Pressure Melting Research Articles

SEAMHex - Fast 6D Additive Manufacturing using an innovative Screw Extruder applied on a Hexapod Parallel Kinematic

The Screw Extrusion Additive Manufacturing (SEAM) technology provides output rates up to 10 kg/h, a melt pressure up to 350 bar and temperatures up to 400 °C as well as strands with an adjustable bead width between 1-8 mm. Due to a bypass nozzle, position jumps without material extrusion, local wall thickness reduction, and the control of the volume flow (0-100 %) are made possible. Further, the extruder is able to process fiber-reinforced as well as highly filled plastics and integrates a regranulation system to return bypassed material into the process. The hexapod parallel kinematic meets the process requirements, as it generates a rapid movement of the workpiece (up to 1 m/s) in 6 degrees of freedom within a large printing workspace (1100 × 800 x 600 mm3), where an additional Z-axis carries the extruder and realizes the part height. Eccentric joints provide high accuracy and stiffness while being cost-efficient at the same time. The commercial Beckhoff TwinCAT control allows G-code processing and provides an HTML based GUI for machine and extruder control. Consequently, high accuracy is achieved, which is verified by the use of a double-ball-bar measuring device and by producing a test workpiece.

Hugoniot equation-of-state and structure of laser-shocked polyimide C22H10N2O5

The Hugoniot equation-of-state, Gr\"uneisen parameter, and structure of laser-shocked polyimide were measured. The polyimide Hugoniots were measured in the pressure range 80--600 GPa and found to be consistent with the extrapolation of previously reported data below 60 GPa. The structural measurements of polyimide shock compressed to pressures of 28--163 GPa were performed using the in situ x-ray diffraction technique, and the results show that the melting pressure of polyimide along its Hugoniot is below 32(\ifmmode\pm\else\textpm\fi{}3) GPa, indicating that the discontinuous volume change of the polyimide Hugoniot at \ensuremath{\sim}26 GPa observed in previous gas-gun experiments denotes the onset of melting. The consistency of the melting pressure between the previous gas-gun results and the present laser experiments suggests that the shock-melting process of polyimide is independent of the duration of the compression, revealing its rapid melting kinetics.

Paradigm shift for controls on basalt magmatism: Discussion with Lustrino et al on the paper I recently published in Earth-Science Reviews

I recently published “Lithosphere thickness controls the extent of mantle melting, depth of melt extraction and basalt compositions in all tectonic settings on Earth – A review and new perspectives” in this journal to demonstratively summarize a major component of my 30-year dedicated research on the basalt problem with the emphasis that the paradigm “mantle potential temperature controls the extent and pressure of mantle melting and basalt compositions” that is inconsistent with observations and experimental petrology must be abandoned. As the change from “temperature control” to “lithosphere thickness control” is fundamental and unfamiliar to many, I encourage members of the community for debate. The community interest in the theme of the paper is reflected by more than 1000 reads and 50 recommendations in RG within 10 days of its publication. In addition to a few email exchanges, the commentary by Lustrino et al. (2022) is the first written discussion with interesting comments of both breadth and depth. Overall, their commentary is more highly affirmative rather than criticism. Most of the comments are not about Niu (2021) but more general and may be shared by the scientific community. Therefore, my response is intended to be thorough, in particular on issues and concepts that I consider the community needs to be correctly informed of. My reply follows four basic principles: [1] I maintain “Objectiveness and open-mindedness (vs. ‘confirmation bias’) are requisite twins for insights and discoveries.”; [2] I express my views based on observations, experimental petrology, well-understood concepts, logical reasoning and objective analysis, rather than personal opinions to “believe” or “disbelieve”; [3] I emphasize that some misattributions may be innocent, but should be avoided because they serve no favor to our science and scientific discussion; and [4] I try to use plain language to ensure my writing readily understood by the reader. For clarity, my reply follows the same numbered questions as in the commentary and I do not discuss issues on which the commenters agree with me. Figures referenced in quotations are those in Niu (2021). For consistency, mantle potential temperature is denoted with TMP (vs. TP)

Topological Aspects of Molecular Networks: Crystal Cubic Carbons

Theory of networks serves as a mathematical foundation for the construction and modeling of chemical structures and complicated networks. In particular, chemical networking theory has a wide range of utilizations in the study of chemical structures, where examination and manipulation of chemical structural information are made feasible by utilizing the numerical graph invariants. A network invariant or a topological index (TI) is a numerical measure of a chemical compound which is capable to describe the chemical structural properties such as melting point, freezing point, density, pressure, tension, and temperature of chemical compounds. Wiener initiated the first distance‐based TI which is considered to be the most important TI to preserve the chemical and physical properties of chemical structures. Later on, degree‐based TI was introduced to find the π‐electron energy of molecules. Recently, connection number‐based TIs are studied which are more efficient than degree and distance‐based TIs. In this paper, we compute the connection number‐based TIs of the structure of crystal cubic carbons which are one of the most significant and interesting composites in modern resources of science due to the involvement of carbon atoms.

Down risers for gravity casting

Based on real experience, as well as on the results of computer simulation, examples of designing of down riser gating systems for complex demanding gravity castings are given and the operation of these systems is analyzed. Effect of hydrostatic pressure of melt on the down riser work during a solidification of hot spot of casting is studied using computer simulation.

Phase diagram prediction and high pressure melting characteristics of GaN

The III-V compound semiconductor, GaN, has become an excellent semiconductor material for developing the high-frequency and high-power electronic devices because of its excellent characteristics, including large band width, high thermal conductivity and fast electron saturation rate, and has received extensive attention in recent years. However, the decomposition temperature of GaN is lower than the melting temperature, some of its fundamental properties, such as melting temperature and high temperature phase transition pressure, are still unclear, and so, now the investigation of fundamental properties dominates the whole process of this material from development to mature applications. In the present work, the classical molecular dynamics simulations combined with the first-principles calculations and lattice dynamics methods are adopted to predict the phase diagrams of GaN with wurtzite and rocksalt structures in a pressure range of 0–80 GPa. The phase transition pressures, 44.3 GPa and 45.9 GPa, obtained from the first-principles calculations and molecular dynamics simulations from wurtzite to rocksalt structure in GaN at zero temperature, are in agreement with the available experimental results (Sadovyi B, et al. <ext-link ext-link-type="uri" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://doi.org/10.1103/PhysRevB.102.235109">2020 <i>Phys. Rev. B</i> <b>102</b> 235109</ext-link>). The melting temperature at 0 GPa is 2295 K obtained by extrapolating the GaN melting curve of the wurtzite structure. With the pressure increasing to 33.3 GPa, the melting curve of wurtzite structure in GaN intersects with the melting curve of rocksalt structure, and the melting temperatures of both structures increase with pressure increasing. It is found that GaN may have a superionic phase and the superionic phase transition occurs in the wurtzite structure at pressures greater than 2.0 GPa and temperatures above 2550 K, whereas the rocksalt structure undergoes a superionic phase transition at pressures and temperatures higher than 33.1 GPa and 4182 K, respectively, and both of the phase transition temperatures increase with pressure increasing. The slope of the phase boundary line of GaN is positive at high temperatures and gradually changes into a curve with a negative slope as the temperature decreases.

<i>In situ</i> X-ray diffraction measurement of shock melting in vanadium

The solid-liquid phase transition under shock wave loading in materials is called shock melting. Shock melting is important not only in fields like high pressure EOS or material dynamic response, but also in applications like device protection in modern industry and national defense construction. The obtaining of precise melting curve is more than understanding the high pressure melting behavior, and it can provide the reliable evidence for the theoretical model of melting mechanism. So the solid-liquid phase transition under extreme conditions is a research hotspot, and a lot of researches have been carried out. But, the enormous discrepancy between the melting curve of dynamic loading and hydrostatic loading in transition metals, especially, the vanadium has been unclear for decades. The difference in melting temperature under 200 GPa between dynamic loading and hydrostatic loadirng is as large as twice (about 4000 K). Recently, Errandonea and Zhang’s experiments present a new insight into this discrepancy, indicating that the new shock melting curve is consistent with the extrapolated melting curve contained by LH-DAC. But all the dynamic loading experimental data are measured by macroscopic quantities; they can determine the occurrence of the phase transition, but cannot provide the microscopic structure of the material under extreme conditions. So, as the technic of in situ X-ray diffraction has developed well in recent years, we use the high power laser driving technic combining with in situ X-ray diffraction measurement to explore the structure of vanadium near the melting line. We measure the micro structure of vanadium at up to 200 GPa in shock experiment for the first time. We find that the bcc phase transition is not observed at around 60 GPa, which is different from previous experiments in DAC or gas gun loading experiments, but consistent with Chen’s leaser driving experiment. The result confirms that when the impact pressure is 155 GPa, vanadium still remains solid BCC phase. It becomes liquid at about 190 GPa. In contract to Zhang’s results, the DXRD melting point is consistent with the new melting line. This work provides the evidence of the consistency of shock and hydrostatic melting curve, confirming the phase boundary of vanadium under 200 GPa. This work has important scientific significance in understanding the pressure melting behavior of transition metals. The method in this work can be applied to the research of melting properties of other materials.

Preparation of high sphericity monodisperse aluminum microspheres by pulsated orifice ejection method

Aluminum microspheres with high sphericity are widely used and urgent demanded in additive manufacturing. However, the current primary atomization method is insufficient in sphericity and particle size distribution. Herein, the monodisperse aluminum microspheres with high sphericity and narrow particle size distribution are successfully prepared by the pulsated orifice ejection method (POEM). The particle size distributions of the prepared aluminum microsphere samples with the average diameter of 325.2 µm are ranged from 315 µm to 332 µm, in which the sphericity of 50% microspheres reached 0.966, and that of 99.59% microspheres reached 0.9. The crucible pressure and interface reaction of aluminum melt with crucible are investigated to explore the influence of technological conditions on aluminum particles. Additionally, the effect of cooling rate on particle size is also studied and the results demonstrate that the sphericity of aluminum microspheres can be improved by decreasing the cooling rate during droplet solidification.

Melting temperature of ice and total gas content of water at the ice-water interface above subglacial Lake Vostok

It is generally assumed that the gas composition and the total gas content of Lake Vostok’s water are, to a large extent, governed by the budget of atmospheric gases entering the lake together with glacier ice melt, mostly in its northern part. Since the ice accretion that prevails in the south of the lake leads to the exclusion of gases during the freezing process, these gases can build up in the lake water. Earlier theoretical works [2, 3] have demonstrated that about 30 water residence times are required to attain equilibrium between gases in solution and those in a hydrate phase, which sets the upper bounds of concentrations of nitrogen and oxygen dissolved in sub-ice water (~2.7 g N2 L–1 and ~0.8 g O2 L–1). Here we attempt to estimate the real gas content of the lake water based on the link between the pressure melting temperature of ice and the concentration of gases dissolved in the liquid phase [2]. We use the stacked borehole temperature profile extended to 3753 m depth and the measurements of temperature of sub-ice water that entered the borehole after the second unsealing of Lake Vostok to estimate the melting temperature of ice (–2.72 ± 0.1 °C) at the ice sheet-lake interface (depth 3758.6 ± 3 m, pressure 33.78 ± 0.05 MPa). The gas content of the near-surface layer of lake that corresponds to this melting temperature is calculated to be 2.23 g.L–1, meaning that the concentration of dissolved oxygen must be as high as 0.53 g.L–1, i. e. one-two orders of magnitude higher than in any other known water bodies on our planet. The inferred gas content of sub-ice water is, by a factor of 1.6, lower than the maximal solubility of air in water in equilibrium with air hydrate, though it is still higher, by a factor of 19, than the total air content of melting glacier ice. The relatively low concentration of dissolved air in the near-surface layer of the lake revealed in this study provides a new experimental constraint for understanding the gas distribution in Lake Vostok as affected by the circulation and mixing of water beneath the ice sheet.

Process Influences in the Combined Compacting and Back-Injection Process to Produce Back-Injected Self-Reinforced Composites (SRCs) – Analysis via Multiple Regression Modelling

Abstract A new process to produce back-injected self-reinforced composites (SRCs) is presented. In contrast to other investigations on back-injection of SRCs, a process is presented which allows compacting and back injection of SRCs in one step where the SRCs are partly consolidated only via melt pressure inside the cavity. The mechanical properties of SRCs depend to a large extent on the process parameters of temperature and pressure during manufacture. These parameters are not yet known for back-injected areas. Sensors inside of the cavity measure the influences on the temperature and pressure conditions in the cavity. Initial studies on adhesion were carried out and analysed. For this purpose, shear tests of the back-injected component were carried out and a maximum shear strength of 5.81 MPa was determined for the materials used here. The investigations also show a dependence on the Distance from the Gate (DG) and the Mass temperature (TM). First microscopic examinations show good bonding between the SRC and the injection molded part, with no voids or air pockets in the boundary layer. It can also be seen that successful consolidation takes place in the area of the back injection.

Equation of State for Solid Benzene Valid for Temperatures up to 470 K and Pressures up to 1800 MPa

The thermodynamic property data for solid phase I of benzene are reviewed and utilized to develop a new fundamental equation of state (EOS) based on Helmholtz energy, following the methodology used for solid phase I of CO2 by Trusler [J. Phys. Chem. Ref. Data 40, 043105 (2011)]. With temperature and molar volume as independent variables, the EOS is able to calculate all thermodynamic properties of solid benzene at temperatures up to 470 K and at pressures up to 1800 MPa. The model is constructed using the quasi-harmonic approximation, incorporating a Debye oscillator distribution for the vibrons, four discrete modes for the librons, and a further 30 distinct modes for the internal vibrations of the benzene molecule. An anharmonic term is used to account for inevitable deviations from the quasi-harmonic model, which are particularly important near the triple point. The new EOS is able to describe the available experimental data to a level comparable with the likely experimental uncertainties. The estimated relative standard uncertainties of the EOS are 0.2% and 1.5% for molar volume on the sublimation curve and in the compressed solid region, respectively; 8%–1% for isobaric heat capacity on the sublimation curve between 4 K and 278 K; 4% for thermal expansivity; 1% for isentropic bulk modulus; 1% for enthalpy of sublimation and melting; and 3% and 4% for the computed sublimation and melting pressures, respectively. The EOS behaves in a physically reasonable manner at temperatures approaching absolute zero and also at very high pressures.

Concurrent characterization of compressibility and viscosity in extrusion-based additive manufacturing of acrylonitrile butadiene styrene with fault diagnoses

Compressibility and viscosity of polymer feedstock are critical to their volumetric flow rate, weld strength, and dimensional accuracy in material extrusion additive manufacturing. In this work, the compressibility and viscosity of an acrylonitrile butadiene styrene (ABS) material is characterized with an instrumented hot end design. Experiments are first performed with a blocked nozzle to characterize the compressibility behavior. The results closely emulate the pressure-volume-temperature (PVT) behavior of a characterized generic ABS. Experiments are then performed with an open nozzle over a range of volumetric flow rates and temperatures. The static pressure data is fit to power-law, Ellis, and Cross viscosity models and the dynamic melt pressure data is then used to jointly fit material constitutive models for compressibility and viscosity. The results suggest that the joint fitting substantially improves the fidelity relative to the separately characterized viscosity and compressibility. The implemented methods support material extrusion process simulation and control including real-time identification of process faults such as (1) limited melting capacity of the hot end, (2) skipping (grinding) of the extruder drive gears, (3) low initial nozzle temperature, (4) varying flow rates associated with the intermeshing gear tooth velocity profile, and (5) delays and reduced melt pressures due to drool prior to extrusion. The ability to monitor the printing process for faults in real time, such as that presented in this work, is critical to born qualified parts. Additionally, these approaches can be used to screen new materials and identify optimal processing conditions that avoid these process faults. • Detailed design of an instrumented hot end is provided. • Two-stage compression is used to characterize compressibility with a blocked nozzle. • Power law, Ellis, and Cross models are fit to apparent viscosity data generated with a stock nozzle having a diameter of 0.4 mm. • Viscosity and compressibility models are fit by minimizing the error between the input mass flow rate and the modeled fluid capacitance and outlet mass flow rate. • Dynamic melt pressure data reveals significant faults occurring during extrusion.

Friction-damage coupled models and macroscopic strength criteria for ice-saturated frozen silt with crack asperity variation by a micromechanical approach

This paper aims to present physical friction-damage coupled models and derive macroscopic nonlinear strength criteria for ice-saturated frozen silt. Two material scales are considered here. The material at the mesoscale is composed of a frozen silt matrix and embedded mesocracks. At the microscale, the frozen silt matrix is composed of elastic mineral grains and elastic ice crystals. Considering this microstructure, for the ice-saturated frozen silt, the plastic deformation is related to frictional sliding along the mesocracks, and damage is due to the propagation of mesocracks. We obtain the effective elastic properties with a two-step linear Mori-Tanaka homogenization procedure. For the second homogenization step, we deduce the macroscopic stress-strain relations and local thermodynamic forces associated with damage and plasticity. Then, an energy release-based damage criterion is developed to capture the evolution of damage, and a friction sliding criterion with an associated/nonassociated local plastic flow rule is introduced to describe the rate of plasticity. The friction sliding criterion considers the variation of surface asperities of mesocracks as a result of pressure melting and damage evolution. In this context, associated/nonassociated multiscale friction-damage models are established. Furthermore, associated/nonassociated macroscopic nonlinear strength criteria as inherent parts of the corresponding multiscale models are derived under a large range of compressive stresses. For application, a semi-implicit local numerical algorithm of the multiscale models is developed. The accuracy of associated/nonassociated multiscale models is assessed by comparing their numerical simulations with conventional triaxial compression (CTC) tests. Although the associated multiscale model correctly predicts the nonlinear strength behavior and axial deformation of the Lanzhou frozen silt under CTC tests with different temperatures, it fails to quantitatively reproduce volumetric deformation. Nonassociated multiscale model predictions with experimental data of volumetric deformation are significantly improved compared to the associated multiscale model.

Revisiting mechanics of ice–skate friction: from experiments at a skating rink to a unified hypothesis

AbstractThe mechanics underlying ice–skate friction remain uncertain despite over a century of study. In the 1930s, the theory of self-lubrication from frictional heat supplanted an earlier hypothesis that pressure melting governed skate friction. More recently, researchers have suggested that a layer of abraded wear particles or the presence of quasi-liquid molecular layers on the surface of ice could account for its slipperiness. Here, we assess the dominant hypotheses proposed to govern ice–skate friction and describe experiments conducted in an indoor skating rink aimed to provide observations to test these hypotheses. Our results indicate that the brittle failure of ice under rapid compression plays a strong role. Our observations did not confirm the presence of full-contact water films and are more consistent with the presence of lubricating ice-rich slurries at discontinuous high-pressure zones (HPZs). The presence of ice-rich slurries supporting skates through HPZs merges pressure-melting, abrasion and lubricating films as a unified hypothesis for why skates are so slippery across broad ranges of speeds, temperatures and normal loads. We suggest tribometer experiments to overcome the difficulties of investigating these processes during actual skating trials.

Development of mechanistic cladding rupture model for integrated severe accident code ISAA. Part II: DVI line small-break LOCA in CAP1400

Cladding ballooning and rupture are the important phenomena at the early stage of a severe accident (SA). For example, the SA caused by the loss of coolant accident (LOCA), the decrease in primary loop pressure and the increase in core temperature will lead to the cladding ballooning and rupture. The cladding deformation affects the flow distribution and causes local flow blockage. Meanwhile, water vapor will enter the fuel gap from the rupture, thereby increasing the surface area of cladding that is oxidized by the steam. At present, the widely used integrated severe accident analysis codes cannot analyze fuel rods thermal-mechanical behavior at the early SA stage, and the judgment of cladding rupture is only based on simple parameter model. This paper integrates the developed FRTMB (core Fuel Rod Thermal-Mechanical Behavior analysis module) module into the integrated severe accident analysis code ISAA, so that the coupled system ISAA-FRTMB can analyze fuel rods thermal–mechanical behavior and judge cladding rupture. Part I introduces the need of developing the FRTMB module, verification of the module, and how the module interactively works in the severe accident analysis code. And evaluates the steady-state fuel rods thermal–mechanical behavior at different enrichment areas of the CAP1400 reactor. Part II focuses on analyzing fuel rods behavior during a hypothetical DVI Line (Direct Vessel Injection line) small break-out accident (break diameter d = 4 in.) of the CAP1400, and predicts the cladding rupture time and the corresponding failure temperature. Due to failure of components of the emergency core cooling system and assumed unavailability of several preventive and mitigative accident management measures (AMM), the accident develops into a severe accident scenario with core melt and reactor pressure vessel failure. The mechanical analysis results show the top of the fuel rod is the first to rupture, rather than the peak node. The primary factor affecting the fuel pellet strain is the deformation caused by thermal expansion, while the densification and swelling change little. These results demonstrate the applicability and reliability of ISAA-FRTMB in analyzing fuel rods thermal–mechanical behavior and judging cladding rupture during transient accidents.

Global continental volcanism controlled the evolution of the oceanic nickel reservoir

Wanning nickel (Ni) abundances in the Neoarchean may have led to a decline in marine methanogenic bacteria due to the loss of a key micronutrient, causing a collapse in atmospheric methane levels and the subsequent rise of atmospheric oxygen – the Great Oxidation Event ∼2.5 Ga. However, this hypothesis currently lacks geological evidence that corroborates the processes that led to a decline in the supply of Ni to the oceans at that time. Here we investigate temporal variations of Ni concentrations in the likely source rocks – various volcanic lithologies - spanning the past 3.5 Byr. By applying a spatially gridded resampling to geochemical data from a global compilation of ∼96,000 continental volcanic rocks, we show that komatiites and basaltic-andesitic rocks largely controlled Ni fluxes to the Earth's surface during the Archean but had a waning influence thereafter due to the secular cooling of the mantle. A new compilation of marine shales (397 samples) and an updated compilation of banded iron formations (2037 samples) further confirms a declining clastic and dissolved supply of terrestrial Ni, respectively. Interestingly, we further observed a stable marine Ni concentration for the last 2 Byr. To explain this unexpected trend, we provide a computational model of mantle melting demonstrating that increasing melting pressures likely inhibited a further decline of Ni concentration in volcanic rocks and led to this relative consistency in Ni supply.

ReversePetrogen: A Multiphase Dry Reverse Fractional Crystallization‐Mantle Melting Thermobarometer Applied to 13,589 Mid‐Ocean Ridge Basalt Glasses

AbstractWe present a new algorithm, ReversePetrogen (RevPet), to infer mantle melting conditions (pressure, temperature, source composition) using evolved basalts that have experienced multiphase fractional crystallization. RevPet measures and minimizes the compositional distance between experimentally predicted phase saturation boundaries and an erupted basalt and the more primitive liquids that return it to a primary melt. We use RevPet to investigate mantle melting conditions at mid‐ocean ridges (MORs) using a global data set of 13,589 basaltic glasses. We find that their average apparent mantle potential temperature (TP*) is 1322°C ± 56°C with melting pressures of 13.0 ± 5 kbars. Inferring the true initial (pre‐melted) TP from TP* requires knowing the style and degree of melting of the input basalts. If MORB glasses were entirely produced by near‐fractional melting of a homogenous source, they would record the cooling of the mantle during melting from an initial TP = ∼1380°C (ΔTP = 0°C) down to TP = ∼1270°C. If, instead, they were all fully pooled near‐fractional melts of the same source, they would record variations in ambient MOR TP from ∼1300°C to 1450°C (ΔTP = 150°C). However, because MOR basalts are thought to be both near‐fractional and variably pooled melts of variable sources, MOR TP must be intermediate between these two extremes. Our best estimate, consistent with MOR crustal thickness, is that ambient MOR TP is homogenous (∼1350°C–1400°C) except near hotspots where TP reaches ∼1600°C. Some primitive glasses found near slow‐spreading ridges and back‐arcs record very low temperatures (TP* < 1250°C) and pressures of melting (<10 kbar) and reflect mantle cooling during melting and melt equilibration in the mantle lithosphere.

Velocity Anomaly of Campbell Glacier, East Antarctica, Observed by Double-Differential Interferometric SAR and Ice Penetrating Radar

Regional changes in the flow velocity of Antarctic glaciers can affect the ice sheet mass balance and formation of surface crevasses. The velocity anomaly of a glacier can be detected using the Double-Differential Interferometric Synthetic Aperture Radar (DDInSAR) technique that removes the constant displacement in two Differential Interferometric SAR (DInSAR) images at different times and shows only the temporally variable displacement. In this study, two circular-shaped ice-velocity anomalies in Campbell Glacier, East Antarctica, were analyzed by using 13 DDInSAR images generated from COSMO-SkyMED one-day tandem DInSAR images in 2010–2011. The topography of the ice surface and ice bed were obtained from the helicopter-borne Ice Penetrating Radar (IPR) surveys in 2016–2017. Denoted as A and B, the velocity anomalies were in circular shapes with radii of ~800 m, located 14.7 km (A) and 11.3 km (B) upstream from the grounding line of the Campbell Glacier. Velocity anomalies were up to ~1 cm/day for A and ~5 cm/day for B. To investigate the cause of the two velocity anomalies, the ice surface and bed profiles derived from the IPR survey crossing the anomalies were analyzed. The two anomalies lay over a bed hill along the glacial valley where stick-slip and pressure melting can occur, resulting in temporal variation of ice velocity. The bright radar reflection and flat hydraulic head at the ice bed of A observed in the IPR-derived radargram strongly suggested the existence of basal water in a form of reservoir or film, which caused smaller friction and the reduced variation of stick-slip motion compared to B. Crevasses began to appear at B due to tensile stress at the top of the hill and the fast flow downstream. The sporadic shift of the location of anomalies suggests complex pressure melting and transportation of the basal water over the bed hill.

Developing a Novel Method for Estimating the Speed of Sound in Biodiesel Known as Grey Wolf Optimizer Support Vector Machine Algorithm.

In the current study, our goal was to obtain a robust model to predict the speed of sound in biodiesel. For this purpose, an extensive databank has been extracted from previously published papers. Then, a Support Vector Machine (SVM) has been optimized by Grey Wolf Optimization (GWO) method to analyze these data and determine the correlation between speed of sound in biodiesel and its related properties including pressure, temperature, molecular weight, and normal melting point. The results were very satisfactory because the values of statistical parameters R2 and RMSE were obtained 1 and 1.4024, respectively. Here, this is the first time that the sensitivity analysis is used to estimate this target value. This analysis shows that the pressure widely affects the output values with relevancy factor 87.92. Also, our proposed method is highly accurate than other machine learning methods used in papers employed for this objective.

Melting of Tantalum at Multimegabar Pressures on the Nanosecond Timescale

Tantalum was once thought to be the canonical bcc metal, but is now predicted to transition to the Pnma phase at the high pressures and temperatures expected along the principal Hugoniot. Furthermore, there remains a significant discrepancy between a number of static diamond anvil cell experiments and gas gun experiments in the measured melt temperatures at high pressures. Our insitu x-ray diffraction experiments on shock compressed tantalum show that it does not transition to the Pnma phase or other candidate phases at high pressure. We observe incipient melting at approximately 254±15 GPa and complete melting by 317±10 GPa. These transition pressures from the nanosecond experiments presented here are consistent with what can be inferred from microsecond gas gun sound velocity measurements. Furthermore, the observation of a coexistence region on the Hugoniot implies the lack of significant kinetically controlled deviation from equilibrium behavior. Consequently, we find that kinetics of phase transitions cannot be used to explain the discrepancy between static and dynamic measurements of the tantalum melt curve. Using available high pressure thermodynamic data for tantalum and our measurements of the incipient and complete melting transition pressures, we are able to infer a melting temperature 8070_{-750}^{+1250} K at 254±15 GPa, which is consistent with ambient and a recent static high pressure melt curve measurement.