Formation of TiC via interface reaction between diamond grits and Sn-Ti alloys at relatively low temperatures

In this paper, interfacial reaction between diamond grit and Sn-6Ti alloy was systematically studied at brazing temperatures from 600 to 1030 °C. A thin and uniform layer of scallop-like nano-sized TiC grains was formed after brazing for 30 min at 600 °C, and interfacial TiC grains subsequently coarsened as brazing temperature increased to 740 and 880 °C. Strip-like columnar TiC grains in a bilayer structure was further grown as brazing temperature increased to 930 °C. After brazing at 1030 °C, a dense layer of columnar TiC grains were formed. Based on the TEM micrographs of interfacial TiC, the formation and evolution of the growth morphologies of interfacial TiC was believed to be controlled by the diffusion of C flux from diamond grits, which is dependent on the brazing temperatures

Reactive wetting of Sn-V solder alloys on polycrystalline CVD diamond

In this paper, the reactive wetting of polycrystalline chemical vapour deposition (CVD) diamond by a novel Sn-V solder alloy was critically examined using the sessile drop method. It has been found the Sn-V solder alloys start to spread on the CVD diamond at around 600 degrees C. Moreover, 0.5 wt% addition of V is adequate to induce an outstanding spreading of Sn-V active solder alloys on CVD diamond; while the original V content in Sn-V alloys has a negligible influence on final contact angles after wetting at 950 degrees C. The spreading kinetics of Sn-3V alloy on CVD diamond can be described using the classical chemical reaction-limited model at 700-850 degrees C. However, ultrafast adsorption of V element to the fresh diamond surface was evidenced by the formation of precursor film on the periphery of solidified Sn-V droplets. Hence, both interface reaction and adsorption of active element are accountable for the reactive spreading of Sn-V alloy on CVD diamond, especially during the early stage of spreading at relatively low temperatures. Results obtained in this study are therefore significant for not only the development of diamond bonding technique, but also the understanding of reactive wetting of metals on diamond and other carbonous materials

3D viscoplastic finite element modeling of dislocation generation in a large size Si ingot of the directional solidification stage

Growing very large size silicon ingots with low dislocation density is a critical issue for the photovoltaic industry to reduce the production cost of the high-efficiency solar cell for affordable green energy. The thermal stresses, which are produced as the result of the non-uniform temperature field, would generate dislocation in the ingot. This is a complicated thermal viscoplasticity process during the cooling process of crystal growth. A nonlinear three-dimensional transient formulation derived from the Hassen-Sumino model (HAS) was applied to predict the number of dislocation densities, which couples the macroscopic viscoplastic deformation with the microscopic dislocation dynamics. A typical cooling process during the growth of very large size (G5 size: 0.84 m × 0.84 m × 0.3 m) Si ingot is used as an example to validate the developed HAS model and the results are compared with those obtained from qualitatively critical resolved shear stress model (CRSS). The result demonstrates that this finite element model not only predicts a similar pattern of dislocation generation with the CRSS model but also anticipate the dislocation density quantity generated in the Si ingot. A modified cooling process is also employed to study the effect of the cooling process on the generation of the dislocation. It clearly shows that dislocation density is drastically decreased by modifying the cooling process. The results obtained from this model can provide valuable information for engineers to design a better cooling process for reducing the dislocation density produced in the Si ingot under the crystal growth process.Published versio

Reactive infiltration and microstructural characteristics of Sn-V active solder alloys on porous graphite

In this work, the reactive wetting and infiltration behaviors of a newly designed Sn-V binary alloy were comprehensively explored on porous graphite for the first time. It was discovered that 0.5 wt. % addition of V can obviously improve the wettability of liquid Sn on porous graphite and the nominal V contents in Sn-V binary alloys has minor effects on the apparent contact angles wetted at 950 °C. Moreover, the V-containing Sn-V alloys were initiated to spread on porous graphite at ~650 °C and reached a quasi-equilibrium state at ~900 °C. Spreading kinetics of Sn-3V alloy on porous graphite well fitted in the classic product reaction controlled (PRC) model. However, our microstructural characterization demonstrated that, besides vanadium carbide formation, the adsorption of V element at the wetting three-phase contact line spontaneously contributed to the reactive spreading and infiltrating of Sn-V alloys on porous graphite. Meanwhile, the formation of continuous vanadium carbides could completely block the infiltration of Sn-V active solder alloy in porous graphite. Affected by the growth kinetics of vanadium carbides, the infiltration depth of Sn-V alloys in porous graphite decreased at increased isothermal wetting temperatures. This work is believed to provide implicative notions on the fabrication of graphite related materials and devices using novel V-containing bonding alloys

Bearing-Based Distributed Formation Control of Unmanned Aerial Vehicle Swarm by Quaternion-Based Attitude Synchronization in Three-Dimensional Space

Most of the recent research on distributed formation control of unmanned aerial vehicle (UAV) swarms is founded on position, distance, and displacement-based approaches; however, a very promising approach, i.e., bearing-based formation control, is still in its infancy and needs extensive research effort. In formation control problems of UAVs, Euler angles are mostly used for orientation calculation, but Euler angles are susceptible to singularities, limiting their use in practical applications. This paper proposed an effective method for time-varying velocity and orientation leader agents for distributed bearing-based formation control of quadcopter UAVs in three-dimensional space. It combines bearing-based formation control and quaternion-based attitude control using undirected graph topology between agents without the knowledge of global position and orientation. The performance validation of the control scheme was done with numerical simulations, which depicted that UAV formation achieved the desired geometric pattern, translation, scaling, and rotation in 3D space dynamically

Analyzing Inland Lake Area Change in Arid Areas Based on MODIS-NDWI-A Case Study on Ebinur Lake in Xinjiang

Ebinur Lake was typical closed lake located in northwest Xinjiang. To obtain a continuous records of Ebinur Lake area change, this study identified its lake areas by synthesizing Normalized Difference Water Index (NDWI) based on EOS/MODIS satellite data from 2000 to 2007. This study showed that the area of Ebinur Lake decreased from 2000 to 2001, and subsequently increased in the next two years till the peaks in 2003, at last it lowly decreased from 2004 to 2007. Seasonally, the lake surface area was larger in spring than in summer. According to the analysis of the water resource bulletin in Bortala Autonomous Prefecture, the result showed that Ebinur Lake was significantly affected by global climatic change and human activities

An ABCG2 non-substrate anticancer agent FL118 targets drug-resistant cancer stem-like cells and overcomes treatment resistance of human pancreatic cancer

Abstract Background Pancreatic cancer is a deadly disease with a very low 5-year patient survival rate of 6–8%. The major challenges of eliminating pancreatic cancer are treatment resistance and stromal barriers to optimal drug access within the tumor. Therefore, effective molecular targeting drugs with high intra-tumor access and retention are urgently needed for managing this devastating disease in the clinic. Methods This study has used the following in vitro and in vivo techniques for the investigation of exceptional anticancer drug FL118’s efficacy in treatment of resistant pancreatic cancer: cell culture; immunoblotting analysis to test protein expression; DNA sub-G1 flow cytometry analyses to test cell death; MTT assay to test cell viability; pancreatic cancer stem cell assays (fluorescence microscopy tracing; matrigel assay; CD44-positive cell colony formation assay); human luciferase-labeled pancreatic tumor orthotopic animal model in vivo imaging; pancreatic cancer patient-derived xenograft (PDX) animal models; and toxicology studies with immune-competent BALB/cj mice and beagle dogs. Results Our studies found that FL118 alone preferentially killed cisplatin-resistant cancer cells, while a combination of FL118 with cisplatin synergistically killed resistant pancreatic cancer cells and reduced spheroid formation of treatment-resistant pancreatic cancer stem-like cells. Furthermore, using in vivo-imaging, we found that FL118 in combination with cisplatin strongly inhibited both drug-resistant pancreatic xenograft tumor growth and metastasis. In PDX model, we demonstrated that FL118 alone effectively eliminated PDX tumors, while FL118 in combination with gemcitabine eliminated PDX tumors that showed relative resistance (less sensitivity) to treatment with FL118. These FL118 efficacy results are consistent with our molecular-targeting data showing that FL118 inhibited the expression of multiple antiapoptotic proteins (survivin, Mcl-1, XIAP, cIAP2) and ERCC6, a critical regulator of DNA repair, in treatment-resistant pancreatic stem-like cancer cells. Furthermore, FL118 toxicity studies in BALB/cj mice and beagle dogs indicated that FL118 exhibits favorable hematopoietic and biochemical toxicities. Conclusion Together, our studies suggest that FL118 is a promising anticancer drug for further clinical development to effectively treat drug-resistant pancreatic cancer alone or in combination with other pancreatic cancer chemotherapeutic drugs