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Using the phase-field crystal method, we investigated the bcc {1 1 0} vicinal surface growth from melts at the atomic scale with emphasis on the growth kinetics of two growth modes: step flow growth and island growth on terrace. S...
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Using the phase-field crystal method, we investigated the bcc {1 1 0} vicinal surface growth from melts at the atomic scale with emphasis on the growth kinetics of two growth modes: step flow growth and island growth on terrace. Simulation results show that, for step flow growth, with the decrease of terrace width, the competition for feeding atoms between neighboring steps causes growth rate vs. step density to deviate from a linear relationship, and finally converge to a finite value. The step crystal direction also strongly influences the growth kinetics: vicinal surface with steps along the closest packed direction— [111] grows slower than that with [001] step. For island growth on terrace, the growth exponent of each layer in multi-layer island gradually transits from 1/2 for the top layer to 1/3 for the bottom layer, which demonstrates the transition from global diffusion controlled growth for top layer to surface diffusion controlled growth for bottom layer. The growth mechanism selection map with respect to terrace width and supersaturation is summarized and atom attaching rates of different growth mechanisms are also compared.
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Our previous study showed that the solubility and crystal growth rate of the protein subtilisin changed with the substitution of small numbers of surface amino acid residues. Structural and energetic comparisons of crystal structu...
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Our previous study showed that the solubility and crystal growth rate of the protein subtilisin changed with the substitution of small numbers of surface amino acid residues. Structural and energetic comparisons of crystal structures of two subtilisin mutants were conducted to explore the reason for changes in the growth rate of subtilisin crystals. Unique lattice contact patches were determined for the two mutants. The loss of solvent accessible surface area (ASA), the average hydrophobicity and the number of hydrogen bonds and salt bridges were calculated to quantify surface properties of the contact patches. The structural comparison showed that the three amino acid mutations (Purafect~(~R)→ Properase~(~R)) are all in contact patches and provide extra atomic contacts. For Properase~(~R) subtilisin, the number of contacting residues and the loss of ASA increased. Binding energetic calculations, based on the detailed protein structures, were performed to determine non-electrostatic interaction contributions for the required crystallographic orientation and the number of energetically favored, false-binding orientations. The agreement and disparity between molecular structure and macroscopic crystallization behavior are discussed.
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Surface morphology of hillocks on the surface of various orientations of a GaAs substrate was observed by an atomic force microscope (AFM). Only (111)A and (211)A substrates formed pyramidal hillocks. The surfaces were the top lay...
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Surface morphology of hillocks on the surface of various orientations of a GaAs substrate was observed by an atomic force microscope (AFM). Only (111)A and (211)A substrates formed pyramidal hillocks. The surfaces were the top layers of seven-period asymmetric double quantum wells or the buffer layer, and the Ga flux and substrate temperature were kept constant at 0.76 ML/s and 520deg.C, respectively.
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Renal stone disease is not only a concern on the Earth but could conceivably pose a serious risk to the astronauts' health and safety in Space. In this study, a combined transport-kinetics model for the growth of calcium oxalate (...
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Renal stone disease is not only a concern on the Earth but could conceivably pose a serious risk to the astronauts' health and safety in Space. In this study, a combined transport-kinetics model for the growth of calcium oxalate (CaOx) crystals is presented. The model is used to parametrically investigate the growth of renal calculi in urine with a focus on the coupled effects of transport and surface reaction on the ionic concentrations at the surface of the crystal and their impact on the resulting growth rates. It is shown that under nominal conditions of low solution supersaturation and low Damkdhler number that typically exist on the Earth, the surface concentrations of calcium and oxalate approach their bulk solution values in the urine and the growth rate is most likely limited by the surface reaction kinetics. But for higher solution supersaturations and large Damkdhler numbers that may be prevalent in the microgravity environment of Space, the calcium and oxalate surface concentrations tend to shift more towards their equilibrium or saturation values and thus the growth process may be limited by the transport through the medium. Furthermore, it is shown that as the crystal size increases a shift towards a transport-limited growth process is likely. In this situation beyond a critical radius that is a function of the physiochemical parameters of the renal environment, the growth rate will not be independent of the radius as in a reaction-limited situation but will decrease as the crystal size increases.
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Most of the secondary dendrite arm spacing (lambda(2)) growth models existing in the literature deal with predictions for binary aluminum (Al) alloys. Only two solutions are available to estimate lambda(2) for chemistries of major...
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Most of the secondary dendrite arm spacing (lambda(2)) growth models existing in the literature deal with predictions for binary aluminum (Al) alloys. Only two solutions are available to estimate lambda(2) for chemistries of major alloying elements in Al alloys, such as copper (Cu) and Silicon (Si). The coarsening models developed by Rappaz-Boettinger and Tiryakioglu were employed in this investigation. The multicomponent models enabled very distinct matches with the experimental data of Al-9 and 11 wt.% Si-3.0 wt.% Cu alloys.
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We study the motion of a planar thermal wave, which is simultaneously a phase boundary in a thin cooled film, driven by the application of an electrical current and Joule heating. Based on theoretical modeling by Brener and Temkin...
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We study the motion of a planar thermal wave, which is simultaneously a phase boundary in a thin cooled film, driven by the application of an electrical current and Joule heating. Based on theoretical modeling by Brener and Temkin (1996) [1] we employ a phase field model that reproduces the analytical predictions for planar front propagation and interface stability. Three-dimensional simulations of the growth of a filament advancing from one electrode to the other demonstrate the applicability of the model towards more complex geometries and problems originating from the microstructure formation in phase change materials.
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Sodium sulfate is one of the most damaging salts for porous building materials. In our quest to increase the durability of civil structures and cultural heritage we need to understand its crystallization behavior. In this paper we...
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Sodium sulfate is one of the most damaging salts for porous building materials. In our quest to increase the durability of civil structures and cultural heritage we need to understand its crystallization behavior. In this paper we investigate the cooling-induced growth of the metastable heptahydrate crystal phase by combining nuclear magnetic resonance, for non-destructive measurement of the concentration, with time-lapse microscopy, to visualize the crystal growth. The growth rate is found to be controlled by interface attachment kinetics. The kinetic growth parameter G_k ranges from 0.001 to 0.007 mm/s for single crystals in a temperature range of 4.8-13 ℃.
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The temperature field created in a tube furnace by thermal radiation is described here with an easy to use model suitable for the determination of the axial and radial temperature profiles in the furnace chamber. Particular attent...
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The temperature field created in a tube furnace by thermal radiation is described here with an easy to use model suitable for the determination of the axial and radial temperature profiles in the furnace chamber. Particular attention is paid to the radial temperature differences and their role in the evaporation-condensation processes―these differences ensure "contactless" crystal growth from the vapour at around 1100K by preventing condensation on the ampoule wall. It is shown that the creation of radial temperature differences of a few degrees is achievable by interaction of the solid material with more distant zones of the furnace. The model has proved to be a tool for the description and control in self-selecting vapour growth as initially applied to Ⅳ-Ⅵ compounds and extended to Ⅱ-Ⅵ wide bandgap compounds and, especially, their solid solutions. Broader use of the model is expected.
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This study assessed the therapeutic efficacy of thrombopoietin (TPO) in the mouse model of ALS using two treatmentparadigms. TPO was administered either daily or in 13-day treatment cycles to SOD1-G93A mice. Quantitative analysis ...
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This study assessed the therapeutic efficacy of thrombopoietin (TPO) in the mouse model of ALS using two treatmentparadigms. TPO was administered either daily or in 13-day treatment cycles to SOD1-G93A mice. Quantitative analysis ofplatelet levels, VEGF and TGF-β1 trophic factors were assessed. The effect of TPO on disease progression was analyzed bybehavioral analysis and clinical examination. TPO treatment increased levels of platelets and TGF-I31 but not VEGF. Thistreatment did not affect onset or survival in these mice. Although biologically active, demonstrated by increased platelet andTGF-β1 levels, rmTPO did not attenuate disease progression in ALS mice.
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? 2021Fluctuations in weather conditions, particularly precipitation and water availability, may strongly affect growth rate patterns and lead to interannual height growth variation. Consequently, height growth models developed us...
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? 2021Fluctuations in weather conditions, particularly precipitation and water availability, may strongly affect growth rate patterns and lead to interannual height growth variation. Consequently, height growth models developed using airborne laser scanning (ALS) data collected at short time intervals may over- or underestimate long-term height growth trends and finally result in different growth forecasts. The objective of this study was to develop height growth models for Norway spruce, including the effect of weather conditions. We used ALS-derived top height (TH) estimates and meteorological data from the research area collected for 2007-2012 and 2013-2018 to develop a weather-sensitive height growth model. The top height (TH) growth of Norway spruce was affected by the mean annual precipitation sum (APS) in the studied periods, and a higher APS resulted in faster TH growth. This study demonstrates the high potential of repeated ALS for detecting short-term variation in the tree height increment and the development of weather-sensitive height growth models.
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