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Palladium-catalyzed aerobic oxidative cyclizations of substituted 2-(1H-pyrrol-1-yl)phenols with isocyanides via an O-H/C-H insertion cascade have been developed. This strategy provides facile access to pyrrolo[2,1-c][1,4]benzoxazine derivatives in good to excellent yields under an O2 atmosphere. The notable features of this protocol include its mild reaction conditions, atom-economy, and broad functional group tolerance.

Background Transcatheter aortic valve replacement (TAVR) is regarded as the most superior alternative treatment approach for patients with aortic stenosis (AS) who are associated with high surgical risk, whereas the effectiveness of TAVR vs surgical aortic valve replacement (SAVR) in low to intermediate surgical risk patients remained inconclusive. This study aimed to determine the best treatment strategies for AS with low to intermediate surgical risk based on published randomized controlled trials (RCTs). Hypothesis and Methods RCTs that compared TAVR vs SAVR in AS patients with low to intermediate surgical risk were identified by PubMed, EmBase, and the Cochrane library from inception till April 2019. The pooled relative risks (RRs) with 95% confidence intervals (CIs) were calculated for the data collected using random‐effects models. Results Seven RCTs with a total of 6929 AS patients were enrolled. We noted that TAVR significantly increased the risk of transient ischemic attack (TIA) (RR: 1.43; 95%CI: 1.04‐1.96; P = .029), and permanent pacemaker implantation (RR: 3.00; 95%CI: 1.70‐5.30; P

In the previous work, the Al–50Si alloy with fine primary Si is prepared by a low-cost technology. In addition, the morphology of primary Si and the metamorphic mechanism as well as the thermal expansibility of alloy are also investigated in this work. The mean size of primary Si can obtain the min value of 33.82 µm when the content of modifier is 3%. The thermal expansibility of alloy decreases with the increasing of modifier. The influence of microstructure, solid solubility as well as porosity on the thermal expansibility are also studied in this research. Moreover, several theoretical models such as ROM model, Turner model, Kerner model and Schapery model are also used to predict the coefficient of thermal expansion (CTE) of alloy.

Palladium-catalyzed aerobic oxidative cyclizations of substituted 2-(1H-pyrrol-1-yl)phenols with isocyanides via an O-H/C-H insertion cascade have been developed. This strategy provides facile access to pyrrolo[2,1-c][1,4]benzoxazine derivatives in good to excellent yields under an O2 atmosphere. The notable features of this protocol include its mild reaction conditions, atom-economy, and broad functional group tolerance.

A dual removable activating group enabled Povarov reaction of N-arylalanine esters was reported. N-Arylalanine ester was utilized as the sole carbon source to generate N-arylimine and its tautomer, enamine, in situ by aerobic oxidation of sp3 C–H bonds, and then the consecutive reaction delivered the desired quinoline-4-carboxylate esters in high yields.

The oxidation of sp 3 C H bonds in N- alkylhydrazides was achieved en route to the efficient synthesis of a broad series of 1,3,4-oxadiazoles. Mechanistic studies have revealed that N- acylhydrazone is a key intermediate in this catalytic transformation.

A facile and efficient radical cation salt-induced approach to dihydroquinazoline derivatives has been developed by sp3 C H oxidation, and the method uses readily available glycine esters as the starting material under aerobic oxidation conditions without addition of any additive. The present method provides a convenient and practical route for construction of quinazoline skeleton.

Directed by the strategy of C–H activation relay (CHAR), an efficient construction of isatin skeleton was developed through catalytic oxidation of glycine esters. The mechanistic study reveals that the oxidation of the relatively active C–H bonds initiated the followed activation of remote and inert C–H bonds, and an intramolecular 1,6-hydrogen shift was involved as a key step.

Designed by fragment-reassembly strategy, the reaction between glycine esters and cyclic enol ethers was achieved in the catalysis of TBPA+·/O2, yielding a series of quinoline-fused lactones and 2,3-disubstituted quinolines. This approach provided an efficient method to construct quinoline skeleton, in which two new rings and two new C–C bonds were built in one pot.

Silica-gel adsorbents PAMAM- n .0SSASG ( n = 1–4) with dendrimer-like polyamidoamine (PAMAM) and 5-sulfosalicylic acid as functional groups were prepared and characterized with FTIR, SEM, TG, elemental analysis and porous structure analysis. Micro-column enrichment and measurement of Pb 2+ with graphite furnace atomic absorption spectroscopy (GFAAS) was studied with PAMAM- n .0SSASG ( n = 1–4) as adsorbent. It was emphasized to investigate the relationship between dynamic adsorption/desorption rates, adsorption capacities, and grafting percentage of PAMAM onto silica-gel surface. Experiments showed that the generation increase of grafted PAMAM changed the pore diameter distribution of adsorbent and obviously improved adsorption/desorption property for Pb 2+ . Adsorption capacity of PAMAM- n .0SSASG ( n = 1–4) was 14.04, 17.43, 20.07 and 25.05 mg g −1 for Pb 2+ respectively. An enrichment factor of 200 was obtained with PAMAM-4.0SSASG as adsorbent and with 2000 mL Pb 2+ solution (1.0 ng mL −1 ). The priority of adsorption property of PAMAM-4.0SSASG was explained by steric hindrance effect of PAMAM on adsorption/desorption, and selective adsorption of 5-sulfosalicylic acid with Pb 2+ . With PAMAM-4.0SSASG as adsorbent, GFAAS method for analysis of Pb 2+ combined with micro-column enrichment was proposed and applied to the determination of Pb 2+ of standard reference sample and sea water sample.

The microstructure evolution and shear behavior of the solder joints for the flip-chip light-emitting diode on the electroless nickel/immersion gold (ENIG) substrate were investigated in this study. The experimental results reveal that the solder joints for the anode and cathode have different microstructures and failure characteristics during the shear test before and after isothermal aging. For the solder joints for the anode, the interfacial intermetallic compound (IMC) is (Au, Ni)Sn4 at the solder/anode interface but dendritic Ni3Sn4 grains at the solder/ENIG interface after reflow. Meanwhile, the dendritic Ni3Sn4 grains are surrounded by (Au, Ni)Sn4, which suppresses the growth of the Ni3Sn4 grains during aging. For the solder joints for the cathode, a nano scaled Au-rich layer can be observed near the cathode/solder layer interface after reflow. And the Au-rich layer moves toward the bulk solder because of the volume expansion by the transformation from Au into (Au, Ni)Sn4 during reflow and isothermal aging. Due to the diffusion of the Au atom from the Au-rich layer into the bulk solder, the Au-rich layer transformed into an interface inside of the solder joint. The average shear force of the solder joints shows a decrease from 380 gf to 250 gf because of the microstructure evolution during the isothermal aging for 1000 h at 85°C. After long time aging, the primary failure mode of the solder joint for the anode changed from the anode broken to the brittle failure of the solder layer. The delamination between the IMC layer and the insulation layer is suggested to be the dominated failure mode of the solder joint for the cathode after aging.

This paper investigates the effect of void percentage in the solder layer on the shear strength and thermal property of DA3547 packages by SAC soldering technology. X-ray observation and shear tests revealed that the increase of solder paste volume significantly decreases the void percentage in the solder layer and thus improved the shear strength of the packages. Furthermore, packages with lower void percentage showed a lower junction temperature based on the results of IR test and finite element simulation. The temperature difference due to the effect void percentage shows a correlation with the input power. For the DA3547 packages studied in this research, voids show limited influence on the junction temperature under 50 mA, the typical current recommended by Cree.

In this paper, the formation and evolution characteristics of the intermetallic compounds (IMCs) in SAC305/Ag/Cu and SAC0705-3.5Bi-0.05Ni/Ag/Cu solder during reflow and 150 °C isothermal aging are investigated. Experimental results indicate that Ag3Sn forms as soon as the SAC305/Ag/Cu solder spheres wetted to the substrates. With increased soldering time, the Ag layer on a Cu substrate dissolved into the molten SAC305 solder and the interfacial IMC consisted of Cu6Sn5. The Ag layers show a faster dissolution rate in SAC0705-3.5Bi-0.05Ni/Ag/Cu than in SAC305/Ag/Cu, which is attributed to a larger concentration gradient of Ag for SAC0705-3.5Bi-0.05Ni/Ag/Cu. The formation and coarsening of a Cu3Sn layer between Cu6Sn5 and the Cu substrate caused the formation of Kirkendall voids and delamination during aging in the SAC305/Ag/Cu. A small addition of Ni in the solder significantly suppressed the formation of a Cu3Sn layer in the SAC0705-3.5Bi-0.05Ni/Ag/Cu, resulting in fewer voids in the soldering interface.

In the present work, the sheets of Al-50Si alloys with different Mg content (0, 5, and 10 wt% Mg) are fabricated by vertical twin-roll casting (VTRC) technology at different roll-casting speeds. The size and morphology of primary Si are studied systematically. The central congregation mechanism of primary Si and the central fracture mechanism as well as the relationship between thickness and roll-casting speed are illuminated in detail. The thickness of the sheet increases with decreasing of roll-casting speed. The central congregation phenomenon of primary Si and the layer phenomenon caused by crack will appear when the roll-casting speed is slow. The size of primary Si and the hardness of alloy are mainly influenced by roll-casting speed and Mg content. The min size of primary Si and the max value of hardness obtained at the speed of 30 m min−1 with 10% Mg content are 7.0 μm and 384, respectively.

The growth of interfacial intermetallic compounds (IMC) and consumption of metal substrate during aging affect interconnection reliability. The interfacial interaction has been significantly influenced by geometric size of solder joints with the solder size shrink from macro-scale to meso-scale. In this paper, the growth behavior of IMC and consumption trend of Cu layer in Cu/Sn-3.0Ag-0.5Cu(SAC305)/Cu sandwich structures of different solder thickness (δ=15~50μm) during high-temperature storage (HTS) aging at 160°C was investigated. The constituents' concentration in solder layer was analyzed after HTS aging. Results showed that solid state diffusion of interfacial elements is greatly dependent upon solder thickness during HTS aging. The thinner the solder layer was, the thinner the Cu6Sn5 layer and Cu3Sn layer grew after HTS aging. The growth rate of IMC layer (Cu6Sn5 layer+Cu3Sn layer) decreased with the decrease of solder thickness during HTS aging. Furthermore, the faster consumption rate of Cu layer tended to appear in the sandwich samples with greater thickness of solder layer. The concentration of Sn in solder layer revealed a decrease trend whereas that of Cu tended to increase with decreasing the solder thickness during HTS aging.

New adsorbents PAMAM-n.0TMSG (n=1,2,3,4) with thiomalic acid as functional group has been prepared based on polyamidoamine dendrimer modified silica gel and characterized with FTIR, SEM and TG. Microcolumn enrichment and measurement of Pb 2+ with graphite furnace atomic absorption spectroscopy (GFAAS) was investigated with PAMAM-n.0TMSG (n=1,2,3,4) as adsorbent. The adsorption conditions were optimized. The increase of grafted generation of PAMAM-n.0TMSG could effectively improved the adsorption performance of adsorbents. The adsorption capacity of adsorbents was 14.42, 16.19, 20.79 and 25.32 mg g -1 respectively, With PAMAM-4.0TMSG as adsorbent, microcolumn enrichment and measurement of Pb 2+ with GFAAS was proposed. The relative standard deviation (R.S.D.) was 1.4% (n=11) for 0.2 μg mL -1 of Pb 2+ . The limit of detection (LOD) of 2.9ng mL −1 was achieved. The proposed column enrichment method was applied for detection of Pb 2+ in tap water and sea water samples successfully.