NASA Astrophysics Data System (ADS)

Andrault, D.; Lo Nigro, G.; Bolfan-Casanova, N.; Bouhifd, M.; Garbarino, G.; Mezouar, M.

2009-12-01

Partial melting of the Earth's deep mantle probably occurred at different stages of its formation as a consequence of meteoritic impacts and seismology suggests that it even continues today at the core-mantle boundary. Melts are important because they dominate the chemical evolution of the different Earth's reservoirs and more generally the dynamics of the whole planet. Unfortunately, the most critical parameter, that is the temperature profile inside the deep Earth, remains poorly constrained accross the planet history. Experimental investigations of the melting properties of materials representative of the deep Earth at relevant P-T conditions can provide anchor points to refine past and present temperature profiles and consequently determine the degree of melting at the different geological periods. Previous works report melting relations in the uppermost lower mantle region, using the multi-anvil press [1,2]. On the other hand, the pyrolite solidus was determined up to 65 GPa using optical observations in the laser-heated diamond anvil cell (LH-DAC) [3]. Finally, the melting temperature of (Mg,Fe)2SiO4 olivine is documented at core-mantle boundary (CMB) conditions by shock wave experiments [4]. Solely based on these reports, experimental data remain too sparse to draw a definite melting curve for the lower mantle in the relevant 25-135 GPa pressure range. We reinvestigated melting properties of lower mantle materials by means of in-situ angle dispersive X-ray diffraction measurements in the LH-DAC at the ESRF [5]. Experiments were performed in an extended P-T range for two starting materials: forsterite and a glass with chondrite composition. In both cases, the aim was to determine the onset of melting, and thus the eutectic melting temperatures as a function of pressure. Melting was evidenced from drastic changes of diffraction peak shape on the image plate, major changes in diffraction intensities in the integrated pattern, disappearance of diffraction rings

Experiments on transient melting of tungsten by ELMs in ASDEX Upgrade

NASA Astrophysics Data System (ADS)

Krieger, K.; Balden, M.; Coenen, J. W.; Laggner, F.; Matthews, G. F.; Nille, D.; Rohde, V.; Sieglin, B.; Giannone, L.; Göths, B.; Herrmann, A.; de Marne, P.; Pitts, R. A.; Potzel, S.; Vondracek, P.; ASDEX-Upgrade Team; EUROfusion MST1 Team

2018-02-01

Repetitive melting of tungsten by power transients originating from edge localized modes (ELMs) has been studied in ASDEX Upgrade. Tungsten samples were exposed to H-mode discharges at the outer divertor target plate using the divertor manipulator II (DIM-II) system (Herrmann et al 2015 Fusion Eng. Des. 98-9 1496-9). Designed as near replicas of the geometries used also in separate experiments on the JET tokamak (Coenen et al 2015 J. Nucl. Mater. 463 78-84 Coenen et al 2015 Nucl. Fusion 55 023010; Matthews et al 2016 Phys. Scr. T167 7), the samples featured a misaligned leading edge and a sloped ridge respectively. Both structures protrude above the default target plate surface thus receiving an increased fraction of the parallel power flux. Transient melting by ELMs was induced by moving the outer strike point to the sample location. The temporal evolution of the measured current flow from the samples to vessel potential confirmed transient melting. Current magnitude and dependency from surface temperature provided strong evidence for thermionic electron emission as main origin of the replacement current driving the melt motion. The different melt patterns observed after exposures at the two sample geometries support the thermionic electron emission model used in the MEMOS melt motion code, which assumes a strong decrease of the thermionic net current at shallow magnetic field to surface angles (Pitts et al 2017 Nucl. Mater. Energy 12 60-74). Post exposure ex situ analysis of the retrieved samples show recrystallization of tungsten at the exposed surface areas to a depth of up to several mm. The melt layer transport to less exposed surface areas leads to ratcheting pile up of re-solidified debris with zonal growth extending from the already enlarged grains at the surface.

Thermophysical and Optical Properties of Semiconducting Ga2Te3 Melt

NASA Technical Reports Server (NTRS)

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

2005-01-01

The majority of bulk semiconductor single crystals are presently grown from their melts. The thermophysical and optical properties of the melts provide a fundamental understanding of the melt structure and can be used to optimize the growth conditions to obtain higher quality crystals. In this paper, we report several thermophysical and optical properties for Ga2Te3 melts, such as electrical conductivity, viscosity, and optical transmission for temperatures ranging from the melting point up to approximately 990 C. The conductivity and viscosity of the melts are determined using the transient torque technique. The optical transmission of the melts is measured between the wavelengths of 300 and 2000 nm by an dual beam reversed-optics spectrophotometer. The measured properties are in good agreement with the published data. The conductivities indicate that the Ga2Te3 melt is semiconductor-like. The anomalous behavior in the measured properties are used as an indication of a structural transformation in the Ga2Te3 melt and discussed in terms of Eyring's and Bachinskii's predicted behaviors for homogeneous melts.

Melt migration modeling in partially molten upper mantle

NASA Astrophysics Data System (ADS)

Ghods, Abdolreza

The objective of this thesis is to investigate the importance of melt migration in shaping major characteristics of geological features associated with the partial melting of the upper mantle, such as sea-floor spreading, continental flood basalts and rifting. The partial melting produces permeable partially molten rocks and a buoyant low viscosity melt. Melt migrates through the partially molten rocks, and transfers mass and heat. Due to its much faster velocity and appreciable buoyancy, melt migration has the potential to modify dynamics of the upwelling partially molten plumes. I develop a 2-D, two-phase flow model and apply it to investigate effects of melt migration on the dynamics and melt generation of upwelling mantle plumes and focusing of melt migration beneath mid-ocean ridges. Melt migration changes distribution of the melt-retention buoyancy force and therefore affects the dynamics of the upwelling plume. This is investigated by modeling a plume with a constant initial melt of 10% where no further melting is considered. Melt migration polarizes melt-retention buoyancy force into high and low melt fraction regions at the top and bottom portions of the plume and therefore results in formation of a more slender and faster upwelling plume. Allowing the plume to melt as it ascends through the upper mantle also produces a slender and faster plume. It is shown that melt produced by decompressional melting of the plume migrates to the upper horizons of the plume, increases the upwelling velocity and thus, the volume of melt generated by the plume. Melt migration produces a plume which lacks the mushroom shape observed for the plume models without melt migration. Melt migration forms a high melt fraction layer beneath the sloping base of the impermeable oceanic lithosphere. Using realistic conditions of melting, freezing and melt extraction, I examine whether the high melt fraction layer is able to focus melt from a wide partial melting zone to a narrow region

Investigation of TiC C Eutectic and WC C Peritectic High-Temperature Fixed Points

NASA Astrophysics Data System (ADS)

Sasajima, Naohiko; Yamada, Yoshiro

2008-06-01

TiC C eutectic (2,761°C) and WC C peritectic (2,749°C) fixed points were investigated to compare their potential as high-temperature thermometric reference points. Two TiC C and three WC C fixed-point cells were constructed, and the melting and freezing plateaux were evaluated by means of radiation thermometry. The repeatability of the TiC C eutectic within a day was 60 mK with a melting range roughly 200 mK. The repeatability of the melting temperature of the WC C peritectic within 1 day was 17 mK with a melting range of ˜70 mK. The repeatability of the freezing temperature of the WC C peritectic was 21 mK with a freezing range less than 20 mK. One of the TiC C cells was constructed from a TiC and graphite powder mixture. The filling showed the reaction with the graphite crucible was suppressed and the ingot contained less voids, although the lack of high-purity TiC powder poses a problem. The WC C cells were easily constructed, like metal carbon eutectic cells, without any evident reaction with the crucible. From these results, it is concluded that the WC C peritectic has more potential than the TiC C eutectic as a high-temperature reference point. The investigation of the purification of the TiC C cell during filling and the plateau observation are also reported.

Hydrogen-alkali exchange between silicate melts and two-phase aqueous mixtures: an experimental investigation

NASA Astrophysics Data System (ADS)

Williams, Thomas J.; Candela, Philip A.; Piccoli, Philip M.

Experiments were performed in the three-phase system high-silica rhyolite melt + low-salinity aqueous vapor + hydrosaline brine, to investigate the exchange equilibria for hydrogen, potassium, and sodium in magmatic-hydrothermal systems at 800 °C and 100 MPa, and 850 °C and 50 MPa. The Kaqm/meltH,Na and Kaqm/meltH,K for hydrogen-sodium exchange between a vapor + brine mixture and a silicate melt are inversely proportional to the total chloride concentration (ΣCl) in the vapor + brine mixture indicating that HCl/NaCl and HCl/KCl are higher in the low-salinity aqueous vapor relative to high-salinity brine. The equilibrium constants for vapor/melt and brine/melt exchange were extracted from regressions of Kaqm/meltH,Na and Kaqm/meltH,K versus the proportion of aqueous vapor relative to brine in the aqueous mixture (Faqv) at P and T, expressed as a function of ΣCl. No significant pressure effect on the empirically determined exchange constants was observed for the range of pressures investigated. Model equilibrium constants are: Kaqv/meltH,Na(vapor/melt)=26(+/-1.3) at 100 MPa (800 °C), and 19( +/- 7.0) at 50 MPa (850 °C) Kaqv/meltH,K=14(+/-1.1) at 100 MPa (800 °C), and 24(+/-12) at 50 MPa (850 °C) Kaqb/meltH,b(brine/melt)= 1.6(+/-0.7) at 100 MPa (800 °C), and 3.9(+/-2.3) at 50 MPa (850 °C) and Kaqb/meltH,K=2.7(+/-1.2) at 100 MPa (800 °C) and 3.8(+/-2.3) at 50 MPa (850 °C). Values for Kaqv/meltH,K and Kaqb/meltH,K were used to calculate KCl/HCl in the aqueous vapor and brine as a function of melt aluminum saturation index (ASI: molar Al2O3/(K2O+Na2O+CaO) and pressure. The model log KCl/HCl values show that a change in melt ASI from peraluminous (ASI = 1.04) to moderately metaluminous (ASI = 1.01) shifts the cooling pathway (in temperature-log KCl/HCl space) of the aqueous vapor toward the andalusite+muscovite+K-feldspar reaction point.

Observational evidence of EHP effects on the melting of snowpack over the Tibetan Plateau

NASA Astrophysics Data System (ADS)

Kim, M.; Lau, W. K.; Kim, K.; Lee, W.

2012-12-01

Observational evidences are presented showing that the Indo-Gangetic Plain (IGP) regions, bounded by the high altitude Himalayan mountains, are subject to heavy loading of absorbing aerosols, i.e., black carbon and dust, which can lead to widespread enhancement warming over the Tibetan Plateau and accelerated snowmelt in the western Tibetan Plateau (WTP) and Himalayas. The two pre-monsoon seasons of 2004 and 2005 were strikingly contrasting in terms of the aerosol loading over IGP. The warming of the TP in 2004 relative to 2005 was widespread, covering most of the WTP and Himalayas. This warming is closely linked to patterns of the snow melt. Consistent with the Elevated Heat Pump hypothesis, we find that increased loading of absorbing aerosols over IGP in the pre-monsoon season is associated with increased heating of the upper troposphere by dynamical feedback induced by aerosol heating, and enhances the rate of snowmelt over Himalayas and the WTP in April-May. Composite analysis with more contrasting years also shows that the heating of the troposphere by elevated dust and black carbon aerosols in the boreal sping can lead to widespread enhanced land-atmosphere warming, and accelated snow melt in the Himalayas and Tibetan Plateau.

Observational Evidence of EHP Effects on the Melting of Snowpack over the Tibetan Plateau

NASA Technical Reports Server (NTRS)

Kim, Maeng-Ki; Lau, William K. M.; Kim, Kyu-Myong; Lee, Woo-Seop

2012-01-01

Observational evidences are presented showing that the Indo-Gangetic Plain (IGP) regions, bounded by the high altitude Himalayan mountains, are subject to heavy loading of absorbing aerosols, i.e., black carbon and dust, which can lead to widespread enhancement warming over the Tibetan Plateau and accelerated snowmelt in the western Tibetan Plateau (WTP) and Himalayas. The two pre-monsoon seasons of 2004 and 2005 were strikingly contrasting in terms of the aerosol loading over IGP. The warming of the TP in 2004 relative to 2005 was widespread, covering most of the WTP and Himalayas. This warming is closely linked to patterns of the snow melt. Consistent with the Elevated Heat Pump hypothesis, we find that increased loading of absorbing aerosols over IGP in the pre-monsoon season is associated with increased heating of the upper troposphere by dynamical feedback induced by aerosol heating, and enhances the rate of snowmelt over Himalayas and the WTP in April-May. Composite analysis with more contrasting years also shows that the heating of the troposphere by elevated dust and black carbon aerosols in the boreal spring can lead to widespread enhanced land-atmosphere warming, and accelerated snow melt in the Himalayas and Tibetan Plateau.

Britte reaction of a high-temperature ion melt

NASA Astrophysics Data System (ADS)

Zimanowski, B.; Büttner, R.; Nestler, J.

1997-05-01

An experimental study on explosive interaction between transparent melt (T = 1120 K) and entrapped water (T = 300 K) has been performed. Intense explosions occurred, resulting from catastrophic fragmentation of the melt and increasing heat transfer to the water in a cascading process. In earlier experiments a quasi-isochoric brittle reaction of the melt was identified to be the major explosion mechanism. Using a transparent melt, this brittle reaction could directly be observed by high-speed cinematography. The pictures revealed two fragmentation mechanisms: a) formation of leading cracks (mm to cm scale) due to excess water pressure, and b) slower μm scaled melt fragmentation induced by strain build-up in the melt during rapid cooling.

Experimental program on nucleation and structure in undercooled melts

NASA Technical Reports Server (NTRS)

1982-01-01

Undercooling and structural refinements in droplets of molten metal levitated in an induction field and/or by dispersion in a fluid carrier were studied. Nickel base and lower melting point alloys levitated in molten carrier fluids are considered. The dispersion of molten alloy droplets in a high temperature fluid following the procedures developed by Perepezko and co-workers for lower melting point alloys; obtaining a similar dispersion by room temperature mechanical mixing of particles of the metal and solidified liquid carrier; and solidification of single relatively large droplets in a transparent fluid carrier, enabling high-speed temperature measurement of the recalescence and subsequent cooling behavior are described.

Molecular dynamics simulations of melting and the glass transition of nitromethane.

PubMed

Zheng, Lianqing; Luo, Sheng-Nian; Thompson, Donald L

2006-04-21

Molecular dynamics simulations have been used to investigate the thermodynamic melting point of the crystalline nitromethane, the melting mechanism of superheated crystalline nitromethane, and the physical properties of crystalline and glassy nitromethane. The maximum superheating and glass transition temperatures of nitromethane are calculated to be 316 and 160 K, respectively, for heating and cooling rates of 8.9 x 10(9) Ks. Using the hysteresis method [Luo et al., J. Chem. Phys. 120, 11640 (2004)] and by taking the glass transition temperature as the supercooling temperature, we calculate a value of 251.1 K for the thermodynamic melting point, which is in excellent agreement with the two-phase result [Agrawal et al., J. Chem. Phys. 119, 9617 (2003)] of 255.5 K and measured value of 244.73 K. In the melting process, the nitromethane molecules begin to rotate about their lattice positions in the crystal, followed by translational freedom of the molecules. A nucleation mechanism for the melting is illustrated by the distribution of the local translational order parameter. The critical values of the Lindemann index for the C and N atoms immediately prior to melting (the Lindemann criterion) are found to be around 0.155 at 1 atm. The intramolecular motions and molecular structure of nitromethane undergo no abrupt changes upon melting, indicating that the intramolecular degrees of freedom have little effect on the melting. The thermal expansion coefficient and bulk modulus are predicted to be about two or three times larger in crystalline nitromethane than in glassy nitromethane. The vibrational density of states is almost identical in both phases.

Fast Xe-129 relaxation in solid xenon near its melting point: Cross-over from Raman scattering of phonons to vacancy diffusion.

NASA Astrophysics Data System (ADS)

Kuzma, N. N.; Patton, B.; Raman, K.; Happer, W.

2002-03-01

NMR measurements of longitudinal relaxation times T1 in pure solid xenon were carried out using both natural-abundance and isotopically-enriched samples of hyperpolarized ^129Xe. At temperatures below 120 K and fields above 500 Gauss, the relaxation rate 1/T1 is field- and abundance-independent, consistent with the model of ^129Xe spin-flip Raman scattering of phonons(R. J. Fitzgerald et al.), Phys. Rev. B 59, 8795 (1999).. Above 120 K, vacancies invade the xenon lattice(P. R. Granfors et al.) Phys. Rev. B 24, 4753 (1981)., and a dramatic cross-over to the nuclear dipole-dipole relaxation due to the diffusion of vacancies is observed. As a result, the measured relaxation times of xenon near its melting point strongly depend on field and somewhat on ^129Xe abundance, and can be as short as several seconds, leading to potential difficulties in cryogenic applications of hyperpolarized ^129Xe. The data are analyzed using the theory of nuclear relaxation due to spin diffusion in cubic crystals(C. A. Sholl, J. Phys. C 21), 319 (1988)., and some estimates of the vacancy density and jump rates are discussed.

Controlled Growth of Rubrene Nanowires by Eutectic Melt Crystallization

NASA Astrophysics Data System (ADS)

Chung, Jeyon; Hyon, Jinho; Park, Kyung-Sun; Cho, Boram; Baek, Jangmi; Kim, Jueun; Lee, Sang Uck; Sung, Myung Mo; Kang, Youngjong

2016-03-01

Organic semiconductors including rubrene, Alq3, copper phthalocyanine and pentacene are crystallized by the eutectic melt crystallization. Those organic semiconductors form good eutectic systems with the various volatile crystallizable additives such as benzoic acid, salicylic acid, naphthalene and 1,3,5-trichlorobenzene. Due to the formation of the eutectic system, organic semiconductors having originally high melting point (Tm > 300 °C) are melted and crystallized at low temperature (Te = 40.8-133 °C). The volatile crystallizable additives are easily removed by sublimation. For a model system using rubrene, single crystalline rubrene nanowires are prepared by the eutectic melt crystallization and the eutectic-melt-assisted nanoimpinting (EMAN) technique. It is demonstrated that crystal structure and the growth direction of rubrene can be controlled by using different volatile crystallizable additives. The field effect mobility of rubrene nanowires prepared using several different crystallizable additives are measured and compared.

Partial melting of lower oceanic crust gabbro: Constraints from poikilitic clinopyroxene primocrysts

NASA Astrophysics Data System (ADS)

Leuthold, Julien; Lissenberg, C. Johan; O'Driscoll, Brian; Karakas, Ozge; Falloon, Trevor; Klimentyeva, Dina N.; Ulmer, Peter

2018-03-01

Successive magma batches underplate, ascend, stall and erupt along spreading ridges, building the oceanic crust. It is therefore important to understand the processes and conditions under which magma differentiates at mid ocean ridges. Although fractional crystallization is considered to be the dominant mechanism for magma differentiation, open-system igneous complexes also experience Melting-Assimilation-Storage-Hybridization (MASH, Hildreth and Moorbath, 1988) processes. Here, we examine crystal-scale records of partial melting in lower crustal gabbroic cumulates from the slow-spreading Atlantic oceanic ridge (Kane Megamullion; collected with Jason ROV) and the fast-spreading East Pacific Rise (Hess Deep; IODP expedition 345). Clinopyroxene oikocrysts in these gabbros preserve marked intra-crystal geochemical variations that point to crystallization-dissolution episodes of the gabbro eutectic assemblage. Kane Megamullion and Hess Deep clinopyroxene core1 primocrysts and their plagioclase inclusions indicate crystallization from high temperature basalt (>1160 and >1200°C, respectively), close to clinopyroxene saturation temperature (<50% and <25% crystallization). Step-like compatible Cr (and co-varying Al) and incompatible Ti, Zr, Y and rare earth elements (REE) decrease from anhedral core1 to overgrown core2, while Mg# and Sr/Sr* ratios increase. We show that partial resorption textures and geochemical zoning result from partial melting of REE-poor lower oceanic crust gabbroic cumulate (protolith) following intrusion by hot primitive mantle-derived melt, and subsequent overgrowth crystallization (refertilization) from a hybrid melt. In addition, towards the outer rims of crystals, Ti, Zr, Y and the REE strongly increase and Al, Cr, Mg#, Eu/Eu* and Sr/Sr* decrease, suggesting crystallization either from late-stage percolating relatively differentiated melt or from in situ trapped melt. Intrusion of primitive hot reactive melt and percolation of interstitial

Laser observations of the moon: Normal points for 1973

NASA Technical Reports Server (NTRS)

Mulholland, J. D.; Shelus, P. J.; Silverburg, E. C.

1975-01-01

McDonald Observatory lunar laser ranging observations for 1973 are presented in the form of compressed normal points and amendments for the 1969-1972 data set are given. Observations of the reflector mounted on the Soviet roving vehicle Lunakhod 2 have also been included.

Laser observations of the moon - Normal points for 1973

NASA Technical Reports Server (NTRS)

Mulholland, J. D.; Shelus, P. J.; Silverberg, E. C.

1975-01-01

McDonald Observatory lunar laser-ranging observations for 1973 are presented in the form of compressed normal points, and amendments for the 1969-1972 data set are given. Observations of the reflector mounted on the Soviet roving vehicle Lunakhod 2 have also been included.

Surface Tension and Viscosity of SCN and SCN-acetone Alloys at Melting Points and Higher Temperatures Using Surface Light Scattering Spectrometer

NASA Technical Reports Server (NTRS)

Tin, Padetha; deGroh, Henry C., III.

2003-01-01

Succinonitrile has been and is being used extensively in NASA's Microgravity Materials Science and Fluid Physics programs and as well as in several ground-based and microgravity studies including the Isothermal Dendritic Growth Experiment (IDGE). Succinonitrile (SCN) is useful as a model for the study of metal solidification, although it is an organic material, it has a BCC crystal structure and solidifies dendriticly like a metal. It is also transparent and has a low melting point (58.08 C). Previous measurements of succinonitrile (SCN) and alloys of succinonitrile and acetone surface tensions are extremely limited. Using the Surface Light Scattering technique we have determined non invasively, the surface tension and viscosity of SCN and SCN-Acetone Alloys at different temperatures. This relatively new and unique technique has several advantages over the classical methods such as, it is non invasive, has good accuracy and measures the surface tension and viscosity simultaneously. The accuracy of interfacial energy values obtained from this technique is better than 2% and viscosity about 10 %. Succinonitrile and succinonitrile-acetone alloys are well-established model materials with several essential physical properties accurately known - except the liquid/vapor surface tension at different elevated temperatures. We will be presenting the experimentally determined liquid/vapor surface energy and liquid viscosity of succinonitrile and succinonitrile-acetone alloys in the temperature range from their melting point to around 100 C using this non-invasive technique. We will also discuss about the measurement technique and new developments of the Surface Light Scattering Spectrometer.

Oceans Melting Greenland (OMG): 2017 Observations and the First Look at Yearly Ocean/Ice Changes

NASA Astrophysics Data System (ADS)

Willis, J. K.; Rignot, E. J.; Fenty, I. G.; Khazendar, A.; Moller, D.; Tinto, K. J.; Morison, J.; Schodlok, M.; Thompson, A. F.; Fukumori, I.; Holland, D.; Forsberg, R.; Jakobsson, M.; Dinardo, S. J.

2017-12-01

Oceans Melting Greenland (OMG) is an airborne NASA Mission to investigate the role of the oceans in ice loss around the margins of the Greenland Ice Sheet. A five-year campaign, OMG will directly measure ocean warming and glacier retreat around all of Greenland. By relating these two, we will explore one of the most pressing open questions about how climate change drives sea level rise: How quickly are the warming oceans melting the Greenland Ice Sheet from the edges? This year, OMG collected its second set of both elevation maps of marine terminating glaciers and ocean temperature and salinity profiles around all of Greenland. This give us our first look at year-to-year changes in both ice volume at the margins, as well as the volume and extent of warm, salty Atlantic water present on the continental shelf. In addition, we will compare recent data in east Greenland waters with historical ocean observations that suggest a long-term warming trend there. Finally, we will briefly review the multi-beam sonar and airborne gravity campaigns—both of which were completed last year—and the dramatic improvement they had on bathymetry maps over the continental shelf around Greenland.

Axial vibration control of melt structure of sodium nitrate in crystal growth process

NASA Astrophysics Data System (ADS)

Sadovskiy, Andrey; Sukhanova, Ekaterina; Belov, Stanislav; Kostikov, Vladimir; Zykova, Marina; Artyushenko, Maxim; Zharikov, Evgeny; Avetissov, Igor

2015-05-01

The melt structure evolution under the action of the low-frequency axial vibration control (AVC) technique was studied in situ by Raman spectroscopy for several complex chemical compound melts: sodium nitrate, margarine acid, paraffin mixture (C17-C20). The measurements were conducted in the temperature range from the melting point up to 60 °C above. Comparison of crystallization heats for AVC activated and steady melts with melting heats of AVC-CZ and conventional CZ produced powders allowed to propose the energy diagram of NaNO3 states for activated and non-activated melts and crystals based on DTA, XRD, DSC and Raman experimental data.

Properties of sugar-based low-melting mixtures

NASA Astrophysics Data System (ADS)

Fischer, Veronika; Kunz, Werner

2014-05-01

Physico-chemical properties of ternary sugar-based low-melting mixtures were determined. Choline chloride, urea and glucose or sorbitol, serving as sugars, were blended in various compositions. The refractive index, density, viscosity, decomposition temperatures and glass transition temperatures were measured. Further, the influence of temperature and water content was investigated. The results show that the mixtures are liquid below room temperature and the viscosity and density are dependent on the temperature and composition. Moreover, the viscosity decreases with increasing water content. These mixtures are biodegradable, low toxic, non-volatile, non-reactive with water and can be accomplished with low-cost materials. In consideration of these advantages and a melting point below room temperature, these low-melting mixtures can be a good alternative to ionic liquids as well as environmentally unfriendly and toxic solvents.

Melt Adsorption as a Manufacturing Method for Fine Particles of Wax Matrices without Any Agglomerates.

PubMed

Shiino, Kai; Fujinami, Yukari; Kimura, Shin-Ichiro; Iwao, Yasunori; Noguchi, Shuji; Itai, Shigeru

2017-01-01

We have focused on melt adsorption as manufacture method of wax matrices to control particles size of granules more easily than melt granulation. The purpose of present study was to investigate the possibility of identifying a hydrophobic material with a low melting point, currently used as a meltable binder of melt granulation, to apply as a novel carrier in melt adsorption. Glyceryl monostearate (GM) and stearic acid (SA) were selected as candidate hydrophobic materials with low melting points. Neusilin US2 (US2), with a particle diameter of around 100 µm was selected as a surface adsorbent, while dibasic calcium phosphate dihydrate (DCPD), was used as a non-adsorbent control to prepare melting granules as a standard for comparison. We prepared granules containing ibuprofen (IBU) by melt adsorption or melt granulation and evaluated the particle size, physical properties and crystallinity of granules. Compared with melt granulation using DCPD, melt adsorption can be performed over a wide range of 14 to 70% for the ratio of molten components. Moreover, the particle size; d50 of obtained granules was 100-200 µm, and these physical properties showed good flowability and roundness. The process of melt adsorption did not affect the crystalline form of IBU. Therefore, the present study has demonstrated for the first time that melt adsorption using a hydrophobic material, GM or SA, has the potential capability to control the particle size of granules and offers the possibility of application as a novel controlled release technique.

Formation of melt channels on ice shelves

NASA Astrophysics Data System (ADS)

Sergienko, Olga

2013-04-01

Melt channels have been observed on ice shelves experiencing strong melting in both Greenland (Petermann Glacier) and Antarctica (Pine Island Glacier). Using a fully-couple ice-shelf/sub-ice-shelf-ocean flow model, it is demonstrated that these channels can form spontaneously in laterally confined ice shelves. These channels have transverse extent of a few kilometers and a vertical relief of about a few hundred meters. Meltrates and sea-water transport in the channels are significantly higher than in between the channels on the smooth flat ice bottom. In circumstances where an ice shelf has no-slip conditions at its lateral boundaries, the ice-shelf/sub-ice-shelf-cavity system exhibits equilibrium periodic states, where the same configurations repetitively appear with a periodicity of about 30-35 years. This peculiar dynamics of the system has strong implications on the interpretation of the remote and in-situ observations and inferences of the system parameters (e.g., melt rates) based on these observations. For instance, the persistent temporal changes in the ice-shelf thickness are caused by internal dynamics of the melt channels, and, in contrast to traditional interpretation, can be independent of the oceanic forcings.

Experimental research of phase transitions in a melt of high-purity aluminum

NASA Astrophysics Data System (ADS)

Vorontsov, V. B.; Pershin, V. K.

2017-12-01

This scientific work is devoted to the studying of the genetic connection structures of solid and liquid phases. In this paper Fourier analysis of acoustic emission (AE) signals accompanying heating of high purity aluminum from the melting point up to 860 °C was performed. The experimental data allowed to follow the dynamics of disorder zones in the melt with increasing melt temperature up to their complete destruction. The presented results of spectral analysis of the signals were analyzed from the standpoint of the theory of cluster melting metals.

Volatile loss during homogenization of lunar melt inclusions

NASA Astrophysics Data System (ADS)

Ni, Peng; Zhang, Youxue; Guan, Yunbin

2017-11-01

Volatile abundances in lunar mantle are critical factors to consider for constraining the model of Moon formation. Recently, the earlier understanding of a ;dry; Moon has shifted to a fairly ;wet; Moon due to the detection of measurable amount of H2O in lunar volcanic glass beads, mineral grains, and olivine-hosted melt inclusions. The ongoing debate on a ;dry; or ;wet; Moon requires further studies on lunar melt inclusions to obtain a broader understanding of volatile abundances in the lunar mantle. One important uncertainty for lunar melt inclusion studies, however, is whether the homogenization of melt inclusions would cause volatile loss. In this study, a series of homogenization experiments were conducted on olivine-hosted melt inclusions from the sample 74220 to evaluate the possible loss of volatiles during homogenization of lunar melt inclusions. Our results suggest that significant loss of H2O could occur even during minutes of homogenization, while F, Cl and S in the inclusions remain unaffected. We model the trend of H2O loss in homogenized melt inclusions by a diffusive hydrogen loss model. The model can reconcile the observed experimental data well, with a best-fit H diffusivity in accordance with diffusion data explained by the ;slow; mechanism for hydrogen diffusion in olivine. Surprisingly, no significant effect for the low oxygen fugacity on the Moon is observed on the diffusive loss of hydrogen during homogenization of lunar melt inclusions under reducing conditions. Our experimental and modeling results show that diffusive H loss is negligible for melt inclusions of >25 μm radius. As our results mitigate the concern of H2O loss during homogenization for crystalline lunar melt inclusions, we found that H2O/Ce ratios in melt inclusions from different lunar samples vary with degree of crystallization. Such a variation is more likely due to H2O loss on the lunar surface, while heterogeneity in their lunar mantle source is also a possibility. A

Using Paraffin with -10 deg C to 10 deg C Melting Point for Payload Thermal Energy Storage in SpaceX Dragon Trunk

NASA Technical Reports Server (NTRS)

Choi, Michael K.

2013-01-01

A concept of using paraffin wax phase change material (PCM) with a melting point between -10 deg C and 10 deg C for payload thermal energy storage in a Space Exploration Technologies (SpaceX) Dragon trunk is presented. It overcomes the problem of limited heater power available to a payload with significant radiators when the Dragon is berthed to the International Space Station (ISS). It stores adequate thermal energy to keep a payload warm without power for 6 hours during the transfer from the Dragon to an ExPRESS logistics carrier (ELC) on the ISS.

Simultaneous feature selection and parameter optimisation using an artificial ant colony: case study of melting point prediction

PubMed Central

O'Boyle, Noel M; Palmer, David S; Nigsch, Florian; Mitchell, John BO

2008-01-01

Background We present a novel feature selection algorithm, Winnowing Artificial Ant Colony (WAAC), that performs simultaneous feature selection and model parameter optimisation for the development of predictive quantitative structure-property relationship (QSPR) models. The WAAC algorithm is an extension of the modified ant colony algorithm of Shen et al. (J Chem Inf Model 2005, 45: 1024–1029). We test the ability of the algorithm to develop a predictive partial least squares model for the Karthikeyan dataset (J Chem Inf Model 2005, 45: 581–590) of melting point values. We also test its ability to perform feature selection on a support vector machine model for the same dataset. Results Starting from an initial set of 203 descriptors, the WAAC algorithm selected a PLS model with 68 descriptors which has an RMSE on an external test set of 46.6°C and R2 of 0.51. The number of components chosen for the model was 49, which was close to optimal for this feature selection. The selected SVM model has 28 descriptors (cost of 5, ε of 0.21) and an RMSE of 45.1°C and R2 of 0.54. This model outperforms a kNN model (RMSE of 48.3°C, R2 of 0.47) for the same data and has similar performance to a Random Forest model (RMSE of 44.5°C, R2 of 0.55). However it is much less prone to bias at the extremes of the range of melting points as shown by the slope of the line through the residuals: -0.43 for WAAC/SVM, -0.53 for Random Forest. Conclusion With a careful choice of objective function, the WAAC algorithm can be used to optimise machine learning and regression models that suffer from overfitting. Where model parameters also need to be tuned, as is the case with support vector machine and partial least squares models, it can optimise these simultaneously. The moving probabilities used by the algorithm are easily interpreted in terms of the best and current models of the ants, and the winnowing procedure promotes the removal of irrelevant descriptors. PMID:18959785

Simultaneous feature selection and parameter optimisation using an artificial ant colony: case study of melting point prediction.

PubMed

O'Boyle, Noel M; Palmer, David S; Nigsch, Florian; Mitchell, John Bo

2008-10-29

We present a novel feature selection algorithm, Winnowing Artificial Ant Colony (WAAC), that performs simultaneous feature selection and model parameter optimisation for the development of predictive quantitative structure-property relationship (QSPR) models. The WAAC algorithm is an extension of the modified ant colony algorithm of Shen et al. (J Chem Inf Model 2005, 45: 1024-1029). We test the ability of the algorithm to develop a predictive partial least squares model for the Karthikeyan dataset (J Chem Inf Model 2005, 45: 581-590) of melting point values. We also test its ability to perform feature selection on a support vector machine model for the same dataset. Starting from an initial set of 203 descriptors, the WAAC algorithm selected a PLS model with 68 descriptors which has an RMSE on an external test set of 46.6 degrees C and R2 of 0.51. The number of components chosen for the model was 49, which was close to optimal for this feature selection. The selected SVM model has 28 descriptors (cost of 5, epsilon of 0.21) and an RMSE of 45.1 degrees C and R2 of 0.54. This model outperforms a kNN model (RMSE of 48.3 degrees C, R2 of 0.47) for the same data and has similar performance to a Random Forest model (RMSE of 44.5 degrees C, R2 of 0.55). However it is much less prone to bias at the extremes of the range of melting points as shown by the slope of the line through the residuals: -0.43 for WAAC/SVM, -0.53 for Random Forest. With a careful choice of objective function, the WAAC algorithm can be used to optimise machine learning and regression models that suffer from overfitting. Where model parameters also need to be tuned, as is the case with support vector machine and partial least squares models, it can optimise these simultaneously. The moving probabilities used by the algorithm are easily interpreted in terms of the best and current models of the ants, and the winnowing procedure promotes the removal of irrelevant descriptors.

The surface morphology of crystals melting under solutions of different densities

NASA Technical Reports Server (NTRS)

Fang, Dacheng; Hellawell, A.

1988-01-01

Examples of solids melting beneath liquids are described for cases where the bulk liquid volume is stabilized against convection by a positive vertical temperature gradient, either with, or without local density inversion at the melting interface. The examples include ice melting beneath brine or methanol solutions and tin or lead melting under molten Sn-20 wt pct Pb or Pb-20 wt pct Sn, respectively. Without density inversion the melting is slow, purely diffusion controlled and the interfaces are smooth; with convection assisted melting the rate increases by some two orders of magnitude and the interfaces develop a rough profile - in the case of ice both irregular and quasi-steady state features are observed. The observations are discussed in terms of prevailing temperature and concentration gradients.

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

NASA Astrophysics Data System (ADS)

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

2014-10-01

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

Critical porosity of melt segregation during crustal melting: Constraints from zonation of peritectic garnets in a dacite volcano

NASA Astrophysics Data System (ADS)

Yu, Xun; Lee, Cin-Ty A.

2016-09-01

The presence of leucogranitic dikes in orogenic belts suggests that partial melting may be an important process in the lower crust of active orogenies. Low seismic velocity and low electrical resistivity zones have been observed in the lower crust of active mountain belts and have been argued to reflect the presence of partial melt in the deep crust, but volcanoes are rare or absent above many of these inferred melt zones. Understanding whether these low velocity zones are melt-bearing, and if so, why they do not commonly erupt, is essential for understanding the thermal and rheologic structure of the crust and its dynamic evolution. Central to this problem is an understanding of how much melt can be stored before it can escape from the crust via compaction and eventually erupt. Experimental and theoretical studies predict trapped melt fractions anywhere from <5% to >30%. Here, we examine Mn growth-zoning in peritectic garnets in a Miocene dacite volcano from the ongoing Betic-Rif orogeny in southern Spain to estimate the melt fraction at the time of large-scale melt extraction that subsequently led to eruption. We show that the melt fraction at segregation, corresponding approximately to the critical melt porosity, was ∼30%, implying significant amounts of melt can be stored in the lower crust without draining or erupting. However, seismic velocities in the lower crust beneath active orogenic belts (southern Spain and Tibet) as well as beneath active magmatic zones (e.g., Yellowstone hotspot) correspond to average melt porosities of <10%, suggesting that melt porosities approaching critical values are short-lived or that high melt porosity regions are localized into heterogeneously distributed sills or dikes, which individually cannot be resolved by seismic studies.

Basal terraces on melting ice shelves

NASA Astrophysics Data System (ADS)

Dutrieux, Pierre; Stewart, Craig; Jenkins, Adrian; Nicholls, Keith W.; Corr, Hugh F. J.; Rignot, Eric; Steffen, Konrad

2014-08-01

Ocean waters melt the margins of Antarctic and Greenland glaciers, and individual glaciers' responses and the integrity of their ice shelves are expected to depend on the spatial distribution of melt. The bases of the ice shelves associated with Pine Island Glacier (West Antarctica) and Petermann Glacier (Greenland) have similar geometries, including kilometer-wide, hundreds-of-meter high channels oriented along and across the direction of ice flow. The channels are enhanced by, and constrain, oceanic melt. New meter-scale observations of basal topography reveal peculiar glaciated landscapes. Channel flanks are not smooth, but are instead stepped, with hundreds-of-meters-wide flat terraces separated by 5-50 m high walls. Melting is shown to be modulated by the geometry: constant across each terrace, changing from one terrace to the next, and greatly enhanced on the ~45° inclined walls. Melting is therefore fundamentally heterogeneous and likely associated with stratification in the ice-ocean boundary layer, challenging current models of ice shelf-ocean interactions.

Basal Terraces on Melting Ice Shelves

NASA Astrophysics Data System (ADS)

Dutrieux, P.; Stewart, C.; Jenkins, A.; Nicholls, K. W.; Corr, H. F. J.; Rignot, E. J.; Steffen, K.

2014-12-01

Ocean waters melt the margins of Antarctic and Greenland glaciers and individualglaciers' responses and the integrity of their ice shelves are expected to depend on thespatial distribution of melt. The bases of the ice shelves associated with Pine IslandGlacier (West Antarctica) and Petermann Glacier (Greenland) have similar geometries,including kilometers-wide, hundreds-of-meter-high channels oriented along and acrossthe direction of ice flow. The channels are enhanced by, and constrain, oceanic melt.New, meter-scale observations of basal topography reveal peculiar glaciated landscapes.Channel flanks are not smooth, but are instead stepped, with hundreds-of-meters-wideflat terraces separated by 5-50 m-high walls. Melting is shown to be modulated by thegeometry: constant across each terrace, changing from one terrace to the next, and greatlyenhanced on the ~45°-inclined walls. Melting is therefore fundamentally heterogeneousand likely associated with stratification in the ice-ocean boundary layer, challengingcurrent models of ice shelf-ocean interactions.

New Equations for the Sublimation Pressure and Melting Pressure of H2O Ice Ih

NASA Astrophysics Data System (ADS)

Wagner, Wolfgang; Riethmann, Thomas; Feistel, Rainer; Harvey, Allan H.

2011-12-01

New reference equations, adopted by the International Association for the Properties of Water and Steam (IAPWS), are presented for the sublimation pressure and melting pressure of ice Ih as a function of temperature. These equations are based on input values derived from the phase-equilibrium condition between the IAPWS-95 scientific standard for thermodynamic properties of fluid H2O and the equation of state of H2O ice Ih adopted by IAPWS in 2006, making them thermodynamically consistent with the bulk-phase properties. Compared to the previous IAPWS formulations, which were empirical fits to experimental data, the new equations have significantly less uncertainty. The sublimation-pressure equation covers the temperature range from 50 K to the vapor-liquid-solid triple point at 273.16 K. The ice Ih melting-pressure equation describes the entire melting curve from 273.16 K to the ice Ih-ice III-liquid triple point at 251.165 K. For completeness, we also give the IAPWS melting-pressure equation for ice III, which is slightly adjusted to agree with the ice Ih melting-pressure equation at the corresponding triple point, and the unchanged IAPWS melting-pressure equations for ice V, ice VI, and ice VII.

Melt structure and self-nucleation of ethylene copolymers

NASA Astrophysics Data System (ADS)

Alamo, Rufina G.

A strong memory effect of crystallization has been observed in melts of random ethylene copolymers well above the equilibrium melting temperature. These studies have been carried out by DSC, x-ray, TEM and optical microscopy on a large number of model, narrow, and broad copolymers with different comonomer types and contents. Melt memory is correlated with self-seeds that increase the crystallization rate of ethylene copolymers. The seeds are associated with molten ethylene sequences from the initial crystals that remain in close proximity and lower the nucleation barrier. Diffusion of all sequences to a randomized melt state is a slow process, restricted by topological chain constraints (loops, knots, and other entanglements) that build in the intercrystalline region during crystallization. Self-seeds dissolve above a critical melt temperature that demarcates homogeneity of the copolymer melt. There is a critical threshold level of crystallinity to observe the effect of melt memory on crystallization rate, thus supporting the correlation between melt memory and the change in melt structure during copolymer crystallization. Unlike binary blends, commercial ethylene-1-alkene copolymers with a range in inter-chain comonomer composition between 1 and about 15 mol % display an inversion of the crystallization rate in a range of melt temperatures where narrow copolymers show a continuous acceleration of the rate. With decreasing the initial melt temperature, broadly distributed copolymers show enhanced crystallization followed by a decrease of crystallization rate. The inversion demarcates the onset of liquid-liquid phase separation (LLPS) and a reduction of self-nuclei due to the strong thermodynamic drive for molecular segregation inside the binodal. The strong effect of melt memory on crystallization rate can be used to identify liquid-liquid phase separation in broadly distributed copolymers, and offers strategies to control the state of copolymer melts in ways of

Solidus and liquidus profiles of chondritic mantle: Implication for melting of the Earth across its history

NASA Astrophysics Data System (ADS)

Andrault, Denis; Bolfan-Casanova, Nathalie; Nigro, Giacomo Lo; Bouhifd, Mohamed A.; Garbarino, Gaston; Mezouar, Mohamed

2011-04-01

We investigated the melting properties of a synthetic chondritic primitive mantle up to core-mantle boundary (CMB) pressures, using laser-heated diamond anvil cell. Melting criteria are essentially based on the use of X-rays provided by synchrotron radiation. We report a solidus melting curve lower than previously determined using optical methods. The liquidus curve is found between 300 and 600 K higher than the solidus over the entire lower mantle. At CMB pressures (135 GPa), the chondritic mantle solidus and liquidus reach 4150 (± 150) K and 4725 (± 150) K, respectively. We discuss that the lower mantle is unlikely to melt in the D″-layer, except if the highest estimate of the temperature profile at the base of the mantle, which is associated with a very hot core, is confirmed. Therefore, recent suggestions of partial melting in the lowermost mantle based on seismic observations of ultra-low velocity zones indicate either (1) a outer core exceeding 4150 K at the CMB or (2) the presence of chemical heterogeneities with high concentration of fusible elements. Our observations of a high liquidus temperature as well as a large gap between solidus and liquidus temperatures have important implications for the properties of the magma ocean during accretion. Not only complete melting of the lower mantle would require excessively high temperatures, but also, below liquidus temperatures partial melting should take place over a much larger depth interval than previously thought. In addition, magma adiabats suggest very high surface temperatures in case of a magma ocean that would extend to more than 40 GPa, as suggested by siderophile metal-silicate partitioning data. Such high surface temperature regime, where thermal blanketing is inefficient, points out to a transient character of the magma ocean, with a very fast cooling rate.

Fatigue behavior of porous biomaterials manufactured using selective laser melting.

PubMed

Yavari, S Amin; Wauthle, R; van der Stok, J; Riemslag, A C; Janssen, M; Mulier, M; Kruth, J P; Schrooten, J; Weinans, H; Zadpoor, A A

2013-12-01

Porous titanium alloys are considered promising bone-mimicking biomaterials. Additive manufacturing techniques such as selective laser melting allow for manufacturing of porous titanium structures with a precise design of micro-architecture. The mechanical properties of selective laser melted porous titanium alloys with different designs of micro-architecture have been already studied and are shown to be in the range of mechanical properties of bone. However, the fatigue behavior of this biomaterial is not yet well understood. We studied the fatigue behavior of porous structures made of Ti6Al4V ELI powder using selective laser melting. Four different porous structures were manufactured with porosities between 68 and 84% and the fatigue S-N curves of these four porous structures were determined. The three-stage mechanism of fatigue failure of these porous structures is described and studied in detail. It was found that the absolute S-N curves of these four porous structures are very different. In general, given the same absolute stress level, the fatigue life is much shorter for more porous structures. However, the normalized fatigue S-N curves of these four structures were found to be very similar. A power law was fitted to all data points of the normalized S-N curves. It is shown that the measured data points conform to the fitted power law very well, R(2)=0.94. This power law may therefore help in estimating the fatigue life of porous structures for which no fatigue test data is available. It is also observed that the normalized endurance limit of all tested porous structures (<0.2) is lower than that of corresponding solid material (c.a. 0.4). © 2013.

Melting behavior of Earth's lower mantle minerals at high pressures

NASA Astrophysics Data System (ADS)

Fu, S.; Yang, J.; Prakapenka, V. B.; Zhang, Y.; Greenberg, E.; Lin, J. F.

2017-12-01

Melting behavior of the most abundant lower mantle minerals, bridgmanite and ferropericlase, at high pressure-temperature (P-T) conditions is of critical importance to understand the dynamic evolution of the early Earth and to explain the seismological and geochemical signatures in the present lowermost mantle. Theoretical calculations [1] and geodynamical models [2] suggested that partial melting of early Earth among MgO-FeO-SiO2 ternary could be located at the eutectic point where a pyrolitic composition formed for the Earth's lower mantle and the eutectic crystallization process could provide a plausible mechanism to the origin of the ultra-low velocity zones (ULVZs) near the core-mantle boundary. Here we have investigated the melting behavior of ferropericlase and Al,Fe-bearing bridgmanite in laser-heated diamond anvil cells coupled with in situ X-ray diffraction up to 120 GPa. Together with chemical and texture characterizations of the quenched samples, these results are analyzed using thermodynamic models to address the effects of iron on the liquidus and solidus temperatures as well as solid-liquid iron partitioning and the eutectic point in ferropericlase-bridgmanite existing system at lower-mantle pressure. In this presentation, we discuss the application of these results to better constrain the seismic observations of the deep lowermost mantle such as large low shear wave velocity provinces (LLSVPs) and ULVZs. We will also discuss the geochemical consequences of the ferropericlase-bridgmanite melting due to the changes in the electronic spin and valence states of iron in the system. ADDIN EN.REFLIST 1. Boukaré, C.E., Y. Ricard, and G. Fiquet, Thermodynamics of the MgO-FeO-SiO2 system up to 140 GPa: Application to the crystallization of Earth's magma ocean. Journal of Geophysical Research: Solid Earth, 2015. 120(9): p. 6085-6101. 2. Labrosse, S., J. Hernlund, and N. Coltice, A crystallizing dense magma ocean at the base of the Earth's mantle. Nature, 2007

Molecular Dynamics Simulations of Shock Wave Propagation across the Nitromethane Crystal-Melt Interface

NASA Astrophysics Data System (ADS)

Jiang, Shan; Sewell, Thomas D.; Thompson, Donald L.

2015-06-01

We are interested in understanding the fundamental processes that occur during propagation of shock waves across the crystal-melt interface in molecular substances. We have carried out molecular dynamics simulations of shock passage from the nitromethane (100)-oriented crystal into the melt and vice versa using the fully flexible, non-reactive Sorescu, Rice, and Thompson force field. A stable interface was established for a temperature near the melting point by using a combination of isobaric-isothermal (NPT) and isochoric-isothermal (NVT) simulations. The equilibrium bulk and interfacial regions were characterized using spatial-temporal distributions of molecular number density, kinetic and potential energy, and C-N bond orientations. Those same properties were calculated as functions of time during shock propagation. As expected, the local temperatures (intermolecular, intramolecular, and total) and stress states differed significantly between the liquid and crystal regions and depending on the direction of shock propagation. Substantial differences in the spatial distribution of shock-induced defect structures in the crystalline region were observed depending on the direction of shock propagation. Research supported by the U.S. Army Research Office.

Terrestrial analogues for lunar impact melt flows

NASA Astrophysics Data System (ADS)

Neish, C. D.; Hamilton, C. W.; Hughes, S. S.; Nawotniak, S. Kobs; Garry, W. B.; Skok, J. R.; Elphic, R. C.; Schaefer, E.; Carter, L. M.; Bandfield, J. L.; Osinski, G. R.; Lim, D.; Heldmann, J. L.

2017-01-01

Lunar impact melt deposits have unique physical properties. They have among the highest observed radar returns at S-Band (12.6 cm wavelength), implying that they are rough at the decimeter scale. However, they are also observed in high-resolution optical imagery to be quite smooth at the meter scale. These characteristics distinguish them from well-studied terrestrial analogues, such as Hawaiian pāhoehoe and ´a´ā lava flows. The morphology of impact melt deposits can be related to their emplacement conditions, so understanding the origin of these unique surface properties will help to inform us as to the circumstances under which they were formed. In this work, we seek to find a terrestrial analogue for well-preserved lunar impact melt flows by examining fresh lava flows on Earth. We compare the radar return and high-resolution topographic variations of impact melt flows to terrestrial lava flows with a range of surface textures. The lava flows examined in this work range from smooth Hawaiian pāhoehoe to transitional basaltic flows at Craters of the Moon (COTM) National Monument and Preserve in Idaho to rubbly and spiny pāhoehoe-like flows at the recent eruption at Holuhraun in Iceland. The physical properties of lunar impact melt flows appear to differ from those of all the terrestrial lava flows studied in this work. This may be due to (a) differences in post-emplacement modification processes or (b) fundamental differences in the surface texture of the melt flows due to the melts' unique emplacement and/or cooling environment. Information about the surface properties of lunar impact melt deposits will be critical for future landed missions that wish to sample these materials.

Direct Observation of Pore Formation and Bubble Mobility during Controlled Melting and Resolidification in Microgravity

NASA Technical Reports Server (NTRS)

Grugel, Richard N.; Anilkumar, A. V.; Lee, C. P.

2004-01-01

Detailed studies on the controlled melting and subsequent re-solidification of succinonitrile were conducted in the microgravity environment aboard the International Space Station (ISS) using the PFMI apparatus (Pore Formation and Mobility Investigation) located in the ISS glovebox facility (GBX). Samples were initially prepared on ground by filling glass tubes, 1 cm ID and approximately 30 cm in length, with pure succinonitrile (SCN) under 450 millibar of nitrogen. During Space processing, experimental parameters like temperature gradient and translation speed, for melting and solidification, were remotely monitored and controlled from the ground Telescience Center (TSC) at the Marshall Space Flight Center. Real time visualization during controlled melting revealed bubbles of different sizes initiating at the solid/liquid interface, and traveling up the temperature gradient ahead of them. Subsequent controlled re-solidification of the SCN revealed the details of porosity formation and evolution. A preliminary analysis of the melt back and re- solidification and its implications to future microgravity materials processing is presented and discussed.

Melting of KCl and pressure calibration from in situ ionic conductivity measurements in a multi-anvil apparatus

NASA Astrophysics Data System (ADS)

Li, J.; Dong, J.; Zhu, F.

2017-12-01

Melting plays an unparalleled role in planetary differentiation processes including the formation of metallic cores, basaltic crusts, and atmospheres. Knowledge of the melting behavior of Earth materials provides critical constraints for establishing the Earth's thermal structure, interpreting regional seismic anomalies, and understanding the nature of chemical heterogeneity. Measuring the melting points of compressed materials, however, have remained challenging mainly because melts are often mobile and reactive, and temperature and pressure gradients across millimeter or micron-sized samples introduce large uncertainties in melting detection. Here the melting curve of KCl was determined through in situ ionic conductivity measurements, using the multi-anvil apparatus at the University of Michigan. The method improves upon the symmetric configuration that was used recently for studying the melting behaviors of NaCl, Na2CO3, and CaCO3 (Li and Li 2015 American Mineralogist, Li et al. 2017 Earth and Planetary Science Letters). In the new configuration, the thermocouple and electrodes are placed together with the sample at the center of a cylindrical heater where the temperature is the highest along the axis, in order to minimize uncertainties in temperature measurements and increase the stability of the sample and electrodes. With 1% reproducibility in melting point determination at pressures up to 20 GPa, this method allows us to determine the sample pressure to oil load relationship at high temperatures during multiple heating and cooling cycles, on the basis of the well-known melting curves of ionic compounds. This approach enables more reliable pressure measurements than relying on a small number of fixed-point phase transitions. The new data on KCl bridge the gap between the piston-cylinder results up to 4 GPa (Pistorius 1965 J. of Physics and Chemistry of Solids) and several diamond-anvil cell data points above 20 GPa (Boehler et al. 1996 Physical Review). We

Convective melting in a magma chamber: theory and numerical experiment.

NASA Astrophysics Data System (ADS)

Simakin, A.

2012-04-01

We present results of the numerical modeling of convective melting in a magma chamber in 2D. Model was pointed on the silicic system approximated with Qz-Fsp binary undersaturated with water. Viscosity was calculated as a function of the melt composition, temperature and crystal content and comprises for the pure melt 104.5-105.5 Pas. Lower boundary was taken thermally insulated in majority of the runs. Size of FEM (bilinear elements) grid for velocity is 25x25 cm and for the integration of the density term 8x8 cm. Melting of the chamber roof proceeds with the heat supply due to the chaotic thermo-compositional convection and conductive heat loose into melted substrate. We compare our numerical data with existing semi-analytical models. Theoretical studies of the assimilation rates in the magma chambers usually use theoretical semi-analytical model by Huppert and Sparks (1988) (e.g., Snyder, 2000). We find that this model has strong points: 1) Independence of the melting rate on the sill thickness (Ra>>Rac) 2) Independence of the convective heat transfer on the roof temperature 3) Determination of the exponential thermal boundary layer ahead of the melting front and weak points: 1) Ignoring the possibility of the crystallization without melting regime for narrow sills and dykes. 2)Neglecting of two-phase character of convection. 3)Ignoring of the strong viscosity variation near the melting front. Independence of convective flux from the sill size (at Ra>>Rac) allows reducing of computational domain to the geologically small size (10-15 m). Concept of exponential thermal boundary layer is also rather important. Length scale (L0) of this layer is related to the melting rate and thermal diffusivity coefficient kT as L0=kT/um and at the melting rate 10 m/yr becomes about 2 m. Such small scale implies that convective melting is very effective (small conductive heat loss) and part of the numerical domain filled with roof rocks can be taken small. In the H&S model

New Observations of Subarcsecond Photospheric Bright Points

NASA Technical Reports Server (NTRS)

Berger, T. E.; Schrijver, C. J.; Shine, R. A.; Tarbell, T. D.; Title, A. M.; Scharmer, G.

1995-01-01

We have used an interference filter centered at 4305 A within the bandhead of the CH radical (the 'G band') and real-time image selection at the Swedish Vacuum Solar Telescope on La Palma to produce very high contrast images of subarcsecond photospheric bright points at all locations on the solar disk. During the 6 day period of 1993 September 15-20 we observed active region NOAA 7581 from its appearance on the East limb to a near-disk-center position on September 20. A total of 1804 bright points were selected for analysis from the disk center image using feature extraction image processing techniques. The measured Full Width at Half Maximum (FWHM) distribution of the bright points in the image is lognormal with a modal value of 220 km (0 sec .30) and an average value of 250 km (0 sec .35). The smallest measured bright point diameter is 120 km (0 sec .17) and the largest is 600 km (O sec .69). Approximately 60% of the measured bright points are circular (eccentricity approx. 1.0), the average eccentricity is 1.5, and the maximum eccentricity corresponding to filigree in the image is 6.5. The peak contrast of the measured bright points is normally distributed. The contrast distribution variance is much greater than the measurement accuracy, indicating a large spread in intrinsic bright-point contrast. When referenced to an averaged 'quiet-Sun' area in the image, the modal contrast is 29% and the maximum value is 75%; when referenced to an average intergranular lane brightness in the image, the distribution has a modal value of 61% and a maximum of 119%. The bin-averaged contrast of G-band bright points is constant across the entire measured size range. The measured area of the bright points, corrected for pixelation and selection effects, covers about 1.8% of the total image area. Large pores and micropores occupy an additional 2% of the image area, implying a total area fraction of magnetic proxy features in the image of 3.8%. We discuss the implications of this

New Observations of Subarcsecond Photospheric Bright Points

NASA Technical Reports Server (NTRS)

Berger, T. E.; Schrijver, C. J.; Shine, R. A.; Tarbell, T. D.; Title, A. M.; Scharmer, G.

1995-01-01

We have used an interference filter centered at 4305 A within the bandhead of the CH radical (the 'G band') and real-time image selection at the Swedish Vacuum Solar Telescope on La Palma to produce very high contrast images of subarcsecond photospheric bright points at all locations on the solar disk. During the 6 day period of 15-20 Sept. 1993 we observed active region NOAA 7581 from its appearance on the East limb to a near-disk-center position on 20 Sept. A total of 1804 bright points were selected for analysis from the disk center image using feature extraction image processing techniques. The measured FWHM distribution of the bright points in the image is lognormal with a modal value of 220 km (0.30 sec) and an average value of 250 km (0.35 sec). The smallest measured bright point diameter is 120 km (0.17 sec) and the largest is 600 km (O.69 sec). Approximately 60% of the measured bright points are circular (eccentricity approx. 1.0), the average eccentricity is 1.5, and the maximum eccentricity corresponding to filigree in the image is 6.5. The peak contrast of the measured bright points is normally distributed. The contrast distribution variance is much greater than the measurement accuracy, indicating a large spread in intrinsic bright-point contrast. When referenced to an averaged 'quiet-Sun' area in the image, the modal contrast is 29% and the maximum value is 75%; when referenced to an average intergranular lane brightness in the image, the distribution has a modal value of 61% and a maximum of 119%. The bin-averaged contrast of G-band bright points is constant across the entire measured size range. The measured area of the bright points, corrected for pixelation and selection effects, covers about 1.8% of the total image area. Large pores and micropores occupy an additional 2% of the image area, implying a total area fraction of magnetic proxy features in the image of 3.8%. We discuss the implications of this area fraction measurement in the context of

Selective Laser Melting of Pure Copper

NASA Astrophysics Data System (ADS)

Ikeshoji, Toshi-Taka; Nakamura, Kazuya; Yonehara, Makiko; Imai, Ken; Kyogoku, Hideki

2017-12-01

Appropriate building parameters for selective laser melting of 99.9% pure copper powder were investigated at relatively high laser power of 800 W for hatch pitch in the range from 0.025 mm to 0.12 mm. The highest relative density of the built material was 99.6%, obtained at hatch pitch of 0.10 mm. Building conditions were also studied using transient heat analysis in finite element modeling of the liquidation and solidification of the powder layer. The estimated melt pool length and width were comparable to values obtained by observations using a thermoviewer. The trend for the melt pool width versus the hatch pitch agreed with experimental values.

Selective Laser Melting of Pure Copper

NASA Astrophysics Data System (ADS)

Ikeshoji, Toshi-Taka; Nakamura, Kazuya; Yonehara, Makiko; Imai, Ken; Kyogoku, Hideki

2018-03-01

Appropriate building parameters for selective laser melting of 99.9% pure copper powder were investigated at relatively high laser power of 800 W for hatch pitch in the range from 0.025 mm to 0.12 mm. The highest relative density of the built material was 99.6%, obtained at hatch pitch of 0.10 mm. Building conditions were also studied using transient heat analysis in finite element modeling of the liquidation and solidification of the powder layer. The estimated melt pool length and width were comparable to values obtained by observations using a thermoviewer. The trend for the melt pool width versus the hatch pitch agreed with experimental values.

A Mathematical Model of Melt Lake Development on an Ice Shelf

NASA Astrophysics Data System (ADS)

Buzzard, S. C.; Feltham, D. L.; Flocco, D.

2018-02-01

The accumulation of surface meltwater on ice shelves can lead to the formation of melt lakes. Melt lakes have been implicated in ice shelf collapse; Antarctica's Larsen B Ice Shelf was observed to have a large amount of surface melt lakes present preceding its collapse in 2002. Such collapse can affect ocean circulation and temperature, cause habitat loss and contribute to sea level rise through the acceleration of tributary glaciers. We present a mathematical model of a surface melt lake on an idealized ice shelf. The model incorporates a calculation of the ice shelf surface energy balance, heat transfer through the firn, the production and percolation of meltwater into the firn, the formation of ice lenses, and the development and refreezing of surface melt lakes. The model is applied to the Larsen C Ice Shelf, where melt lakes have been observed. This region has warmed several times the global average over the last century and the Larsen C firn layer could become saturated with meltwater by the end of the century. When forced with weather station data, our model produces surface melting, meltwater accumulation, and melt lake development consistent with observations. We examine the sensitivity of lake formation to uncertain parameters and provide evidence of the importance of processes such as lateral meltwater transport. We conclude that melt lakes impact surface melt and firn density and warrant inclusion in dynamic-thermodynamic models of ice shelf evolution within climate models, of which our model could form the basis for the thermodynamic component.

Molecular dynamics study of melting and fcc-bcc transitions in Xe.

PubMed

Belonoshko, A B; Ahuja, R; Johansson, B

2001-10-15

We have investigated the phase diagram of Xe over a wide pressure-temperature range by molecular dynamics. The calculated melting curve is in good agreement with earlier experimental data. At a pressure of around 25 GPa and a temperature of about 2700 K we find a triple fcc-bcc liquid point. The calculated fcc-bcc boundary is in nice agreement with the experimental points, which, however, were interpreted as melting. This finding suggests that the transition from close-packed to bcc structure might be more common at high pressure and high temperature than was previously anticipated.

The melting curve of Ni to 125 GPa: implications for Earth's Fe rich core alloy

NASA Astrophysics Data System (ADS)

Lord, O. T.; Wood, I. G.; Dobson, D. P.; Vocadlo, L.; Thomson, A. R.; Wann, E.; Wang, W.; Edgington, A.; Morard, G.; Mezouar, N.; Walter, M. J.

2014-12-01

The melting curve of Ni has been determined to 125 GPa using laser-heated diamond anvil cell (LH-DAC) experiments and two melting criteria: the appearance of liquid diffuse scattering (LDS) during in situ X-ray diffraction (XRD) and simultaneous plateaux in temperature vs. laser power functions [1]. Our melting curve (Fig. 1) is in good agreement with most theoretical studies [e.g. 2] and the available shock wave data (Fig. 2). It is, however, dramatically steeper than the previous off-line LH-DAC studies in which the determination of melting was based on the visual observation of motion aided by the laser speckle method [e.g. 3]. We estimate the melting point of Ni at the inner-core boundary (ICB; 330 GPa) to be 5800±700 K (2σ), ~2500 K higher than the estimate based on the laser speckle method [3] and within error of Fe (6230±500 K) as determined in a similar in situ LH-DAC study [4]. We find that laser speckle based melting curves coincide with the onset of rapid sub-solidus recrystallization, suggesting that visual observations of motion may have misinterpreted dynamic recrystallization as melt convection. Our new melting curve suggests that the reduction in ICB temperature due to the alloying of Ni with Fe is likely to be significantly smaller than would be expected had the earlier experimental Ni melting studies been correct. We have applied our methodology to a range of other transition metals (Mo, Ti, V, Cu). In the case of Mo, Ti and V the melting curves are in good agreement with the shock compression and theoretical melting studies but hotter and steeper than those based on the laser speckle method, as with Ni. Cu is an exception in which all studies agree, including those employing the laser speckle method. These results go a long way toward resolving the the long-standing controversy over the phase diagrams of the transition metals as determined from static LH-DAC studies on the one hand, and theoretical and dynamic compression studies on the other

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

NASA Astrophysics Data System (ADS)

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

2017-12-01

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

Solidification and Re-melting Phenomena During Slurry Preparation Using the RheoMetal™ Process

NASA Astrophysics Data System (ADS)

Payandeh, M.; Sabzevar, Mohsen Haddad; Jarfors, A. E. W.; Wessén, M.

2017-12-01

The melting sequence of the enthalpy exchange material (EEM) and formation of a slurry in the RheoMetal™ process was investigated. The EEM was extracted and quenched, together with a portion of the slurry at different processing times before complete melting. The EEM initially increased in size/diameter due to melt freezing onto its surface, forming a freeze- on layer. The initial growth of this layer was followed by a period of a constant diameter of the EEM with subsequent melting and decrease of diameter. Microstructural characterization of the size and morphology of different phases in the EEM and in the freeze-on layer was made. Dendritic equiaxed grains and eutectic regions containing Si particles and Cu-bearing particles and Fe-rich particles were observed in the as-cast EEM. The freeze-on layer consisted of dendritic aluminum tilted by about 30 deg in the upstream direction, caused by the rotation of the EEM. Energy dispersion spectroscopy analysis showed that the freeze-on layer had a composition corresponding to an alloy with higher melting point than the EEM and thus shielding the EEM from the surrounding melt. Microstructural changes in the EEM showed that temperature rapidly increased to 768 K (495 °C), indicated by incipient melting of the lowest temperature melting eutectic in triple junction grain boundary regions with Al2Cu and Al5Mg8Si6Cu2 phases present. As the EEM temperature increased further the binary Al-Si eutectic started to melt to form a region of a fully developed coherent mushy state. Experimental results and a thermal model indicated that as the dendrites spheroidized near to the interface at the EEM/freeze-on layer reached a mushy state with 25 pct solid fraction, coherency was lost and disintegration of the freeze-on layer took place. Subsequently, in the absence of the shielding effect from the freeze-on Layer, the EEM continued to disintegrate with a coherency limit of a solid fraction estimated to be 50 pct.

Cloudy Windows: What GCM Ensembles, Reanalyses and Observations Tell Us About Uncertainty in Greenland's Future Climate and Surface Melting

NASA Astrophysics Data System (ADS)

Reusch, D. B.

2016-12-01

Any analysis that wants to use a GCM-based scenario of future climate benefits from knowing how much uncertainty the GCM's inherent variability adds to the development of climate change predictions. This is extra relevant in the polar regions due to the potential of global impacts (e.g., sea level rise) from local (ice sheet) climate changes such as more frequent/intense surface melting. High-resolution, regional-scale models using GCMs for boundary/initial conditions in future scenarios inherit a measure of GCM-derived externally-driven uncertainty. We investigate these uncertainties for the Greenland ice sheet using the 30-member CESM1.0-CAM5-BGC Large Ensemble (CESMLE) for recent (1981-2000) and future (2081-2100, RCP 8.5) decades. Recent simulations are skill-tested against the ERA-Interim reanalysis and AWS observations with results informing future scenarios. We focus on key variables influencing surface melting through decadal climatologies, nonlinear analysis of variability with self-organizing maps (SOMs), regional-scale modeling (Polar WRF), and simple melt models. Relative to the ensemble average, spatially averaged climatological July temperature anomalies over a Greenland ice-sheet/ocean domain are mostly between +/- 0.2 °C. The spatial average hides larger local anomalies of up to +/- 2 °C. The ensemble average itself is 2 °C cooler than ERA-Interim. SOMs extend our diagnostics by providing a concise, objective summary of model variability as a set of generalized patterns. For CESMLE, the SOM patterns summarize the variability of multiple realizations of climate. Changes in pattern frequency by ensemble member show the influence of initial conditions. For example, basic statistical analysis of pattern frequency yields interquartile ranges of 2-4% for individual patterns across the ensemble. In climate terms, this tells us about climate state variability through the range of the ensemble, a potentially significant source of melt

Depth and Differentiation of the Orientale Melt Lake

NASA Technical Reports Server (NTRS)

Vaughan, W. M.; Head, J. W.; Hess, P. C.; Wilson, L.; Neumann, G. A.; Smith, D. E.; Zuber, M. T.

2012-01-01

Impact melt emplacement and evolution in lunar multi-ring basins is poorly understood since impact melt deposits in basins are generally buried by mare basalt fill and obscured by subsequent impact cratering. The relatively young Orientale basin, which is only partially flooded with mare basalt, opens a rare window into basin-scale impact melts. We describe the geology of impact melt-related facies in Orientale and suggest that the central depression of Orientale may represent a solidified impact melt lake that vertically subsided shortly after basin formation due to solidification and cooling. We use Lunar Orbiter Laser Altimeter (LOLA) data to measure the depth (approx. 1.75 km) and diameter (approx 350 km) of this central depression. If all the observed subsidence of the central depression is due to solidification and cooling, the melt lake should be approx 12.5-16 km deep, far more voluminous (approx 106 km3) than the largest known differentiated igneous intrusions on Earth. We investigate the possibility that the Orientale melt lake has differentiated and model 1) the bulk composition of the melt lake, 2) the operation of melt mixing in the melt lake, and 3) the chemical evolution of the resulting liquids on the An-Fo-Qz ternary in order to predict the lithologies that might be present in the solidified Orientale melt lake. Finally, we consider the possible significance of these lithologies.

Thermocapillary convection in zone-melting crystal growth - An open-boat physical simulation

NASA Technical Reports Server (NTRS)

Kim, Y. J.; Kou, Sindo

1989-01-01

Thermocapillary convection in a molten zone of NaNO3 contained in a boat with a free horizontal surface, that is heated from above by a centered wire heater, was studied to simulate flow in zone-melting crystal growth. Using a laser-light-cut technique and fine SiO powder as a tracer, convection in the melt zone was visualized in two different cases. In the first case, the entire melt surface was free, while in the second the melt surface was free only in the immediate vicinity of one vertical wall and was covered elsewhere, this wall being to simulate the melt/crystal interface during crystal growth. It was observed that thermocapillary convection near this wall prevailed in the first case, but was reduced significantly in the second. Since thermocapillary rather than natural convection dominated in the melt, the effect of the partial covering of the melt surface on thermocapillary convection in the melt observed in this study is expected to be similar under microgravity.

Realization of the Temperature Scale in the Range from 234.3 K (Hg Triple Point) to 1084.62°C (Cu Freezing Point) in Croatia

NASA Astrophysics Data System (ADS)

Zvizdic, Davor; Veliki, Tomislav; Grgec Bermanec, Lovorka

2008-06-01

This article describes the realization of the International Temperature Scale in the range from 234.3 K (mercury triple point) to 1084.62°C (copper freezing point) at the Laboratory for Process Measurement (LPM), Faculty of Mechanical Engineering and Naval Architecture (FSB), University of Zagreb. The system for the realization of the ITS-90 consists of the sealed fixed-point cells (mercury triple point, water triple point and gallium melting point) and the apparatus designed for the optimal realization of open fixed-point cells which include the gallium melting point, tin freezing point, zinc freezing point, aluminum freezing point, and copper freezing point. The maintenance of the open fixed-point cells is described, including the system for filling the cells with pure argon and for maintaining the pressure during the realization.

Experimental Investigation of Concrete Runway Snow Melting Utilizing Heat Pipe Technology

PubMed Central

Su, Xin; Ye, Qing; Fu, Jianfeng

2018-01-01

A full scale snow melting system with heat pipe technology is built in this work, which avoids the negative effects on concrete structure and environment caused by traditional deicing chemicals. The snow melting, ice-freezing performance and temperature distribution characteristics of heat pipe concrete runway were discussed by the outdoor experiments. The results show that the temperature of the concrete pavement is greatly improved with the heat pipe system. The environment temperature and embedded depth of heat pipe play a dominant role among the decision variables of the snow melting system. Heat pipe snow melting pavement melts the snow completely and avoids freezing at any time when the environment temperature is below freezing point, which is secure enough for planes take-off and landing. Besides, the exportation and recovery of geothermal energy indicate that this system can run for a long time. This paper will be useful for the design and application of the heat pipe used in the runway snow melting. PMID:29551957

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

PubMed

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

2018-01-01

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

Segregation effects during solidification in weightless melts

NASA Technical Reports Server (NTRS)

Li, C.

1973-01-01

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

Experimental testing of olivine-melt equilibrium models at high temperatures

NASA Astrophysics Data System (ADS)

Krasheninnikov, S. P.; Sobolev, A. V.; Batanova, V. G.; Kargaltsev, A. A.; Borisov, A. A.

2017-08-01

Data are presented on the equilibrium compositions of olivine and melts in the products of 101 experiments performed at 1300-1600°C, atmospheric pressure, and controlled oxygen fugacity by means of new equipment at the Vernadsky Institute. It was shown that the available models of the olivine-melt equilibrium describe with insufficient adequacy the natural systems at temperatures over 1400°C. The most adequate is the model by Ford et al. (1983). However, this model overestimates systematically the equilibrium temperature with underestimating by 20-40°C at 1450-1600°C. These data point to the need for developing a new, improved quantitative model of the olivine-melt equilibrium for high-temperature magnesian melts, as well as to the possibility of these studies on the basis of the equipment presented.

Permeability and 3-Dimensional Melt Distribution in Partially Molten Rocks

NASA Astrophysics Data System (ADS)

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

2010-05-01

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

Dynamic Melting of Freezing Droplets on Ultraslippery Superhydrophobic Surfaces.

PubMed

Chu, Fuqiang; Wu, Xiaomin; Wang, Lingli

2017-03-08

Condensed droplet freezing and freezing droplet melting phenomena on the prepared ultraslippery superhydrophobic surface were observed and discussed in this study. Although the freezing delay performance of the surface is common, the melting of the freezing droplets on the surface is quite interesting. Three self-propelled movements of the melting droplets (ice- water mixture) were found including the droplet rotating, the droplet jumping, and the droplet sliding. The melting droplet rotating, which means that the melting droplet rotates spontaneously on the superhydrophobic surface like a spinning top, is first reported in this study and may have some potential applications in various engineering fields. The melting droplet jumping and sliding are similar to those occurring during condensation but have larger size scale and motion scale, as the melting droplets have extra-large specific surface area with much more surface energy available. These self-propelled movements make all the melting droplets on the superhydrophobic surface dynamic, easily removed, which may be promising for the anti-icing/frosting applications.

Melting of Boltzmann particles in different 2D trapping potential

NASA Astrophysics Data System (ADS)

Bhattacharya, Dyuti; Filinov, Alexei; Ghosal, Amit; Bonitz, Michael

2015-03-01

We analyze the quantum melting of two dimensional Wigner solid in several confined geometries and compare them with corresponding thermal melting in a purely classical system. Our results show that the geometry play little role in deciding the crossover quantum parameter nX, as the effects from boundary is well screened by the quantum zero point motion. The unique phase diagram in the plane of thermal and quantum fluctuations determined from independent melting criteria separates out the Wigner molecule ``phase'' from the classical and quantum ``liquids''. An intriguing signature of weakening liquidity with increasing temperature T have been found in the extreme quantum regime (n). This crossover is associated with production of defects, just like in case of thermal melting, though the role of them in determining the mechanism of the crossover appears different. Our study will help comprehending melting in a variety of experimental realization of confined system - from quantum dots to complex plasma.

Observation of enhanced infrared absorption in silicon supersaturated with gold by pulsed laser melting of nanometer-thick gold films

NASA Astrophysics Data System (ADS)

Chow, Philippe K.; Yang, Wenjie; Hudspeth, Quentin; Lim, Shao Qi; Williams, Jim S.; Warrender, Jeffrey M.

2018-04-01

We demonstrate that pulsed laser melting (PLM) of thin 1, 5, and 10 nm-thick vapor-deposited gold layers on silicon enhances its room-temperature sub-band gap infrared absorption, as in the case of ion-implanted and PLM-treated silicon. The former approach offers reduced fabrication complexity and avoids implantation-induced lattice damage compared to ion implantation and pulsed laser melting, while exhibiting comparable optical absorptance. We additionally observed strong broadband absorptance enhancement in PLM samples made using 5- and 10-nm-thick gold layers. Raman spectroscopy and Rutherford backscattering analysis indicate that such an enhancement could be explained by absorption by a metastable, disordered and gold-rich surface layer. The sheet resistance and the diode electrical characteristics further elucidate the role of gold-supersaturation in silicon, revealing the promise for future silicon-based infrared device applications.

Results from a lab study of melting sea ice

NASA Astrophysics Data System (ADS)

Wiese, M.; Griewank, P.; Notz, D.

2012-04-01

Sea-ice melting is a complex process which is not fully understood yet. In order to study sea-ice melt in detail we perform lab experiments in an approximately 2x0.7x1.2 m large tank in a cold room. We grow sea ice with different salinities at least 10 cm thick. Then we let the ice melt at different air temperatures and oceanic heat fluxes. During the melt period, we measure the evolution of ice thickness, internal temperature, salinity and surface temperature. We will present results from roughly five months of experiments. Topics will include the influence of bulk salinity on melt rates and the surface temperature. The effects of flushing on the salinity evolution and detailed thermal profiles will also be included. To investigate these processes we focus on the energy budget and the salinity evolution. These topics are linked since the thermodynamic properties of sea ice (heat capacity, heat conductivity and latent heat of fusion) are very sensitive to salinity variations. For example the heat capacity of sea ice increases greatly as the temperature approaches the melting point. This increase results in non-linear temperature profiles and enhances heat conduction into the ice. The salinity evolution during the growth phase has been investigated and measured in multiple studies over the last decades. In contrast there are no detailed lab measurements of melting ice available to quantify the effects of flushing melt water and ponding. This is partially due to the fact that the heterogeneity of melting sea ice makes it much more difficult to measure representative values.

Experimental Melting Study of Basalt-Peridotite Hybrid Source: Melting model of Hawaiian plume

NASA Astrophysics Data System (ADS)

Takahashi, E.; Gao, S.

2015-12-01

Eclogite component entrained in ascending plume is considered to be essentially important in producing flood basalts (e.g., Columbia River basalt, Takahashi et al., 1998 EPSL), alkalic OIBs (e.g., Kogiso et al.,2003), ferro-picrites (Tuff et al.,2005) and Hawaiian shield lavas (e.g., Hauri, 1996; Takahashi & Nakajima, 2002, Sobolev et al.,2005). Size of the entrained eclogite, which controls the reaction rates with ambient peridotite, however, is very difficult to constrain using geophysical observation. Among Hawaiian shield volcanoes, Koolau is the most enriched end-member in eclogite component (Frey et al, 1994). Reconstruction of Koolau volcano based on submarine study on Nuuanu landslide (AGU Monograph vol.128, 2002, Takahashi Garcia Lipman eds.) revealed that silica-rich tholeiite appeared only at the last stage (Makapuu stage) of Koolau volcano. Chemical compositions of lavas as well as isotopes change abruptly and coherently across a horizon (Shinozaki et al. and Tanaka et al. ibid.). Based on these observation, Takahashi & Nakajima (2002 ibid) proposed that the Makapuu stage lava in Koolau volcano was supplied from a single large eclogite block. In order to study melting process in Hawaiian plume, high-pressure melting experiments were carried out under dry and hydrous conditions with layered eclogite/peridotite starting materials. Detail of our experiments will be given by Gao et al (2015 AGU). Combined previous field observation with new set of experiments, we propose that variation in SiO2 among Hawaiian tholeiites represent varying degree of wall-rock interaction between eclogite and ambient peridotite. Makapuu stage lavas in Koolau volcano represents eclogite partial melts formed at ~3 GPa with various amount of xenocrystic olivines derived from Pacific plate. In other words, we propose that "primary magma" in the melting column of Hawaiian plume ranges from basaltic andesite to ferro-picrite depending on the lithology of the source. Solidus of

Modeling the exhumation path of partially melted ultrahigh-pressure metapelites, North-East Greenland Caledonides

NASA Astrophysics Data System (ADS)

Lang, Helen M.; Gilotti, Jane A.

2015-06-01

Pseudosection modeling constrains the pressure-temperature (P-T) exhumation path of partially melted ultrahigh-pressure (UHP) metapelites exposed in the North-East Greenland UHP terrane. A robust peak P and T estimate of 3.6 GPa and 970 °C based on mineral assemblages in nearby kyanite eclogites is the starting point for the P-T path. Although the peak assemblage for the metapelite is not preserved, the calculated modeled peak assemblage contained substantial clinopyroxene, garnet, phengite, K-feldspar and coesite with minor kyanite and rutile. Combining the pseudosection and observed textures, the decompression path crosses the coesite-quartz transition before reaching the dry phengite dehydration melting reaction where phengite is abruptly consumed. In the range of 2.5 to 2.2 GPa, clinopyroxene is completely consumed and garnet grows to its maximum volume and grossular content, matching the high grossular rims of relict megacrysts. Plagioclase joins the assemblage and the pseudosection predicts up to 12-13 vol.% melt in the supersolidus assemblage, which contained garnet, liquid, K-feldspar, plagioclase, kyanite, quartz and rutile. At this stage, the steep decompression path flattened out and became nearly isobaric. The melt crystallization assemblage that formed when the path crossed the solidus with decreasing temperature contains phengite, garnet, biotite, 2 feldspars, kyanite, quartz and rutile. Therefore, the path must have intersected the solidus at approximately 1.2 GPa, 825 °C. The pseudosection predicts that garnet is consumed on the cooling path, but little evidence of late garnet consumption or other retrograde effects is observed. This may be due to partial melt loss from the rock. Isochemical PT-n and PT-X sections calculated along the P-T path display changes in mineral assemblage and composition that are consistent with preserved assemblages.

Unlabeled oligonucleotides as internal temperature controls for genotyping by amplicon melting.

PubMed

Seipp, Michael T; Durtschi, Jacob D; Liew, Michael A; Williams, Jamie; Damjanovich, Kristy; Pont-Kingdon, Genevieve; Lyon, Elaine; Voelkerding, Karl V; Wittwer, Carl T

2007-07-01

Amplicon melting is a closed-tube method for genotyping that does not require probes, real-time analysis, or allele-specific polymerase chain reaction. However, correct differentiation of homozygous mutant and wild-type samples by melting temperature (Tm) requires high-resolution melting and closely controlled reaction conditions. When three different DNA extraction methods were used to isolate DNA from whole blood, amplicon Tm differences of 0.03 to 0.39 degrees C attributable to the extractions were observed. To correct for solution chemistry differences between samples, complementary unlabeled oligonucleotides were included as internal temperature controls to shift and scale the temperature axis of derivative melting plots. This adjustment was applied to a duplex amplicon melting assay for the methylenetetrahydrofolate reductase variants 1298A>C and 677C>T. High- and low-temperature controls bracketing the amplicon melting region decreased the Tm SD within homozygous genotypes by 47 to 82%. The amplicon melting assay was 100% concordant to an adjacent hybridization probe (HybProbe) melting assay when temperature controls were included, whereas a 3% error rate was observed without temperature correction. In conclusion, internal temperature controls increase the accuracy of genotyping by high-resolution amplicon melting and should also improve results on lower resolution instruments.

Unlabeled Oligonucleotides as Internal Temperature Controls for Genotyping by Amplicon Melting

PubMed Central

Seipp, Michael T.; Durtschi, Jacob D.; Liew, Michael A.; Williams, Jamie; Damjanovich, Kristy; Pont-Kingdon, Genevieve; Lyon, Elaine; Voelkerding, Karl V.; Wittwer, Carl T.

2007-01-01

Amplicon melting is a closed-tube method for genotyping that does not require probes, real-time analysis, or allele-specific polymerase chain reaction. However, correct differentiation of homozygous mutant and wild-type samples by melting temperature (Tm) requires high-resolution melting and closely controlled reaction conditions. When three different DNA extraction methods were used to isolate DNA from whole blood, amplicon Tm differences of 0.03 to 0.39°C attributable to the extractions were observed. To correct for solution chemistry differences between samples, complementary unlabeled oligonucleotides were included as internal temperature controls to shift and scale the temperature axis of derivative melting plots. This adjustment was applied to a duplex amplicon melting assay for the methylenetetrahydrofolate reductase variants 1298A>C and 677C>T. High- and low-temperature controls bracketing the amplicon melting region decreased the Tm SD within homozygous genotypes by 47 to 82%. The amplicon melting assay was 100% concordant to an adjacent hybridization probe (HybProbe) melting assay when temperature controls were included, whereas a 3% error rate was observed without temperature correction. In conclusion, internal temperature controls increase the accuracy of genotyping by high-resolution amplicon melting and should also improve results on lower resolution instruments. PMID:17591926

The Surface Layer of a Crystal and Its Specific Role in the Process of Melt Formation

NASA Astrophysics Data System (ADS)

Sobolev, R. N.

2018-04-01

A crystal becomes melted in a few stages. The structure of the crystal surface differs from that of its interior. Therefore, as its interior is gradually involved in the melting process, the phase transition temperature becomes higher. The melting point becomes constant when all atoms have the same number of unsaturated bonds.

Coupled phase field, heat conduction, and elastodynamic simulations of kinetic superheating and nanoscale melting of aluminum nanolayer irradiated by picosecond laser.

PubMed

Hwang, Yong Seok; Levitas, Valery I

2015-12-21

An advanced continuum model for nanoscale melting and kinetic superheating of an aluminum nanolayer irradiated by a picosecond laser is formulated. Barrierless nucleation of surface premelting and melting occurs, followed by a propagation of two solid-melt interfaces toward each other and their collision. For a slow heating rate of Q = 0.015 K ps(-1) melting occurs at the equilibrium melting temperature under uniaxial strain conditions T = 898.1 K (i.e., below equilibrium melting temperature Teq = 933.67 K) and corresponding biaxial stresses, which relax during melting. For a high heating rate of Q = 0.99-84 K ps(-1), melting occurs significantly above Teq. Surprisingly, an increase in heating rate leads to temperature reduction at the 3 nm wide moving interfaces due to fast absorption of the heat of fusion. A significant, rapid temperature drop (100-500 K, even below melting temperature) at the very end of melting is revealed, which is caused by the collision of two finite-width interfaces and accelerated melting in about the 5 nm zone. For Q = 25-84 K ps(-1), standing elastic stress waves are observed in a solid with nodal points at the moving solid-melt interfaces, which, however, do not have a profound effect on melting time or temperatures. When surface melting is suppressed, barrierless bulk melting occurs in the entire sample, and elastodynamic effects are more important. Good correspondence with published, experimentally-determined melting time is found for a broad range of heating rates. Similar approaches can be applied to study various phase transformations in different materials and nanostructures under high heating rates.

A double-observer approach for estimating detection probability and abundance from point counts

USGS Publications Warehouse

Nichols, J.D.; Hines, J.E.; Sauer, J.R.; Fallon, F.W.; Fallon, J.E.; Heglund, P.J.

2000-01-01

Although point counts are frequently used in ornithological studies, basic assumptions about detection probabilities often are untested. We apply a double-observer approach developed to estimate detection probabilities for aerial surveys (Cook and Jacobson 1979) to avian point counts. At each point count, a designated 'primary' observer indicates to another ('secondary') observer all birds detected. The secondary observer records all detections of the primary observer as well as any birds not detected by the primary observer. Observers alternate primary and secondary roles during the course of the survey. The approach permits estimation of observer-specific detection probabilities and bird abundance. We developed a set of models that incorporate different assumptions about sources of variation (e.g. observer, bird species) in detection probability. Seventeen field trials were conducted, and models were fit to the resulting data using program SURVIV. Single-observer point counts generally miss varying proportions of the birds actually present, and observer and bird species were found to be relevant sources of variation in detection probabilities. Overall detection probabilities (probability of being detected by at least one of the two observers) estimated using the double-observer approach were very high (>0.95), yielding precise estimates of avian abundance. We consider problems with the approach and recommend possible solutions, including restriction of the approach to fixed-radius counts to reduce the effect of variation in the effective radius of detection among various observers and to provide a basis for using spatial sampling to estimate bird abundance on large areas of interest. We believe that most questions meriting the effort required to carry out point counts also merit serious attempts to estimate detection probabilities associated with the counts. The double-observer approach is a method that can be used for this purpose.

The geometry and volume of melt beneath Ethiopia

NASA Astrophysics Data System (ADS)

Kendall, J. M.; Hammond, J. O. S.

2016-12-01

A range of seismic measurements can be used to map melt distribution in the crust and uppermost mantle. These include seismic P- and S-wave velocities derived from surface- and body-wave tomography, Vp/Vs ratios obtained from receiver functions, and estimates of seismic anisotropy and attenuation. The most obvious melt parameter that seismic data might be sensitive to is volume fraction. However, such data are more sensitive to the aspect ratio of melt inclusions, which is controlled by the melt wetting angle or in other words the shape of the melt inclusion. To better understand this we perform numerical modelling, varying the shape and amount of melt, to show how various seismic phases are effected by melt. To consider the effects on seismic anisotropy we assume that the melt can be stored in pockets of melt that are either horizontally or vertically aligned (e.g., sills versus dykes). We then consider a range of seismic observations from the rifting environment of Ethiopia. Recent studies of P- and S-wave tomography, Rayleigh and Love waves, and Pn or wide angle P-wave refractions provide provide complimentary constraints on melt volume, orientation and inclusion aspect ratio. Furthermore, receiver functions and shear-wave splitting in body waves show strong anisotropy in this region and can be used to constrain the strike of vertically-aligned partial melt. We show that melt in the mantle beneath Ethiopia is likely stored in low aspect ratio disk-like inclusions, suggesting melt is not in textural equilibrium. We estimate that 2-7% vertically aligned melt is stored beneath the Main Ethiopian Rift, >6% horizontally and vertically aligned melt is stored beneath the Afar-region of the Red Sea Rift and 1-6% horizontally aligned melt is stored beneath the Danakil microplate. This supports ideas of strong shear-derived segregation of melt in narrow parts of the rift and large volumes of melt beneath Afar.

Miniature Fixed Points as Temperature Standards for In Situ Calibration of Temperature Sensors

NASA Astrophysics Data System (ADS)

Hao, X. P.; Sun, J. P.; Xu, C. Y.; Wen, P.; Song, J.; Xu, M.; Gong, L. Y.; Ding, L.; Liu, Z. L.

2017-06-01

Miniature Ga and Ga-In alloy fixed points as temperature standards are developed at National Institute of Metrology, China for the in situ calibration of temperature sensors. A quasi-adiabatic vacuum measurement system is constructed to study the phase-change plateaus of the fixed points. The system comprises a high-stability bath, a quasi-adiabatic vacuum chamber and a temperature control and measurement system. The melting plateau of the Ga fixed point is longer than 2 h at 0.008 W. The standard deviation of the melting temperature of the Ga and Ga-In alloy fixed points is better than 2 mK. The results suggest that the melting temperature of the Ga or Ga-In alloy fixed points is linearly related with the heating power.

Microstructures define melting of molybdenum at high pressures

NASA Astrophysics Data System (ADS)

Hrubiak, Rostislav; Meng, Yue; Shen, Guoyin

2017-03-01

High-pressure melting anchors the phase diagram of a material, revealing the effect of pressure on the breakdown of the ordering of atoms in the solid. An important case is molybdenum, which has long been speculated to undergo an exceptionally steep increase in melting temperature when compressed. On the other hand, previous experiments showed nearly constant melting temperature as a function of pressure, in large discrepancy with theoretical expectations. Here we report a high-slope melting curve in molybdenum by synchrotron X-ray diffraction analysis of crystalline microstructures, generated by heating and subsequently rapidly quenching samples in a laser-heated diamond anvil cell. Distinct microstructural changes, observed at pressures up to 130 gigapascals, appear exclusively after melting, thus offering a reliable melting criterion. In addition, our study reveals a previously unsuspected transition in molybdenum at high pressure and high temperature, which yields highly textured body-centred cubic nanograins above a transition temperature.

Microstructures define melting of molybdenum at high pressures

PubMed Central

Hrubiak, Rostislav; Meng, Yue; Shen, Guoyin

2017-01-01

High-pressure melting anchors the phase diagram of a material, revealing the effect of pressure on the breakdown of the ordering of atoms in the solid. An important case is molybdenum, which has long been speculated to undergo an exceptionally steep increase in melting temperature when compressed. On the other hand, previous experiments showed nearly constant melting temperature as a function of pressure, in large discrepancy with theoretical expectations. Here we report a high-slope melting curve in molybdenum by synchrotron X-ray diffraction analysis of crystalline microstructures, generated by heating and subsequently rapidly quenching samples in a laser-heated diamond anvil cell. Distinct microstructural changes, observed at pressures up to 130 gigapascals, appear exclusively after melting, thus offering a reliable melting criterion. In addition, our study reveals a previously unsuspected transition in molybdenum at high pressure and high temperature, which yields highly textured body-centred cubic nanograins above a transition temperature. PMID:28248309

Ice Melt, Sea Level Rise and Superstorms: Evidence from Paleoclimate Data, Climate Modeling, and Modern Observations that 2C Global Warming Could Be Dangerous

NASA Technical Reports Server (NTRS)

Hansen, J.; Sato, Makiko; Hearty, Paul; Ruedy, Reto; Kelley, Maxwell; Masson-Delmotte, Valerie; Russell, Gary; Tselioudis, George; Cao, Junji; Rignot, Eric;

Local melting in Al-Mg-Zn-alloys

NASA Astrophysics Data System (ADS)

Droenen, Per-Erik; Ryum, Nils

1994-03-01

The internal melting of several Al-Mg-Zn-alloys has been studied by rapid upquenching in a salt bath of specimens slowly cooled at a rate of 2 °C/h down to 375 °C. The melting reaction was studied metallographically in the light- and electron-scanning microscope, and local concentrations were measured in the microprobe. Local melting of both the equilibrium phases T and η was observed to occur. There were, however, essential differences between the melting kinetics for the two phases. While the T-phase particles melted spontaneously at temperatures at or above the invariant temperature, 489 °C, and after some period of time at lower temperatures, the η-phase particles either melted spontaneously at or above the invariant temperature, T - 475 °C, or dissolved into the matrix at temperatures below 475 °C. This difference in behavior can be accounted for if the α(Al)-η section is not a quasi-binary section. The industrial implications of the internal melting in these alloys are discussed and compared to the same reaction in the Al-Mg-Si alloys. A model is developed in the Appendix to quantify the different behaviors of these two classes of alloys.

Melt Heterogeneity and Degassing at MT Etna from Melt Inclusions

NASA Astrophysics Data System (ADS)

Salem, L. C.; Edmonds, M.; Maclennan, J.; Corsaro, R. A.

2014-12-01

The melts feeding Mt Etna, Italy, are rich in volatiles and drive long-lasting powerful eruptions of basaltic magma in both effusive and explosive styles of activity. The volatile systematics of the volcanic system are well understood through melt inclusion and volcanic gas studies. Etna's melts are generated from a complex mantle setting, with subduction-related chemical modifications as well as OIB-type features, and then the melts must travel through thick carbonate-rich crust. The continual influx of mantle-derived volatile-rich magma controls the major compositional and eruptive features of Mount Etna and magma mixing has been recognized as an important process driving large eruptions [Kamenetsky, 2007]. Our study focusses on the 1669 eruption, the largest in historical times. Olivine-hosted melt inclusions were analyzed for volatile, trace and major elements using electron microprobe and ion probe (SIMS). We use volatile systematics and geochemical data to deconvolve mantle-derived heterogeneity from melt mixing and crystal fractionation. Our data are well described by a mixing trend between two distinct melts: a CO2-rich (CO2~1000ppm), incompatible trace element depleted melt (La/Yb~16), and a CO2-poor, enriched melt. The mixing also generates a strong correlation between Sr and CO2 in the melt inclusions dataset, reflecting the presence of a strong Sr anomaly in one of the end-member melts. We investigate the origin of this Sr anomaly by considering plagioclase dissolution and crustal assimilation. We also investigate degassing processes in the crust and plumbing system of the volcano. We compare our results with similar studies of OIB and arc-related basalts elsewhere and assess the implications for linking eruption size and style with the nature of the mantle-derived melts. Kamenetsky et al. (2007) Geology 35, 255-258.

The anomalously high melting temperature of bilayer ice.

PubMed

Kastelowitz, Noah; Johnston, Jessica C; Molinero, Valeria

2010-03-28

Confinement of water usually depresses its melting temperature. Here we use molecular dynamics simulations to determine the liquid-crystal equilibrium temperature for water confined between parallel hydrophobic or mildly hydrophilic plates as a function of the distance between the surfaces. We find that bilayer ice, an ice polymorph in which the local environment of each water molecule strongly departs from the most stable tetrahedral structure, has the highest melting temperature (T(m)) of the series of l-layer ices. The melting temperature of bilayer ice is not only unusually high compared to the other confined ices, but also above the melting point of bulk hexagonal ice. Recent force microscopy experiments of water confined between graphite and a tungsten tip reveal the formation of ice at room temperature [K. B. Jinesh and J. W. M. Frenken, Phys. Rev. Lett. 101, 036101 (2008)]. Our results suggest that bilayer ice, for which we compute a T(m) as high as 310 K in hydrophobic confinement, is the crystal formed in those experiments.

The Role of CO2 on Silica Undersaturated Melt Structure: Implication for Melt Physical Properties

NASA Astrophysics Data System (ADS)

Scaillet, B.; Morizet, Y.; Paris, M.; Gaillard, F.

2012-12-01

Silica undersaturated melts such as nephelinite and melilitite are very peculiar magmatic materials. Their occurrence on the Earth surface is often associated with carbonatites melts. These low-silica melts can dissolve a large quantity of CO2 issued from mantle fluid metasomatism. However, the melt structure, the way CO2 dissolves into these melts and the effect of different alkalis element are poorly constrained. We present preliminary experimental results on the melt structure of synthetic nephelinite (NBO/T = 1.25) and Ca-melilitite (NBO/T = 2.50) synthesized in the NKCMAS system and equilibrated at high-pressure (200-300 MPa), high-temperature (1250°C) with an excess C-O-H fluid phase. The nephelinite glasses were synthesized with varying K2O / K2O+Na2O (0-10 mol.% K2O) ratio so as to investigate the differential effect of those two cations. All experiments were conducted under oxidizing conditions (ΔNNO+5) resulting in binary fluid phase composition with CO2 and H2O species. The silicate melt structure, CO2 solubility and speciation were investigated using Micro-Raman and Solid State NMR spectroscopies for 13C, 1H, 29Si, 27Al and 23Na nuclei. The replacement of Na by K does not change the nephelinite melt structure for volatile-free sample suggesting that the basicity of these glasses is not dramatically affected by the presence of mixed alkali. Within 5 mol.% K2O, the CO2 solubility (measured in relative to Raman signature of the melt structure) is only slightly affected with an increasing CO2 solubility with increasing K2O content. As a function of pressure, we observe an increase in CO2 solubility consistent with previous studies. The 13C NMR investigation of the CO2 speciation show three different carbonates environments for CO2 in nephelinite melts attributed to non-network carbonates: 1) 170 ppm shift assigned to NBO-carb. Na or K; 2) 169 ppm assigned to NBO-carb. Ca; and 3) 165 ppm assigned to isolated Na+..CO32- carbonates. As K2O is increased into

Experimental observations on noble metal nanonuggets and Fe-Ti oxides, and the transport of platinum group elements in silicate melts

NASA Astrophysics Data System (ADS)

Anenburg, Michael; Mavrogenes, John A.

2016-11-01

Platinum group element (PGE) nanonuggets are a nuisance in experimental studies designed to measure solubility or partitioning of noble metals in silicate melts. Instead of treating nanonuggets as experimental artifacts, we studied their behaviour motivated by recent discoveries of PGE nanonuggets in a variety of natural settings. We used an experimental setup consisting of AgPd, Pt or AuPd capsules and Fe(-Ti) oxide-saturated hydrous peralkaline silicate melts to maximise nanonugget production. TABS (Te, As, Bi, Sb, Sn) commonly occur in PGM (platinum group minerals), prompting addition of Bi to our experiments to investigate its properties as well. Three-dimensional optical examination by 100× objective and immersion oil reveals variable colour which correlates with nanonugget size and shape due to plasmon resonance effects. We observe two textural types: (1) intermediate-sized nanonuggets dispersed in the glass and adhering to oxides, and (2) abundant fine nanonuggets dispersed in the glass with coarse euhedral crystals in contact with oxides. Slow cooling removes dispersed nanonuggets and greatly coarsens existing oxide-associated metal crystals. Nanonugget-free halos are commonly observed around oxide grains. All metal phases are composed of major (Ag, Pd) and trace (Pt, Ir, Au) capsule material. Our results show reduction processes, imposed by growing oxides, causing local metal saturation in the oxide rich zones with preferential nucleation on smaller oxide grains. The redox gradient then blocks additional metals from diffusing into oxide rich zones, forming halos. As the entire experimental charge is reduced throughout the run, nanonuggets form in the distal glass. Bismuth contents of metal phases do not depend on Bi2O3 amounts dissolved in the melt. Further PGM crystallisation consumes nanonuggets as feedstock. We conclude that the appearance of metallic PGE phases happens in two stages: first as nanonuggets and then as larger PGM. Once formed

Modeling the basal melting and marine ice accretion of the Amery Ice Shelf

NASA Astrophysics Data System (ADS)

Galton-Fenzi, B. K.; Hunter, J. R.; Coleman, R.; Marsland, S. J.; Warner, R. C.

2012-09-01

The basal mass balance of the Amery Ice Shelf (AIS) in East Antarctica is investigated using a numerical ocean model. The main improvements of this model over previous studies are the inclusion of frazil formation and dynamics, tides and the use of the latest estimate of the sub-ice-shelf cavity geometry. The model produces a net basal melt rate of 45.6 Gt year-1 (0.74 m ice year-1) which is in good agreement with reviewed observations. The melting at the base of the ice shelf is primarily due to interaction with High Salinity Shelf Water created from the surface sea-ice formation in winter. The temperature difference between the coldest waters created in the open ocean and the in situ freezing point of ocean water in contact with the deepest part of the AIS drives a melt rate that can exceed 30 m of ice year-1. The inclusion of frazil dynamics is shown to be important for both melting and marine ice accretion (refreezing). Frazil initially forms in the supercooled water layer adjacent to the base of the ice shelf. The net accretion of marine ice is 5.3 Gt year-1, comprised of 3.7 Gt year-1 of frazil accretion and 1.6 Gt year-1 of direct basal refreezing.

A benchmark initiative on mantle convection with melting and melt segregation

NASA Astrophysics Data System (ADS)

Schmeling, Harro; Dannberg, Juliane; Dohmen, Janik; Kalousova, Klara; Maurice, Maxim; Noack, Lena; Plesa, Ana; Soucek, Ondrej; Spiegelman, Marc; Thieulot, Cedric; Tosi, Nicola; Wallner, Herbert

2016-04-01

In recent years a number of mantle convection models have been developed which include partial melting within the asthenosphere, estimation of melt volumes, as well as melt extraction with and without redistribution at the surface or within the lithosphere. All these approaches use various simplifying modelling assumptions whose effects on the dynamics of convection including the feedback on melting have not been explored in sufficient detail. To better assess the significance of such assumptions and to provide test cases for the modelling community we carry out a benchmark comparison. The reference model is taken from the mantle convection benchmark, cases 1a to 1c (Blankenbach et al., 1989), assuming a square box with free slip boundary conditions, the Boussinesq approximation, constant viscosity and Rayleigh numbers of 104 to 10^6. Melting is modelled using a simplified binary solid solution with linearly depth dependent solidus and liquidus temperatures, as well as a solidus temperature depending linearly on depletion. Starting from a plume free initial temperature condition (to avoid melting at the onset time) five cases are investigated: Case 1 includes melting, but without thermal or dynamic feedback on the convection flow. This case provides a total melt generation rate (qm) in a steady state. Case 2 is identical to case 1 except that latent heat is switched on. Case 3 includes batch melting, melt buoyancy (melt Rayleigh number Rm) and depletion buoyancy, but no melt percolation. Output quantities are the Nusselt number (Nu), root mean square velocity (vrms), the maximum and the total melt volume and qm approaching a statistical steady state. Case 4 includes two-phase flow, i.e. melt percolation, assuming a constant shear and bulk viscosity of the matrix and various melt retention numbers (Rt). These cases are carried out using the Compaction Boussinseq Approximation (Schmeling, 2000) or the full compaction formulation. For cases 1 - 3 very good agreement

Development of an inhalation system of high melting point metal fumes and its use for exposure of rats to chromium and nickel fumes.

PubMed

Serita, F; Homma, K; Fukuda, K; Sawatari, K; Suzuki, Y; Toya, T

1990-01-01

An experimental inhalation system was developed for fumes generated from powders of high melting point metals such as chromium, nickel, manganese and iron. The system consisted of a plasma flame metal sprayer as a fume generator, a granular bed type fume collector, a fluidized bed aerosol generator, an exposure and a control chamber of a horizontal-flow type and inhalant monitoring and controlling units. Performance of the chambers was ensured by a distribution test using flyash as a test aerosol. Using this system, rats were exposed to chromium fumes for one week or to nickel fumes for two months. The exposure concentrations of the chromium and nickel fumes were 1.85 +/- 0.55 mg/m3 and 0.51 +/- 0.15 mg/m3 (mean +/- SD), near the target levels of 2 mg/m3 and 0.5 mg/m3, respectively. The mass median aerodynamic diameter and the geometric standard deviation of the chromium fumes were 2.1 microns and 2.00, respectively. Those of the nickel fumes were 3.7 microns and 1.74, respectively. Species analysis of these fume particles revealed that 26.4% of the total chromium was hexavalent and the residue was trivalent and that 1-3% of the total nickel was nickel(III) and the residue was nickel(II). Inhaled-metal concentrations in the lungs showed steady increases with the exposure periods and were within the normal range of variation. On the basis of these results, it is concluded that this system is useful for long-term inhalation experiments using high melting point metal fumes.

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

NASA Astrophysics Data System (ADS)

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

2018-06-01

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

Seismic multiplet response triggered by melt at Blood Falls, Taylor Glacier, Antarctica

NASA Astrophysics Data System (ADS)

Carmichael, Joshua D.; Pettit, Erin C.; Hoffman, Matt; Fountain, Andrew; Hallet, Bernard

2012-09-01

Meltwater input often triggers a seismic response from glaciers and ice sheets. It is difficult, however, to measure melt production on glaciers directly, while subglacial water storage is not directly observable. Therefore, we document temporal changes in seismicity from a dry-based polar glacier (Taylor Glacier, Antarctica) during a melt season using a synthesis of seismic observation and melt modeling. We record icequakes using a dense six-receiver network of three-component geophones and compare this with melt input generated from a calibrated surface energy balance model. In the absence of modeled surface melt, we find that seismicity is well-described by a diurnal signal composed of microseismic events in lake and glacial ice. During melt events, the diurnal signal is suppressed and seismicity is instead characterized by large glacial icequakes. We perform network-based correlation and clustering analyses of seismic record sections and determine that 18% of melt-season icequakes are repetitive (multiplets). The epicentral locations for these multiplets suggest that they are triggered by meltwater produced near a brine seep known as Blood Falls. Our observations of the correspondingp-wave first motions are consistent with volumetric source mechanisms. We suggest that surface melt enables a persistent pathway through this cold ice to an englacial fracture system that is responsible for brine release episodes from the Blood Falls seep. The scalar moments for these events suggest that the volumetric increase at the source region can be explained by melt input.

Antarctic sub-shelf melt rates via PICO

NASA Astrophysics Data System (ADS)

Reese, Ronja; Albrecht, Torsten; Mengel, Matthias; Asay-Davis, Xylar; Winkelmann, Ricarda

2018-06-01

Ocean-induced melting below ice shelves is one of the dominant drivers for mass loss from the Antarctic Ice Sheet at present. An appropriate representation of sub-shelf melt rates is therefore essential for model simulations of marine-based ice sheet evolution. Continental-scale ice sheet models often rely on simple melt-parameterizations, in particular for long-term simulations, when fully coupled ice-ocean interaction becomes computationally too expensive. Such parameterizations can account for the influence of the local depth of the ice-shelf draft or its slope on melting. However, they do not capture the effect of ocean circulation underneath the ice shelf. Here we present the Potsdam Ice-shelf Cavity mOdel (PICO), which simulates the vertical overturning circulation in ice-shelf cavities and thus enables the computation of sub-shelf melt rates consistent with this circulation. PICO is based on an ocean box model that coarsely resolves ice shelf cavities and uses a boundary layer melt formulation. We implement it as a module of the Parallel Ice Sheet Model (PISM) and evaluate its performance under present-day conditions of the Southern Ocean. We identify a set of parameters that yield two-dimensional melt rate fields that qualitatively reproduce the typical pattern of comparably high melting near the grounding line and lower melting or refreezing towards the calving front. PICO captures the wide range of melt rates observed for Antarctic ice shelves, with an average of about 0.1 m a-1 for cold sub-shelf cavities, for example, underneath Ross or Ronne ice shelves, to 16 m a-1 for warm cavities such as in the Amundsen Sea region. This makes PICO a computationally feasible and more physical alternative to melt parameterizations purely based on ice draft geometry.

Modeling the Spreading of Glacial Melt Water from the Amundsen and Bellingshausen Seas

NASA Astrophysics Data System (ADS)

Nakayama, Y.; Timmermann, R.; Rodehacke, C. B.; Schröder, M.; Hellmer, H. H.

2014-12-01

The ice shelves and glaciers of the West Antarctic Ice Sheet (WAIS) are rapidly thinning, especially in the Amundsen Sea (AS) and Bellingshausen Sea (BS). The high basal melting of these small ice shelves is caused by relatively warm Circumpolar Deep Water (CDW) that, based on observations, mainly intrudes via two submarine glacial troughs located at the eastern and central AS continental shelf break. When CDW reaches the grounding line of the fringing glaciers, it melts the glaciers and forms buoyant melt water plumes. As the glacial melt becomes part of the AS shelf circulation, it may cause a freshening of the shelf water locally as well as remotely in the Ross Sea (RS). To test whether the observed freshening of the RS is a consequence of the enhanced basal melting of AS ice shelves, we use Finite-Element Sea-ice/ice-shelf/Ocean Model (FESOM) with a horizontal resolution of 2-10 km on the AS and BS continental shelves. The model is forced with 6-hourly atmospheric data from the National Centers for Environmental Prediction Climate Forecast System Reanalysis (NCEP-CFSR) for the period 1979-1988. The model results show bottom temperatures in the AS and BS close to observations, and basal melt rates of AS and BS ice shelves consistent with other observation-based estimates. Using several independent virtual passive tracers to identify pathways of the glacial melt, we find that the melt water from the ice shelves in the AS flows towards the Ross Ice Shelf front. After 10 years of simulation, about half of the melt water in the Ross Sea originates from the Getz Ice Shelf. Further, we investigate the sensitivity of the melt water transport into the RS associated with the strength of the basal melt water flux. When this flux is increased by 30%, the transport of glacial melt into the RS more than doubles, supporting the idea that the basal melting of AS and BS ice shelves is one of the main reasons for the freshening of the RS continental shelf.

Filtering with Marked Point Process Observations via Poisson Chaos Expansion

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

Sun Wei, E-mail: wsun@mathstat.concordia.ca; Zeng Yong, E-mail: zengy@umkc.edu; Zhang Shu, E-mail: zhangshuisme@hotmail.com

2013-06-15

We study a general filtering problem with marked point process observations. The motivation comes from modeling financial ultra-high frequency data. First, we rigorously derive the unnormalized filtering equation with marked point process observations under mild assumptions, especially relaxing the bounded condition of stochastic intensity. Then, we derive the Poisson chaos expansion for the unnormalized filter. Based on the chaos expansion, we establish the uniqueness of solutions of the unnormalized filtering equation. Moreover, we derive the Poisson chaos expansion for the unnormalized filter density under additional conditions. To explore the computational advantage, we further construct a new consistent recursive numerical schememore » based on the truncation of the chaos density expansion for a simple case. The new algorithm divides the computations into those containing solely system coefficients and those including the observations, and assign the former off-line.« less

Equations for obtaining melting points for the ternary system ethylene glycol/sodium chloride/water and their application to cryopreservation.

PubMed

Woods, E J; Zieger, M A; Gao, D Y; Critser, J K

1999-06-01

The present study describes the H(2)O-NaCl-ethylene glycol ternary system by using a differential scanning calorimeter to measure melting points (T(m)) of four different ratios (R) of ethylene glycol to NaCl and then devising equations to fit the experimental measurements. Ultimately an equation is derived which characterizes the liquidus surface above the eutectic for any R value in the system. This study focuses on ethylene glycol in part because of recent evidence indicating it may be less toxic to pancreatic islets than Me(2)SO, which is currently used routinely for islet cryopreservation. The resulting physical data and previously determined information regarding the osmotic characteristics of canine pancreatic islets are combined in a mathematical model to describe the volumetric response to equilibrium-rate freezing in varying initial concentrations of ethylene glycol. Copyright 1999 Academic Press.

Role of crystallizational differention in the origin of island-arc andesitic melts: evidence from data on melt inclusions and oxygen isotopes

NASA Astrophysics Data System (ADS)

Krasheninnikov, S. P.; Portnyagin, M.; Bindeman, I. N.; Bazanova, L. I.

2012-12-01

Several recent studies of melt inclusions in island-arc rocks revealed a strong bimodality of the melt compositions at the predominance of basic and silicic melts and the scarcity of intermediate melts with SiO2=59-66 wt% (e.g. [1]). These observations were used to interpret the origin of island-arc andesites by magma mingling, crustal assimilation and crystal accumulation rather than by fractional crystallization of basaltic magmas. In this work we addressed the question about the scarcity of andesitic melts in island-arc setting by systematic study of bulk compositions, melt inclusions and oxygen isotopes in minerals from Avachinskiy volcano in Kamchatka. We studied ~500 melt inclusions in 6 different mineral phases (Ol, Cpx, Opx, Pl, Amph, Mt), and concentrated on rapidly-quenched tephra samples from 40 Holocene eruptions of andesites and basaltic andesites. The melt inclusions span a large range of compositions from basalts to rhyolites. In comparison with host bulk tephra samples, melt inclusions tend to have more silicic compositions (up to 10 wt% of SiO2), and this disparity tend to increase with increasing SiO2 content in the host rocks. Both melt inclusion and host rock compositions form trends along the line dividing low- and middle-K island-arc series, and variations of major elements are continuous, without apparent bimodality, which is observed in data set from [1]. The MI statistical distribution is rather three-modal with maxima at ~56-58, ~66 and 74 wt% of SiO2. Much of the major element variability in MI can be explained by fractional crystallization from parental basaltic melts using numerical modeling of crystallization path. Magnetite crystallization starts at ~58 wt% of SiO2 and affects significantly on the evolutional path of melts. Abundant crystallization of magnetite lead to formation of more silica rich coexistent melts and change of crystallizing assemblage occurred at ~60 wt% of SiO2, when Opx replaced Ol, and Amph and Ap become stable

Experimental evidence for flux-lattice melting. [in high-Tc superconductors

NASA Technical Reports Server (NTRS)

Farrell, D. E.; Rice, J. P.; Ginsberg, D. M.

1991-01-01

A low-frequency torsional oscillator has been used to search for flux-lattice melting in an untwinned single crystal of YBa2Cu3O(7-delta). The damping of the oscillator was measured as a function of temperature, for applied magnetic fields in the range H = 0.1-2.3 T. A remarkably sharp damping peak has been located. It is suggested that the temperature of the peak corresponds to the melting point of the Abrikosov flux lattice.

Hot melt recharge system. [repairing damaged or missing tiles on space shuttle orbiter

NASA Technical Reports Server (NTRS)

Progar, D. J. (Inventor)

1983-01-01

A package assembly is described for pecisely positioning a charge of hot melt adhesive onto an attachment pad or point of use. The adhesive is heated to softening or melt temperature (280 F to 325 F) and thereafter cooled to resolidifying temperature. A single sided pressure sensitive polyimide film tape serves with another film strip to protect a sandwiched adhesive strip until use and to hold the adhesive in precise position until thermally bonded to its point of use. Tab ends serve as aids in stripping tapes and from the adhesive charge.

Silicate and Carbonatite Melts in the Mantle: Adding CO2 to the pMELTS Thermodynamic Model of Silicate Phase Equilibria

NASA Astrophysics Data System (ADS)

Antoshechkina, P. M.; Shorttle, O.

2016-12-01

The current rhyolite-MELTS algorithm includes a mixed H2O-CO2 vapor phase, and a self-consistent speciation model for CO2 and CaCO3 in the silicate liquid (Ghiorso & Gualda 2012; 2015). Although intended primarily to model crustal differentiation and degassing, GG15 captures much of the experimentally-observed melting behavior of CO2-rich mafic lithologies, including generation of small-degree carbonatite melts, a miscibility gap between carbonatite and silicate liquids at low P and a smooth transition to a single carbonated-silicate melt at high P (e.g. Dasgupta et al. 2007). However, solid and liquid carbonate phases were not used in calibration of GG15, and it is suitable only for P < 3 GPa. We present a preliminary model, based on pMELTS (Ghiorso et al. 2002), for melting of nominally-anhydrous carbonated peridotite and pyroxenite. In Antoshechkina et al. (2015; and references therein) we developed a scheme for calibration of molar volumes that directly interfaces with a MySQL database, adapted from LEPR (Hirschmann et al. 2008). Here, we further extend our database, e.g. to include multiple carbonate phases, and combine the calibration scheme with the libalphaMELTS interface to the rhyolite-MELTS, pMELTS, and H2O-CO2 fluid thermodynamic models (see magmasource.caltech.edu/alphamelts). We use a Monte-Carlo type calibration approach to fit the observed phases and compositions, though stop short of a fully Bayesian formulation. The CO2-fluid experimental database has been updated to include more recent and higher P studies, adding approximately 40 pure fluid plus liquid constraints that conform to the selection criteria used in GG15. To further expand the database, we plan to use some or all of: solid carbonate-bearing experiments; coexisting silicate and carbonatite liquids; phase-present, and phase-absent constraints. As a first approximation, we include four carbonate phases: pure calcite and aragonite, and binary solutions for dolomite-ankerite and magnesite

Hydrous melt-rock reaction in the shallow mantle wedge

NASA Astrophysics Data System (ADS)

Mitchell, A.; Grove, T. L.

2017-12-01

In subduction zone magmatism, hotter, deeper hydrous mantle melts rise and interact with the shallower, cooler depleted mantle in the uppermost part of the mantle wedge. Here, we experimentally investigate these hydrous reactions using three different ratios of a 1.6 GPa mantle melt and an overlying 1.2 GPa harzburgite from 1060 to 1260 °C. At low ratios of melt/mantle (20:80 and 5:95), the crystallizing assemblages are dunites, harzburgites, and lherzolites (as a function of temperature). When the ratio of deeper melt to overlying mantle is 70:30, the crystallizing assemblage is a wehrlite. This shows that wehrlites, which are observed in ophiolites and mantle xenoliths, can be formed by large amounts of deeper melt fluxing though the mantle wedge during ascent. In all cases, orthopyroxene dissolves in the melt, and olivine crystallizes along with pyroxenes and spinel. The amount of reaction between deeper melts and overlying mantle, simulated here by the three starting compositions, imposes a strong influence on final melt compositions, particularly in terms of depletion. At the lowest melt/mantle ratios, the resulting melt is an extremely depleted Al-poor, high-Si andesite. As the fraction of melt to mantle increases, final melts resemble primitive basaltic andesites found in arcs globally. Wall rock temperature is a key variable; over a span of <80 °C, reaction with deeper melt creates the entire range of mantle lithologies from a depleted dunite to a harzburgite to a refertilized lherzolite. Together, the experimental phase equilibria, melt compositions, and calculated reaction coefficients provide a framework for understanding how melt-wall rock reaction occurs in the natural system during melt ascent in the mantle wedge.

A review of the deformation behavior of tungsten at temperatures less than 0.2 of the melting point /K/

NASA Technical Reports Server (NTRS)

Stephens, J. R.

1974-01-01

The deformation behavior of tungsten at temperatures below 0.2 times the absolute melting temperature is reviewed with primary emphasis on the temperature dependence of the yield stress and the ductile-brittle transition. It is concluded that a model based on the high Peierls stress of tungsten best accounts for the observed mechanical behavior at low temperatures. Recent research suggests an important role of electron concentration and bonding on the mechanical behavior of tungsten. Future research on tungsten should include studies to define more clearly the correlation between electron concentration and mechanical behavior of alloys of tungsten and other transition metal alloys.

Melt containment member

DOEpatents

Rieken, Joel R.; Heidloff, Andrew J.

2014-09-09

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

Transient induced tungsten melting at the Joint European Torus (JET)

NASA Astrophysics Data System (ADS)

Coenen, J. W.; Matthews, G. F.; Krieger, K.; Iglesias, D.; Bunting, P.; Corre, Y.; Silburn, S.; Balboa, I.; Bazylev, B.; Conway, N.; Coffey, I.; Dejarnac, R.; Gauthier, E.; Gaspar, J.; Jachmich, S.; Jepu, I.; Makepeace, C.; Scannell, R.; Stamp, M.; Petersson, P.; Pitts, R. A.; Wiesen, S.; Widdowson, A.; Heinola, K.; Baron-Wiechec, A.; Contributors, JET

2017-12-01

Melting is one of the major risks associated with tungsten (W) plasma-facing components (PFCs) in tokamaks like JET or ITER. These components are designed such that leading edges and hence excessive plasma heat loads deposited at near normal incidence are avoided. Due to the high stored energies in ITER discharges, shallow surface melting can occur under insufficiently mitigated plasma disruption and so-called edge localised modes—power load transients. A dedicated program was carried out at the JET to study the physics and consequences of W transient melting. Following initial exposures in 2013 (ILW-1) of a W-lamella with leading edge, new experiments have been performed on a sloped surface (15{}\\circ slope) during the 2015/2016 (ILW-3) campaign. This new experiment allows significantly improved infrared thermography measurements and thus resolved important issue of power loading in the context of the previous leading edge exposures. The new lamella was monitored by local diagnostics: spectroscopy, thermography and high-resolution photography in between discharges. No impact on the main plasma was observed despite a strong increase of the local W source consistent with evaporation. In contrast to the earlier exposure, no droplet emission was observed from the sloped surface. Topological modifications resulting from the melting are clearly visible between discharges on the photographic images. Melt damage can be clearly linked to the infrared measurements: the emissivity drops in zones where melting occurs. In comparison with the previous leading edge experiment, no runaway melt motion is observed, consistent with the hypothesis that the escape of thermionic electrons emitted from the melt zone is largely suppressed in this geometry, where the magnetic field intersects the surface at lower angles than in the case of perpendicular impact on a leading edge. Utilising both exposures allows us to further test the model of the forces driving melt motion that

Cold crucible levitation melting of biomedical Ti-30 wt%Ta alloy.

PubMed

Fukui, H; Yang, W; Yamada, S; Fujishiro, Y; Morita, A; Niinomi, M

2001-06-01

Recently, titanium-tantalum alloys have been studied as implant materials for dental and orthopedic surgery. However, titanium and tantalum are difficult to mix by common arc melting and induction melting, because of their high melting point and the marked difference between their densities (Ti: 1,680 degrees C, 4.5 g/cm3, Ta: 2,990 degrees C, 16.6 g/cm3). Thus, the Cold Crucible Levitation Melting (CCLM) method was chosen to produce a Ti-30 wt%Ta binary alloy in the present study. The CCLM furnace, with 1 kg capacity, consisted of a water-cooled crucible comprising oxygen-free high purity copper segments and coils wrapped around the crucible and connected to a frequency inverter power supply. A qualified ingot of 1.0 kg of Ti-30 wt%Ta alloy was obtained. The ingot was characterized from the surface quality, chemical composition distribution and microstructure, and finally the melting process was discussed.

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

NASA Astrophysics Data System (ADS)

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

2017-04-01

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

The initiation of segmented buoyancy-driven melting during continental breakup

PubMed Central

Gallacher, Ryan J.; Keir, Derek; Harmon, Nicholas; Stuart, Graham; Leroy, Sylvie; Hammond, James O. S.; Kendall, J-Michael; Ayele, Atalay; Goitom, Berhe; Ogubazghi, Ghebrebrhan; Ahmed, Abdulhakim

2016-01-01

Melting of the mantle during continental breakup leads to magmatic intrusion and volcanism, yet our understanding of the location and dominant mechanisms of melt generation in rifting environments is impeded by a paucity of direct observations of mantle melting. It is unclear when during the rifting process the segmented nature of magma supply typical of seafloor spreading initiates. Here, we use Rayleigh-wave tomography to construct a high-resolution absolute three-dimensional shear-wave velocity model of the upper 250 km beneath the Afar triple junction, imaging the mantle response during progressive continental breakup. Our model suggests melt production is highest and melting depths deepest early during continental breakup. Elevated melt production during continental rifting is likely due to localized thinning and melt focusing when the rift is narrow. In addition, we interpret segmented zones of melt supply beneath the rift, suggesting that buoyancy-driven active upwelling of the mantle initiates early during continental rifting. PMID:27752044

Laser observations of the moon - Normal points for 1972

NASA Technical Reports Server (NTRS)

Shelus, P. J.; Mulholland, J. D.; Silverberg, E. C.

1975-01-01

The lunar laser observations taken at the McDonald Observatory during 1972 are presented in the form of compressed normal points, using the technique of an earlier paper. Refinements in the knowledge of the lunar motion have permitted corresponding increases in the ability to discriminate observations contaminated by equipment malfunctions; a list of amendments is given for the 1969-1971 data. The geometry of the telescope must be taken into account in the application of these data.

Hetero-phase fluctuations in the pre-melting region in ionic crystals

NASA Astrophysics Data System (ADS)

Matsunaga, S.; Tamaki, S.

2008-06-01

The theory of the pre-melting phenomena in ionic crystals on the basis of the concept of the hetero phase fluctuation has been applied to KCl and AgCl crystal. The large scale molecular dynamics simulations (MD) in KCl and AgCl crystals are also performed to examine the ionic configuration in premelting region in the vicinity of their melting points. The size of the liquid like clusters are estimated by the theory and MD. The structural features of liquid like clusters are discussed by MD results using the Lindemann instability condition. The ionic conductivities in the pre-melting region are also discussed on the same theoretical basis.

Special relativity from observer's mathematics point of view

NASA Astrophysics Data System (ADS)

Khots, Boris; Khots, Dmitriy

2015-09-01

When we create mathematical models for quantum theory of light we assume that the mathematical apparatus used in modeling, at least the simplest mathematical apparatus, is infallible. In particular, this relates to the use of "infinitely small" and "infinitely large" quantities in arithmetic and the use of Newton - Cauchy definitions of a limit and derivative in analysis. We believe that is where the main problem lies in contemporary study of nature. We have introduced a new concept of Observer's Mathematics (see www.mathrelativity.com). Observer's Mathematics creates new arithmetic, algebra, geometry, topology, analysis and logic which do not contain the concept of continuum, but locally coincide with the standard fields. We use Einstein special relativity principles and get the analogue of classical Lorentz transformation. This work considers this transformation from Observer's Mathematics point of view.

A benchmark initiative on mantle convection with melting and melt segregation

NASA Astrophysics Data System (ADS)

Schmeling, Harro; Dohmen, Janik; Wallner, Herbert; Noack, Lena; Tosi, Nicola; Plesa, Ana-Catalina; Maurice, Maxime

2015-04-01

In recent years a number of mantle convection models have been developed which include partial melting within the asthenosphere, estimation of melt volumes, as well as melt extraction with and without redistribution at the surface or within the lithosphere. All these approaches use various simplifying modelling assumptions whose effects on the dynamics of convection including the feedback on melting have not been explored in sufficient detail. To better assess the significance of such assumptions and to provide test cases for the modelling community we initiate a benchmark comparison. In the initial phase of this endeavor we focus on the usefulness of the definitions of the test cases keeping the physics as sound as possible. The reference model is taken from the mantle convection benchmark, case 1b (Blanckenbach et al., 1989), assuming a square box with free slip boundary conditions, the Boussinesq approximation, constant viscosity and a Rayleigh number of 1e5. Melting is modelled assuming a simplified binary solid solution with linearly depth dependent solidus and liquidus temperatures, as well as a solidus temperature depending linearly on depletion. Starting from a plume free initial temperature condition (to avoid melting at the onset time) three cases are investigated: Case 1 includes melting, but without thermal or dynamic feedback on the convection flow. This case provides a total melt generation rate (qm) in a steady state. Case 2 includes batch melting, melt buoyancy (melt Rayleigh number Rm), depletion buoyancy and latent heat, but no melt percolation. Output quantities are the Nusselt number (Nu), root mean square velocity (vrms) and qm approaching a statistical steady state. Case 3 includes two-phase flow, i.e. melt percolation, assuming a constant shear and bulk viscosity of the matrix and various melt retention numbers (Rt). These cases should be carried out using the Compaction Boussinseq Approximation (Schmeling, 2000) or the full compaction

Low melting high lithia glass compositions and methods

DOEpatents

Jantzen, Carol M.; Pickett, John B.; Cicero-Herman, Connie A.; Marra, James C.

2003-09-23

The invention relates to methods of vitrifying waste and for lowering the melting point of glass forming systems by including lithia formers in the glass forming composition in significant amounts, typically from about 0.16 wt % to about 11 wt %, based on the total glass forming oxides. The lithia is typically included as a replacement for alkali oxide glass formers that would normally be present in a particular glass forming system. Replacement can occur on a mole percent or weight percent basis, and typically results in a composition wherein lithia forms about 10 wt % to about 100 wt % of the alkali oxide glass formers present in the composition. The present invention also relates to the high lithia glass compositions formed by these methods. The invention is useful for stabilization of numerous types of waste materials, including aqueous waste uranium oxides The decrease in melting point achieved by the present invention desirably prevents volatilization of hazardous or radioactive species during vitrification.

Ice melt, sea level rise and superstorms: evidence from paleoclimate data, climate modeling, and modern observations that 2 °C global warming could be dangerous

NASA Astrophysics Data System (ADS)

Hansen, James; Sato, Makiko; Hearty, Paul; Ruedy, Reto; Kelley, Maxwell; Masson-Delmotte, Valerie; Russell, Gary; Tselioudis, George; Cao, Junji; Rignot, Eric; Velicogna, Isabella; Tormey, Blair; Donovan, Bailey; Kandiano, Evgeniya; von Schuckmann, Karina; Kharecha, Pushker; Legrande, Allegra N.; Bauer, Michael; Lo, Kwok-Wai

2016-03-01

We use numerical climate simulations, paleoclimate data, and modern observations to study the effect of growing ice melt from Antarctica and Greenland. Meltwater tends to stabilize the ocean column, inducing amplifying feedbacks that increase subsurface ocean warming and ice shelf melting. Cold meltwater and induced dynamical effects cause ocean surface cooling in the Southern Ocean and North Atlantic, thus increasing Earth's energy imbalance and heat flux into most of the global ocean's surface. Southern Ocean surface cooling, while lower latitudes are warming, increases precipitation on the Southern Ocean, increasing ocean stratification, slowing deepwater formation, and increasing ice sheet mass loss. These feedbacks make ice sheets in contact with the ocean vulnerable to accelerating disintegration. We hypothesize that ice mass loss from the most vulnerable ice, sufficient to raise sea level several meters, is better approximated as exponential than by a more linear response. Doubling times of 10, 20 or 40 years yield multi-meter sea level rise in about 50, 100 or 200 years. Recent ice melt doubling times are near the lower end of the 10-40-year range, but the record is too short to confirm the nature of the response. The feedbacks, including subsurface ocean warming, help explain paleoclimate data and point to a dominant Southern Ocean role in controlling atmospheric CO2, which in turn exercised tight control on global temperature and sea level. The millennial (500-2000-year) timescale of deep-ocean ventilation affects the timescale for natural CO2 change and thus the timescale for paleo-global climate, ice sheet, and sea level changes, but this paleo-millennial timescale should not be misinterpreted as the timescale for ice sheet response to a rapid, large, human-made climate forcing. These climate feedbacks aid interpretation of events late in the prior interglacial, when sea level rose to +6-9 m with evidence of extreme storms while Earth was less than 1 �

Analysis of the effect of symmetric/asymmetric CUSP magnetic fields on melt/crystal interface during Czochralski silicon growth

NASA Astrophysics Data System (ADS)

Daggolu, Parthiv; Ryu, Jae Woo; Galyukov, Alex; Kondratyev, Alexey

2016-10-01

With the use of 300 mm silicon wafers for industrial semiconductor device manufacturing, the Czochralski (Cz) crystal growth process has to be optimized to achieve higher quality and productivity. Numerical studies based on 2D global thermal models combined with 3D simulation of melt convection are widely used today to save time and money in the process development. Melt convection in large scale Cz Si growth is controlled by a CUSP or transversal magnetic field (MF) to suppress the melt turbulence. MF can be optimized to meet necessary characteristics of the growing crystal, in terms of point defects, as MF affects the melt/crystal interface geometry and allows adjustment of the pulling rate. Among the different knobs associated with the CUSP magnetic field, the nature of its configuration, going from symmetric to asymmetric, is also reported to be an important tool for the control of crystallization front. Using a 3D unsteady model of the CGSim software, we have studied these effects and compared with several experimental results. In addition, physical mechanisms behind these observations are explored through a detailed modeling analysis of the effect of an asymmetric CUSP MF on convection features governing the heat transport in the silicon melt.

Characterization of Metals Melting Discs: Skylab Experiment M551

NASA Technical Reports Server (NTRS)

Monroe, R. E.

1973-01-01

Information developed to characterize flight and ground based samples from the metals melting experiment is detailed in this report. Included are the characteristics determined by nondestructive examination, visual observation, metallographic examination and posttest measurements. Comparisons of the flight and ground based discs showed that an electron beam heat source can be used successfully in zero gravity for cutting, welding, or melting. Few differences were observed that could be attributed to the absence of gravity in these operations.

Models and Experiments of Melt-Rock Interaction in the Lower Oceanic Crust

NASA Astrophysics Data System (ADS)

Orton, W. H., II; Liang, Y.; Sanfilippo, A.

2017-12-01

Understanding the processes of melt-rock interaction in the lower oceanic crust isimportant to the interpretation of mid-ocean ridge basalt (MORB) and the petrogenesis of lowercrustal cumulates. Petrologic and geochemical studies of cumulates from the lower crustalregions of oceanic lithosphere have identified a number of textural and chemical features that arepertinent to melt-rock reaction (e.g., high-Mg# clinopyroxene oikocrysts within local gabbroicregions in troctolite bodies). The purpose of the present study is to provide some referenceexamples of MORB melt and cumulate mush interaction under controlled conditions. Suchsimple experiments are useful in sorting out crystallization, dissolution, re-precipitation, anddiffusion processes in the cumulate mush and in developing better models for melt transport andmelt-rock interaction in the lower oceanic crust.We performed piston cylinder experiments at 0.5-0.7 GPa and 1000-1250°C reacting anolivine or olivine + plagioclase cumulate mush and an intruding MORB melt in a graphite-linedmolybdenum capsule. Our experiments consist of two steps: (1) reaction at 1250°C for 10 to 24hours; and (2) reactive crystallization to a lower temperature through controlled cooling overseveral days. Cooling promotes in situ crystallization of interstitial melts, allowing us to bettercharacterize the mineral compositional trends produced and observed by melt-rock reaction andcrystallization. Reaction at 1250°C produced an olivine + melt mush with small rounded crystalscharacteristic of dissolution. Significant crystal settling was also observed at large melt-to- rockratio. Cooling with continued reaction resulted in the formation of a plagioclase matrix withpoikilitic clinopyroxene oikocrysts containing plagioclase and relict olivine as chadacrysts.Clinopyroxenes were in a reaction relationship with both plagioclase and olivine. In somesamples, multiple phases of clinopyroxene and plagioclase were present, each with

Observing Coronal Mass Ejections from the Sun-Earth L5 Point

NASA Astrophysics Data System (ADS)

Gopalswamy, N.; Davila, J. M.; St Cyr, O. C.

2013-12-01

Coronal mass ejections (CMEs) are the most energetic phenomenon in the heliosphere and are known to be responsible for severe space weather. Most of the current knowledge on CMEs accumulated over the past few decades has been derived from observations made from the Sun-Earth line, which is not the ideal vantage point to observe Earth-affecting CMEs (Gopalswamy et al., 2011a,b). The STEREO mission viewed CMEs from points away from the Sun-Earth line and demonstrated the importance of such observations in understanding the three-dimensional structure of CMEs and their true kinematics. In this paper, we show that it is advantageous to observe CMEs from the Sun-Earth L5 point in studying CMEs that affect Earth. In particular, these observations are important in identifying that part of the CME that is likely to arrive at Earth. L5 observations are critical for several aspects of CME studies such as: (i) they can also provide near-Sun space speed of CMEs, which is an important input for modeling Earth-arriving CMEs, (ii) backside and frontside CMEs can be readily distinguished even without inner coronal imagers, and (iii) preceding CMEs in the path of Earth-affecting CMEs can be identified for a better estimate of the travel time, which may not be possible from the Sun-Earth line. We also discuss how the L5 vantage point compares with the Sun-Earth L4 point for observing Earth-affecting CMEs. References Gopalswamy, N., Davila, J. M., St. Cyr, O. C., Sittler, E. C., Auchère, F., Duvall, T. L., Hoeksema, J. T., Maksimovic, M., MacDowall, R. J., Szabo, A., Collier, M. R. (2011a), Earth-Affecting Solar Causes Observatory (EASCO): A potential International Living with a Star Mission from Sun-Earth L5 JASTP 73, 658-663, DOI: 10.1016/j.jastp.2011.01.013 Gopalswamy, N., Davila, J. M., Auchère, F., Schou, J., Korendyke, C. M. Shih, A., Johnston, J. C., MacDowall, R. J., Maksimovic, M., Sittler, E., et al. (2011b), Earth-Affecting Solar Causes Observatory (EASCO): a mission at

Structure, Frictional Melting and Fault Weakening during the 2008 Mw 7.9 Wenchuan Earthquake Slip: Observation from the WFSD Drilling Core Samples