Microstructures and Properties of Sn2.5Ag0.7Cu0.1RE Composite Solders Reinforced with Cu-Coated Graphene Nanosheets Synthesized by Pyrolysis.

Composite solder is a promising route to improve the properties and reliability of Sn-based lead-free solder. In this study, Cu-coated graphene nanosheets (Cu-GNSs) were synthesized using pyrolysis. Cu-GNSs reinforced Sn2.5Ag0.7Cu0.1RE composite lead-free solders were prepared via powder metallurgy. The size, distribution, and adsorption type of Cu nanoparticles on the GNSs were studied. The relation of the Cu-GNSs content and microstructure to the physical, wettability, and mechanical properties of composite solders was discussed. The results show that Cu nanoparticles (with a mean size of 13 nm) present uniform distribution and effective chemisorptions on the GNS. Microstructural evolution of composite solders is dependent on the addition of Cu-GNSs. With increasing Cu-GNSs addition, ß-Sn grains become finer and the eutectic phase proportion becomes larger, while the morphology of the eutectic phase transforms from dispersion to network-type. The improvement of the tensile strength of the composite solder can be attributed to grain refinement and load transfer. While the existence of Cu-GNSs can effectively improve the wettability and slightly change the melting point, it can also lead to the decline of elongation and electrical conductivity of the composite solder.

Estimation of genome sizes of Astragalus membranaceus based on flow cytometry and K-mer analysis / 中草药

Objective: To determinate the genome size and complexity of Astragalus membranaceus by using flow cytometry (FCM) and K-mer analysis, which can lay the foundation for the screening of functional genes of A. membranaceus. Methods Lycopersicon esculentum was served as an internal reference in this study. The mixed sample of A. membranaceus cell nucleus and L. esculentum cell nucleus was stained using propidium iodide (PI). The PI fluorescence intensities of the sample were measured by FCM. The genome size of A. membranaceus was calculated by comparing the multiple relationship between the peak of DNA content in the cells of A. membranaceus and L. esculentum. The genome of A. membranaceus was sequenced by using high-throughput sequencing technologies. The genome size of A. membranaceus was calculated by K-mer analysis. The hybridity percentage, repetitive sequence, and GC of A. membranaceus were estimated by bioinformatics analysis. Results The genome size of A. membranaceus was about 1 426 Mb. For K-mer analysis, more than 95 Gb high quality data from the genome was generated. The average genome size and sequencing coverage depth of A. membranaceus was about 1 456 Mb and 39 times respectively. The genome of A. membranaceus had obvious hybridity peak by K-mer method, and the hybridity percentage as high as 2.1%. Conclusion The genome size of A. membranaceus was about 1.45 Gb and the heterozygosity is high. These data would provide a reference for the genomic research in A. membranaceus.

Simultaneous quantitative determination of five alkaloids in Catharanthus roseus by HPLC-ESI-MS/MS / 中国天然药物

AIM@#To establish a method to simultaneously determine the main five alkaloids of Catharanthus roseus for trace samples, a high-performance liquid chromatography-electrospray ionization-tandem mass spectrometry (HPLC-ESI-MS/MS) analysis method was developed.@*METHOD@#The five Catharanthus alkaloids, vinblastine, vincristine, vinleurosine, vindoline, and catharanthine were chromatographically separated on a C18 HPLC column. The mobile phase was methanol-15 nmol·L(-1) ammonium acetate containing 0.02% formic acid (65 : 35, V/V). The quantification of these alkaloids was based on the Multiple Reaction Monitoring (MRM) mode.@*RESULTS@#This method was validated, and the results achieved the aims of the study. The intra- and inter-day precision and accuracy of the five alkaloids were within 1.2%-11.5% (RSD%) and -10.9%-10.5% (RE%). The recovery rates of the five alkaloids of samples were from 79.9% to 91.5%. The five analytes were stable at room temperature for 2 h, at 4 °C for 12 h, and at -20 °C for two weeks. The developed method was applied successfully to determine the content of the five alkaloids in three plant parts of three batches of C. roseus with a minute amount collected from three regions of China.@*CONCLUSION@#The HPLC-ESI-MS/MS method can be used for the simultaneous determination of five important alkaloids in trace C. roseus samples.

Derivation, culture and in vitro differentiation of human embryonic stem cells / 国际生物医学工程杂志

Human embryonic stem(hES) cells can self-renew and have the ability to differentiate into any type of cells of the body. These characteristics make hES cells a good candidate for cell-based therapies. Current techniques for derivating and culturing embryonic stem cells are very mature. However, concerns arise that pathogen contamination may make these cells unsuitable for therapeutic purposes. An optimal growth environment is greatly needed. Through various in vitro differentiation methods, human embryonic stem cells can be induced into many specialized cell types. However the mechanism of committed differentiation is still unknown.

Determination of carboxylic acid vapour by a thickness-sheer-mode acoustic wave sensor coated with crown ethers.

The frequency response sensitivities for 39 organic vapours by thickness-sheer-mode (TSM) acoustic wave sensors coated with monobenzo-15-crown-5 (B15C5), monobenzo-18-crown-6 (B18C6) and dibenzo-30-crown-10 (DB30C10) have been reported. It shows that crown ethers are the most efficient adsorptively active material for sensing carboxylic acid vapour, particularly B15C5 can be used for sensing formic acid vapour. The B15C5 based sensor possesses good reproducibility, high stability and short response time with wide linear detection range and a low detection limit down to 0.0201 mg l(-1) (about 5.70 ppm, V/V) of formic acid vapour while coating with 12 mug of B15C5. There is no significant interference from other organic vapours except for some nitrogen containing compounds such as diethylamine, pyridine and N,N-dimethylformamide, and carboxylic acid homologues such as acetic and propionic acids. The effect of humidity is easily controllable. Compared with acid-base titration method, the sensor can be used for the determination of HCOOH vapour with recovery rate of 98.4 approximately 103.8%, the analytical results are in good agreement with those obtained by the more time consuming acid-base titration method.