Development and Application of Phase-Field Models to Study the Solidification of Steels in a Weld Pool

The quality of welded products is largely determined by solidified structures and dendrite is the predominant pattern. However, studying the evolution of morphology during solidification at micrometre scale using experimental techniques is of high cost. Therefore, in this PhD project phase-field (PF) models were developed and applied to simulate the dendritic growth of industrially important steels in a weld pool. The problem of Ohno and Matsuuras proposal to include solid diffusivity in PF simulations is that a priori unknown term associated with the solute flux needs to be input. In this work, mathematical and numerical analyses indicate that credible results can be obtained by setting that term as zero. The effect of solid diffusivity on the steady-state dendrite under free growth was next investigated, showing that the solid diffusivity of C should be included for Fe-C alloys. The evolution of side branches under the imposed transient conditions by decreasing the velocity was examined because dendrites do not grow under steady state in a weld pool. It was observed that the remelting of the smaller side branches started from the side branch tips and the necklace width of the surviving side branches increased during the ripening process whether under steady state or transient conditions. However, the final necklace widths of the surviving side branches are finer under the transient conditions, implying that the detachment of side branches is more likely to occur under the transient condition, in agreement with the published experimental reports. Finally a new quantitative thin-interface PF solidification model for ternary alloys was extended and validated. The proposed model has the advantages: (1) the schemes of thin-interface limit analysis and anti-trapping current are adopted to simultaneously ensure the calculation efficiency and accuracy, and (2) the solid diffusivity can be included for steels

Experimental Study of Salicylic Acid as a Calcium Sulfate Dihydrate Scale Inhibitor, Analyzed from Surface Properties and Crystal Growth

Static and dynamic experiments were carried out to study the antiscale performance of salicylic acid (SA) to calcium sulfate dihydrate (CSD) scale. The CSD scale formed in the reuse of processing of wastewater of phosphorite flotation. The scale surface physicochemical properties have been investigated by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), ζ potential, and contact angle measurements. The antiscale mechanisms of SA to CSD were studied from surface properties and crystal growth. The results showed that the scale inhibition efficiency of SA to CSD reached 98.9% (6 mg/L) under static conditions. Under dynamic conditions, the faster the fluid velocity, the less CSD formed. The order of scaling capability on different material surfaces was 20#CS > 304SS > PC > PE. The growth of CSD was inhibited by SA resulting in the surface becoming porous. The deprotonated SA could easily interact with the Ca2+ to make the CSD surface potential negative. The wettability properties of the CSD are greatly improved when the contact angle is reduced. The surface tension values of CSD without and with 6 mg/L SA are 19.06 and 240.69 mN/m2, respectively. SA as a scale inhibitor can significantly inhibit crystallization of CSD

Construction of Vibronic Diabatic Hamiltonian for Excited-State Electron and Energy Transfer Processes

Photoinduced excited-state electron and energy transfer processes are crucial in biological photoharvesting systems and organic photovoltaic devices. We discuss the construction of a diabatic vibronic Hamiltonian for the proper treatment of these processes involving the projection approach acting on both electronic wave functions and vibrational modes. In the electronic part, the wave function projection approach is used to construct the diabatic Hamiltonian in which both local excited states and charge-transfer states are included on the same footing. For the vibrational degrees of freedom, the vibronic couplings in the diabatic Hamiltonian are obtained in the basis of the pseudonormal modes localized on each monomer site by applying delocalized-to-localized mode projection. This systematic approach allows us to construct the vibronic diabatic Hamiltonian in molecular aggregates

Analysis of the Geometrical Evolution in On-the-Fly Surface-Hopping Nonadiabatic Dynamics with Machine Learning Dimensionality Reduction Approaches: Classical Multidimensional Scaling and Isometric Feature Mapping

On-the-fly trajectory-based nonadiabatic dynamics simulation has become an important approach to study ultrafast photochemical and photophysical processes in recent years. Because a large number of trajectories are generated from the dynamics simulation of polyatomic molecular systems with many degrees of freedom, the analysis of simulation results often suffers from the large amount of high-dimensional data. It is very challenging but meaningful to find dominating active coordinates from very complicated molecular motions. Dimensionality reduction techniques provide ideal tools to realize this purpose. We apply two dimensionality reduction approaches (classical multidimensional scaling and isometric feature mapping) to analyze the results of the on-the-fly surface-hopping nonadiabatic dynamics simulation. Two representative model systems, CH₂NH₂⁺ and the phytochromobilin chromophore model, are chosen to examine the performance of these dimensionality reduction approaches. The results show that these approaches are very promising, because they can extract the major molecular motion from complicated time-dependent molecular evolution without preknown knowledge

Ultrafast Nonadiabatic Dynamics of Singlet Fission: Quantum Dynamics with the Multilayer Multiconfigurational Time-Dependent Hartree (ML-MCTDH) Method

Singlet fission (SF) is supposed to potentially improve the efficiency of solar energy conversion in organic photovoltaic systems. The multilayer multiconfigurational time-dependent Hartree (ML-MCTDH) method was employed to describe the singlet fission of the pentacene system with a three-state model. The ML-MCTDH result agrees well with the previous simulations using the Redfield theory, the hierarchical equation of motion (HEOM) and the symmetrical quasi-classical (SQC) theory. We carefully investigated the role of vibrational modes with different frequencies in singlet fission dynamics. Interestingly, we observed the important contribution of a few modes with frequency resonance to electronic transition. Such a finding can be understood by revisiting the superexchange mechanism within the framework of Fermi’s golden rule. As a numerically exact method, ML-MCTDH not only provides an accurate description of the microscopy insight of the SF dynamics but also provides benchmark results to examine the performance of other approximated dynamical methods

Improved Functional Expression of Human Cardiac Kv1.5 Channels and Trafficking-Defective Mutants by Low Temperature Treatment

<div><p>We herein investigated the effect of low temperature exposure on the expression, degradation, localization and activity of human Kv1.5 (hKv1.5). In hKv1.5-expressing CHO cells, the currents were significantly increased when cultured at a reduced temperature (28°C) compared to those observed at 37°C. Western blot analysis indicated that the protein levels (both immature and mature proteins) of hKv1.5 were significantly elevated under the hypothermic condition. Treatment with a proteasome inhibitor, MG132, significantly increased the immature, but not the mature, hKv1.5 protein at 37°C, however, there were no changes in either the immature or mature hKv1.5 proteins at low temperature following MG132 exposure. These observations suggest that the enhancement of the mature hKv1.5 protein at reduced temperature may not result from the inhibition of proteolysis. Moreover, the hKv1.5 fluorescence signal in the cells increased significantly on the cell surface at 28°C versus those cultured at 37°C. Importantly, the low temperature treatment markedly shifted the subcellular distribution of the mature hKv1.5, which showed considerable overlap with the trans-Golgi component. Experiments using tunicamycin, an inhibitor of N-glycosylation, indicated that the N-glycosylation of hKv1.5 is more effective at 28°C than at 37°C. Finally, the hypothermic treatment also rescued the protein expression and currents of trafficking-defective hKv1.5 mutants. These results indicate that low temperature exposure stabilizes the protein in the cellular organelles or on the plasma membrane, and modulates its maturation and trafficking, thus enhancing the currents of hKv1.5 and its trafficking defect mutants.</p></div

Subcellular fractionations of hKv1.5 and the related marker proteins isolated from the HEK-hKv1.5s cells.

<p>The gradient fractionation of extracts, from the HEK-hKv1.5s cells cultured at 37°C or 28°C, was fractionated through iodixanol gradient centrifugation. (A) Densitometry from western blots of hKv1.5 mature form as in B, to allow the distribution of hKv1.5 mature protein to be compared in different temperature (*<i>P</i><0.05 vs 37°C culture). (B) Western blot analysis showing the subcellular distribution of hKv1.5, GM130 (Cis-Golgi marker), TGN46 (trans-Golgi marker), Calnexin (ER marker) and Na⁺/K⁺ ATPase beta-1 (membrane marker). The dotted line square indicates that the subcellular distribution of the mature hKv1.5 is shifted to the lighter fractions.</p

Controllable Preparation and Catalytic Performance of Heterogeneous Fenton-like α‑Fe₂O₃/Crystalline Glass Microsphere Catalysts

Highly dispersed α-Fe₂O₃ nanoparticles were immobilized onto crystalline glass microspheres for the first time to be heterogeneous Fenton catalysts (FeCG) with favorable activity. The average particle size of the supported iron oxides ranges from 2.6 to 6.5 nm and can be achieved controllably with great ease. Typically, through hydrothermal treatment, it was found that an amorphous glass support develops into mixed crystals of primitive SiO₂, CaSi₂O₅, and Ca₂MgSi₂O₇, with ∼180% improvement in specific surface areas. Most importantly, after Fe loading, not only OH· but also HO₂· radical species with high intensity were generated for FeCG, while OH· alone was produced for commercial α-Fe₂O₃ in the presence of H₂O₂, thus accelerating the redox recycling between Fe­(II) and Fe­(III) and presenting much superiority in the azo dye AO7 decoloration. The pseudo-zero-order reaction constant was determined to be 0.384 mg/(L·min), an ∼65.5% improvement over that of commercial α-Fe₂O₃ under the same experimental conditions. Only 1.26 mg/L Fe leaching was detected under optimum conditions in addition to simple catalyst recovery by gravity. No remarkable decrease in the AO7 decoloration efficiency was observed after six cycles, indicating the favorable stability

The accumulation of hKv1.5 in the plasma membrane is promoted by low- temperature cultivation.

<p>(A) Western blot analysis of the plasma membrane and soluble fractions of the hKv1.5 protein isolated from the HEK-hKv1.5s cells cultured at 37°C or 28°C; Na⁺/K⁺ ATPase beta-1 was used as a plasma membrane marker. (B) Confocal images of the HEK-hKv1.5s cells cultured at 37°C or 28°C. (C) A representative linear plot analysis of the hKv1.5 fluorescent intensity. The x-axis indicates the length across the cell area and the y-axis indicates the fluorescence intensity. The summarized fluorescence intensities measured within the peak of the fluorescent intensity (inset). (D) Western blot analysis for the hKv1.5 mutants (I508A, I502A), transiently expressed in CHO cells, under two temperature conditions (37°C and 28°C). (E) Confocal images of the HEK cells transiently expressing hKv1.5 I502A and I508A, cultured at 37°C or 28°C (**<i>P</i><0.01 vs 37°C culture).</p

The process of N-glycosylation of hKv1.5 is more effective at 28°C than at 37°C.

<p>(A) Western blot analysis of the hKv1.5 expression cultured at 37°C or 28°C for 24 h in the presence of tunicamycin (Tunic), a N-glycosylation inhibitor. (B) The CHO-hKv1.5s cells were pre-treated with tunicamycin for 24 h at 37°C, and then washed to stop its blocking action. The cells were continuously cultured at 37°C or 28°C for the indicated times.</p