7YSZ coating prepared by PS-PVD based on heterogeneous nucleation

Plasma spray-physical vapor deposition（PS-PVD） as a novel coating process based on low-pressure plasma spray（LPPS） has been significantly used for thermal barrier coatings（TBCs）.A coating can be deposited from liquid splats, nano-sized clusters, and the vapor phase forming different structured coatings, which shows obvious advantages in contrast to conventional technologies like atmospheric plasma spray（APS） and electron beam-physical vapor deposition（EBPVD）. In addition, it can be used to produce thin, dense, and porous ceramic coatings for special applications because of its special characteristics, such as high power, very low pressure, etc. These provide new opportunities to obtain different advanced microstructures, thus to meet the growing requirements of modern functional coatings. In this work, focusing on exploiting the potential of gas-phase deposition from PS-PVD, a series of 7 YSZ coating experiments with various process conditions was performed in order to better understand the deposition process in PS-PVD, where coatings were deposited on different substrates including graphite and zirconia. Meanwhile, various substrate temperatures were investigated for the same substrate. As a result, a deposition mechanism of heterogeneous nucleation has been presented showing that surface energy is an important influencing factor for coating structures. Besides, undercooling of the interface between substrate and vapor phase plays an important role in coating structures.

Coating deposition regularity depended on orientation difference in PS-PVD plasma jet

The YSZ coatings are prepared by the plasma spray-physical vapor deposition(PS-PVD)technology based on a specific experimental design.The structure,thickness and growth angle of YSZ coatings on the entire circumferential surface of the cylindrical sample are studied.The results indicated that the structure,thickness and deflection growth angle of YSZ coatings are related to the orientation of deposition location.The numerical simulation of the multiphase mixed fluid near the substrate is carried out and the deposition regularity and mechanism of YSZ coatings prepared by PS-PVD is deduced.The growth rate is related to the local characteristics of the plasma flow field,and is directly proportional to the field pressure and inversely proportional to the field velocity.The growth angle of the coating is generally affected by the flow direction of the plasma jet.Especially,the normal component of velocity vector,V_(norm),mainly affects the speed at which the coating grows vertically upwards.The tangential component of velocity vector,V_(tan),determines the degree that the coating growth direction deviates from the vertical direction.When V_(tan)≠0,the coating forms a fine column with a certain deflection angle and finally develops into an oblique columnar structure.

High-temperature oxidation behavior and analysis of impedance spectroscopy of 7YSZ thermal barrier coating prepared by plasma spray-physical vapor deposition

Quasi-columnar structure 7YSZ（yttria stabilized zirconia） thermal barrier coatings（TBCs） are prepared by plasma spray-physical vapor deposition（PS-PVD） onto pretreated and un-pretreated bond coating, respectively. An isothermal oxidation experiment of 7YSZ TBCs is carried out in the atmosphere of 950 °C in order to simulate the high-temperature oxidation process of engine blades. The isothermal oxidation process of 7YSZ thermal barrier coatings is investigated systematically by impedance spectroscopy. The electrochemical physical model and equivalent circuit of columnar 7YSZ coatings are established. Results show that the isothermal oxidation kinetic curve of columnar 7YSZ thermal barrier coatings appears to follow the parabolic law. A pretreatment of bond coating can reduce the growth rate of the thermally grown oxide（TGO） layer, restraining the initiation and propagation of microcracks between YSZ and TGO layers. The oxidation rate constants of 7YSZ coatings with pretreated and un-pretreated bond coating are 0.101×10^（-12） cm^2·s^（-1） and 0.115 × 10^（-13） cm^2 ·s^（-1）, respectively. Impedance analysis shows that the content of oxygen vacancies decreases and the density increases after the TGO layer is oxidized for 150 h. In addition, shrinkage microcracks formed by sintering during the oxidation process is the main reason for an increase of the capacitance and a decrease of the resistance in the grain boundary of YSZ.

Nuclear Aurora kinase A switches m^(6)A reader YTHDC1 to enhance an oncogenic RNA splicing of tumor suppressor RBM4

Aberrant RNA splicing produces alternative isoforms of genes to facilitate tumor progression,yet how this process is regulated by oncogenic signal remains largely unknown.Here,we unveil that non-canonical activation of nuclear AURKA promotes an oncogenic RNA splicing of tumor suppressor RBM4 directed by m^(6)A reader YTHDC1 in lung cancer.Nuclear translocation of AURKA is a prerequisite for RNA aberrant splicing,specifically triggering RBM4 splicing from the full isoform(RBM4-FL)to the short isoform(RBM4-S)in a kinase-independent manner.

Mechanism of vertical crack formation in Yb_(2)SiO_(5) coatings deposited via plasma spray-physical vapor deposition

Plasma spray-physical vapor deposition(i.e.,PS-PVD)is a promising method for obtaining advanced environmental barrier coatings(EBCs).The EBCs must meet some requirements in the application,in which the thermal cycle performance affects the service lifetime.The preparation of artificial vertical cracks in Yb_(2)SiO_(5) coatings is an effective approach for meeting the requirements above because vertical cracks provide a strain tolerance.To clarify the formation mechanism of vertical cracks during the PSPVD,the effects of coating thickness and substrate temperature on the formation of vertical cracks were investigated.In addition,the interactions of spray powder and plasma flame during coating deposition were also characterized by optical spectroscopy.It is indicated that vertical cracks are formed due to a thermal expansion mismatch between Yb_(2)SiO_(5) and mullite coating,transient cooling after deposition and the nucleation of evaporated Yb_(2)SiO_(5) as well.

New insights from the widening homogeneity perspective to target intratumor heterogeneity

Precision medicine has shed new light on the treatment of heterogeneous cancer patients.However,intratumor heterogeneity strongly constrains the clinical benefit of precision medicine.Thus,rethinking therapeutic strategies from a different facet within the precision medicine framework will not only diversify clinical interventions,but also provide an avenue for precision medicine.Here,we explore the current approaches for targeting intratumor hetero-geneity and their limitations.Furthermore,we propose a theoretical strategy with a“homogenization”feature based on iatrogenic evolutionary selection to target intratumor heterogeneity.

Transcriptomic but not genomic variability confers phenotype of breast cancer stem cells

Background:Breast cancer stem cells(BCSCs)are considered responsible for cancer relapse and drug resistance.Understanding the identity of BCSCs may open new avenues in breast cancer therapy.Although several discoveries have been made on BCSC characterization,the factors critical to the origination of BCSCs are largely unclear.This study aimed to determine whether genomic mutations contribute to the acquisition of cancer stem-like phenotype and to investigate the genetic and transcriptional features of BCSCs.Methods:We detected potential BCSC phenotype-associated mutation hotspot regions by using whole-genome sequencing on parental cancer cells and derived serial-generation spheres in increasing order of BCSC frequency,and then performed target deep DNA sequencing at bulk-cell and single-cell levels.To identify the transcriptional program associated with BCSCs,bulk-cell and single-cell RNA sequencing was performed.Results:By using whole-genome sequencing of bulk cells,potential BCSC phenotype-associated mutation hotspot regions were detected.Validation by target deep DNA sequencing,at both bulk-cell and single-cell levels,revealed no genetic changes specifically associated with BCSC phenotype.Moreover,single-cell RNA sequencing showed profound transcriptomic variability in cancer cells at the single-cell level that predicted BCSC features.Notably,this transcriptomic variability was enriched during the transcription of 74 genes,revealed as BCSC markers.Breast cancer patients with a high risk of relapse exhibited higher expression levels of these BCSC markers than those with a low risk of relapse,thereby highlighting the clinical significance of predicting breast cancer prognosis with these BCSC markers.Conclusions:Transcriptomic variability,not genetic mutations,distinguishes BCSCs from non-BCSCs.The identified 74 BCSC markers have the potential of becoming novel targets for breast cancer therapy.